383 stroker vibration

Hi,

I just finiched a 58 corvette retro car for a friend, and I'm having fits with the engine. It's a 383 stroker motor that he purchased from a reputable builder. It has a Demon 600, JEGS HEI with no vacuum advance, rebuilt 700R4, Autolite 3924 plugs, 93 octane gas, stock exhaust manifolds.

The problem is that the engine vibrates at about 2000 rpm in any gear, or standing stationary. It also has a bad vibration if I stick my foot in it at about 4000 rpm. I don't think that it is in the driveline. It's about the same feeling you get if two plug wires are crossed--it just doesn't seem to be firing right. I have the total timing set at 32, and the idle timing set at 14. I've tried moving that around, but just get pinging when I advance it much more. The harmonic balancer seems to be ok. Could the plugs be to cold?? If you get the car out on the road, and just hold speed, it's fine. The minute that you accelerate, and it hits the 2000 rpm mark, the vibration is back. I can push past it, until the engine really starts to wind, and then I feel it again. Any advice would be appreciated. Thanks.

Most of the 383 strokers use a 400 crank which requires the use of the externally balanced harmonic balancer and counterweighted flywheel/flex plate.

Use of the zero balance flywheel and balancer will causew a severe imbalance.

yup, what mike said. was the engine balanced before it was built?

Thanks guys,

I pulled the transmission last night and discovered that I didn't have the flexplate indexed right. There was an alignment hole, but no pin. Since I usually buy crate motors, the flexplate is already installed, and I frankly didn't realize that there was a "correct" index. Thanks again--you put me on the right track. I'll test it just as soon as it gets daylight. Mike

sounds like you found the problem... keep us posted