C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

Heads only on my 89?

Old 05-10-2019, 08:51 AM
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Default Heads only on my 89?

I have a 1989 Six-speed that is stock. Has 32,000 miles. I was thinking of selling and moving into a C5 for a while. Then I took it out for a ride and realized that I love the car and I am really a C4 guy! So now that I am going to keep it I was thinking of pulling the heads and replacing with AFR 180 Eliminator heads. I called AFR and my compression will stay the same, I will not loose the L98 torque due to staying with 65cc chambers. Of course a lot more flow. Not looking for a race car just more power and throttle response. I will need to stay smog legal due to living in CA.

Some questions I have - Will I need to worry about tune with replacing of the heads? I would replace the stock rockers and use a Lunati 1.5 roller tip rocker. I would replace the push rods with a hardened push rod. Would I be ok to replace the lifters with new? Can I put new lifters on the stock cam? I know it is roller. Thank you in advance for any input/direction.
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Old 05-10-2019, 09:30 AM
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I don't see much point in upgrading the push rods/rockers with a stock cam. The only real benefit with a stock cam would be rockers with a higher ratio.
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Old 05-10-2019, 10:47 AM
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The stock heads are 58cc, and the new ones are 65cc? unless you are changing other parts or running a steel shim head gasket like the Felpro 1094 you will lose some compression.

As far as lifters go you could replace them but if yours are fine just sue them. You could use self aligning rockers arms and not have to use hardened push rods, (Your choice). I would run 1.6 rockers if you plan to change the rockers, more lift same drivability.
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Old 05-10-2019, 11:32 AM
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IDK it alot of money for not alot of reward. You may come out better to get stock heads and intake reworked. Along with higher flow runners. Since there no cam swap ECM may not needed tuned. Don't overlook exhaust, the increase in air in will need to exit efficiently.
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Old 05-10-2019, 01:33 PM
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What biankuski said...

Stock exhaust manifolds are a choke point as well as the TPI intake.

Suggest headers first then address the intake.
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Old 05-10-2019, 01:58 PM
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I had 300chp from my prior '88 (A4): only 30chp below a C5
-K&N w/ open lid
-160deg T-stat w/ fan switch
-siamesed runners, ported plenum, 52mm intake
-AFPR w/ bumped fuel pressure
-OEM headers, 2 1/2" mandrel-bent Y, Random Tech cat, hi-flow cat-back
-HEI ignition, cut-back spark plugs gapped to .045", 50ohm/ft wires
-Comp Cams: Pro Magnum 1.6:1 RRs, stronger springs, Ti retainers, hardened push-rods, new rocker studs

My engine was old (~90k miles) and tired. With 32k miles yours likely is young and strong, netting >300chp with such mods.

Whatever your choices enjoy that '89. Just purchased an '89, MN6 Vert and freakin' love it.
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Old 05-10-2019, 04:52 PM
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Id do the heads, have them milled, small cam;port the base aftermarket runners/headers
It will run pretty strong, you wont lose any torque;even with the stock cam it will pick up but if you got it that far apart why not? Cams are cheap enough
hotcam for example, works well with a stick (lots of others out there also.
Wish I had th $ to pick yours up!
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Old 05-10-2019, 05:24 PM
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Be careful. Since the '89 is OBD1, you still need to pass the CA "sniffer" test. Do you have experience with the smog test procedures in your area? They go over my engine with a fine tooth comb, looking for mods, including a creeper crawl under my car to check the part number on my cat, to be sure it's CA certified! They even check my ignition timing! I doubt they'll pass you without CA certified headers

Last edited by Hot Rod Roy; 05-15-2019 at 07:39 PM.
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Old 05-11-2019, 08:34 AM
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Thank you as always for the great information. If it wasn't for this forum and all of your knowledge I probably would have already spent money on incorrect parts. Not sure what I am going to do now. I need to do some more reading and decide.
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Old 05-15-2019, 08:44 PM
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With AFR heads you can't use self aligning rockers. They have smaller 8mm valves and the self aligning rockers would fit too loose on the valve. You would want to use non self aligning rockers with hardened pushrods with their guide plates
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