Exhaust sizing

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straightlinespeed

straightlinespeed

Sometimes I pretend to be normal
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Fellow FABOer's.

Im curious as to how one sizes the exhaust system. I bought my car with the exhaust set up, and it had me thinking. This is how its set up.

-TTI's 3" collector
-Reduced down to 2.25" right after the collector to the intake of the mufflers
-Out of the mufflers its reduced again to 2" out to the rear of the car.

Also it is not mandrel bent, so each bend is drastically smaller. Is this system sized properly, with the exception of the bends?

I know some back pressure in the exhaust is needed, but how do you determine what exhaust size should be ran.
 
as the fire moves back it cools and shrinks so pipes become progressively smaller.
..340 cars were 2 1/4 to the muffler and i think 1 7/8 out to the tailpipe.Some think they are gaining hp with mandrel bends and H pipes...i don't know, but can't see it.
 
I tend to agree about the one size all the way through. I am going with a 3" system on the truck when I redo it. Generally, I do not like the system to neck down from whatever the collector is. So, 3" collector gets a 3" exhaust system. Let the arguing begin, but that's my personal preference.....whether the extra size is needed or not. That's just how I like doin it.
 
First,please tell us what engine/displacement your running, and what you intend to do
with it.Then we can give accurate advice.
Second,some backpressure is NOT needed,that is an old wives tale perpetuated by
those unaware or unwilling to re-jet their carbs accordingly.The only exception is running
open headers,where a collector extension is absolutely needed to maintain the pulse signal
and directional flow velocity.
If you go to Burns exhaust tubing's website, I believe they state that anything past
5ft. beyond the collector results in a power loss,regardless of sizing.The exhaust "cools as it
goes" theory is fact,but only applies in a non racing type situation,where the tail end of the
system has lots of low flow time to cool.
For reference, I did some heads on an AAR 340,cc'd 9.7:1,292 purple shaft,9.5"converter
heddman of the shelf 1 5/8" units,OE port matched 6pk intake w/ heat blocked,carbs jetted up
drilling the outboard plates.Runs 3" thru the muffs then dumps B4 the axle.
On pump premium as driven w/a set of slicks the 'cuda has run a best of 12.35@109mph.
I believe the avg. times were around 12.45-12.50,not bad for a .030 over 340 in an E-body.
 
Personally I use this site as a guide. The guy goes through the math showing you how he arrives at his figures. And the math makes sense and adds up. But the quick guide at the bottom really sums it up nicely. Obviously this is probably more aimed at WOT in terms of how much flow you need. But really, why restrict something that you KNOW should flow as freely as possible?

http://www.exhaustvideos.com/faq/how-to-calculate-muffler-size-pipe-diameter/
 
Running a 360 and would say 90% street, 10% strip. But want to have some fun with it on the street as well.

I was thinking of down the road getting rid of the standard bends and swapping it all out to 2.5" mandrel bent the entire distance.
 
straightlinespeed said:
Running a 360 and would say 90% street, 10% strip. But want to have some fun with it on the street as well.

I was thinking of down the road getting rid of the standard bends and swapping it all out to 2.5" mandrel bent the entire distance.
Click to expand...

gotta go w/ rusty on this too. I like em same as the collectors all the way . mine are 3 1/2'', w/ short bullit roundy round mufflers that have 3 1/2" spiral inserts welded in the back half of those short mufflers. flows like h---, and isn't overly loud.
 
straightlinespeed said:
Running a 360 and would say 90% street, 10% strip. But want to have some fun with it on the street as well.

I was thinking of down the road getting rid of the standard bends and swapping it all out to 2.5" mandrel bent the entire distance.
Click to expand...

My fault, should've made a "checklist", anyway here goes.If You're cammed in the under
270's advertised,and running a stock converter w/3.23's or less,that system will be fine and
definitely a step up.However a 3" system won't hurt, and leaves room for a hotter combo
down the road,something to keep in mind.
As an aside, if you want to see an eye opener,check out the new engine masters issue
where Steve Dulcich and crew dyno'd a chebby sb to test the effects of header dings on
output!You need to see that to believe it!Lets just say most of us will sleep better after a
rough install!!
 
Killer6 said:
My fault, should've made a "checklist", anyway here goes.If You're cammed in the under
270's advertised,and running a stock converter w/3.23's or less,that system will be fine and
definitely a step up.However a 3" system won't hurt, and leaves room for a hotter combo
down the road,something to keep in mind.
As an aside, if you want to see an eye opener,check out the new engine masters issue
where Steve Dulcich and crew dyno'd a chebby sb to test the effects of header dings on
output!You need to see that to believe it!Lets just say most of us will sleep better after a
rough install!!
Click to expand...

Sorry I misunderstood also.

Yes Im running a 268 cam and right now 3:23 gears but I do have a set of 3:73's that I could swap in if I want to do some racing or what not.

I appreciate the input once again guys. Thanks
 
Heh Rusty...are you messin' with us?
i thought you were trying to teach us to beware of overkill?
 
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