So my car is finally back together after 6 weeks being off the road with a blown motor. I went with a Sneed4Speed Super Sport Jr short block, got a pretty clean used head from AllMag, and did a full service while everything was apart. Including new timing chain kit, turbo oil line, head gasket, passenger side motor mount, and much more. I followed Sneed's break in procedure of a 500 mile oil and filter change and now the new engine has about 1000 miles on it. Everything has been great so far with CELs or trouble codes.

However just this past Tuesday I noticed a very distinct vibration when decelerating or accelerating. Specifically any time I get the engine RPM over 3000 and it will vibrate going up and down until it is below 3000 RPM. It will do this in all gears, in neutral, and with the clutch depressed. But it is much more noticeable while in gear and decelerating without braking, and if I give it some gas it will go away while maintaining speed. I immediately thought the worst and checked my dipstick for metal shavings but didn't see any. I haven't dropped the oil pan yet but I'm tempted to check that. I have a very slight oil leak from the oil pan "gasket" (high temp silicone) so I need to drop it to re-seal it anyway. I have been maintaining the oil level in the meantime so low oil is not the issue.

My only other thoughts are flywheel/clutch related. I was very diligent about making sure the flywheel and pressure plate were torqued to spec before mating my transmission. I'm not completely ruling it out but dropping the trans again would be a huge pain. I don't think it's trans input shaft bearings because it will vibrate with the clutch depressed.

I just find it overall very strange because the car runs like a top otherwise. No issues overheating, no knocking, no strange noises, goes into every gear smooth and still pulls with full power with a peak boost of 22.5 psi on Manic 3B.

 

Any chance the vibration has been there all along and you're just now noticing it? It takes awhile to get used to the new-found power and performance associated with a fresh build, and maybe that "masked" the vibration. Pretty easy to put the OEM Passenger side motor mount back in, stiffer versions are a common cause of noticeable engine vibration. I also get engine vibration transferred thru the JMTC ICI pipe --- there's constant contact between a VC bolt and chassis. Since you're getting the vib on both accel and decel, it's probably not due to engine torquing / rotation.

Have you inspected the axle CV joints? Is the vibration only when rolling?

 

Pretty sure its new, or at least I only noticed it this past Tuesday, and a friend I had in the car said it seemed new too. I already ordered a new BSH torque mount and an OEM trans mount. The engine mount I replaced is OEM, not aftermarket. I have new axles on the way as well, as I have been getting an on and off axle vibration which is different than this one. But neither of my axles seem to be throwing grease or bent, which leads me to lean more towards a trans mount issue as well. I'll update this thread once everything is replaced.

 

I found the source of my vibration. The bracket that attaches tot he engine that holds the lower torque mount and passenger side axle carrier bearing in place was coming loose. Two of the bolts were finger tight and one was completely missing, so literally only one bolt was holding it in place. Got everything tightened down and it's okay now. I went to go install a BSH torque mount while I was in there and it doesn't fit though. I suspect my whole engine is slightly too far to the driver's side. Factory torque mount with Powerflex bushings will have to do for now.