Taking the Cougar in to get exhaust on Monday

The car will make between 350-400rwhp(I hope) ending close to 6000 rpm when is all done. Will be running high flow catalysts, and the exhaust man said he could fit a fairly large muffler under the rear to flow well and keep it quiet. Im hoping the catalysts will act as a resonator.

I wanted some opinions on what size to run. I always just said screw it and go with 2.5. But, the exhaust guy I talked to said that dual 2.25" would be better for the car. Said, 2.5 dual is over kill and would add to highway drone. Im seeing people support staying 2.25 dual, and 2.5 dual. I had seen a old post with a argument going on this subject. Im kind of leaning toward 2.5 dual. This exhaust man does great work. But, it may just be one of those different things with these cars; the exhaust just has to be a little bigger. What do you guys think?

i did a 2.5 into the resonator, single 3" out around early style gas tank, and dual 3" the rest of the way. The dual three inch out the back was more for convenience than anything.

If i did the math right, the dual 2.25 is still bigger than the single three. Even so, if it were me i would do dual 2.5.

There will likely be drone no matter what you do... i know 10 people after me will say theirs has no drone (but I still wont believe them) Mine has moderate drone around highway rpms, but it sounds sweet at idle. i get a lot of compliments on how good it sounds.

Well I will say I did the true dual 2.5" on my car, and I have been fighting drone ever since. I honestly don't know whether I would go with dual 2.25" if I had it to do over again, or if that would even fix the drone issue, or if it would hurt my performance any, but for what it is worth, here is my experience.

1) Bought the car with a complete hack-job exhaust, one cat gutted, mid-mounted flowmaster dual 2.5" inlet single 3" outlet, then made a turn and dumped before going around the gas tank so right at the back of the driver's door. It was horrible in every respect, was obnoxiously loud, droned at all times, leaked, and hung so low that it scraped a lot.

2) Bought the true dual 2.5" kit for around the gas tank to the back of the car. Cut off the crappy flow-master and replaced with straight-pipe into the 2.5" system, then a pair of Thrush welded mufflers out back. Much better than it was, but still too loud, and droned like crazy from about 50mph to about 90mph. Above 90 it sounded good, but I didn't think that would be a viable excuse with the police, so back in for more exhaust work

3) 2 new spun high flow 2.5" cats. This is where I found out that the one cat was gutted before. At this time, I also put in an X-pipe right after the cats to tie the 2 banks together. Volume was now at a managable level, and the drone was greatly reduced, but still there from 50-90, and still driving me nuts.

4) Bought a knock-off brand DIDO glasspack on ebay and mid-mounted after the X-pipe. This brought the volume down some more to a level that I would be happy with if this car weren't a daily driver, and the drone is now only there from 60-85. The only downside to doing this is it hangs fairly low, and the car is pretty low, so now that scrapes on speed bumps and larger bumps in the road.

My next step, is I am actually going to install a second set of high-flow cats in line with the previous set, so the car will have 4 cats on it. I don't know how much this will help, but I know cats do help quiet it down, and they do help eliminate drone, so we will see. If that doesn't work, the knock-off DIDO muffler will be replaced with a Magnaflow DIDO with the built-in X-pipe, so it will then have a better mid-mounted muffler and 2 X-pipes and 4 cats, and we'll see if that can eliminate the drone and quiet this thing down a little while still flowing well.

Thanks for the input. I think I will ask the exhaust man if he can do 3.5" and if he can maybe dual 2.5 to single 3.5 back to dual 2.5. If not, then its dual 2.5.