port size vs torque

[grumpyvette]

there seems to be a HUGE mis-understanding about port size and how it potentially effects your engines torque range,

port size should be thought of more as a restriction to reaching necessary flow than a benefit to making a significant torque curve PROVIDED your matching the total engine component list to the intended rpm range and expected hp peaks the engine will be expected to produce and run at!

its not port size but the ports cross sectional area and length matched to the other components like the engines displacement,compression, cam timing and bore/stroke ratio PLUS the exhaust systems designed scavage effiecincy range at any give RPM level has a major effect on results, the size of the ports in your cylinder heads are one of the least> THATS RIGHT I SAID THE LEAST important of the factors that determine where in the rpm range your engine builds its best power, while its true that smaller port cross sectional areas due cause the airflow speeds to increase,its also very true that the runner length and cross sectional area of the intake used, the compression ratio and the cam timing and the design of the header primary tubes are at least two to three times as important simply because they control the airflow thru the cylinder to a much greater extent, and the engines stroke and total displacement are extremely important, changing JUST the displacement and cam timeing has a HUGE EFFECT on WHEN and HOW the airflow in the ports gets its vacuum signal and how the port responds to that change in pressure.

you can build a torque monster engine with large ports in the cylinder heads, quiet easily if the other factors are carefully matched

 

notice that the 180cc AFR heads which are known for torque production have basically the SAME cross sectional area as the TRICKFLOW 195 cc heads and that the differance between the AFR 180cc haeds and the 210cc heads is only approximatly a 6% increase in size so the true air flow thru a 210cc head will be only approximately 6% slower on the same engine.........swap to a 383 from a 350 which is approximately 8% larger and you quickly see where the smaller heads can become more of a restriction than a benefit to the combo!

 

know I know from experiance building engines for years that a rought guide to matching hp to the intended engine port flow requirements can be guessed at fairly closely useing these formulas below, play with them then measure the port cross sectional area in your engine at its narrow point, and don,t forget the cam lift your restricted too and the valves curtain areas in the combustion chambers

 

"Fortunately for our purposes, these complex calculations can be broken down into a very simple formula that is useful for us as speed crafters.

Intake Runner Area = Cylinder Volume X Peak Torque RPM 88200

This formula takes into account the best theoretical speed that air can move down the runners, to give the best volumetric efficiency. Peak Torque occurs in an engine at the RPM where the engine is enjoying its highest volumetric efficiency. "

 

 

 

 

 

below youll find some things to read/play with

 

http://www.n2performance.com/lectures/airflow.pdf

 

http://www.rbracing-rsr.com/runnertorquecalc.html

 

heres a chart FROM THE BOOK,HOW TO BUILD BIG-INCH CHEVY SMALL BLOCKS with some comon cross sectional port sizes

(measured at the smallest part of the ports)

...........................sq inches........port cc

edelbrock performer rpm ....1.43.............170

vortec......................1.66.............170

tfs195......................1.93.............195

afr 180.....................1.93.............180

afr 195.....................1.98.............195

afr 210.....................2.05.............210

dart pro 200................2.06.............200

dart pro 215................2.14.............215

brodix track 1 .............2.30.............221

dart pro 1 230..............2.40.............230

edelbrock 23 high port .....2.53.............238

edelbrock 18 deg............2.71.............266

tfs 18 deg..................2.80.............250

 

Potential HP based on Airflow (Hot Rod, Jun '99, p74):

Airflow at 28" of water x 0.257 x number of cylinders = potential HP

or required airflow based on HP:

HP / 0.257 / cylinders = required airflow

NO!ITS NOT FOOLPROOF! BUT ITS A VERY GOOD TOOL!

what tends to make me crazy is guys that insist on running vortec or similar small port heads and a dual plane intake for max low rpm torque, when I or someone elsae builds thier engine,who then come back and want thier 383-421 sbc to run the big hp/tq numbers and pull hard at 6000rpm and above where those small ports are far past there effective air flow limits

Ive built some KILLER engines useing the 215cc and 230cc IRON EAGLE heads and SIMILAR larger port heads that made great torque in the low and mid ranges, a dual plane intake,with long runners and a 600cfm-750cfm carb helps, as does a cam thats designed for the midrange torque, and full length headers , with 1 5/8" primairies,its NOT the port size in the cylinder heads ALONE that determines the results! its the COMPLETE MATCHED COMBO and the thought that was put into makeing the components match the intended power curve, and matching the cars rear gear and stall speed to that power curve, sure you might be running slightly higher average rpms, to get the best power ,but youll be making a whole lot more power at the rear wheels too!

if you want to get good mileage and decent torque and limit yourself to 1500rpm-3500rpm the small port vortec type heads work great on a 350,thats what G.M. spent the money researching the design to do! ,they are after all TRUCK HEADS!

but increase the displacement to 383 or more and spin the engine to 6500rpm and they become a huge restriction!

while a larger head can give up very little if anything down low in the rpm range but pull far bigger numbers on the hp/tq up higher in the rpm range simply because its still able to flow the necessary voluum of air the engine needs, G.M. knows that! but they also know that 90% plus of the time EMISSIONS and GAS MILEAGE and smooth just off idle low rpm torque is where most engines are used, so they build to fit MOST users expectations

 

http://www.rbracing-rsr.com/runnertorquecalc.html

 

 

play with the calculator,, notice the vortec heads 1.66 are would peak the torque at about 3100rpm on a 383, while a dart 215 cc with its 2.14 port only moves it up to about 3950 rpm AND THATS ASSUMING the larger port head has a matching larger intake runner the whole way to the carb venturies, if you stuck the same intake and other mathing components on BOTH cylinder heads the differance in rpm ranges would be more likely to be in the 300rpm range

 

EXAMPLE

 

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=33615&item=7965364790&rd=1

 

