Low RPM vibration or exhaust note after motor swap and RV6 HFPC install
 

Hi everyone,

I recently had to replace a neglected J35A8 with 227K in my RL due to oil consumption that led to a burnt valve on Cyl #5. I sourced a 60K mile engine and installed it myself. I was also getting codes for the rear cat before the swap, so I decided to buy the RV6 HFPC kit and replace both of them. After pulling the old engine, I found that the side, front and rear engine mounts were broken, so I replaced them. I did not touch the transmission mount, though I left the trans in the car when I pulled the motor. Now that everything is together and I've driven it for a week, I noticed (on day one) that there is excessive vibration/noise at low RPMs and low rpm 5th gear cruising. What do you think the issue could be? do the HFPCs cause that much of an exhaust note change that I can feel and hear it in the car? I equate the vibration/noise to that of my old CRX with a b series swap on Hasport poly bushing mounts. It was very loud from the vibration, but I expected and enjoyed it since it was purpose built to go fast and be fun.

The car runs and shifts great otherwise and I don't hear this noise outside of the cabin area. There's no knocking noise like something is hitting the sub-frame or anything. It's just so drone-y compared to what it was before. I'd like to get it back to the very quiet operation that it was before, but I cannot for the life of me, find the source of my problem. I hope someone can confirm if the RV6 cats cause the low RPM noise or if they would not and if the new motor mounts could cause it, due to a break-in period. I doubt it's the mounts though.

the auto manufactures work hard to tune certain frequencies or vibrations out, you effectively changed the exhaust which may have created a frequency the car isnt built to overcome.

or perhaps something is rubbing against something, which would create a frequency or vibration.

I have doubts that that is the reason. Not only from experience, but because I found this guy and others in the thread with the same issue after replacing mounts only...Also, the vibration cannot be heard outside the car. Only while sitting inside. I've been under it while it runs and can't find a single thing vibrating. I think it's purely mount related. Maybe the bolt that goes through the mount into the bracket on the motor is too tight? Should there be some play in there? I can't imagine that there should be...

https://acurazine.com/forums/second-...e-help-978353/