exhaust IO diameters and sizes

[vitai0]

I dont know too much about exhausts so i was gonna ask you guys ..hopefully someone knows:

How bad is it to put a 2.5 inch muffler on to 2.25 piping. Ive seen this done before and i really feel its a bad thing to do...

[gil_ong81]

i don't see how it'd really adversely affect things. you just won't be making full use of the muffler.

[BAC5.2]

Why do you feel it's a really bad thing to do?

You might be able to answer your own question.

At any rate, it won't really make much difference other than sound. That far away from everything, pipe size doesn't effect exhaust scavenging on N/A cars.

The larger muffler isn't really an exhaust restriction that far back either. At the worst, it MIGHT reduce performance slightly, but not significantly. Depending on the car, it may help performance too. All depends on the car. If the car is pumping more air than can be flowed by a 2.25" exhaust, the 2.5" axleback will not really slow the air down. But a car that barely flows enough air to fill a 2.25" exhaust, will probably have the exhaust slow down a tad with the 2.5" axleback. With those examples, the first would reduce backpressure (which is good), the second could increase it (which is bad).

Backpressure is ALWAYS bad. So you want to reduce backpressure as much as possible. But using a pipe too large for the amount of air flowing through the system, will actually INCREASE backpressure. Funny how that works, a larger pipe being a restriction of sorts.

This is why Diesel trucks can use up to 5" pipes for really high output. They fill the tube and it's NOT a restriction. High output Supra's can get away with 4" pipes sometimes too.

Fluid dynamics is a tricky subject.

[Wiscon_Mark]

If you can get the muffler cheap, go for it, but I'd personally want to mate my piping with a matching muffler diameter.

As Phil said, backpressue is ALWAYS bad. it does not create torque. What creates torque is the exhaust gasses staying hot and flowing freely all the way through the exhaust system, instead of becoming cool halfway through, and slowing the airflow rate down (backpressure). That's why performance vehicles have full exhaust wrap, all the way down the line, to keep the piping from cooling the gasses down.

[vitai0]

yeah thermodynamics is a bitch...

thanks again for the help..

~m.

[white96gt]

This is why Diesel trucks can use up to 5" pipes for really high output. They fill the tube and it's NOT a restriction. High output Supra's can get away with 4" pipes sometimes too.

I think you are missing a variable here, both of these vehicles are turbo'ed, and that is why they need (well, benifit from)such large exhausts. a n/a car has more to worry about with backpressure, a turbo car, any backpressure will slightly hinder the turbo, so less will always be more.
other then that I fully agree with you
Don

[Wiscon_Mark]

wtf?!

I didn't remember typing that, and I definitely didn't. :lol: (it was Phil's post, not mine)

[rougeben83]

Your exhaust will only flow as good as the smallest restriction. So in your case, 2.25 to 2.5 shouldn't be that big of a deal. Moreover, it's near the end of the exhaust path anyway, so whatever loss in exhaust velocity will not be significant as the exhaust gas directly exits after the change to larger pipe.

[GrassyKnoll]

haha timely response :roll: :wink: