Cam/intake changes

[Guest zfan]

Im rethinking my build as the car is pretty sluggish under 2500 rpm's and lacks torque in a major way! My car is a 1971 240Z with vette 700r4, 3.54 gears with 235/60-15's. Stall converter is a 2300/2500 b/m. Motor specs are:

 

350 four bolt .30 over

eagle rods

10.25 to 1 KB hypers

Comp cams extreme hyd. roller xr288hr-10

1.50 roller rockers

Edelbrock RPM 64cc heads

Victor jr. intake

750 double pumper

MSD Ignition

Hooker supercomp headers(full length)

2 1/2" exhaust with 2 chamber flowmasters.

 

Im seriously considering a cam change plus intake as well. The intake would probably be a weiand stealth dual plain. hoping to gain some torque there as well.

 

The cam is where Im stuck if I swap cams Im not really sure what cam to go with.

 

Grumpy you out there? Do you have any suggestions on how to get more go out of this combo? Would just changing intakes give me much of that much needed lower end torque.

 

I do not have desktop dyno but was wondering if my current set up is really a 2500/6000k set up as Comp cams advertised as the car doesnt really come on until 3300-3500 rpms and runs strong past the point of where my set up was built to go. By accident I pushed her to 7k and she was pulling hard all the way! Im looking for a combo thats in the 2k to 6k range as the motor wasnt built for 7k which is what my friend said that cam is for.

 

Several people have commented that the cam in my car is a 3500/7000k cam not 2500/6000 as comp cams advertised.

 

Mike

[Mike C]

I agree with the cam thing. My mech roller is 236 @.050 and pulls 6400 or so it is 236 @ .050. How much do your drive on the highway? I'd just swap in 3.90s and watch that thing spool up! Other wise, check into the (I think) 282 HR, but NOT the XR cam. The XR are way more aggressive IMO than the advertising implies. What's the .050 on the XR you've got? If memory seves, it's over 240 degrees which to me means 3500-7000 rpm power band. Another fix would be to lose the 2500 rpm converter and go 3500. The vitor JR might be hurting you a little bit, but in my experience swapping intakes does very little to change the seat-of-the-pants feel of the combo. Any of the other three (gears, cam, converter) will have a MAJOR effect.

[grumpyvette]

the first thing your going to need to do is determine what rpm range you want your engine to produce peak power in,now your present intake and cam are designed for the 4000rpm and above range,but your rear gear is for the 1500-4500rpm range, if thats not where you want your power you will need to change parts, a swap to a CRANE #114142 cam and a performer rpm intake would match that 3.5 rear gear ratio.or a change of rear gear to a 4.11-4.33 rear gear will match the engines torque curve now.

 

mike c

 

gave you good info, while the intake swap would give you a shift in the torque range and more low rpm torque, that shift comes at a price in that what it gives you in low speed torque due to the higher airflow speeds in the ports it takes away in high rpm power due to that same restrictive airflow. swapping to the dual plane intake will give you part of the boost in low rpm torque your looking for but a higher rear gear (4.11s) would be my choice because you will keep your high rpm power and the 700r4 trans overdrive will still keep your highway driveing rpms reasonable. swapping to a smaller durration cam will also have the effect of dropping your peak hp and boosting your low rpm torque but again why drop your power,changeing the rear gear and then the intake only if the gear change alone does not get you where you want to be would be in my opinion the better plan.

[Kevin Shasteen]

ZFan,

 

Dont look at it as if "You've Chosen The Wrong Cam". Instead look at it in a sence of, "What is Optimum Performance For Your Goals & Required Needs".

 

Mike illuded to it when he asked if this is a street driven car. Your engine really is a nicely set up engine. 355's w/your components of choice are excellant performers.

 

What you have to decide is:

1) Do you want a heavy hitting Street-mobile

2) Are you willing to give up Low Rpm Power for High Rpm HP

3) What is acceptable Performance

 

From your questing which initiated this thread it appears you have built a heavy street engine/car. So it is the later two questions that you now are now pondering.

 

Your cam's overlap is only 71*'s overlap; that really is borderline too much for a true street engine whereby one expects peak torque to come in to play around 3000-3500rpm's providing one wanted an [even-keeled] power band as opposed to a [peaky] power band. The 70*-75*'s overlap figure is considered a heavy hitting Street Engine's Cam and one many Oval Track Racers begin with.

 

Your duration is also a duration that is on the Borderline of too much for a street engine; AKA: Heavy Hitting Street Engine/Moderate Race Cam. Anytime one chooses a cam whose duration exceeds 260 or 270 then you can expect to lose low rpm power in exchange for high rpm power.

 

Your 355 V8 currently has somewhere between 10:1 SCR (Static Compression Ratio) up to a 10.3:1 SCR.

Your cam's IVC (Intake Valve Closing) occurs at 70*'s ABDC. This IVC rate actually requires a higher SCR of around 11:1 for optimum low end power.

 

Even still, your Dynamic Compression is currently around the 7.9:1 DCR area; this isn't really all that bad for a heavy hitting street engine.

 

If you want more low rpm power and you want it in a manner of "swapping out a cam" I'ld suggest a cam somewhere in the 260 or 270 Duration; and instead of the 110*'s LSA (Lobe Separation Angle) maybe a 112 for the street. Remember, LSA's are as important useful tools in determing low rpm power as Duration; as the LSA has its effect and comes into play during the low lift of the valve; they have as much a say in low rpm power as the IVC does.

 

Mike illuded to the answer and GrumpyVetter hit it the nail right on the head; in that, you may wish to get a steeper rear geared differential. A 3.90 diff. would increase your rpm's by about 300 rpm's in each gear. That would get you that much closer to your "Peak Power Band" of your engine/cam combo: and with your 700r4 your .7 4th gear and 26.10" tires would still allow decent cruise on the hwy. A 3.90 diff would be better but with your engine combo you actually need a much higher rear diff. gear ratio.

 

Remember, your true dilemma is do you want a heavy hitting street machine or do you want a moderate street machine w/good low rpm power to match acceptable but not extreme high rpm power. Regardless of which you choose-gearing always plays an important part in maximizing your engine/tranny; it isnt a matter of "Have I chosen Poorly" but rather, "What am I willing to Accept as Optimum Performance"(?).

 

Just my .02cents worth.

 

Kevin,

(Yea,Still an Inliner)

[Guest zfan]

Spoke to the guys at Comp cams and he recommended this cam for my set up. Part number #12-423-8.

224/230..502-510 with 110 lobe seperation. This is a Hyd. roller cam.

What do you think? Also thinking about looking at Herbert cams I believe thats what they call them?

 

Mike

[Mike C]

Those numbers are excellent for the rest of your combo. Should idle nice and have an excellent power band. I don't like split pattern cams myself so I would choose one that was 230/230 at .050, but hey, it's your motor!

[Kevin Shasteen]

Originally posted by zfan:

.., Spoke to Comp cams and they recommended #12-423-8. 224/230..502-510 with 110 lobe seperation. This is a Hyd. roller cam.., Mike

Mike,

 

Before going any further; it is important to know that my first calculations were based on a pretty big assumption. That assumption was that you:

 

1) Actually Have 10:1 SCR

2) AND.., that SCR or DCR alone determines your Performance (SCR=Static Compr.Ratio & DCR=Dynamic Compr.Ratio)

 

The reality is: What if You Dont Truely Have 10.1 SCR? Junk in eauals junk out. Furthermore, When we calculate Compressions we are dealing with only one of the three essential elements: Volume, when we should be considering all three elements, which are:

 

1) Velocity: Speed of the Air

2) Volume: Port & Chamber Configuration (Size)

3) Density: Moisture Content of the Air

 

Obviously we cant control Density. Velocity is a control issue if we knew the Intake Port's Measurements where the air initially enters the Cylinder Head as well as the cross sectional "diameter" of the port just where the air begins to approach the intake valve: but we dont know these measurents w/out measuring them, so we move on to Volume.

 

For this exercise in futility, Volume is about all we can measure, & before we can acurately do this we need to know for certain what your SCR really is.

