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Discussion Starter · #1 ·
I'd like to do some exhaust work on a 1st gen with an L28et.
The general consencus seems to be to go with 3" all the way.
I dont like how that looks though.....

I understand that there are options though.
If I used dual exit pipes after the muffler what size would they have to be in order to give the same flow?
I recall that it isn't something as simply as 1.5" each....

I donno... anyone care to shed some light on this?
 

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Calculate the area of a circle for the 3" exhaust pipe:
3.14 * (1.5 * 1.5) = 6.75

Calculate the area of a 2.5" exhaust pipe:
3.14 * (1.25 * 1.25) = 4.91

Calculate the area of a 2.25" exhaust pipe:
3.14 * (1.125 * 1.125) = 3.97

Calculate the area of a 2" exhaust pipe:
3.14 * (1 * 1) = 3.14

Looks like you'll need two 2.25" outlets to match the flow of your 3" pipe.

- John
 

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John's right...

I've used a dual-outlet 50mm twin-pipe system on mine for years. The twin pipe system has an advantage on the 240's as it was a Factory Option (Take a look at the Z 432 undercarrige sometime!) That's what the TWO bumps in the front differential x-member are for! The Z432 used a dual 60mm pipe, which is 2.36", so the 2.25 John mentioned should clear just fine. The hangars are positioned off the two ears at the back of the tranny, and on each side of the diff (mirror image of the stock hanger location there). I wish I could take a shot under my car for you, but right now it's in mud, and I won't be moving is too soon.
 

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Re: John's right...

Keep in mind even a good dual outlet exhaust (other than true duals) will not flow as good as a single outlet system. single inlet & dual outlet mufflers create backpressure and backpressure creates turbo lag. you'll notice that alot of Pontiac/ SLP Firehawks are upgraded to a single outlet exhaust.
 

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Discussion Starter · #5 ·
well...maybe

so Tom... your saying that even two 2.25" exit pipes after the muffler wont flow as well as one 3"?

hmmm... I mean I've heard other wise.... anyone care to comment?
I mean... even if it doesn't flow "as good" what type of performance drop are we looking at?
 

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Re: well...maybe

Two pipes have more internal surface area and boundary layer turbulence than a single pipe. Does it affect performance? Yes. Can the affect be measured on a dyno? Probably not.

- John
 

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Go John!

Consider this: You could actually use larger piping, like 2.5" on your duals. That would flow MORE than the single 3", and STILL package as the factory intended, with nothing lower than it should be. I know getting a 3" to tuck up where it needs to be isn't as easy as routing two 2.5's through the factory channels...
 

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Re: Go John!

The problem is not the flow of two 2.5" pipes, Two 2.5" pipes WILL flow more than a single 3" pipe. the problem is the muffler you use. a single in dual out muffler Won't folw as well as a single in/out of the same style. My sugestion id to use a Y-pipe and two mufflers that would flow best.
 

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turbine=bottleneck

The turbo will resist flow of exhaust gases as they try to exit the manifold, so your best exhaust layout is to dump it just behind the front wheel using the shortest length possible. This will allow the maximum HP by eliminating any back pressure on the outlet side of the turbo...and the possibility of CO2 inhalation, well that's another story. I've seen guy's run Twin Turbo on a V-8 with the exhaust routed to the forward side of the front wheels. This guy was serious about HP! But the general idea is to limit back pressure, large tube (one is always better than multiple layouts) and limited curves. And for those who are real anal, Mandel radials ONLY!
 

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Who would use dual outlet?

Two pipes means two mufflers. Single inlet dual outlet is a domestic bean-counter/marketing ploy. Not for use here. Simple enough to get a Burns Stainless header collector for the appropriate sized pipes, and run that off the collector/downpipe. You then run the big-cored glasspacks up front, and whatever you want out back. Two mufflers will fit in the back, but it's tight. Unless you stack the pipes on top of each other and use big cored glasspacks out back, too, like the stock system. Looks like an "8" from the back, instead of what you get when you use turbo mufflers out back on duals, which inevitably has to look like an "8" on it's side...
 
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