Heads and Flow and Stuff

[Pop N Wood]

I have been reading these posting for the last week or so and I have a question concerning heads.

 

First let me state that I have been reading about engines since the days before catalytic converters, but I have never actually built one. Years of looking at engine specs has convinced me that one of the keys to serious horse power is the heads. The problem I am having is figuring out how to balance all the advice I have read over the years.

 

Seems like anytime someone asks gumpyvette (who by the way really explains things well ) to select between two heads, he recommends the head with the highest flow rating. Yet pick up an issue of Hot Rod and they are always talking about maintaining adequate flow velocity. Get on the Edlebrock site and they tout their "total power package" and how it matches the induction components.

 

Now I guess my questions are: shouldn't the heads be selected with the rest of the intake system in mind? And if this is true, then wouldn’t it also be true that the higher flowing head is not always the best? If engine drivability and longevity is not totally a non-issue, then how does one scale back the choice in heads? If I decide to go with a 302 or 327 to build a slalom racer that revs, how does this affect things? When is a smaller intake plenum a better choice?

 

GM produced a ZZ430 engine as an example of what can be built from their catalog. This engine uses their fast burn heads and HOT cam to kick out 430 HP. Seems like a pretty potent package. If I had the money for this crate engine and liked this target HP, how would I be better served building such an engine from other manufactures components? Or are you guys saying for the same money I could get a lot more engine?

 

Look forward to any comments or opinions you guys have.

[grumpyvette]

now thats alot of questions so lets try and answer a few of them, first read this, I already posted before but you need to understand it.

 

.ever wonder why your engines torque curve gets higher with the engines rpm level untill 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 theres not enough air velocity to mix the fuel correctly or produce a effective ram tuneing effect but as the rpms increase the cylinders fill very efficiently untill 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 thats only about 35% of the time and theres 41.6 intake strokes per second , thats only 1/60th of a second for air to flow into the cylinder, I found this graph that shows the relationship between V.E.(VOLUMETRIC EFFICIENCY) and AN ENGINEs torque CURVE

http://www.n2performance.com/lectures/lect1/n2perf5.gif

 

WHAT THAT GRAPH SHOWS RATHER EFFECTIVELY is that 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 acomplish that at the more power your engine makes, remember the formula for hp is (torque x rpm/ 5252=hp)so moveing the torque curve higher in the rpm range increases hp. btw heres info on how to find the effective tuneing lengths for th intake and exhaust lengths,

--------------------------------------------------------------------------------

ram tuned and rpm matched cam timeing for the effective use of the headers and intake system can get you to slightly over 100% V.E. at (1) rpm range where the tuneing is most effective, look here,

http://www.grapeaperacing.com/GrapeApeRacing/tech/intaketuned.cfm

heres how to find the correct tuneing lengths

http://www.engr.colostate.edu/~allan/fluids/page7/PipeLength/pipe.html

 

now read this,

look this site over for ideas,

http://www.ryanscarpage.50megs.com/combos1.html

http://www.airflowresearch.com/

(look over the dynoed engine combos and take special note of the fact that the heads flow big numbers but the cams are relatively mild)

 

the first thing you will notice is the HEADS AND CAM CHOICE are the key to makeing power, now if you have been around cars long enough youll remember those killer 375hp;) 396 camaros that could beat most hemi powered road runners in 1969 well they had 305cc rectangle port heads and really had about 425 hp but with headers,great tuneing and a cam change 500 hp was within reach now the main reason I bring that up is that those engines had 49.5 cubic inche per cylinder and ports of 305cc for a 6.16cc to cubic inch port to displacement ratio, a 350 with the same port to cylinder ratio would have a 269cc port size!now the reason those engines made that kind of power was those engines could effectively fill their cylinders at high rpms because those heads flowed massive anounts of air, (around 325cfm) but you also found if you owned a few (I DID)that the cam that came in them had too much duration and not enought lift to produce the best and broadest torque curve. yet even with the stock cam they had plenty of power to totally destroy the rear tires just by flooring the car at any speed under 25mph.