 

Things we do know:

 

1) 355cu.in's = Total Displacement of engine

2) Cyl.Heads have 64cc chambers

3) .036-.041" Head Gasket crushed thickness

4) 1.2cc's Crevice Volume of a SBC Piston

5) Current Cam's Profile & Future Cam's Profile

 

What I dont know:

 

1) Piston to Block Deck Clearance

2) Piston Dome/Dish cc's

 

*NOTE: I'm assuming a typical SBC Piston to Block Deck Clearance of .022"

 

The variable here that is within our control that I dont know is your piston: what Dish/Dome cc's does your piston have? I went to the KB-Perf.Piston site & looked at the 350 SBC pistons. The only one I found remotely close was a piston that gave 10.2:1; with your .030" overbore that would put the piston close to your [alleged] 10:1 SCR. This piston alwo has a 7cc dish; so let us play w/this number to determine SCR & DCR w/your current cam & future cam. BTW, correct me on your dish cc's of your piston if I'm wrong & we'll start over from scratch & do it all again w/the correct #'s.

 

727.17cc's Cyl.Displacement

 

.041" Crushed Gasket Thickness and .022" Deck Clearance coupled w/a 64cc Head Chamber, 1.2cc Crevice cc's and 7cc dish: = 85.37cc Total Chamber cc's

 

727.17cc + 85.37cc / 85.37cc = 9.51:1 SCR

 

Using the above, you dont have a 10:1 SCR; if I've "ASSUMED" correctly, for the second time, then you actually only have 9.5:1 SCR. Using this we can now determine what your true DCR is with your current cam.

 

Using the Slider Crank Mech. to determine Piston Location in a cylinder for a 3.48 stroke 5.703 Con.Rod engine we know that your current cam's 70* IVC (Intake Valve Closing) leaves .740 cylinder volume above the piston after the IVC.

 

727.17 x .740% = 538.11

 

538.11 + 85.37 / 85.37 = 7.30:1 DCR

 

In my previous post my assuming you had a 10:1 SCR gave us a 7.9:1 DCR; we now see where assuming gets us. If this second attempt at assuming is correct; then you actually only have a 7.3:1 DCR and that is why your engine is so sluggish at low rpm's.

 

Now, using this second set of "Assumed #'s" let us consider your latest cam of choice, the #12-423-8. Comp.Cam's list this cam as the XR276-10 which gives a Seat Duration of 276/282, lift .502/.510 w/1.5 rockers and a 110 LSA.

 

This cam allows the IVC @ 64* ABDC. This leaves the Cyl.Volume above the piston of .782% after the IVC. Now determine your DCR with that number, like so:

 

727.17 x .782% = 568.65cc

 

568.65cc + 85.37cc / 85.37cc = 7.66:1 DCR

 

As far as DCR's go; this isnt going to get you that much better of a low rpm idle nor will it add to your low rpm power: it will be improved but it wont be great. If you want low rpm power-then you need to get closer to the 8:1 DCR. Yea, I know this is going to be a compromise but that is how the ole engine works. When you subjugate longer duration for lessor duration-then you get sluggish low rpm power: JUST NO WAY AROUND IT.

 

If a cam change is what you truely want as opposed to swapping differential gears, then you need to be looking for the 264 Roller or the 270 Roller. The 264 Roller would give you an exact 8.0:1 DCR where as the 270 Roller would give you an 7.8:1 DCR; which may be borderline for your expectations. Again, all this is speculative without knowing what the Velocity will be as I dont know your port's entry measurements nor do I know your port's valve throat measurements.

 

Another option would be similar cam profiles from another mfg'er but with a 112 LSA. Comp.Cam's have concentrated truely on the performance enthusiast in that they believe the 106 Intake Centerline to be the optimum for airflow Velocity in filling the cylinders (actual intake centerline 106 w/exhayust centerline of 114; 106+114 = 220/2 = 110LSA) keeping in mind the lobes are 4*'s advanced. Where as other cam grinders will often give other LSA's of 112 up to 116 for their perf.cams Comp.Cam's prefers to concentrate on a 110 LSA which allows the engine to rev up quicker to its Peak Power range.

 

Hope this helped; aint all this SCR & DCR stuff just too too cool?

 

Kevin,

(Yea,Still an Inliner)

[Guest zfan]

Kevin,

 

If I remember right, The engine builder at Competition Machine said the pistons were kb flat tops 9:8 to 1 but used a very thin Head gasket made for Corvettes a few years back. I believe he said they were 21 or 23 thousands thick giving me 10:23 0r 10:25 to 1 compression.

