concerned with compression ratio LT1 383 build

Hi everyone, thanks in advance for any helpful comments to this post. i have a 97 z28 6 speed with a bad crank and bad cam bearings so i am putting together my rebuild and I keep running into pistons and engine kits that put the compression ratio up over 12:1 with the stock 54cc heads. this will not be a race motor, rather the opposite: i want to run 87 pump gas and it will be a daily driver / weekend warrior.

here is the set up i am considering based on feedback from the engine builder i am planning on using below. my question is regarding the pistons. since the LT1 comes stock around 10.5 : 1, will this engine run well? or does the reverse cooling flow and knock sensor allow / mandate a higher than normal compression ratio on the LT1 due to the nature of the beast?

scat 9000 crank
scat 6.0 inch forged pro series rods
wiseco forged -24cc dish pistons (according to builder this will put me at 10.05:1 compression ratio)

i am looking for a strong torquey and reliable motor that is smooth and streetable with plenty of power on tap for rowdy racing on the highway and the occasional drag race. so do you think this will be enough compression to accomplish my goals? 400 hp and 500 tq at the crank would be ideal but i know those are lofty numbers.

thanks guys!

A totally stock LT1 w/ 10.5:1 (sometimes shown as 10.4:1) static CR will retard the timing on 87 octane fuel, unless you are at some high altitude above sea level. The Owner's Manual requires 91 octane for max performance, and cautions you could lose performance with 87 octane. Why do you want to use 87? Will kill "strong, torquey".

The reverse flow cooling and aluminum heads allow the LT1 to use the higher compression ratio, with fairly aggressive timing. Does not "mandate"...... it "allows".

OP

does your builder understand the LT1 reverse cooling....not like a Gen 1 SBC so "higher" compression with the LT1 can be 11:3 ish with 91 octane all day long. Your tune (timing) will also factor in what octane you want to use. If 87 than the tuner would have some timing pulled.

Did the builder say how far in or out of the hole the pistons would be with the wiseco pistons and what thickness of the head gasket he would use and target "quench" is says he is aiming for?

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Originally Posted by JesseBowman

Hi everyone, thanks in advance for any helpful comments to this post. i have a 97 z28 6 speed with a bad crank and bad cam bearings so i am putting together my rebuild and I keep running into pistons and engine kits that put the compression ratio up over 12:1 with the stock 54cc heads. this will not be a race motor, rather the opposite: i want to run 87 pump gas and it will be a daily driver / weekend warrior.

here is the set up i am considering based on feedback from the engine builder i am planning on using below. my question is regarding the pistons. since the LT1 comes stock around 10.5 : 1, will this engine run well? or does the reverse cooling flow and knock sensor allow / mandate a higher than normal compression ratio on the LT1 due to the nature of the beast?

scat 9000 crank
scat 6.0 inch forged pro series rods
wiseco forged -24cc dish pistons (according to builder this will put me at 10.05:1 compression ratio)

i am looking for a strong torquey and reliable motor that is smooth and streetable with plenty of power on tap for rowdy racing on the highway and the occasional drag race. so do you think this will be enough compression to accomplish my goals? 400 hp and 500 tq at the crank would be ideal but i know those are lofty numbers.

thanks guys!

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with the same rods and pistons and an .040 compressed head gasket on stock heads we were at 9.25:1ish for boost......with the cut trick flows same gasket we are at 10.25ish. are you sure he is calculating static compression ratio correctly?

also, why regular gas? technically the lt1 should have premium stock. with how shit fuel is now adays I wouldn't build something to run regular

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Need to know what your cam specs are for a better answer. Your dynamic compression ratio is far more relevant than the static compression ratio.

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Originally Posted by Injuneer

A totally stock LT1 w/ 10.5:1 (sometimes shown as 10.4:1) static CR will retard the timing on 87 octane fuel, unless you are at some high altitude above sea level. The Owner's Manual requires 91 octane for max performance, and cautions you could lose performance with 87 octane. Why do you want to use 87? Will kill "strong, torquey".

The reverse flow cooling and aluminum heads allow the LT1 to use the higher compression ratio, with fairly aggressive timing. Does not "mandate"...... it "allows".

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thanks for the reply my friend. i just totalled an 08 Dodge Charger with 5.7 hemi, long tube BBK headers, flowmasters, spectre CAI, and hptuners dyno tune that ran really well on 87. the goal for this camaro is a similar set up (v8 with mild tune and low comp ratio for pump gas, unrestricted.) I drive aggressively and just want to be able to keep my fuel costs down

i haven't chosen a cam yet but i am open to suggestions. i am looking for 1500 to 5500 RPM and a slight lope would be acceptable. i want more torque than hp. my charger made 380 lb/ft to the rear wheels and 350 hp to the rear wheels. looking for similar power out of this 383 (but more)

that is interesting. i don't know how he is calculating the CR to be totally honest and i need to study up on static CR, myself. i just want to run 87 to keep fuel costs down and have a reliable motor that won't detonate.

Quote:

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Originally Posted by BALLSS

OP

does your builder understand the LT1 reverse cooling....not like a Gen 1 SBC so "higher" compression with the LT1 can be 11:3 ish with 91 octane all day long. Your tune (timing) will also factor in what octane you want to use. If 87 than the tuner would have some timing pulled.

Did the builder say how far in or out of the hole the pistons would be with the wiseco pistons and what thickness of the head gasket he would use and target "quench" is says he is aiming for?

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that's exactly what i was hoping; for an aftermarket tune that would allow it to run well on 87. this is my first LT1 but basic engine knowledge tells me that i should be able to run 87 octane and 10:1 all day long. i am okay with losing a few hp due to the tune if necessary. this is not a race car by any means. i honestly did not question him on how far in or out the pistons would be and we didn't discuss quench, either. we were putting the parts together over the phone, he ran some numbers and told me the -24cc dish pistons would put me at the 10.05:1. he is aware it's and LT1 but he isn't an LT1 guy like you fellers

you really can have higher compression than 10:5 on a gen 2 LT1 and run 87 octane. Ask your builder what thickness head gasket he used in "calculating" the compression ratio. If stock .049....might want to run the Mr Gasket .026 to bump the compression up slightly

for a bunch of TQ down low and mid range, the 218/224 cam from Lloyd Elliott

http://elliottsportworks.com/?page_id=32