 

now thats a lot of reading to give you a base of info so heres some answers,

 

"Seems like anytime someone asks gumpyvette (who by the way really explains things well ) to select between two heads, he recommends the head with the highest flow rating. Yet pick up an issue of Hot Rod and they are always talking about maintaining adequate flow velocity. Get on the Edlebrock site and they tout their "total power package" and how it matches the induction components."

edelbrock has a lot of money tied up in those performer rpm heads so they have got to try and sell them, while not bad heads for the street they make WAY LESS POWER THAN THE LARGER AFR or PRO-LIGHTNING HEADS but thats because edelbrock built those heads to get a combination of very high air speed in those small 170cc ports for good fuel mixing in the 1000rpm -3000rpm range because they expect most of those heads to be used in heavy cars with 283-350 engines for daily driveing so they designed the heads to be most efficient in that range. but the engines in this forum are used in light weight cars with in most cases reasonably high rear gearing where low rpm torque just destroys your tires. the larger port heads work much better in the higher rpms and remember the hp is (torque x rpm/5252=hp)so the higher the rpms you can effectively fill the cylinders at the more power strokes per second your engine can make and the more total torque the engine makes per minute, now it takes only about 60hp-70hp to move a car in traffic at 65mph while your engines in the 1000rpm-2500rpm band for daily driveing so as long as the CAM YOU CHOOSE has timeing points that EFFECTIVELY fill the cylinders in that rpm range any size port will work at least adequately, its not the port size that has the biggest effect its the cam timeing and the carb and plenum size and runner length of your intake manifold that determines the torque curve but its the port size and chamber shape, valve size and valve shrouding and total flow numbers that effect your max power

 

"GM produced a ZZ430 engine as an example of what can be built from their catalog. This engine uses their fast burn heads and HOT cam to kick out 430 HP. Seems like a pretty potent package. If I had the money for this crate engine and liked this target HP, how would I be better served building such an engine from other manufactures components? Or are you guys saying for the same money I could get a lot more engine?"

yes you can get alot more engine for your money if you carefully match parts for max power production, for that same $6500 you would spend on a ZZ-430hp engine (LOOK AT THE FINAL PRICE NOT THE BASE PRICE) you can get 500hp building it (your own custom engine)yourself (look at combos #15,#16,#17,#71 on the RAYN SITE) and remember the new pro action heads flow just as much air and are cheaper

 

http://www.sdpc2000.com/cart.asp?action=prod_detail&catid=120&pid=464

 

http://www.sallee-chevrolet.com/Photos/zz430pics.html

 

http://www.sallee-chevrolet.com/ChevySmallBlockV8s/SalleeZZ430HP.html

 

http://www.sallee-chevrolet.com/Ascripts/prices.cgi <-$6500plus shipping

[Pop N Wood]

Yeow! Wish my cable company returned calls this fast!

 

Looks like I will have a lot more reading to do, thanks for the info.

 

You seem to be saying a lot of what I wanted to hear. Most Hot Rod articles are tailored toward building torque to power heavy cars. But Z specific articles always talk about the trouble such a lightweight car has in hooking up low-end torque. That is why I keep leaning toward a shorter stroke engine. I've always wondered if just building a 350 toward higher RPM flow would do the same (and save me $ using the more common 350 internals). You are one of the first people to give me a specific combo.

 

My immediate goals are much more modest: just find a good donor car and drop in a near stock engine/trans combo. Then, once the paint and brakes are done, start mapping out the go fast parts!

[grumpyvette]

read this it will help

 

http://www.vettenet.org/torquehp.html

 

http://ryanscarpage.50megs.com/street.html

[Pop N Wood]

OK, one last question (maybe two).

 

Read what you forwarded and found it very informative. I especially like the Ryan page...will spend some time on that. I am comfortable with the math and physics and already understand the concept of volumetric efficiency. From reading other postings I now realize you often recommend balancing the available intake pieces, but seem to prefer canfield heads when they are an option.

 

But the question I still have is when is more engine too much, especially for a Z? I don’t want to build a drag racer. My car will be summer’s only street machine that will hopefully see some short slalom club racing. Thus the idle to 2500 RPM band will be more than just something to get through in the first 100 feet of the drive.