 

The car when at idle or slightly higher rpm doesnt pick up steam until 2500 rpm's and really screams after 33-3400 rpm's. Don't get me wrong the car from a dead stop will flat out haul butt but at a cruise speed you have little zip without down shifting and holding it at high rpm to play with the chevy and ford boys on the street.

 

Mike

 

Also Im going to G-Tech it thursday evening so I'll get a real feel for where Im at. Maybe Im just to picky?

[Kevin Shasteen]

Mike,

 

If your pistons are true Flat-Tops, .023" Crushed Head Gasket, 64cc Cyl.Head Chamber Volume and your block has the usual .022" Piston to Block Deck Height for a 3.48" Stroke/5.703" Rod SBC: then your SCR should be 10.75:1

 

This would give a DCR for various Comp.Cams Roller Cams:

 

1) XR258HR = IVC 55* = 9.17:1 DCR

2) XR264HR = IVC 58* = 9.0:1 DCR

3) XR270HR = IVC 61* = 8.87:1 DCR

4) XR276HR = IVC 64* = 8.61:1 DCR

5) XR282HR = IVC 67* = 8.4:1 DCR

6) XR288HR = IVC 70* = 8.2:1 DCR

 

Still; none of this takes into consideration the Veloicty. Your Intake Manifold's restrictive or non-restrictive characteristics will have an effect, but when considering component modifications: such as an intake manifold, keep in mind that their profiles should match your Cyl.Head Port Volumes ability to flow in relation to the intention of the engine.

 

Every engine has its "Optimum" component needs. If you slap a dual plane manifold on your current engine, then you are in essence "Suffocating" your Heavy Hitting Street Engine. This will then be less of an efficient engine. So when considering your camshaft and or intake manifold: keep in mind that what you may actually need is a cylinder head w/smaller ports, smaller cam, dual plain intake. There is a [fine] very fine line between "Throttling" an engine -vs- "Suffocating" an egnine.

 

Remember, it's a Total Pkg, as no one particular component makes an engine. You currently have a nice engine; when you go to a smaller cam you will be diminishing its peak rpm power and this wont automatically make your low rpm power return if the Velocity of the airflow is still lumbering at low rpms due to the Cyl,Head Ports being too large for a street engine. Just something to think about.

 

Anyway; let us know how it turns out. I always enjoy crunchen #'s. Since I dont have a V8 of my own; I have to live out my V8Z aspirations thru you guys.

 

Kevin,

(Yea,Still an Inliner)

[Guest zfan]

Grumpy, You seggested the crane 114-142. Im currently running a hyd. roller cam, that cam is a non roller cam. Can you suggest a hyd. roller cam. Also does crane cams work with Comp cams lifters,rods etc.. probably a stupid question but figured Id ask as i usually dont mix parts.

 

Also can I reuse the push rods or will they be to long with a milder cam?

 

My friend drove the car tonite and was suprised at the lack of torque and underpowered feeling.

He's running simular set up as me motor wise with the exception of solid roller cam 234/246-488/498-110. We have almost exact compression,manifold,carb and exhaust.

 

Mike

[grumpyvette]

sorry about that,I answer over 100 of these questions aday and sometimes old age sets in and the mind just gets fuzzy, yes you can use comp cam HYDROLIC rollers on a crane HYDROLIC ROLLER CAM, the correct cam number would be something like the #119831

http://dab7.cranecams.com/SpecCard/DisplayCatalogCard.asp?PN=119831&B1=Display+Card

 

because roller cams have faster ramps you will get away with it ,(notice the timeing specs at .050 lift are very close)

#114142 flt tap.........119831 hydr roller

io=1..ic=35............io=4..ic=38

exo=51..exc=-3.........exo=52..exc-2

 

but for that matter the comp cams grind suggested is also very close, what it comes down to is you need to get a cam in the 218-224 intake duration and no more than 230 exhaust duration area to get the low rpm torque your after, the crane grind on the wider LSA should have an extremely small advantage due too a wider torque curve but the comp cams grind should also have its tourque curve build slightly faster (both cams are so close I doubt youll ever tell the differance!)

[Kevin Shasteen]

Dont forget about the Lobe Intensity of a cam. The comp.cam you are currently running has a 52* lobe intensity compared to the cam card on the Crane which indicates a 35* lobe intensity.

