I thought about getting AFR heads with bigger combution chamber, that would lower my CR. Don't know what CR is best, but somewere around 8.5-9.5

I was thinking of Procharger P1-sc or D1-sc, with innercooler. More then likely P1sc.

Will this combo work until i have money to stroke out and really build a serious motor.

I was thinking of only 8 psi on the stock parts with lower CR.

How well would the stock bottom with lower CR hold up to 8psi?

OK, Just 8# of boost with stock parts. What would the life be like.

Thanks to all

 

Heads alone won't drop CR that low. Add some forged pistons while you've got it torn down.

 

I'm pretty sure you can go that much lower with larger combustion chambers. I wouldn't go more than 8# intercooled and I wouldn't expect that to last very long with the power you would be making through those heads.

 

i figure a lot of people are running 8#s with stock motor, and yet they will eventualy brake something, but if the CR was lower, i thought that would save some life on the internals. Enough to have some fun and save up for the 381. I know i wouldn't go over 8#s with stock parts, but......

 

The pistons just can't handle it.....low compression or not...more than 8lbs that is. Hell..some push it to 9 but not more...and 9 is risky.

Joe

 

I will disagree... all things else equal, an 8.5:1 CR motor, 8 to 10# of boost with the stock hyper pistons and a good tune would *probably* last a long time. Believe it or not, the stock pistons can take a considerable amount of power - it's detonation that they can't handle. With that low of a compression ratio and a decent tune, I can't see less than 10# of boost hurting a piston...

 

hyper pistons and boost just are not a good combo. With the money you have spent why not just spend another 420 for some forged srp pistons. With a good tune i bet it wont last more than 15k with stockers in. I also cant see how you will able to lower the comp that much with out touching the pistons. Hyper slugs work better with gas than induction. So long your not detonating the comp will not make any dif in saving parts just up the power some, and the you can run less boost with same gain.

 

It's very easy to get the C/R lower without changing pistons... You can get very larger combustion chambers with aftermarket heads. I have personally done this on a T-76 setup without a wink of problems from the pistons - the stock hypers looked as good as new when they came out.

C/R makes no difference in saving parts in a forced induction setup? Less boost on a lower C/R engine will make more power? Do you have ANY idea what it is you're talking about?

 

Well Eddie.....what you see and what MANY people on this board have said from experience are two different things. The proof is in the pudding I guess. I'm running an 8lb pulley on mine (making 7 lbs) and it is fine...only been there for 900 miles so far. I already purchased a short block and will be going with some SRP pistons. If he wants to risk it more power to him...and you...but i'm not willing to risk the damage and downtime....I like to have know when and for how long my car will be down. It is just crazy to assume that the stock pistons will handle 10 lbs...even intercooled with lower compression. The ringlands will not handle it.

Joe

Ask Krause for his opionion and personal experience in this matter.

BTW...just keep in mind ....with the stock pistons...it only takes one time to pop em...that could even be a fuel pump that goes south...forged pistons will better resist the damage usually caused by detonation.

 

Not sure why you're tying to lump the results of people with the stock compression with what the original poster was asking - they are completely different circumstances. Whether you want to believe it or not, C/R on a forced induction car changes a lot. In the absense of detonation, the stockers are probably mechanically sound to 450rwhp, if not more... you're not going to have near the same cylinder pressure after dropping the CR down to 8.5:1, and I think detontaion with 10# on 8:5 to 1 is *very* unlikely.

 

You are entitled to an opinion....but as for the person who started this thread...if you go over 8lb of boost....you are asking for it.

Joe

 

8# boost ONLY with stock internals.

HOW WILL THE STOCK INTERNALS HOLD UP TO 8# OF BOOST WITH LOWER CR OF 8-9.

Higher boost when i build the motor up to either 381 or 353

I just wanted to know how well the stock internal;s with lower CR and 8# of boost only.

 

8lbs should be fine for a while on stock internals....just have a tune and/or pull some timing with an MSD boost retard box.

Joe

 

Also if you put AFR's on your motor, it will flow very well, thus making less boost. Probably 6 psi instead of 8. Here is the comp. ratio with AFR's and stock shortblock: 64cc is 9:5:1, 66cc is 9:3:1, 68cc is 9:3:1, and 70 would be 8:9:1. I got those straight from AFR also. A mild blower cam would really help.

 

Rods will die somewhere between 550-600HP, so pistons and detonation are not the only "weak" point.