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Compression ratio of a stock LO5 truck 350 TBI

This is a discussion on Compression ratio of a stock LO5 truck 350 TBI within the Performance forums, part of the General Discussion category; I've seen a lot of different answers online (8.3 - 9.2) and I'm looking for the one that's the truth. ...

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    GearheadDezign.com woody80z28's Avatar
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    Compression ratio of a stock LO5 truck 350 TBI


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    I've seen a lot of different answers online (8.3 - 9.2) and I'm looking for the one that's the truth. If the compression really is in the low 8's I'm not going to dump any money into it for performance. But if it is in the 9's I can make some power for cheap. Mine's a 94.
    80 Camaro Z28 - 550hp AFR 383 EFI / T56 6spd
    91 Beretta "SS" - 220hp 3400 MPFI / HM282 5spd
    94 Silverado Z71 - 300hp Vortec 357 TBI / NV4500 5spd build thread

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    Re: Compression ratio of a stock LO5 truck 350 TBI

    Quote Originally Posted by woody80z28 View Post
    I've seen a lot of different answers online (8.3 - 9.2) and I'm looking for the one that's the truth. If the compression really is in the low 8's I'm not going to dump any money into it for performance. But if it is in the 9's I can make some power for cheap. Mine's a 94.
    ALL 350 TBI heads are right at 64-65cc chambers. There are multiple different LO5 350 TBI engines with multiple seperate piston types. Truck L05s were available in 3 different types. Two were setup at 8.75:1 compression and the third at 9.3:1.
    1997 G1500 Cobra Conversion, 5.7, 4L80E, 3.73 14-bolt 9.5", L31 Marine Intake, CFM TB, 02 MAF, 0411, Custom cam. Doug Thorley Tri-Ys, full exhaust soon.

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    Re: Compression ratio of a stock LO5 truck 350 TBI

    8600 GVWR gets you the lower compression, so there's one of the 3.
    Quote Originally Posted by Quyonmob View Post
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    Re: Compression ratio of a stock LO5 truck 350 TBI

    You have to look at the VIN to know for sure. My truck is 8600 GVWR and has the higher compression. I've got a book at home that tells which letter in the VIN to identify the engine by. I'll try and post up before all our Easter company arrives tonight....

    92 K1500 WT - Gone
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    Re: Compression ratio of a stock LO5 truck 350 TBI

    Quote Originally Posted by adam728 View Post
    You have to look at the VIN to know for sure. My truck is 8600 GVWR and has the higher compression. I've got a book at home that tells which letter in the VIN to identify the engine by. I'll try and post up before all our Easter company arrives tonight....
    That would be awesome. Thank you. 9.3 I would be happy with.
    80 Camaro Z28 - 550hp AFR 383 EFI / T56 6spd
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    Re: Compression ratio of a stock LO5 truck 350 TBI

    My VIN is 1GCEK14K5RZ262834. Thanks.
    80 Camaro Z28 - 550hp AFR 383 EFI / T56 6spd
    91 Beretta "SS" - 220hp 3400 MPFI / HM282 5spd
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    Re: Compression ratio of a stock LO5 truck 350 TBI

    Book isn't helping like I thought. Says 8th digit calls out engine type. One area of the book says a K is the higher compression engine, A is the low compression in heavy duty trucks. Another page says a K only verifies that it's a 350, and an A actually indicates the 4 cylinder Iron Duke (in S10's).


    As far as I know the Z71's never got the low compression engine.

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    Re: Compression ratio of a stock LO5 truck 350 TBI

    Maybe the vans had the 2nd low comp engine?
    Quote Originally Posted by Quyonmob View Post
    Straight pipes are for peckerheads. . .
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    Re: Compression ratio of a stock LO5 truck 350 TBI

    Quote Originally Posted by adam728 View Post
    Book isn't helping like I thought. Says 8th digit calls out engine type. One area of the book says a K is the higher compression engine, A is the low compression in heavy duty trucks. Another page says a K only verifies that it's a 350, and an A actually indicates the 4 cylinder Iron Duke (in S10's).


