I have read through the message boards here and at iroc.fbody.com and still have not found a complete solution to my problem. I have a '88 IROC-Z, 350TPI, Auto trans, G92 susp, everything bone stock except steering wheel (although i have the original) and the car just clocked 120K miles. I have had this problem with every centerbolt headed vehicle ive owned, 2 IROC's and a 89 SWB Chevy truck w/350 TBI. If I am driving at maybe 40, 50, or 60 MPH and i slam on the throttle or punch it pretty good to pass a semi or something I hear the loud tapping sound that increases in speed as the RPM's climb. I do not hear it at low speeds and low RPM's, just highs, say 3,500 RPM's and higher. I saw that someone suggested using synthetic motor oil while someone else suggested getting some engine flush. WHile some say readjust my rockers. I dont know what to do. If i have to adjust my rockers, the driver side is not bad but the pass. side is a PIA with all the A/c stuff. From what everyone says it sounds like it might be sludge built up in the lifters which i would not doubt with the mileage of the car. If anyone has any suggestions or experience stories, I would love to hear them. Thanks.

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In my opinion, if it were the rockers you would be able to tell at idle.

Synthetic motor oil and an engine flush is not the answer. Can you describe the "tapping"? Is it knock? If it is knock it could be numerous things but first check if the timing is too far advanced . Set it to stock-6btdc. Also, use 91 or higher octane gas. Are you getting any codes? If so which ones?

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91 Formula
305 TPI 5speed
1LE/G92/WS6
Cold air ind. w/K&N, SLP airfoil, ported/polished plenum, March pulleys, TB coolant bypass,Crane AFPR(43psi),Crane Gold 1.6rrs,MSD coil,MSD6AL, Holley 9mm wires, fastchip, Bosch O2sensor, SLP headers & catback,short shifter,3:73s w/Auburn posi,160* t-stat,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.

 

I was wondering if it was a "knock" or possibly an exhaust leak?