BTW notice the 215cc heads and the strong torque curve????? its fairly obvious from the dyno chart this combo is UNDER CAMMED to make good low rpm tq at the sacrifice of potential top rpm power,

power/tq starts to fall off at about 3700rpm,while thats a good idea in a street engine, you could pick up some mid and top rpm power by swapping to a slightly wilder durration cam PROVIDED THE REST OF YOUR COMBO, like the trans stall speed and rear gear allow it

just some info

a 10.3:1 cpr 383 with 215cc alunminum heads if its matched to a 3000rpm stall converter and 3.73-4.56 rear gears makes a really nice power curve with a cam similar to the CRANE 114681 or lunati voodoo 60104 or for that matter most cams with a 235-245 intake duration and about a .510 or greater lift on a 110-112 LSA

swapping to a cam like that would boost power significantly (40-50hp)_but also make it less street driver friendly in that it would require the drivetrain changes above ans sound like a race engine at idle and would be unlikely to pass emmission testing

 

"Is there any problems with an “under cammed “ engine? "

 

 

no! not if low and mid range torque and NOT peak horsepower is the goal.....but Id like to point out again that the 215cc ports size makes very good low an mid range rpm torque if the compression and cam used are designed for very good low an mid range rpm torque, the comon crap you always hear about port size being very critical to low rpm torque is just that ( mostly CRAP), its just not as important as displacement, compression or cam timing to the results and small cross section ports restrict high rpm power far more than large ports hurt low rpm torque IF THE OTHER COMPONENTS in the combo are DESIGNED to produce mid range tq/power

 

EXAMPLE

 

heres a 427 sbc with 227cc port heads, that does not seem to be losing a great deal of low rpm torque do to its large ports

[boodlefoof]

I think a case in point to your post is the newer GM gen III heads. Correct me if I am wrong, but the LS1 has an intake port of somewhere around 210cc. Most people looking at a roughly 350 cubic inch engine would say that this is a big port that will kill intake velocity at lower speeds. Yet, the LS1 definitely isn't lacking in the torque department.

[Michael]

Grumpy, thanks for another illuminating post! It’s good to hear some one with authority mentioned that port volume comes from cross-sectional area and runner length; so, two heads of different design from different engine families can have significantly different port volume, and yet very similar cross sectional area – and vice versa.

 

Do you have a derivation of the formula, “Intake Runner Area = Cylinder Volume X Peak Torque RPM 88200� Is it from Jim McFarland’s web sites?

 

Often one hears that 240 ft/s is a “good number†for speed of the intake charge going into the cylinder, at the max torque rpm. Let’s make a crude approximation that intake runner cross-sectional area is about equal to the product of the average effective valve curtain area and the discharge coefficient (the discharge coefficient is an attempt to account for aerodynamic losses in flow past the valve). Then, from the above formula and cylinder head flow data from a flow bench, we can approximate the speed of the intake charge.

 

And here’s what happens. If we select 4500 RPM as the desired torque peak, and use 460 cubic inches for the typical BBC and 300 CFM for the typical BBC aftermarket head flow at max lift, the intake charge speed comes out to 244 ft/s. That’s good. But if we use a much lower torque peak, say 2500 RPM, the intake speed becomes 440 ft/s – this is too fast. Evidently, the heads need to flow LESS CFM to return to a more reasonable intake charge speed; for example, 175 CFM works nicely. And if we use 6500 RPM, the speed becomes 170 ft/s (too slow); but 400 CFM returns the intake charge velocity to a reasonable value.

 

So, by using intake charge flow speed as a guide, the rule of thumb implies that we can “select†what head flow value to shoot for. Of course, if the apparent CFM value is too high, the solution is to open the valves by a lower amount. The solution is NOT so simple if the CFM value is too low. This, I think, is why “too large†of a cylinder head can be acceptable for low RPM applications.

 

 

However, I would like to mention what I believe are some limitations of the rules of thumb:

 

1. The various equations and formulas that we use are just CRUDE APPROXIMATIONS! They can easily be off by 10% or 20%. And yet, the difference between a “small†SBC head (180 cc) and a “large†SBC head (say, 210 cc) is only about 17%. So, it’s entirely possible to be consistent with the rules of thumb, and yet end up with a selection of parts on either end of the extreme! The same thing holds for cam duration/overlap/whatever, carb flow rates, you name it. For my engine, the rules of thumb equally smile upon a 700 cfm carb and a 850 cfm. It’s all a matter of assumptions, guesses and mitigating circumstances.

 

2. The more unusual your application, the less reliable the rules of thumb! Meaning, that you have to GUESS – precisely in that circumstance, where experience is LEAST available and numerical predictions are most important!

[grumpyvette]

first let me say (GOOD REPLY POST)

 

to answer your question, AND keep anyone reading this up to speed on what we are talking about I think we need to explain a few factors that also need to be looked at. look here

these are the valve timeing overlap ranges that are most likely to work correctly

 

trucks/good mileage towing 10-35 degs overlap

daily driven low rpm performance 30-55degs overlap

hot street performance 50-75 degs overlap

oval track racing 70-95degs overlap

dragster/comp eliminator engines 90-115 degs overlap

torque is basically the result of cylinder pressure (dynamic compression) and leverage (stroke) plus the NUMBER OF POWER STROKES PER MINUTE (rpm) from the cylinders that are efficiently filled (volumetric efficiency). up to a certain rpm level the cylinders don,t efficiently fill due to low port air speed, above that level the valves and pistons move too fast to effectively fill the cylinders due to lack of time. your highest torque will be at the point where the engine spins the fastest it can while still packing the cylinders to the max efficiency.

here read this info on cams

http://www.newcovenant.com/speedcrafter/tech/camshaft/1.htm

(lessons 1-8)

then look at the chart to get a rough idea as to the duration necessary to fill the cylinders effectively . duration , lift and LSA are all a combo that must match compression, displacement, rod length to stroke ratio,port size and length,exhaust scavageing effectiveness, ETC.