    As far as I know the Z71's never got the low compression engine.
    I dont think a 1/2 ton 350 was ever made with a low compression 350, unless it was a heavy half truck. but im sure the 2500/3500 trucks had the low compression 350

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    Re: Compression ratio of a stock LO5 truck 350 TBI

    So it's really a 9.2:1 engine then hopefully. I'll do a compression PSI test and get an idea of what I can do from there for cam, etc.
    80 Camaro Z28 - 550hp AFR 383 EFI / T56 6spd
    91 Beretta "SS" - 220hp 3400 MPFI / HM282 5spd
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    Re: Compression ratio of a stock LO5 truck 350 TBI

    Quote Originally Posted by speedracer326 View Post
    Maybe the vans had the 2nd low comp engine?
    Well the 1-tons had the lower compression engines.

    However the 2nd engine I was talking about was used in the C60 trucks, school buses, tow trucks, dump trucks and the like. The only real difference was intake valve rotators, single roller timing chain, and a forged cranshaft.
    1997 G1500 Cobra Conversion, 5.7, 4L80E, 3.73 14-bolt 9.5", L31 Marine Intake, CFM TB, 02 MAF, 0411, Custom cam. Doug Thorley Tri-Ys, full exhaust soon.

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    Re: Compression ratio of a stock LO5 truck 350 TBI

    Any confirmation that all half tons were 9.2-9.3:1 compression?
    80 Camaro Z28 - 550hp AFR 383 EFI / T56 6spd
    91 Beretta "SS" - 220hp 3400 MPFI / HM282 5spd
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    Re: Compression ratio of a stock LO5 truck 350 TBI

    Quote Originally Posted by adam728 View Post
    You have to look at the VIN to know for sure. My truck is 8600 GVWR and has the higher compression. I've got a book at home that tells which letter in the VIN to identify the engine by. I'll try and post up before all our Easter company arrives tonight....
    all L05 equipped trucks have a K in the VIN... you can't tell compression ratio by the VIN.
    77 Chevy K20 - 80 GMC K2500 (in pieces)
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    Re: Compression ratio of a stock LO5 truck 350 TBI

    Compression test results: 120, 120, 125, 125, 130, 130, 130, 135. That seems kinda low to me.
    80 Camaro Z28 - 550hp AFR 383 EFI / T56 6spd
    91 Beretta "SS" - 220hp 3400 MPFI / HM282 5spd
    94 Silverado Z71 - 300hp Vortec 357 TBI / NV4500 5spd build thread

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    Re: Compression ratio of a stock LO5 truck 350 TBI

    Quote Originally Posted by woody80z28 View Post
    Compression test results: 120, 120, 125, 125, 130, 130, 130, 135. That seems kinda low to me.
    That has nothing to do with compression ratio though, engine could be worn.

    1/2tons got 9.3:1


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    Re: Compression ratio of a stock LO5 truck 350 TBI

    Quote Originally Posted by woody80z28 View Post
    Compression test results: 120, 120, 125, 125, 130, 130, 130, 135. That seems kinda low to me.
    That has nothing to do with compression ratio though, engine could be worn.

    1/2tons got 9.3:1


    1978 K20 RCLB, 400 SBC, 4-Speed, Lifted
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    Re: Compression ratio of a stock LO5 truck 350 TBI

    Quote Originally Posted by GreaseDog View Post
    all L05 equipped trucks have a K in the VIN... you can't tell compression ratio by the VIN.


    And compression ratio had zip to do with Z71.


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    GearheadDezign.com woody80z28's Avatar
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    Re: Compression ratio of a stock LO5 truck 350 TBI

    What should the compression test come to?
    80 Camaro Z28 - 550hp AFR 383 EFI / T56 6spd
    91 Beretta "SS" - 220hp 3400 MPFI / HM282 5spd
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    Re: Compression ratio of a stock LO5 truck 350 TBI

    Make sure you have WOT when you crank for the test, and batteries are fully charged.

    Engine should actually be warm, but who wants to pull plugs on a warm engine.

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    Registered User Jamesd's Avatar
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    Re: Compression ratio of a stock LO5 truck 350 TBI

    Well from my 1992 Chevy sales brochure it lists it like this:
    Light duty emissions-all series 1500 and 2500 w/o C6P: L05 9.1:1 HP 210@4000 TQ 300@2800
    Heavy duty emissions-all series 2500 w/C6P and 3500: L05 8.3:1 HP 190@4000 TQ 300@2400

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