 

Now like your articles say gearing will go a long way to keeping me in the power band, even with short tracks. But what I am trying to get a feel for is how much “drivability†can be retained and still have an awesome engine? I know this is a very subjective question. I also know money will probably be the limiting factor anyway. The thought of 500 HP is captivating and since this won’t be a daily driver I don’t mind (and would even like) a grumpy idle. But I would like to stop short of something that would be miserable to drive on a long road trip.

 

The second question concerns your opinions of roller cams. I have noticed in several posts that you like to recommend solid lifter cams. Any particular reason?

 

Thanks again.

[grumpyvette]

"Read what you forwarded and found it very informative. I especially like the Ryan page...will spend some time on that. I am comfortable with the math and physics and already understand the concept of volumetric efficiency. From reading other postings I now realize you often recommend balancing the available intake pieces, but seem to prefer canfield heads when they are an option."

 

all parts of an engine build must be ballanced to get the most possiable hp from an engine(matched as to their intended rpm and hp range)or the resulting engine will in most cases run down to or even below the level of the lowest potential (hp wise) part level, now I think the AIR FLOW REASEARCH cylinder heads are as good or in some cases better than the CANFIELD HEADS and the TRICKFLOW ® series and the DART PRO1 series heads are also great heads but I think the CANFIELD 223cc head is one of the best deals for the money spent, look here,

 

http://www.dartheads.com/sbpro227.htm

http://www.airflowresearch.com/

http://www.canfieldheads.com/sbc_2600.html

http://www.trickflow.com/product/prhomefeature_index.htm

 

what youll find is the canfield heads give you about the most features and flow for the money spent if your looking for a true high performance head, now the other choices may even be better heads but they cost quite a bit more money, it just hard to get 300cfm of flow in a head for the $ 1,145.00

canfield charges

"But the question I still have is when is more engine too much, especially for a Z? I don’t want to build a drag racer. My car will be summer’s only street machine that will hopefully see some short slalom club racing. Thus the idle to 2500 RPM band will be more than just something to get through in the first 100 feet of the drive."

if you want the most responsive head out there for almost all rpm ranges its probably the AIRFLOW RESEARCH 195cc CNC head but it costs about $1250-$1750 depending on the option you choose.

 

"Now like your articles say gearing will go a long way to keeping me in the power band, even with short tracks. But what I am trying to get a feel for is how much “drivability” can be retained and still have an awesome engine? I know this is a very subjective question. I also know money will probably be the limiting factor anyway. The thought of 500 HP is captivating and since this won’t be a daily driver I don’t mind (and would even like) a grumpy idle. But I would like to stop short of something that would be miserable to drive on a long road trip."

 

your not going to get a 460hp- 500hp engine of 350-406 displacement thats suitable for long trips and has a relatively smooth idle unless your running a supercharger, to get enough fuel air mix through an engine without a supercharger you will need a cam and heads that can breath in the higher rpm levels and that will require too much duration for smooth low rpm use (idle to 1800rpm) dropping back to about 425-450 hp though and you can get to have almost what your looking for but that will be a compromise in that you will be giveing up about 50hp in exchange for an engine with better street manors, if you want both you need either a bigger engine or a supercharger, look here,this is what your asking for

http://www.sdpc2000.com/cart.asp?action=prod_detail&catid=120&pid=693

 

"The second question concerns your opinions of roller cams. I have noticed in several posts that you like to recommend solid lifter cams. Any particular reason?"

roller cams are great, I would use them exclusively but they have one bad point COST!!! a good roller cam and kit will cost $700-$900 while slightly less but reasonable performance can be had for about $150 with a solid lifter cam, thats the main reason I recommend them, and hydrolic flat tappet cams while excellent can not quite match the hp or rpm potential of a good solid lifter cam so i figure that if you know enought to be able to change a cam and tune an engine the idea that you might need to adjust your valves every 4 months is no big deal

[Pop N Wood]

I guess I could live with "only" 425-450 HP. It would be a step up from the inline 6 anyway .

 

Thanks for the info. Once again, your words speak valuable and true.

 

This board is sure cheaper and more to the point than any Hot Rod subscription.