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Compression Ratio for 383

This is a discussion on Compression Ratio for 383 within the Performance forums, part of the General Discussion category; Can anyone tell me what my compression will be for my 383?? .030 350 block, 3.75 stroke, 6" connecting rods, ...

  1. #1
    Registered User 5speedz71's Avatar
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    Compression Ratio for 383


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    Can anyone tell me what my compression will be for my 383?? .030 350 block, 3.75 stroke, 6" connecting rods, wiseco flat top pistons (5.40cc piston head volume) with 2 valve relief and a set of brodix race rite 200cc heads with 67cc combustion chamber..really shooting for a 10.0.1 cr. But if its a tad more that's fine
    06 GMC VortecMax CC 4wd- Leveled, 33" MTZ'S, Factory 17's, 4.10s, G80 locker, HIDS, Magnaflow Exhaust, AirAid CAI, Suncoast Creations hood

    87' Chevy P/U SWB 4x4, Mild 383 stroker, TH400, 6" Suspension, 10 bolt/ 14 bolt SF, 4.56s, Locker in Rear, 35x14.50-15 TSL Radials

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    Registered User Doober's Avatar
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    Depends on combo. 10:1 will be ok with longer duration (230-235+), but isn't necessary for the street... unless it's for the track you'll be fine with 180cc intake... really need more usage and cam info.

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    '92 Sierra (TBI 383/Vortecs/Comp 08-412-8/EBL/4L60/3.08s), '78 Malibu (Vortec'd 350/4-speed/2.29s), '87 Pontiac Fiero GT (2.8 v6/5-speed)


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    Registered User Doober's Avatar
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    I misread a little, sounds right around 10-10.5:1. I have Speed Pros with 4 reliefs and a small dish and they're 9.6:1.

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    '92 Sierra (TBI 383/Vortecs/Comp 08-412-8/EBL/4L60/3.08s), '78 Malibu (Vortec'd 350/4-speed/2.29s), '87 Pontiac Fiero GT (2.8 v6/5-speed)


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    Supporting Member odom1957's Avatar
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    Re: Compression Ratio for 383

    A couple of numbers are missing to accurately give you the compression ratio. Assuming a zero deck height and a .040 gasket, your compression will be 10.7. If your pistons are in the hole .010, then compression is 10.4.

    To give a 100% accurate number, I would need the gasket thickness and bore, and the deck height. What cam are you going with? Compression might be too high for pump gas, depending on cam selection.

  5. #5
    Registered User 5speedz71's Avatar
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    Re: Compression Ratio for 383

    This motor is for my 87 mud truck in my sig..the cast crank split in half so I'm rebuilding ot and adding some.more influence to it..its a zero deck and yes standard size gaskets..the bore is 4.030 and the cam is a Lunati hydraulic roller..advertised duration is 282/290, 231/239 @ .50..535/.550 lift, 110 lsa, 106 centerline
    .I will be using 1.6 roller rockers and that will bring the lift numbers to. 570/.586...I'm almost positive that will be at least a 11.5 ratio with flat tops..which I wouldn't mind that all if race gas wasn't so expensive..probably gonna have to have some dished pistons
    Last edited by 5speedz71; 09-29-2013 at 02:23 AM.
    06 GMC VortecMax CC 4wd- Leveled, 33" MTZ'S, Factory 17's, 4.10s, G80 locker, HIDS, Magnaflow Exhaust, AirAid CAI, Suncoast Creations hood

    87' Chevy P/U SWB 4x4, Mild 383 stroker, TH400, 6" Suspension, 10 bolt/ 14 bolt SF, 4.56s, Locker in Rear, 35x14.50-15 TSL Radials

  6. #6
    Registered User 5speedz71's Avatar
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    Re: Compression Ratio for 383

    The truck is a weekend mudder and will be opened quite a bit..keeping the rpms and wheel speed up is key down here..it does see some street use as well
    Last edited by 5speedz71; 09-29-2013 at 02:27 AM.
    06 GMC VortecMax CC 4wd- Leveled, 33" MTZ'S, Factory 17's, 4.10s, G80 locker, HIDS, Magnaflow Exhaust, AirAid CAI, Suncoast Creations hood

    87' Chevy P/U SWB 4x4, Mild 383 stroker, TH400, 6" Suspension, 10 bolt/ 14 bolt SF, 4.56s, Locker in Rear, 35x14.50-15 TSL Radials

  7. #7
    Supporting Member odom1957's Avatar
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    Re: Compression Ratio for 383

    Compression will be 10.7 on a zero deck. Dynamic compression will be 8.2 with that cam. You should be fine on 93 octane. If you haven't bought the heads yet, then you need to order those with springs installed at 1.95" so they can handle the lift with the 1.6 rockers. You will also need some free flowing exhaust. The exhaust ports on those don't flow really good compared to the intakes.

  8. #8
    Registered User 5speedz71's Avatar
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    Re: Compression Ratio for 383

    I have longtube headers and 2.5" exhaust with flowmaster 40s dumped before the axle..10.7 with the flat tops o originaly mentioned?? That would be fine with me as long as 93 octane could be used like ya said
    06 GMC VortecMax CC 4wd- Leveled, 33" MTZ'S, Factory 17's, 4.10s, G80 locker, HIDS, Magnaflow Exhaust, AirAid CAI, Suncoast Creations hood

    87' Chevy P/U SWB 4x4, Mild 383 stroker, TH400, 6" Suspension, 10 bolt/ 14 bolt SF, 4.56s, Locker in Rear, 35x14.50-15 TSL Radials

 

 

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