LT1-LT4 Modifications 1993-97 Gen II Small Block V8

Highest CR on pump gas?

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Old May 22, 2013 | 04:50 PM
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Default Highest CR on pump gas?

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.
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Old May 22, 2013 | 05:22 PM
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I ran 12.6 on 93.

Got to have your **** together to do it.
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Old May 22, 2013 | 06:03 PM
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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.
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Old May 22, 2013 | 06:14 PM
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I am running 12.8. Like said above, make sure you have a good tune.
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Old May 22, 2013 | 07:00 PM
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12.5:1 compression here.

Not only is the tuning important but the cooling system needs to be up to snuff as well.
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Old May 22, 2013 | 07:20 PM
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Running real close to 13.0:1 with my setup.
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Old May 22, 2013 | 08:54 PM
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Originally Posted by RamAir95TA
12.5:1 compression here.

Not only is the tuning important but the cooling system needs to be up to snuff as well.
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.
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Old May 22, 2013 | 09:11 PM
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I'm using a stock radiator and a csr water pump
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Old May 22, 2013 | 09:17 PM
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Depends a lot on camshaft also.
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Old May 22, 2013 | 09:20 PM
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Originally Posted by matt94z
I'm using a stock radiator and a csr water pump
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.
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Old May 23, 2013 | 01:07 AM
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Interesting convo here. Subscribed.
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Old May 23, 2013 | 01:24 AM
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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.
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Old May 23, 2013 | 06:40 AM
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Originally Posted by Ed Wright
Depends a lot on camshaft also.
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?
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Old May 23, 2013 | 07:22 AM
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Originally Posted by VAformula
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.
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Old May 23, 2013 | 07:22 AM
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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.
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Old May 23, 2013 | 07:26 AM
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Originally Posted by FASTFATBOY
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.
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.
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Old May 23, 2013 | 08:57 AM
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Originally Posted by VAformula
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.
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.
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Old May 23, 2013 | 12:40 PM
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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.
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Old May 23, 2013 | 01:18 PM
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Originally Posted by FASTFATBOY
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.
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?
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Old May 23, 2013 | 08:23 PM
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Cam changes don't effect static compression, only dynamic. Bigger cam=lower cylinder pressures.
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