Lower compression or stay at stock compression

[csb85]

Car currently has a p1sc which I may upgrade to a d1. With the current setup the car made 605/ 480 I would like to be between 650-700 eventually. I have no desire to go with an after market fuel system and dont have e85 in my state only 93octane. So with these goals do I stay with the stock compression and run less boost or do i lower the compression and run more boost ?

 

[me32]

for safety on pump gas go with lower compression. if you had E85 i would high compression.

 

[csb85]

Idk what I want to do one part of me says go stock compression and stay around 10 psi. The other part says go low compression get a d1 or f1 blower and run 12-14 psi. Decisions decisions !

 

[truebluedevil02]

stay stock. If you lower the compression you'll just end up putting a smaller pulley on it to get back to the same hp its at now vs leaving it where it is.

 

[kevinp]

Idk what I want to do one part of me says go stock compression and stay around 10 psi. The other part says go low compression get a d1 or f1 blower and run 12-14 psi. Decisions decisions !

FWIW the D1SC is very capable of moving enough air. I ran 9.0s with a 9.5:1 347 LS1 car with a D1SC pulley'd for max impeller, 780rwhp or something like that.

P1SC I would say keep the higher compression, the D1SC is a very capable blower. F1A will get you to 1000 flywheel hpi and has a great midange punch, great for a smaller CID engine.

But with variable cam timing and pentroof chamber these can obviously tolerate a good amount of boost with stock compression. To me it would depend on what pistons are available. Or you can always just compromise and get some 10.5:1 pistons made

Also look into the difference between 4032 and 2618 pistons, I prefer the 2618s myself but there is a lot to be said for the 4032s on an everyday car.

 

[csb85]

Yeah I'll stay with the p1sc for a little while. And maybe down the road upgrade it to d1. Really don't have the money now to upgrade the blower. Plan is to either have my block built or just drop an aluminator in and then sell off my engine as is. Might add headers boss intake and Id 1000 injectors.

 

[kevinp]

Yeah I'll stay with the p1sc for a little while. And maybe down the road upgrade it to d1. Really don't have the money now to upgrade the blower. Plan is to either have my block built or just drop an aluminator in and then sell off my engine as is. Might add headers boss intake and Id 1000 injectors.

Its a tough call, depends on your ultimate goal. You will lose maybe 20hp for a point of compression unless the blower can move enough air to make up for it (without overspinning it or getting too hot). Off boost driveability will be affected as well with lower compression.

Maybe the P1SC with the headers might be enough fr you..

Unless you plans are fairly big power I would probably stick with the stock compression..

 

[kingnut]

for safety on pump gas go with lower compression. if you had E85 i would high compression.

cylinder pressure is cylinder pressure. i think all the lower compression stuff has been debunked. higher compression means less boost to achieve the same goal.

 

[kevinp]

cylinder pressure is cylinder pressure. i think all the lower compression stuff has been debunked. higher compression means less boost to achieve the same goal.

Yes and no, higher compression can spike combustion temps pretty quick (think diesel), especially on a small bore. But flame travel, chamber design, hot spots etc also play a big part. Plus with these you have variable cam timing and can decrease dynamic compression, pentroof chamber, 4 valves etc, all good for detonation resistance. Plus on real high HP stuff lower compression = more room to pack fuel in there.

I dont like to lower compression just to lower it, if you can control detonation and use less boost to make the same power I'll take the higher compression any day.

 

[alex12gt]

i stayed with stock once you go lower you have to push harder

 

[slow306stang]

Car currently has a p1sc which I may upgrade to a d1. With the current setup the car made 605/ 480 I would like to be between 650-700 eventually. I have no desire to go with an after market fuel system and dont have e85 in my state only 93octane. So with these goals do I stay with the stock compression and run less boost or do i lower the compression and run more boost ?

My boss manifold, long tube, D1sc setup made 640/512 on the same dyno at 10.1psi. I'm sure your P1sc would have made similar numbers with the addition of the boss and long tubes.

I'd do the boss intake and longtubes with an 11:1 engine. It may take 11-12psi to achieve the goal of 650+ with the P1sc. Do you have the stage 2 procharger kit?

 

[mtrsprt]

You can't go wrong with D1SC. I love mine. I'm still 10,000RPM impeller speed below max....

 

[csb85]

My boss manifold, long tube, D1sc setup made 640/512 on the same dyno at 10.1psi. I'm sure your P1sc would have made similar numbers with the addition of the boss and long tubes.

I'd do the boss intake and longtubes with an 11:1 engine. It may take 11-12psi to achieve the goal of 650+ with the P1sc. Do you have the stage 2 procharger kit?

Yeah I have the stage 2 currently running the P1sc at 8 psi

 

[csb85]

You can't go wrong with D1SC. I love mine. I'm still 10,000RPM impeller speed below max....

What fuel you running with the numbers in your sig? Still on the stock fuel system ?

 

[mtrsprt]

What fuel you running with the numbers in your sig? Still on the stock fuel system ?

I was running a 96 octane blend at the time. 16.5-17* of timing. BAP and ID725 injectors. The fuel delivery was maxed out. I have a 21V JMS Booster on the way. Another 3-4V should get me up to about 750-760 safely.

 

[slow306stang]

I was running a 96 octane blend at the time. 16.5-17* of timing. BAP and ID725 injectors. The fuel delivery was maxed out. I have a 21V JMS Booster on the way. Another 3-4V should get me up to about 750-760 safely.

I posted on your thread in the Boss section. You're flurting with disaster and that car needs a fuel system. It's simply making too much power for the stock fuel setup.

 

[mtrsprt]

I posted on your thread in the Boss section. You're flurting with disaster and that car needs a fuel system. It's simply making too much power for the stock fuel setup.

I've been doing this for over 17 years. I know what the limits are. Thanks.
I know exactly what's going on with my setup at all times. One of the benefits of data logging and paying complete attention to how a supercharged EFI system works..........like I said before... I will see how much further I can get with 3-4V more to my pump. If I feel I can run in the 750 range safely, then I will leave it at that. If I want to step up into the 800's, I will do a drop in return system.

 

[slow306stang]

I've been doing this for over 17 years. I know what the limits are. Thanks.
I know exactly what's going on with my setup at all times. One of the benefits of data logging and paying complete attention to how a supercharged EFI system works..........like I said before... I will see how much further I can get with 3-4V more to my pump. If I feel I can run in the 750 range safely, then I will leave it at that. If I want to step up into the 800's, I will do a drop in return system.

I hate to ruin the OP's thread but I gotta disagree. Your dyno graph was awful because the car simply isn't getting fuel. Once it gets fuel guess what happens? You will be making alot more hp and still need a fuel system. I'm not trying to be disrespectful but just trying to help out. I'd kill for a gotta have it green boss. You are pushing it and i'd hate to see you wreck an engine.

 

[mtrsprt]

I hate to ruin the OP's thread but I gotta disagree. Your dyno graph was awful because the car simply isn't getting fuel. Once it gets fuel guess what happens? You will be making alot more hp and still need a fuel system. I'm not trying to be disrespectful but just trying to help out. I'd kill for a gotta have it green boss. You are pushing it and i'd hate to see you wreck an engine.

I promise, I won't wreck my engine. One of the reasons why I pulled timing back, and set my limiter to 6800 until I install the JMS unit. Cheers.

 

[slow306stang]

I promise, I won't wreck my engine. One of the reasons why I pulled timing back, and set my limiter to 6800 until I install the JMS unit. Cheers.

Do what you want to do. Run a large extension cord and give the fuel pump 115v for all I care. Somehow you're the exception to needing a fuel system with making 750whp.