look here

http://www.iskycams.com/ART/techinfo/ncrank1.pdf

then look at your cam spec sheet, the piston compresses nothing untill the piston has reached the point where both valves are closed, from that point on your compressing the voluum in the cylinder. look at this cam

 

http://www.compcams.com/information/search/CamDetails.asp?PartNumber=12-433-8

the pistons not compressing anything untill 77 degrees past BDC, looking at the other chart we see that the piston is about 2.4" down the bore on a 350 chevy not the 3.5 inches that the engines static compression in theory could compress

 

 

heres the answer to a similar post that fits here very closely

 

 

first is that the port can only flow when the valve is open......and THAT depends on the cam timing and displacement and rod to stroke ratio,.and .050 lift is a good place to judge or compare port flow from so you have some basis to compare from when looking into potential changes.

next, the chevy v8 operates on a 720 degree repetative cycle of which ,if we measure from .050 lift we find ONLY about 200-250 of those 720 degrees are potentially flowing air thru the port or 28% to 35% of the time

 

PORT SIZE FLOW AND THE RELATION TO CAM DURATION

 

 

FIRST, This will not be anything more that a brief glimpse into a subject that takes years to understand fully and I’m sure there are a few people on the site that can give more exact info! This is meant to apply to the 350-383 sbc engines most of us are useing

My purpose is merely to give an idea as to the relationship between the factors and yes IM ignoring several minor factors to make things easier to understand like dynamic compression and valve timing overlap

But lets look a a few concepts

(1) There are 720 degrees in a 4 cycle engines repetitive cycle of which between about 200degrees to about 250 degrees actually allow air to pass into the cylinder, (the valves open far enough to flow meaningful air flow) and the piston has a maximum ability to draw air into that cylinder based mostly on the engines displacement and the inertia of column of air in both the intake port and the suction (or negative pressure the PROPERLY designed headers provide) this produced a max air flow thru the ports, the greater the volume of fuel/air mix effectively burn per power stroke the greater the engines potential torque production, the faster you spin an engine the greater the NUMBER OF POWER STROKES PER MINUTE, and up to the point where the cylinder filling effectiveness starts falling off due to not enough time available to fill that cylinder the torque increases, above that rpm or peak torque it’s a race between more power stokes and lower power per stroke

(2) look at this diagram

(3)

As air enters an engine it normally travels thru both an intake system and the cylinder heads intake port to eventually pass into the cylinder thru the valve. The valves in a normal small block corvette engine are between 1.94 and 2.08 in diameter, that’s between 2.9sq inches and 3.4 sq inches of area, but because the valves require a seat that at a minimum are about 85%-90% of that flow area we find that the intake port even with out any valve has a max flow of not more than about 90% of the flow thru a port of valve size. Or in this case 2.46 sq inches-2.9 sq inches of port area, Since you gain little if any flow having a port that’s substantially larger than the valves AT NORMAL ATMOSPHERIC pressures and since you can’t substantially increase the valve sizes for several mechanical reasons you must improve efficiency, this is done in two major ways, you can match the intake port length and cross sectional area to the engines most efficient rpm range on the intake side, to build a positive pressure behind the intake valve as it opens and match the exhaust length and diameter on the exhaust side to provide a negative pressure to help draw in more volume this will require the cam timing match that same rpm range of course. By experimentation its been found that air flow port speeds in the 200-320 cubic feet per minute range are about the best for a chevy V-8 now lets say you have a 383. 383/8=47.875 cubic inches per cylinder, the rpm range most used is 1500rpm-6000rpm so that’s where are cam and port size must match, you can do the math , (47.875 x ½ engine rpms = cubic inches, divided by your cams effective flow duration, (use 210-235) as a default for a stock cam) x 720 degrees/1728 (the number of cubic inches in a cubic foot) to get the theoretical max port flow required (I will save you the trouble its 250cfm-275cfm at max rpms and about 2.4-2.9 sq inches of port cross section, depending on where you want the torque peak, or use this handy calculator,

 

Intake Runner Area = Cylinder Volume X Peak Torque RPM 88200

Or this helpful site http://www.newcovenant.com/speedcrafter/calculators/intake.htm

Either way you’ll find that you’ll want a port size in the 2.4sq –2.9 sq inch area

Now use this calculator to figure ideal port length, REMEMBER youll need to add the 6†in the cylinder head to the intake runner length to get the total length and you can,t exceed the engines REDLINE RPM which with hydrolic lifters seldom is higher than 6400rpm

http://www.bgsoflex.com/intakeln.html

 

 

Ever wonder why your engines torque curve gets higher with the engines rpm level until about 4000rpm-5500rpm(DEPENDING ON YOUR COMBO) but fades above that rpm level?

well it depends on several factors, first as long as the cylinders can fill completely you get a good fuel/air burn so you get a good cylinder pressure curve against the piston each time the cylinder fires, THE ENGINES TORQUE CURVE INCREASES WITH THE NUMBER OF EFFECTIVE POWER STROKES PER SECOND, at very low speeds there’s not enough air velocity to mix the fuel correctly or produce a effective ram tuning effect but as the rpms increase the cylinders fill very efficiently until the rpms reach a point where the cylinders just don’t have the time necessary to flow

enough air through the valves to fill the cylinders , remember a 5000rpm the intake valve out of 720 degs. in each cycle opens for about 250degs of effective flow even with a hot roller cam, now that’s only about 35% of the time and there’s 41.6 intake strokes per second , that’s only 1/60th of a second for air to flow into the cylinder

Its your engines ability to fill the cylinders that increases your power and the more efficiently you do that the higher the rpm level you can accomplish that at the more power your engine makes, remember the formula for hp is (torque x rpm/ 5252=hp) so moving the torque curve higher in the rpm range increases hp but at some point the time available to fill the cylinders becomes so short that efficiency begins to drop off rapidly, the peak of efficiency is reached normally in the 4500rpm-5500rpm range, and as rpms increase its a race between more power strokes per minute trying to raise the power and the increasingly less effective percentage of cylinder filling dropping the power.

