Need some advice on what is causing major vibrations in the steering column/floor boards/seats at low RPM's. When we rev the engine between 1200-1800 RPM, everything vibrates inside the car. I don't think it could be a balance problem with the motor.We recently installed a new dyno'd Motown 415 SBC in a 70 Nova (sorry, not a Chevelle, but I have one!!). Everything is new on this car including motor mounts and transmission mounts. It does have sub frame connectors and the new exhaust isn't touching the floor boards, but I think those are the likely choice. Or could it be because everything is so tight, it's causing the vibrations inside the car??

Did the engine come with a flexplate?
400 SB engines are externally balanced and would require a 400SB flexplate.....that has a weight welded on it.
I can't imagine that they would sell the engine w/o it????
Ditto for the harmonic balancer.............
Ron

Does it vibrate fast or slow? What I mean is, if it's vibrating rather slow it could be a balance prob or the flexplate / converter. If it's vibrating with the sound of the engine you have something touching the shell or the steering column. Check for Header clearance. Also check tranny bellhousing and filler tube clearance. What mufflers do you have? I just recently installed a Flowmaster system and recognized that the Flowmaster mufflers create a lot of resonance at WOT, almost sounds like they are touching the floorboards, but they aren't, I checked.

Olli

Ron, The engine came dyno'd with the balancer attached and I bought a new flex plate with the weight welded on it.
Olli, The vibration coincides with the engine speed. The steering column is clear,headers are clear and exhaust/ mufflers not touching. I will check the trans filler tube and bell housing. I believe the tube may be touching the fire wall. Thanks for the quick replies!! Don

Do you know if the engine is internally or externally balanced?

it could be that your engine came with inter. bal., and you put the wrong flywheel on it(ext. bal) you need to contact the engine builder-if its a stock balancer, see if you can feel or look @ the back side of it, and if it feels the same all around, its prob. int. bal-if you feel a diff.
around the inside, it might be ext. bal(they could have even installed the wrong bal.-humans do error-either way, you need to call the engine builder

Rapid Robert / Forced Ind,
Did a little investigating on this. The engine is internally balanced which requires a "neutrally" balanced flex plate. Luckily, I saved all my receipts and checked the part number of the flex plate I purchased. And there you have it; externally balanced flex plate with an internally balanced engine. Now the quesion is, did I damage the engine??? Only ran it about an hour or so. Thanks for the help!!!

Don,
Its a good idea to keep the posts to just one forum so people dont have to answer twice (or more) See my reply at your other location.