 

Crane's card also indicates the valve spring "Open Seat" pressure of 330lb/psi compared to your Comp.Cam's requiring their 290lb/psi and slightly different installed height/open seat height's compared to the Crane's cam card.

 

Indicating that the Crane cam has a slightly more agressive lobe which will require [slightly] that much more pressure on the valve.

 

Crane measures their seat to seat events at .004" while Comp.Cam's measures theirs at .006; Like Grumpy said-close enough to compare these apples to oranges.

 

If you are not going to put in lower differential gears then I would not entertain a camshaft w/duration close to what you already have; IMHO, I'ld consider a duration in the Advertised 270 range: But then again-I'm not really good at spending other people's money. Just something to think about.

 

Any chance you might call Edelbrock and ask their tech lines what their port volumes are for your cyl.heads?

 

Dont ya just hate all these variables; oh yea/would you like paper or plastic with that new camshaft?

 

Kevin,

(Yea,Still an Inliner)

[Guest zfan]

Kevin, Im going with the 3.90 gears as well. Sometime within the next month I will trash the 3.54 rear. Also think I will try the weiand stealth intake manifold, it's a dual plain. I would put my Edelbrock rpm air gap on but it will not fit under the hood with the holley 750 double pumper .

 

I will call Edelbrock today and get specific numbers!

 

Mike

[Guest zfan]

By the way to give you an idea of what a dog this car is, yesterday on the way home from Mckinney I ran into a 1990 5.0 mustang with a chip, exhaust and cold air intake. From a roll 30/40 mph I could not shake him up to 90 mph. Shifted at 6200.

How embarassing!

 

Mike

[Kevin Shasteen]

Mike,

 

Just had a thought; How well is your 750 double pumper tuned? If is not properly tuned, you could be dumping too much fuel at too low of an rpm. This could be "flooding" your engine, till the air velocity in the heads pick up(?). Have you pulled any spark plugs lately & checked their colors/conditions?

 

When you call Edelbrock, try to not only get their flow #'s in .100 increments up to .600; but also get their Intake Port measurements where the air first enters the cylinder heads Length"xWidth" just adjacent to where the push rod's travel through the head.

 

Also, if they have the info available, try to get the port valve's throat cross diameter, this area is exactly at the point where the air hits the valve stem guide just before it hits the top side of the valve; as this area bottle necks. These two measurements will determine "Velocity" of a cyl.head at any one specific "RPM".

 

BTW: Unless you know the driver of that 5.0 personally-dont simply accept what he claims he has in his engine; many rodders will lie thru their teeth just to get in you head, knowing the whole time they have more mod's than what they are leading on.

 

Having said that, I think if you are going to a lower gear ratio, then you will want more than a 3.90 as that would only net you 300rpm's more than what you currently have. Consider something a little larger and your engine will really come alive.

 

Let us know what Edelbrock tells you.

 

Kevin,

(Yea,Still an Inliner)

[DavyZ]

Mike (zfan),

 

If you are parting out your old Victor manifold, I'm interested. This is a shameless post, sorry

 

Email me, Dude.

 

Davy

[Guest zfan]

My friend just installed a zz4 crate motor in his Jenson Healy and man with 700r4 and 345 rear gears that thing flies. At 3 grand he punches it and breaks the wheels loose in 2nd and sometimes in drive. It's the 385 horse zz4,Im seriously looking at swapping in that cam. I believe it is a hyd. roller but I do not have cam specs as of yet. What do you know about them? He has the same heads as me and is running a rpm manifold with 670 holley vacuum secondaries.

 

Mike

[Guest zfan]

Davey, If I decide to get rid of the Victor Jr. I will give you first shot.

 

Mike

[Kevin Shasteen]

Mike,

 

Have you called Edelbrock yet to find out which Cylinder Heads do you have? Surely Edelbrock has some part# in a readable place whereby you can simply look at them and tell which cylinder heads you have; yes/no?

 

Completely assuming here, I'm betting that your 750 double pumper may also be a part of the problem. Completely assuming here, it may be dumping to much fuel at low rpms; causing enough of a stumble that it impedes the power build up process up till the airflow speeds up which you have said-is around the 3500 rpm range. This is just an assumption though. This extra fuel adds to your single plane intake manifold's phenomena of slower Velocity within the Airflow characteristics making things doubly (is that even a word?) as bad; again, right up until Velocity speeds up-which for your engine appears to be at the 3500rpm range.