Volumetric Efficiency

The volumetric efficiency of a 4-stroke engine is the relationship between the quantity of intake air and the piston displacement. In other words, volumetric efficiency is the ratio between the charge that actually enters the cylinder and the amount that could enter under ideal conditions. Piston displacement is used since it is difficult to measure the amount of charge that would enter the cylinder under ideal conditions. An engine would have 100% volumetric efficiency if, at atmospheric pressure and normal temperature, an amount of air exactly equal to piston displacement could be drawn into the cylinder. This is not possible, except by supercharging, because the passages through which the air must flow offer a resistance, the force pushing the air into the cylinder is only atmospheric, and the air absorbs heat during the process. so, volumetric efficiency is determined by measuring (with an orifice or venturi type meter) the amount of air taken in by the engine, converting the amount to volume, and comparing this volume to the piston displacement.

this increases until the torque peak then falls as the rpms increase. Here is a rough guide to match duration to port flow at different rpm level

 

if you’ve been following along you’ll find that you’ll need intake ports about 2.3-2.9†sq inches in cross section, and between 12†and 21 “ long (DEPENDS ON WHERE THE ENGINE IS DESIGNED TO MAKE MAX HP) and cam timing in the 215@.050 to -240@.050 lift range, as the rpms or displacement increase either the port flow or the cams duration must increase or the engines cylinder fill efficiency rpm will drop!

Now this is important, as the port flow efficiency goes up though the use of longer and larger intake ports the cam duration could remain the same or even be lower and you get more efficient cylinder filling as the rpms increase, that’s why high efficiency port designs like on the LS1 can use lower duration cams to flow similar total air flow thru the ports than the lower efficiency ports like the old fuelie heads could but at some point all ports reach max flow and an increase in the time the valves remain open at higher rpms increases the cylinder fill efficiency and that increases the engines ability to make torque at that rpm range

if you pick a smaller runner or longer runner you should pick a cam with a shorter duration to match the resulting lower torque peak that will likely result

 

 

Id like to point out something here!

EXAMPLE (DYNO SHEET)

LOOK CLOSELY AT THE TORQUE CURVE

heres the combo

SBC 407

· Block, 509, +30, Zero deck, Blanked water passages, Clearanced oil ways, Lifter valley vents, ARP main & head studs, Durabond cam & Clevite 77 main bearings.

· Crank, Scat 4340 forged steel, 3.75â€, internal balance, Pioneer SFI balancer + ARP bolt.

· Rods, Comp. Products 6.00†H beam bronze bushed + ARP bolts Clevite 77 bearings.

· Pistons, SRP #4032 flat top, 5cc relief, Speed Pro plasma moly file fit rings.

· Complete rotating assembly balanced. Including - Flywheel, Clutch, Balancer & Crank pulley.

· Heads, AFR 210 Race Ready, 76cc, 2.080/1.600 valves, drilled for steam. FelPro #1014 gasket.

· Cam, Comp. Cams ‘Magnum’ #12-450-8 (286HR) Hydraulic roller.

230/230 @ .050, .377 lift 110 LSA 106 ICL.

· Pushrods, Howards Cams heavy wall 5/16†7.4†long.

· Rockers, Pro Magnum roller, 1.6, 7/16†stud.

· Lifters, Pro Magnum hydraulic roller. AFR Hydr-Rev kit.

· Comp Cams Springs #950 + #740 retainers installed at 1.875â€

· AFR rev kit, AFR stud girdle.

· Lube, Melling M99HVS pump, Canton 7qt 5 trap pan with inbuilt windage and scraper, Cooler, Accumulator, oil stat, remote filter.

· Holley 800cfm #4780C, 1†spacer, Victor Jr single plane.

· Static CR 10.32, Dynamic CR 7.9.

· Quench 0.0415†(Gasket .039†+ .0025†down hole).

· MSD Pro Billet Street Dizzy, MSD 6AL, MSD Blaster 2 coil, MSD 8,5mm leads.

 

 

RPM BHP Torque

3800 367.3 507.7

3900 384.0 517.1

4000 395.1 518.8

4100 407.9 522.5

4200 418.9 523.8

4300 429.4 524.5

4400 439.6 524.7

4500 449.6 524.7

4600 462.1 527.6

4700 467.4 522.3

4800 476.6 521.5

4900 485.4 520.3

5000 489.2 513.9

5100 498.5 513.4

5200 496.0 501.0

5300 506.1 501.5

5400 508.4 494.5

5500 508.7 485.8

5600 505.6 474.2

5700 505.8 466.0

5800 505.8 458.0

5900 494.6 440.3

6000 491.9 430.6

 

Id like to point out something here to those of you who keep insisting that your required to run small ports sizes and dual plane intakes to make decent mid range torque

look closely at what the combo uses

 

Heads, AFR 210 Race Ready, 76cc, 2.080/1.600 valves, drilled for steam. FelPro #1014 gasket.

· Cam, Comp. Cams ‘Magnum’ #12-450-8 (286HR) Hydraulic roller.

230/230 @ .050, .377 lift 110 LSA 106 ICL.

