Hey guys, have a question. I have a 70 mustang fastback. We pulled the 302 and did a top half upgrade with new cam and aluminum heads and aluminum intake. The original tranny had issues so we swapped it for a later model c4.
Now, the engine vibrates on low rpm. I assume its the flywheel, but not 100% sure. Anyone have this problem before?

 

C4 wont use a flywheel but a flexplate. if flexplate is imbalanced I would think it makes more vibrations the higher you rev the engine (as in unbearable at 2000+).
if it's on slow revs only but does _seem_ to disappear on higher revs, there might be a chance of a single cylinder not firing.
what exaclty did you put in (parts, especially cam). if it's a long duration cam and you run it low, then the engine will shake

post the parts list (top half) and how it vibrates (does it get better when you rev it slowy up? if yes at what rpm). can you make sure it runs on all cylinders?

Kalli

 

thanks for the response,the upper half build included edelbrock performer alum. heads,190 int.160 ex.170 cc runners 60 cc chambers.cam is mild,don't remember the duration but lift is something like 474,chinese air gap intake?(probably should have used edelbrock)roller rockers 1.7,i think 600 holley carb.like i said,the vibration is from idle to about 2000 rpm,then it goes away.you can feel it in the steering wheel.all cilinders seem to be firing.could a bad dist.cause this shaking?bad converter?what else could cause such a hing?thanks in advance.

 

the timing is likely off just a tad... had the same problem on mine, it was off so soo little and after adjusting the vibration went away. if the flywheel is not bent and is in good shape then thats def. not the issue, they can only be put in one way...

 

I agree with KALLI

The cam and induction change may induce a rough idle but the engine is smooth at speed. Changing flexplates with the wrong imbalance will vibrate all over the rpm range.

Check for proper ignition timing and vacuum leaks. Report back.

 

Hey , thanks for the responses. I am having everything checked right now. I had the original tranny dropped off a few days ago, thought it might be the converter. Any chance that could be an issue as well?

 

Can a poor casting on an intake cause vibrations? Ive heard alot of bad stories about the chinese made intakes,