Need Some Technical Info On Mufflers (Flow/restriction)

[Bennis]

Ok, basic question.

Car A: From the factory has a 2.0L engine making 123kw with a 2.25" exhaust, one muffler and one resonator. (And a cat)

Car B: From the factory has a 2.5L engine making 123kw with a 1.75" exhaust, one muffler and one resonator. (And a cat)

I own Car A, and the aftermarket muffler on it is too loud for my daily needs. I can get the muffler off Car B for $20. Being that they make the same power, will putting the muffler from Car B onto Car A cause a restriction due to the drop in pipe size?

Cheers

p.s. purpose of this is to save money. OEM replacement for my car is $400. Universal muffler is still alot more than $20 and may be louder than a stock option off another car.

Edited January 14, 2014 by Bennis

[r31slpr]

What if car A needs no more than 2.25" to flow freely and reach it's calculated power output.

And car B, given that it has a bigger motor has the potential to make more power, but the manufacturer uses a 1.75" for nvh purposes which also has the effect of restricting power to 123kw.

Disclaimer: I know absolutely nothing about exhaust design haha

Edit: My point is it may be a restriction

Edited January 14, 2014 by r31slpr

[niZmO_Man]

You're going from 2.25" to 1.75", of course it will there will be restriction. If the goal is to quieten your exhaust and you're too poor to buy anything other than that muffler mentioned, then you don't have much of a choice do you?

If you have a crappy hotdog resonator, replace it with an oval type (bigger/heavier the better, more baffling). Same goes for a cannon rear muffler.

[scotty nm35]

The muffler is the cheap part, fabricating it into the exhaust might be a pain in the arse if you need to change pipe size as well as install hangers etc...

[Stinky Rooster]

I doubt very much that a drop in size of 0.5" at the muffler will make enough difference to be discernable.

Do a bit of reading on Charles Law, and you will see why. The gas temp at the muffler is about 25% of the temp at the manifold, ergo you can quite drastically reduce the diameter of the exhaust a fair whack (and a lot of manufacturers do) without causing a restriction. There are also more than a few proponents out there that support the idea that reducing the back end of the exhaust diameter will actually help pulse scavenging (in an NA car, obviously not in a turbo application) which will contribute to low end pulling power.

Its also for this reason why hi-flow cats make a difference to performance, and cannons do not.

Personally, I would not let the back end diameter get below the std exhaust size from the manufacturer though.

[sucram]

Put a 2'' flange between your rear most flanges, the reduction in size will also reduce noise