Holley 800cfm #4780C, 1†spacer, Victor Jr single plane

 

like IVE CONSTANTLY SAID, ITS THE CAM AND PROPERLY MATCHED COMPRESSION RATIO THAT HAS THE LARGEST EFFECT ON THE ENGINES TORQUE POTENTIAL, while its true that smaller ports can increase the volumetric efficiency at low rpms, they are not always required, and the tend to hurt the high rpm performance, you also don,t need a great deal of duration in the cam you pick,if the heads your useing flow decently, notice hes only running 230 @.050 lift

LARGE ports matched to the correct compression ratio and cam can make very good torque.

as always its the total combo OF PARTS and how the parts match the displacement and intended rpm range, NOT the result of a SINGLE PART choice!

[pparaska]

Great post, Grumpy. I've been thinking along those lines myself - and that's why I went to 215cc Canfield heads.

 

Interestingly, my 407 is very similar in specs to that engine, except for the cam (Cam Motion low lash solid roller, 274/279 @.020", 244/250 @ .050", .574/.577 lift with 1.5:1 rockers, 112 LSA), I have about 10.5:1 CR and with a 900cfm carb and large tube headers with mufflers, DD2000 says the following:

_RPM_HP_TQ

3500 343 515

4000 407 535

4500 464 541

5000 507 533

5500 533 509

6000 534 467

6500 515 416

 

I also think that one has to look at the "discharge coefficient" as Michael puts it, or in another way of looking at it, the flow versus advertised port volume of a head. My Canfields flow 297cfm at .500" and beyond. That's pretty good for 215cc heads. Sure, I'd like to really look at this versus port cross section, but that number I don't have. (Any advice on what kind of pourable rubber, etc. to use to make a mold of the port? The valves are out at the moment.) What I'm saying is that if you look at flow versus cc of two heads, the one with the higher flow/cc ratio will have higher average port velocities anyway. Just looking at port volume or even cross section isn't enough.

[Guest bucnasty]

now this is a bad *** thread

 

im loving it and subscribing

now if ud kick some knowledge about the head for turbo single or twin applications.

 

chris.

[pparaska]

Chris, you are reading yet another thread by Grumpyvette. He got that name, I hear because everytime his wife stuck her head in the garage while he was working on the vette, he, uh, came off as grumpy . Just a rumor I'm sure!

 

Seriously though, grumpyvette is one of (if not THE) engine theory and practice experts here on HybridZ. He has no Z (unless he bought one recently), but joined to help us out - we have enquiring minds here at HybridZ, and it attracts some incredibly sharp people! I love it, I've learned a bunch a member here.

 

Grumpyvette also is moderator of of the Performance board on Chevytalk.org.

 

I rated this thread 5 stars - I totally agree it's a bad a$$ thread!

[grumpyvette]

a coup;e other forums

 

 

http://www.chevytalk.org/threads/postlist.php/Cat/0/Board/UBB64

 

http://www.crossedflags.com/nuke/html/modules.php?name=Forums&file=viewforum&f=10

 

http://www.digitalcorvettes.com/forums/forumdisplay.php?s=&forumid=68

 

http://kustomauto.2.forumer.com/

[pparaska]

So, grump, no comment on that rumor, huh?

[Guest bucnasty]

sweet well ive tried searching but who has info on the ls1/6 swap into the 280?seems to be my best drop in bet for efi and then to fi

 

chris.

[grumpyvette]

"I hear because everytime his wife stuck her head in the garage while he was working on the vette, he, uh, came off as grumpy . Just a rumor I'm sure!"

 

"So, grump, no comment on that rumor, huh? "

 

WHAT RUMOR!....I finally get my old wife of 35 years 1/2 trained to stay away from the garage....and you guys want to tell her its all an ACT???

[pparaska]

LOL!!!!

 

Thanks for that response, Grumpyvette - the people at work wanted to know what I was cracking up about (your response).

[Michael]

The conventional wisdom is that the mean flowpath is biased toward the short-side of turns inside the port. So, a crude approximation to port pathlength should be obtainable by taking a wire or piece of string, centering one end of the wire in the intake port face (towards the intake manifold), centering the other end in the plane of the valve seat, and pulling the string or wire taut. Assuming that this works, an estimate for mean cross-sectional area would be the published port volume divided by the length of the wire.

 

It would be interesting to compare this area with the result of averaging width and height measurements at different locations along the port path, using inside dividers.

Curiously, often heads in the same family but with different intake port volume ratings will nevertheless have the same published port cross-sectional area at the intake flange! For example, 1.7â€x2.43†seems to be a pretty standard number for rectangular-port BBC heads, with published intake port volumes from 305cc all the way to 345 cc.

 

But, in defense of smaller-port heads, it sometimes happens that amongst heads of the same family the larger-port heads actually flow LESS at low valve lift; example: the AFR 265cc oval-port BBC heads flow significantly more at 0.300â€-0.500†lift than do the rectangular-port 305cc AFRs. For high-lift cams this is irrelevant, but for low-lift applications one has to wonder.

[pparaska]

...

But' date=' in defense of smaller-port heads, it sometimes happens that amongst heads of the same family the larger-port heads actually flow LESS at low valve lift; example: the AFR 265cc oval-port BBC heads flow significantly more at 0.300â€-0.500†lift than do the rectangular-port 305cc AFRs. For high-lift cams this is irrelevant, but for low-lift applications one has to wonder.[/quote']

 

Good point. That's one of the reasons the AFR and Canfield SBC heads are so nice - they typically have very good mid-lift flow (below .500"). For instance, here are the flow #'s for my 215cc Canfield SBC heads, advertised, tested out of the box, and after minor exhaust port/seat entry work:

 

[Kevin Shasteen]

there seems to be a HUGE mis-understanding about port size and how it potentially effects your engines torque range' date='

port size should be thought of more as a restriction to reaching necessary flow than a benefit to making a significant torque curve PROVIDED your matching the total engine component list to the intended rpm range and expected hp peaks the engine will be expected to produce and run at!

[/quote']

 

Hey guys - long time no post...(I still visit and read a lot, just havent had much time to post).

