i'm beginning to think i've got an original flexplate that i think might be out of whack. when i put in the 331 i checked it and it looked straight but who knows? i get a nasty vibration around 3000 rpm and it somewhat goes away, pinion angle and all that jazz is fine. wife just complains about it (it's different now that i'm in the passenger seat lol) but i'm wondering if i should replace it with a new one and also, my first balancer was a summit balancer that was on the 289 that was weird, it was like 10lbs but as soon as i took it off and put the stock style on the motor sure rev'd up faster. i'm wanting to replace mine with a SFI spec one from professional products, but they list the weight around 10lbs also and i'm wondering what's the deal with that? if the heavier weighted balancer itself is going on the front that creates more rotating mass which theoretically will slow my revs down like it did on the 289, so whats the point in me changing it out then if it's gonna slow me down? or is it?

 

the heavier weight also help in getting you moving

is your stroker balanced for 28 or 50 oz? maybe its just mismatched?

 

it's a 28oz balance stroker

 

A mismatched flex plate or balancer will cause that. I have also seen the wrong part get put in the wrong packages, so do not take that for granted (happened last week to my buddy). What balance is your balancer and flexplate? You say the flexplate is stock, but they were different balances depending on the year.

Rmodel is right about rotational weight. A lighter rotational weight will spin up faster (easier to get things moving), but more weight will help preventing stall because you have inertia helping you. Typically trucks and heavy cars like more rotational weight while a high performance car or race application like the lighter rotational mass. I put a light weight aluminum flywheel in my car. It was half the weight of the steel one. It does spool up much faster, but you have to watch it in traffic because it will stall.

 

28oz flexplate. came off a 67 289 - the original motor

 

So does it happen when your cruising down the road at 3000 rpm or when the engine is @ 3000 rpm staticly?

 

just to make sure. does that happen as well when you sit in the car (not driving) and revving at 3000 as well? i'm just asking because you mention pinion angle etc.

if it doesn.t then the problem is rather gearbox and back instead of engine
if it does then the first thing I'd check if you have clearance from engine to chassis. any part from engine touching *only so slightly) will cause bad vibration