I recently installed an oil pan brace using the stock motor mounts. I was previously aware of the strut tower bar clearance issues that result from the increased motor height due to the brace. However, I think I've found another issue today.

I noticed a big exhaust leak where the downpipe and main cat meet up. I'd never had a leak there before. I changed the gasket to a brand new one today and tried to realign the flanges properly but no matter what I did I couldn't get the top of the main cat to seal properly with the downpipe. The bottom of the flanges seal nicely. I'm wondering if the slight increase in height of the rear of the motor has caused the angle of the downpipe to change just enough to prevent my from being able to get a good seal here.

Has anyone run into this issue and if so, how did you solve it? There doesn't seem to be enough flexibility in the main cat to get it to match the new angle of the downpipe. One thought I had was to hack up the downpipe and weld in a flex section before the flange, but I'd honestly rather not remove it if I can avoid it.

Also of note - in other cars I've noticed that changing the angle of the driveshaft can cause premature wear and unusual drivetrain noises to occur. Again I know we're dealing with small differences in angle here, but has anyone considered this before?

 

ArmitageGVR4,

Based on the information you've provided, I may suggest the following steps in order, if you haven't done this already:

1-clean off the rust from the threads and bolts with a wire brush
2-remove the cat entirely
3-bolt the forward part cat to the downpipe, but without fully tightening the bolts
4-bolt the rear part of the cat to the catback exhaust, again without fully tightening the bolts
5-alternate between tightening the forward and rear cat bolts until you get everything aligns

I've run 4 different sets of motor mounts on my FD, and each one resulted in a different motor height. Combined with several mix-and-match combinations of stock cat, high flow cat, stock catback, GReddy Evo and RB duals, everything has always fit, but your going to have to put in some muscle and a little bit of coaxing to get everything to bolt together. The rubber hangers are flexible, but they were also designed to keep 60 lbs of (stock cat and stock exhaust) metal from flopping around under the car. Placing some oil on the rubber hangers helps tremendously in removing and reinstalling them.

The driveshaft angle shouldn't be an issue.

 

I have the Banzai Racing oil pan brace installed on mine with Noltec urethane motor mounts, and I didn't have any problem with exhaust leaks, that's strange. The extra 1/4'' increase didn't affect anything the car drove perfect after I installed it and I drive it everyday and have no problems.

I don't think modifying the driveshaft will be necessary I agree with JuicyJosh