 

Grumpy - this first paragraph has been a pet peave of mine for the last few years. As usual a great post - I always learn something when you post; thanks again!

 

I think a lot of the confusion about port sizing is that fact that it is a relative term. What is a large port -vs- a small port? Who decides what is large or small? It is a hard concept to grasp, at least it was until I realized the deciding factor was the INTENT of the engine-car combo and the DISPLACEMENT of the engine that decided what is a large port -vs- a small port: and all this is further decided by the specific tageted rpm range wherein the required output of the engine is expected to surface....this ties in to Grump's statement he made in one of the posts above,

 

"as rpm or displacement increases - either port flow or the cam's duration must increase or efficiency decreases."

 

That sentance alone really rings home the idea of port pressure & cylinder pressure.

 

It helped me to grasp the intake port concept once I classified "performance". I really mirrored what performance guru's consider a phase 1,2,3,4,or Phase 5 engine. Yet I broke down my categories into 6 categories, as follows:

 

1) Pure Street: Turbo, Supercharged, or Nitrous

2) Pure Street: Normally Aspirated

3) H/O Street: Mild Race Engine

4) Weekend Warrior: Moderate Race Engine

5) Dedicated Race: Normally Aspirated

6) Dedicated Race: Turbo, Supercharged, or Nitrous

 

What I do with these categories is I take the displacement of the engine and divide it by the number of cylinders to obtain cylinder displacement. Then I convert the cylinder displacement into cc's. Then I divide the cylinder displacement into the port displacement of the cylinder head I am looking at; this then gives me a Ratio (%), or percentage which then allows me to categorize the cylinder head's intake port. I call it the Intake Port to Cylinder Volume Ratio..., or IP/CV%.

 

The 6 categories now look like this:

 

1) .24 - .27 Pure Street: Turbo, Supercharged, or Nitrous

2) .20 - .24 Pure Street: Normally Aspirated

3) .25 - .27 H/O Street: Mild Race Engine

4) .28 - .30 Weekend Warrior: Moderate Race Engine

5) .30 - .33 Dedicated Race: Normally Aspirated

6) .35 - .38 Dedicated Race: Turbo, Supercharged, or Nitrous

 

I've come up with these ratio's based on all the magazine articles I've read. What is interesting is that all engine articles follow this to a tee...providing THE REST OF THE ENGINE COMPONENTS MATCH THE INTENT OF THE ENGINE-CAR COMBO!

 

The math is simple for calculating your own IPCV %:

 

1) Required Eng.Displacement = ((In.Port cc's / IPCV) / 16.387) x #ofCyl's in Block)

 

2) Resulting IPCV% = In.Port cc's / ((Eng.Displacement / #ofCyl's) x 16.387)

 

3) Required In.Port cc's = (((Eng.Displacement / #ofCyl's) x 16.387) x IPCV%

 

I hope the parenthesis are correct.

 

As examples lets take grumpy's example 427 c.i./227cc heads, 407 c.i./210cc heads, and Pete's 407 c.i./215cc heads and work the math to obtain their IPCV%: this requires us to use the second math equation to obtain the resulting IPCV%.

 

1) 427 SBC with 227 cc's Intake Ports

 

427 / 8 = 53.375 Cylinder Displacment

53.375 x 16.387 = 874.656 Cylinder Displacement in cc's

227 In.Port cc / 874.656 Cyl.Displacement cc's = .259 IPCV%

 

so our answer is .259, or .26; if you look at the IPCV% category you will see that this port falls in the "H/O Street: Mild Race" category.

 

2) 407 SBC with 210 cc's Intake Ports

 

407 / 8 = 50.875

50.875 x16.387 = 833.688 cc

210 / 833.688 = .251 IPCV%

 

so our answer is .25 IPCV%: again this falls in the "H/O Street: Mild Race" category.

 

3) 407 SBC with 215 cc Intake Ports

 

407 / 8 = 50.875

50.875 x 16.387 = 833.688

215 / 833.688 = .257 IPCV%

 

again our answer falls into the "H/O Street: Mild Race" category.

 

The only point Im trying to make is that port sizing is relative to the desired engine ouput at a specific rpm. In order to obtain this desired effect the engine components must compliment one another as stated earlier by grumpy.

 

Kevin,

(Yea, UNFORTUNATELY, Still an Inliner)

[pparaska]

Interesting analysis! I'd be very grateful to see your database of articles with the data that makes up your 6 categories - I don't recall ever seeing this kind of analysis before - very interesting! Looks like the kind of thing we could make as an FAQ !

 

I think one thing to add is that the build of the car (weight, gearing) has a lot to do with what's an acceptable category engine to use in that vehicle. A H/O Street/ Mild Race engine may sound radical if you think in terms of a heavy muscle car with a 3.55:1 rear and 28" tires, but a much less radical street ride if the car is light like a Z with 3.70:1 gears and 25" tires.

 

BTW, just one nit. The ratios you've calculated are actually 25%, not .25%. To get %, you have to multiply the ratio by 100.

 

This topic of "too big a port" is very much like "double pumper carbs are for racing", and "more than 225 degrees of .050" duration will be unstreetable".

 

The double pumper taboo was something I somewhat believed until I tried first a vac sec Holley on my 327, and then a double pumper. The light car with 3.7:1 gearing and 26" tires made for a great match to the double pumper - bog was only an issue if you did something stupid like mash the gas in 5th at 45mph.

 

The 225 degree duration @.050" thing is also too general of a "rule of thumb". Streetability is very much a function of having good Low rpm torque which is dependent on dynamic compression, which is dependent on static compression ratio and SEAT timing (intake valve closing in particular) which is dependent on the SEAT duration numbers and lobe separation angle. Many of the newer cams (Comp Cams Xtreme, Lunati Voodoo, Crane Powermax) have very quick action, meaning that a 230 or 240 degree duration @.050" cam can have 270-ish seat duration, unlike the cams of 20 years ago. That means you really don't have to give up low rpm as much as the old rules of thumb used to dictate.

