I've heard different numbers as to the highest compression ratio you can run pump gas in a LT1 is. I know in older engines 11:1 was about max. In lt1's I've heard 12:1 to 13:1. I was wondering if anyone had run more than 12:1 and if they were able to run pump gas?? Thanks for the help guys.

 

I ran 12.6 on 93.

Got to have your **** together to do it.

 

I was aiming for 12.5 but was only able to get 12:1 with my cylinder heads.

Your tuner will need to be on point...I wouldn't go past 12.5:1 on a street car to have a bit more leeway in case you get a bad batch of gas.

 

I am running 12.8. Like said above, make sure you have a good tune.

 

12.5:1 compression here.

Not only is the tuning important but the cooling system needs to be up to snuff as well.

 

Running real close to 13.0:1 with my setup.

 

What upgrades for cooling would you guys suggest?

I would be willing to run race gas, I would just like to have the option to not spend 8 bucks a gallon on gas.

 

I'm using a stock radiator and a csr water pump

 

Depends a lot on camshaft also.

 

I have a stock waterpump (brand new)
A 160 Thermostat
Tuned Fans
And stock radiator

Also have some free airflow to get fresh airflow in around it. But that's it.

 

Interesting convo here. Subscribed.

 

Agreed, I'm curious why or how the cam plays into it as well. I'm still toying with the idea of just making a HCR N/A motor with my spare 4 bolt block.

 

I've heard this also, I would guess because it changes the rate of detonation?

I have a superb tuner, he used to work on all the race cars in the area, even worked on the Grave Digger and other monster trucks and he's worked on many LTX's before.

Here's my cam specs from AI; 228/234 @.050, .612/.612 111LSA

What do you think Ed?

 

Not enough cam in my opinion. Your tuner better be good.......REAL good.

I ran a big Griffin radiator, I built my car to cruise.........to sit in traffic for hours. I ran an electric water pump also.

I got a bad batch of gas in mine once and killed 2 of the corner pistons. I had no knock sensors though because of the solid roller cam.

 

Also, would a bigger cam allow a higher CR or would a smaller cam? I'm thinking a bigger cam, but I may be wrong.

 

Its a 355, prolly will be pushing exactly 12:1, at MAX 12.5:1.

It won't be sitting in traffic, at max it will go to work which is a 30 minute trip in the worst traffic here. I mean I would like to go on cruises, not just make it a strip car because it was my first car and I'd like to take it to shows and such.

 

Yes, its all about overlap vs bleed off vs cylinder pressure. Bigger cam, more overlap= more bleed off.

AKA Dynamic compression ratio.

I ran a 254/254 @.050 on a 108 , car made good power. But it was in a 383.

 

I haven't seen much over 12.8 on a pump gas motor, even those ones weren't driven much. Now that I run alky I'm glad I was running at least closer to 12:1 I can only get 91 here and some of that is hit or miss.

 

So a car with say with a cc503 cam would have less cylinder pressure at 6k at full throttle vs a car with a stock cam all else being equal?

 

Cam changes don't effect static compression, only dynamic. Bigger cam=lower cylinder pressures.