 

About the ZZ4 cam; I dont have any spec's on that cam so without knowing anything I'ld be afraid to venture a guess.

 

Kevin,

(Yea,Still an Inliner)

[Kevin Shasteen]

Mike,

 

The #6089 Edelbrock heads IMHO are not the problem, in that they are considered to be in the upper-mid range as far as a [sTREET] cylinder head is concerned. But, again IMHO, your cylinder heads react to a problem you already have; in that they are too small for the Camshaft, Single Plane Intake Manifold and possibly Carb that you have chosen. Providing that the carb is improperly tuned, then it may be exaggerating the effect of the "High Duration/Single Intake Manifold, by dumping too much fuel at low rpms (if we assume it isnt properly tuned to begin with).

 

The notes I've collected on the #6089 heads indicate the airflow #'s, taken at 28" H2O, to be:

 

Lift...Int/Exh

.100...67/58

.200...130/108

.300...183/144

.400...226/169

.500...229/175

.600...232/182

 

Now if you were to look at the airflow #'s of other cylinder heads-such as the Airflow 190 & 195, Trick Flow G2 (190 CC Intakes) you will notice that their airflow #'s within your .500-.600" lift area are going to only be about 20-25cfm difference(?). Not that big of a change; so what gives then?

 

The difference will be the fact that your overlap (the Lobe Separation Angle) is also effecting the slumbering Airflow Velocity at low rpms. The LSA effects Low Rpm Airflow because it is the overlap that determines the amount of Reversion at low lift...smack dab in the middle of your Cam's OVERLAP is where your camshaft will find itself at low lift. So Overlap has an equal important role in determining Airflow Velocity Characteristics "AT LOW RPMS" as will your Dynamic Compression has which is determined by the IVC event. Once the rpm's pick up then the Velocity of the Airflow also picks up and LSA has no real effect anymore; now Duration is the key indicator of your peak power at higher rpm's and not the overlap. Overlap will still have an effect on the range of your peak power but once Airflow increases/Velocity Increases-and Overlap no longer will have the final say-Duration will have the final say.

 

Other articles I've read indicate that Edelbrocks Cylinder Heads dont have as good of "Swirl" numbers as the newer designed Alluminum Heads. This will also exacerbate the slumbering Airflow Velocity at low rpms, especially if the parts are mismatched.

 

I'm betting if you go with a properly tuned carb, dual plain manifold, and cam with a smaller duration that includes a 112 LSA; your engine will act like an entirely different engine. BTW: In Lingenfelters book he states that when looking at cams if you find a cam w/exact spec's whereby the only difference is the Duration-he suggests to take the cam with the smaller duration as it will allow better cylinder pressures while still breathing in the same amount of air.

 

Lastly, when looking at GM's cams-be aware they have interesting ways of measureing their Asvertised Duration. So their .050" will give you an at .050" measurement, but it wont give you the Lobe Intensity. Remember Lobe Intensity will tell you if the lobe ramp is a passive ramp or an aggressive ramp. I dont have any info on the ZZ4 cam. I do know that most of GM's perf.cam's have ramps similar to the old muscle car cams: Excessive Duration -vs- Moderate Lift with a 114, 115 or 116 LSA. Their roller cams follow this w/the exception to having a higher lift.

 

If I were you; I'ld concentrate on a dual plain manifold, the first ZZ4 cam (Pete likes that rumpity rump sound of Reversion ) and a smaller or properly tuned carb...I'm betting that will get you where you want to be for a street performing engine.

 

Lastly; when looking at the Duration spec, remember that the higher the Duration is on a cam-usually the higher the rpm will be that your engine comes on to Peak Power. You've already said you dont like the 3500rpm onward Peak Power and that you'ld like a cam whereby you have low rpm power also-dont get to crazy with high duration cams or you might find yourself making the exact same mistake of slumbering Airflow at low rpms: "Caveat Emptor-Let the Buyer Beware".

 

Hope all this wasnt too long & helpful in some manner.

 

Kevin,

(Yea,Still an Inliner)