 

I often laugh when I see magazine articles where the owner chose a 180cc port for a 400+ cube engine, so that the engine wouldn't lose low speed torque, and then puts a cam with alot of seat duration and little lobe separation to make more power. He ends up with a narrow power band - the cam is tuned more for mid-high rpm and the heads become a restriction trying to breathe at the mid high rpms. It would be better to go with a larger port and less cam seat duration and/or more LSA. You just can't make power if the heads can't flow enough air - no matter how big the cam!

[Guest tony78_280z]

The math in this thread is making my head hurt. Some one please summerize for us dummys. All I've learned is don't change anything (internal engine wise) until I first run it past Grumpy. 'Cause even the high performance auto mags seem to buy into these myths.

[jt1]

What a killer thread. Tons of stuff to think about here.

 

Kevin, IPV vs. CV is an interesting thing to consider, and like Pete, I don't think I've ever seen anybody bring that up. It's a great idea, but I think you'll need to adjust the %'s somewhat for different brand engines. Since the port length varies, that is a minor variable that could skew the results somewhat. SBF ports are shorter than SBC's which are shorter than BBC's.

 

Would cross sectional area or head flow be a better criteria, since it would not include the port length?

 

Along similiar lines, it's unusual to see anyone consider CID when talking about cam specs. The same cam has different qualities in a 302 than in a 406, yet that's rarely mentioned in discussion.

 

John

[dr_hunt]

I too have found that large port sbc heads don't necessarily kill midrange torque, but that depends on what you call midrange. I call midrange 2500 to 4K for street and 3500 to 5K for circle track or drag.

 

The effects of cylinder heads on engines directly relates to bore and stroke and piston speed as well, which helps determines port air velocity which is why small heads can't fill large cylinder volumes whether they are created using larger bore or stroke or both and why cams are so important in making the combination work. So as it has been said the cylinder heads are to be thought of as a restriction but so are cams. Low lift long duration cams are better suited to heads that flow better at low valve lifts and heads that have larger flow at low lift tend to make more power at lower rpm's because the valves reach the low lift numbers twice, once on the way open and once on the way closed, where they reach peak lift only once.

 

Grumpy is correct, valve timing is the only true variable once an engine is built, mostly due to cost of heads and the fact that cams are alot cheaper, however I have seen teams dyno with several different heads on the same short block to see which set made the most TQ and HP. DD programs can help you play with valve timing to give you an idea on how changes will effect TQ and HP and where. Selecting the most suitable heads and cam is the key to extracting the most out of your combo, but it doesn't end there, intake, carb, exhaust and ignition are all players and I'd rate tuning as number 2 on the all time list of how to make it work. Tuning can easily make 100HP+ difference especially in a forced induction engine.

 

The point of all of this is to select the correct combination. Where most newcomers to hotrodding make errors is in choosing parts, as they are simply incompatible or not optimal in most cases, but tuning the combination for optimum results takes alot of time.

 

How many have played with timing, changing headers/collector length, spark plug gap, ignition coils, jetting, tire pressure, gearing, converter stall, suspension changes to see what settings produced the optimum results?

 

It doesn't take years to build one, but it takes years to know "how" to build one, and I'm not talking mechanical aspect here, and takes years to learn "how" to tune it correctly. That is why top tuners are sought after big time by the top teams.

 

Interesting thread, opens up alot for discussion and sharing of knowledge.

[Kevin Shasteen]

Thanks Pete regarding the % -vs- decimal point thing: I was pressed for time yesturday and again this morning: my bad.

 

Jt1, Regarding the data I've used - it is bascially all the auto magazines I've collected in the past years as well as the numerous how to books I've purchased. The interesting thing I've discovered is that the smaller IPCV numbers to the left work best for the smaller displacements and according to the numbers this rule of thumb the smaller numbers fall into line, with every engine article, for any engine with a 454 displacement or smaller (I know a 454 is not a small block - that is just how the numbers work out: please dont kill the messager). Any displacement larger than a 454 can utilize the larger IPCV numbers to the right.

 

Regarding engine builders using smaller heads to obtain 400 hp and utilizing an rpm specific cam profile - I've thought about this long and hard also. I didnt really know why they would do this until I decided to put the "Cylinder Pressure" formula on a spreadsheet to calculate exactly how these engine builders were effecting said cylinder pressure: then things got a lot clearer for me. I would venture a guess that their purpose is to mirror rodders on a tight budget who cant afford expensive cyl.heads or they are attempting to manipulate peak port pressure (Peak HP) to surface at a specific rpm or they are attempting to manipulate peak cyl.pressure (Peak TQ) at a specific rpm: remember peak TQ equals peak VE%. If you set one, Peak TQ - then you have set the other; or vise/versa.

 

We all know there is more than one way to skin a cat. As grumpy alluded to earlier and we've all heard it a million times, "You cant look at any one engine component - every engine component must compliment each other." This means there MUST be a plan when we first decide to approach our engine build. This is why I chose to divide the IPCV categories into 6 phases. I was attempting to understand why the professional engine builders utilze certain components; it was the only thing that made any sence to me.

 

Remember - to see how effective any engine is you need to know the VE%: otherwise is doesnt really mean anything.

 

The rest of the criteria for those categories are:

 

I)

1) Pre-Boost and Pre-Nitrous BMEP cylinder pressures 100 – 130 psi

2) Post-Boost and Post Nitrous BMEP cylinder pressures 165 – 185 psi

3) Any Boost higher than 6 lbs is no longer in the pure street category

4) Smooth idle in the 600 – 700 rpm range

5) Intake Manifold Pressure at idle 18 – 21 (in. hg.)

