OK, Exhaust... Plain and simple question.

Size matters, no matter what they say... Right?

So what have you all found to be the best tube size to be?

I am not going into mufflers, I am using a Flowmaster. assgas:

I am not going into the Cat because... well just because. :explosion

I do not know what the stock size is, but I am guessing 2" or 1 7/8" ?


So would 2.5" all the way be good?


Or would 2.25" through to the muffler be best for torque? and maybe 2.5 out (for sound) :dunno:

Kevin

actually stock size is 2 1/4

Stock motor=stock sizes. Thousands of dollars were spent testing to find the right size exhaust pipe for a vehicle. The biggest I'd go would be 2.5". There's a certain point where you get so big you start to have weird turbulence in the pipes causing funny back pressures and surges that hurt engine efficiency. With the Flowmaster muffler, I'd use the stock (I think 2.25) from the manifold to the muffler. Then you can go 2.5" from the muffler back. As for the cat, there are several brands of cats that use a screen type material instead of all the passageways like the older ones. I use one of them on my camaro.

go cat back 2.5 like rustys, etc. and consider it done

Thats what I am thinking is 2.25 then 2.5 out. I just wondered what had been tried and true tested.

Thanks,
Kevin

Its what my XJ came with and what I'll be going back with when I get it re-done. I'm just going to put on a better cat and go with something like a Thrush Super Turbo muffler or maybe the old 2.5 Delta 40 off my camaro.

LOL @ Plain and simple question :roflmao:

The PO's of my 87 put on a Borla catback system. Nice and throaty, I haven't ever driven a stock Renix XJ, so i couldn't do a fair comparison.

The only thing I can compare it to is an old work buddies 96 XJ. His felt a hair slower (and alot quieter) using my butt as a dyno.....

My XJ came with 2.5 from the down pipe (cross over pipe to the inlet of the muffler then 2.25 out back. I replaced it with Rusty's FM 50 cat back 2.5 all the way out. It was very loud too loud for me. I thought I would grow into it but I did not after more than six months. I called and spoke to one of the engineers at FM. He explained to me that because of the cubic inch and the RPM's of the 4.0 a 2.25 from the muffler back would be better. The drowning I heard was a result of the loss of exhaust velosity due to cooling ect; ect. I cut the tail pipe at the hanger next to the fuel tank and replaced that piece with a 2.25" pipe from Auto Zone. It made a lot of differrence to the sound. There is no noticable difference to torque and power, at least not to the butt dyno.