Compression question here.....

[EspanolaGuitarista]

I have a 1995 3100.
I assume it's 9.5:1 comp. ratio
I would like to go to 11:1 or 12:1 if it's possible on pump.
I would want a bigger cam since more compression seems to help
bigger cams anyways.
Is this possible? Where do I go for the program to reflash my chip. I have a laptop. I think if I took out maybe 2-4 degrees of timing I should get by. I am in California so it has to be C.A.R.B. legal. Any help would be appreciated. How muh horsepower per cylinder would I net from this? I was thinking 3-5 but maybe that is with big blocks.

[SappySE107]

9.6:1 stock. You can run the iron head flat top pistons for 12+:1 compression. I dont know about your computer but the older computers running the stock 3.1 gen 2 spark table have no issues with spark 95% of the time. That is running premium though.

There is no place to reflash your ECM that is worth a shit right now. Perhaps digital horsepower can help but I am not sure if they touch OBD1 flash.

HP gains...dunno.

[EspanolaGuitarista]

Thanks for the info. 12:1 would be very high for a street car. I wouold have to run premium plus a bottle of octane booster. Which would be ok. I don't know if octane boosters work. So my next question is: What octane booster works and what doesn't? Can I squeak by with 12:1 compression with it?
I definately would like to have that then I can have an excuse to put in a 220 deg. cam. If I can actually get it to pass smog in California. Didn't someone say a Memcal prog.or something? There must be a way to pull out some timing without breaking the bank.

[SappySE107]

You dont have a memcal, you have flash. The people running 12:1 compression also have a 260 or 272 crane cam in their gen 2...so you would want to get a wilder cam than stock for sure. I dont think you need to worry about octane booster, but finding a place to reprogram the computer is essential for smog testing.

[EspanolaGuitarista]

So...hmmm.Thanks for the input SappySE. Is this ODB2? I was reading that it is ODB1 with an eprom flash and I could use GMPCM on it. Is this correct? I used to write code as a hobby but this seems to be a whole different beast. I read your article but it didn't say whether this works for my 3100 or not. Please help!

[SappySE107]

Im not aware of GMPCM doing anything for the flash ECM. The guy that wrote the program is on here but he never posts. You have OBD1. OBD started in 96.

[EspanolaGuitarista]

I thought I had ODB1 but wasn't sure. What can I do? How do I flash? Flashing a whole computer doesn't seem right. There must be some memory chip that can be re-flashed. What kind of connector do I need to patch into the computer?

[SappySE107]

It takes a special computer setup I believe. Ive never done it and dont know the full extent. GM Tech1 will do it.

[v6h.o.]

i run slightly over 11:1 on my stock computer programing and premium pump gas.

have never had any issues with detonation. but the ecm needs to be tuned to get the most out of this engine with the way its setup... stupid stock programing..

[Kreb]

I'm surprised that you can run 11 to one on standard gas. Does the ECU do knock sensing/retard? I thought that 10 to 1 was the highest safe ratio. I'm going to be running an old S-10 distributor and 390 Holley on my stalker. Will there be any difference in the ability of that setup versus a newer OBD/injection to deal with detonation at higher than stock compression ratios?

Also, what sort of HP gains can I expect with compression increases? Using a 94' Camaro iron block - is it worth upping the compression on my rebuild?

Thanks

[bszopi]

The aluminum heads will allow for higher compression ratios than the iron heads. If you use a Camaro engine, swap on a 3x00 top end, switch over to EFI and DIS, and you'll have a pretty mean little engine. I think if you keep the stock pistons, the CR might be a little too high (>13), but you can swap out pistons and get into the ~11 range.

[v6h.o.]

genral rule of thumb for compression power increase/decrease is 4% power.

example 9:1 200 hp, up to 10:1 you'd see roughly 208hp + -.

sounds little but its when you start playing with big hp numbers that you start seeing larger gains. such as if you had a 450 HP v8 and change the compression one full point roughly youd end up with: 468hp..
camshaft selection for the CR range and other variables then come into play to help make most and take advantage of the higher CR but roughly thats the typical measured dyno gains for CR change- 4% for 1 full point.

[Rhedalert]

I'm able to run 93 octane without knock detected....on RARE occasion the scan tool will detect knock at WOT during or just before a shift, but that's it. I'm using the gen 1 pistons and crane H272 cam

[EspanolaGuitarista]

Thanks for the info. So I should stay with the 11:1 idea. But I'm tempted to push it. Maybe I shouldn't. 4%? Well, I guess on a v8 this would be a much bigger improvement. 6%(1.5 pts) of 150baseline= 9hp. So, if that is the case then I should work on everything else to get my baseline hp up to say maybe 200. Then 6% of 200 = 12 hp. Not bad. Wish it was better. 12:1 at 200hp = 20hp. Can I run a 272 cam in a California car? Probably not.

[XLR8ING]

V6HO.....your running 11:1?? I thought you had the Gen 3 pistons?
Guess I was confuzzed.