331 STROKER COMPRESSION INPUT NEEDED

d_gtracer · Oct 22, 2006

I am having my 87 GT 331 stroker motor being built by S&B RACING ENGINES out of florida, and have heard different opinions on compression and cylinder head intake runner size. I know everyone has an opinion so please if you can give recommendation based on your knowlegde and not what you hear is appreciated. GUTS of motor are forged rods, forged crank, ross pistons, It was recommended to stay around 10:1 compression with a 185, 195CC intake runner AFR HEAD(possibly Dart) ,Motor will see occasional nitrous(is lower compression better? and why such a big intake runner head? to get the flow an AFR 185 puts out? builder stated motor will be 10 1/2 :1 and wants to use 210CC intake runner aluminum cylinder head, output between 420-450HP. Is bigger better??

woodsy · Oct 22, 2006

Nitrous loves compression, the more the better. For a pump gas ride leave it between 10-11:1, as for the cylinder head runnner size. I am very curious as to what 210cc runner head they want to use! 185-195-205 is not too big either. It's all in the cam.

retro50 · Oct 22, 2006

If nitrous is in the plans run the 210 c.c. heads he (The builder) wants to use or some A.F.R. 205's. Run the compression in the mid to high 10's And keep the quench in check. Nitrous doesn't really care what the compression ratio is. This will make a nice street/strip combo. And 420-450 at the flywheel is not out of the question.

304billet · Oct 23, 2006

I agree with the above 10.5 to 11:1 CR and a 205cc head. I would do either a AFR 205 or TFS Track heat 205 head. I think ur builder is thinking of a Victor Jr. head with 210cc. AFR makes a 205cc head with a nitrous exhaust port. Part # 1452.

I would also do a custom cam designed around the head and intake cfm flow among other things. Cam Motion, FTI or Jay Allen.

I would also suggest if ur running EFI a Holley systemax ll intake or TFS-R intake port matched.

u s/b hitting 375-400 @ the RW, before the nitrous. Remember, that stock 302 roller block is good to 450-500rwhp. with a 75-100 shot u will be at it's max.

u may want to consider finding a mexican 302 roller or buying a dart sportmen block good to 1200hp for around $1700.

d_gtracer · Oct 23, 2006

Thank you for your input, the builder is looking to use PBM performance aluminum cylinder heads the name I believe was Strike Force. the heads can be found at www.pbmperformance.com. but when I called the company the cannot give me any flow numbers. The cam I will be using is a Comp 236 XFI 236/248 .579/.579 . I can check flow numbers for AFR, DART, WINDSOR. But do I really want to spend $1200 on a set of cylinder heads with no flow numbers when putting together a solid bottom end? the answer I got was the heads would flow in the 250 range, but at what lift is the key isnt it? on both the intake and exhaust . The AFR 205 has a 180CC intake runner, should I be looking for good flow or just a high intake runner size ? FLOW CORRECT?

d_gtracer · Oct 23, 2006

The car is running 24lb injectors, trick flow street heat intake ( Not the track one) , full msd, car is pretty much set up for street/strip. I just dont want to be concerned with detonation at 10 1/2 :1 like I have heard is very likely. Will detonation be an issue at 10 1/2 :1 whether I spray the car or not. It is my weekend driver, not a flat out drag car.

bullitstang1313 · Oct 24, 2006

Pump gas will not stand up to 10:1 or 11:1 compression without knock. Most vehicles built today use a 8.5:1 or 9:1 compression ratio. The higher the compression the higher the octane you will need. Forced induction needs lower compression since you are effectively increasing compression by increasing the amount of air in the cylinder. Nitrous doesn't require either. If you go with a higher compression it is the same as NA except for the fact that nitrous will increase the power output. Higher compression will give you more power all around, but you will need the proper safety aspects in order to avoid detonation. This can be done by retarding the timing during use of nitrous.

woodsy · Oct 24, 2006

bullitstang1313 said:
Pump gas will not stand up to 10:1 or 11:1 compression without knock.

craziest thing I have read thus far today on this forum. It's so blatantly false its not funny.