6) 2500 – 4500 rpm = Peak Torque range

7) 4500 – 5500 rpm = Peak Horsepower range

8 ) .20 - .24 IP/CV ratio

9) 7.50:1 – 8.5:1 SCR

10) 8.25:1 – 8.5:1 DCR

11) Cam Profile Required – Each power adder has its own approach to making power, therefore it is in your best interest to consult the experts before settling on one profile.

 

II) Pure Street Engine: Normally Aspirated

 

1) BMEP cylinder pressures 130 – 150 psi

2) Smooth idle in the 600 – 700 rpm range

3) Intake Manifold Pressure at idle 18 – 21 (in hg)

4) 2500 – 3500 rpm = Peak Torque range

5) 4500 – 5200 rpm = Peak Horsepower range

6) .20 – .24 IP/CV ratio

7) 8.75:1 – 9.25:1 SCR range

8 ) 8.25:1 – 8.50:1 DCR range

9) Cam Profile Required

a) Duration in the 240˚ – 250˚ range

Valve Lift in the .400" – .425" range

c) LSA in the 114" – 118" range (actual LSA depends on lobe duration and displacement)

d) Overlap at 35˚ or less

 

III) H/O Street – Mild Race Engine

 

1) BMEP cylinder pressures 155 – 165 psi

2) Semi-Smooth to Choppy idle in the 700 – 850 rpm range

3) Intake Manifold Pressure at idle 15 – 18 (in hg)

4) 3000 – 4500 rpm = Peak Torque range

5) 5000 – 6000 rpm = Peak Horsepower range

6) .25 – .27 IP/CV ratio

7) 9.25:1 – 9.7:1 SCR range

8 ) 8.25:1 – 7.5:1 DCR range

9) Cam Profile Required

a) Duration in the 260˚ – 270˚ range

Valve Lift in the .440" – .470" range

c) LSA in the 110˚ – 114˚ range (actual LSA depends on lobe duration and displacement)

d) Overlap in the 35˚ – 55˚ range

 

IV) Weekend Warrior – Moderate Race (Amateur Drag class or Amateur AutoX)

1) BMEP cylinder pressures 165 – 185

2) Choppy to Wavy idle in the 850 – 1000 rpm range

3) Intake Manifold Pressure in the 6 – 12 (in hg) range

4) 3500 – 4500 rpm = Peak Torque range

5) 5000 – 6500 rpm = Peak Horsepower range

6) .28 – .30 IP/CV ratio

7) 9.75:1 – 11.0:1 SCR range

8 ) 7.50:1 to 7.0:1 DCR range

9) Cam Profile required

a) Duration in the 280˚ – 290˚ range

Valve Lift in the .480" – .560" range

c) LSA in the 108˚ – 114˚ range (actual LSA depends on lobe duration and displacement)

d) Overlap in the 50˚ to 75˚ range

 

V) Dedicated Racer (Sportsman Drag class or Professional AutoX)

1) BMEP cylinder pressures 185 – 210 (Normally Aspirated)

2) BMEP cylinder pressures 240 – 300+ (Turbo, Supercharged, or Nitrous)

3) Sporadic Choppy idle at 1000+ rpms (idle is not an issue in this class)

4) Intake Manifold Pressures (no data for me to form an opinion with)

5) 5500+ = Peak Torque

6) 7000+ = Peak Horsepower

7) .30 – .33 IP/CV ratio for Normally Aspirated race engines

8 ) .35 – .38 IP/CV ratio for Turbo, Supercharged, Nitrous race engines

9) 12.5:1 SCR or higher

10) 8.8:1 – 9.1:1 DCR

11) Cam Profile Required

a) Duration in the 290˚ – 325˚ range

Lobe Lift in the .540" – .870" range

c) LSA in the 106˚ – 114˚ range (actual LSA depends on lobe duration and displacement)

d) Overlap in the 75˚ – 110˚ range

 

VI) Top Fuel Dragsters

1) I have no knowledge on the actual specifics of these engines other than they are extreme torque monsters and high rpm specific

 

 

 

These are just rule of thumbs and not absolutes - once your mind grasps how to manipulate the airflow velocity - then you can mix certain components. Remember, as our engines are concerned all we are doing is mainpulated peak Cyl.Pressure or Peak Airflow to surface at a certain rpm range and with a specific intensity - hence why the BMEP (Brake Mean Effective Pressure) column and VE% column is so important in any engine dyno print out. It allows you to see exactly how the airflow velocity is being manipulated.

 

The BMEP formula is:

 

MEP = ((HP x 792,000) / (Displacement x RPM))

 

If you can put this equation on an Excell Spreadsheet in 20 RPM increments you and use it for every engine build you read about - you will begin to see just how the airflow is being manipulated.

 

Whenever I read an engine mag w/an engine build up I always look for certain data: after all, its all about recongnizing patterns. These criteria are:

 

Required Data for Engine Comparisons

 

1.) Confirm Total Engine Displacement

2.) Calculate Cylinder Displacement

3.) Confirm the article’s SCR

4.) Calculate the Total Chamber Volume for that SCR

5.) Confirm or Calculate Cam Timing Events

6.) Confirm which Intake Manifold was used

7.) Calculate DCR

8.) Was a Dyno Printout offered-BMEP given?

9.) Note how the Engine behaves with the Intake Manifold, Cam Profile - Duration, LSA, and Lift

10.) Did the article offer idle characteristics: vacuum readings, idle rpm-smooth, choppy or wavy?

11.) Confirm the Cylinder Head’s IP/CV ratio and E/I %

12.) Once Cylinder Heads are confirmed, go to the internet and locate their CFM Airflow numbers

13.) Calculate the Cylinder Head’s cfm needed to make the HP the article says the engine has reached

14.) If possible-notice the actual cylinder head’s port opening (Cross Sectional Area)

 

Kevin,

(Yea,Still an Inliner)