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Old 09-18-2010, 12:28 PM   #243
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Join Date: Aug 2007
Location: GERMANY
Posts: 14
My Ride: 330Ci
Originally Posted by hoveringuy View Post
I am also learning that one cat gets hot as a mofo.
Yes, and running too hot is also bad. I've seen already melted down cats.


Now, if it goes about stock Y-pipe in M54. Put this # 18301733901 into your realoem, and tell me what you got.


OK, once again about pipe merging. I hope, it will be the final proof to confirm I'm right about my pipe diamater ratito theory.

Check this ->

Supersprint offers 63,5mm pipes for headers back exhaust. Now, you can also choose something like this:

diameter? 76mm

what do we get than? 76 / 63,5 = 1,1968



Iceman00, could you explain the relation beetwen stepped headers and merging several pipes into one (creating Y-pipe). I agree that stepped headers work. Stepping helps in cylinder scavenging. But why than, for example, supersprint do not offer whole exhaust stepped, but just the headers? That's because it's only benefical when gases are travelling very fast, which happens just at the cylinder head.

Now about the situation farther from the head.

You have a pipe, 10 feet long, 2" dia. Is it going to flow more water if you make one end of the pipe 4" ?
Answer is no. Because you still have a 2" restriction on the other end, which just can't flow more.

So, what is the point of using big pipe diameters at the end of exhaust? None.
Doing so just hurts low end torque, due to no backpressure.

And for now, I donít want to judge anything from AA and BW graphs, unless we have some proper info about dynoíed cars.

For low end torque you need a system with proper backpressure,

For high end torque you need big flowing system,

With stock setup you get nearly optimal balance for wide torque curve. Nearly because they are limited by emissions, noise levels and costs.

And what AggieE46 has? Definitely a big flowing exhaust. Low end torque is down, but where is his top end? Nowhere, because he is now limited by stock head. Thatís why bigger bored throttle didnít help either.
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