bullitstang1313 · Oct 24, 2006

By pump gas, i'm talking about 87 to 93 octane. If you stick with stock timing of 12 degrees or the typical advanced timing of 14-18 and are running 10:1 or 11:1 compression on a fuel injected engine you will experience knock. You can use 10:1 or 11:1 compression with 93 octane and retarded timing and not experience knock, but knock will be common with this high of compression. If this wasn't the case automotive engines would be built with this high of compression in order to be more efficient and with more power.

woodsy · Oct 24, 2006

bullitstang1313 said:
By pump gas, i'm talking about 87 to 93 octane. If you stick with stock timing of 12 degrees or the typical advanced timing of 14-18 and are running 10:1 or 11:1 compression on a fuel injected engine you will experience knock. You can use 10:1 or 11:1 compression with 93 octane and retarded timing and not experience knock, but knock will be common with this high of compression. If this wasn't the case automotive engines would be built with this high of compression in order to be more efficient and with more power.

I dont know how my 557 inch, 377 inch cleveland and 418 inch motors are running on 93 then. That damn toyota prius running 13:1 from the factory is a miracle. You can run 10-11:1 all day long on pump gas. There are beyond countless amounts of mustangs running 10-11:1 on pump gas, injected with 12-16 degrees initial timing.

BlownFiveLiter · Oct 24, 2006

Stock timing is 10° BTC, and yes, you can run 10:1ish compression on pump gas. Many cars come from the factory with compression that high, and the key to fighting off detonation is in the tune.

bullitstang1313 · Oct 24, 2006

I dont know how my 557 inch, 377 inch cleveland and 418 inch motors are running on 93 then. That damn toyota prius running 13:1 from the factory is a miracle. You can run 10-11:1 all day long on pump gas. There are beyond countless amounts of mustangs running 10-11:1 on pump gas, injected with 12-16 degrees initial timing.

Many cars come from the factory with compression that high, and the key to fighting off detonation is in the tune.

I'm not trying to say that it is impossible, what I am saying is that it has to do with the technology used. Carbed vehicles don't have to worry as much because they are not typically designed for stoich air fuel ratio and the extra fuel will help prevent detonation. Toyota uses advanced technology and controls as well as redesigned combustion chambers in order to reach their targets of higher C.R. which helps emissions reduction. What i'm trying to say is that an inexperienced car owner, who doesn't have a clear idea of the desired engine and who doesn't have tuning experience should play it safer than those with more experience and knowledge. I'm not trying to insult d_gtracer or you either woodsy, I'm just expressing that d_gtracer should get a clear view of the requirements and the consequences of any decision decided. I didn't mean to come off as arrogant and ignorant.

mstngjoe · Oct 24, 2006

d_gtracer said:
....the builder is looking to use PBM performance aluminum cylinder heads the name I believe was Strike Force.......but when I called the company the cannot give me any flow numbers........The AFR 205 has a 180CC intake runner........

Those heads are all over ebay.....most likely chinese knockoffs similar to Victor Jr heads.

"Can't" or won't give flow numbers??? Probably not too proud of them.

The AFR 205 head has a 205cc intake runner.....

EDC · Oct 24, 2006

mstngjoe said:
Those heads are all over ebay.....most likely chinese knockoffs similar to Victor Jr heads.

"Can't" or won't give flow numbers??? Probably not too proud of them.

The AFR 205 head has a 205cc intake runner.....

The heads "are" definitely the Chinese Edelbrock knock-offs. I know what PBM and other WDs like them sells.

Visit that "other" web site for an 11 page diatribe on how much work it takes to get them "decent"...

Save money and get AFR 205 heads right off the bat. They cost more in the beginning but in the end, a lot less money and aggrevation!

Ed

304billet · Oct 24, 2006

Listen to Ed. Get the AFR 205's or new TFS Track Heat 205 cnc'd head. Those new track heat's flow 300/220 @ .500 lift. Also don't use an off the shelf cam, go custom.

ur CR of 10.5:1 on the street with pump gas is fine. with a good tune u won't ever see detonation.

d_gtracer · Nov 18, 2006

Thank you for taking the time to help me with the concerns I had, I understand everyone has different opinions. Engine builder and I have made the decision. Motor will be 10:1 compression, most likely the AFR heads, oh and 1968 302 mexican block is on its way! Thanks to all that replied

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