I have a little question about my stock 1987 Pontiac Trans Am GTA Analog Tach. I have figuered out exactly what my rpms should be at say 60mph and they calculate to 1920 with my gears, however, my tach reads more like 2150-2200! I have an MSD 6AL ignition and originally needed to use the MSD Tach Adapter because my tach would just fall to the floor. I have it hooked up, but I see there is this fairly large error. My question is does anyone no if this is correctable or if that is simply the error in the tach and is there anyway to tell? I was thinking about putting in a new Autometer tach, but would like to keep it in the dash, I'm also curious if anyone as done this? What size tach did you use, were there any special adapters, and how did it look when you were done. I would like to change the tach and speedo, but keep the rest of the gauges, I was wondering if this was possible? Thanks alot guys.

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87 GTA 350 L98
K&N filters, beefed up TH-700r4, Accel Manifold, Ported Plenum and Runners, Fuel Press. Regulator 49.5psi, air foil, modified MAF, SLP cold air box, Hypertech Thermomaster chip w/160 thermostat, MSD 6AL and Blaster 3, B&M shift kit & megashifter, Moser Ford 9in Rear with Richmond 3.50 and locker, Edlebrock TES headers and Cat Back,Hotchkis setup in rear, Poly suspension and Koni in the front, relocated MAT, bypassed TB coolant, 300 lbs lighter

Fastest ET's
Stock-0-60 6.8, 1/4 15.0 @ 94
Best-0-60 4.7, 1/4 12.8 @ 112
Norm-0-60 5.2, 1/4 13.2 @ 108