3" down pipe to 4" exhaust???!
04-10-2008, 11:45 AM
#1
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3" down pipe to 4" exhaust???! i've been thinking about installing my 4" magnaflow and running a full 4" exhaust from my 3" down pipe. would this be benificial or would the 3" down pipe take away from purpose of doing the 4" exhaust. right now i have the stock exhaust with a magnaflow muffler. stock, my exhaust goes into a single in dual out muffler then it y's back into one pipe and goes out the side.
i just got the trick kit and don't want to redo the down pipe already. plus mine has rear heat and a/c so not sure if i could fit much bigger of a down pipe in there.
i just got the trick kit and don't want to redo the down pipe already. plus mine has rear heat and a/c so not sure if i could fit much bigger of a down pipe in there.
04-10-2008, 11:55 AM
#2
Install the 3"--4" merge as FARRRRR towards the front of the truck as possible. The less 3" piping, the less back pressure=more power and faster spool. If you are speed density tuned.....you will want to have it looked at as it will lean ya out a tad.
04-10-2008, 12:05 PM
#3
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the 3" down pipe ends as soon as it goes under the fire wall. i still have the maf at the moment but it will be going away. i use hptuners.
04-10-2008, 12:17 PM
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what do you think of this replay?
i think personally that n/a exhaust and turbo exhaust have a different set of rules. but i'm no pro here and i'm still learning.
In an exhaust you want high velocity with little back pressure. As exhaust exits the exhaust port (or turbo) it is cooling down and shrinking. Since the air molecules are physically occupying less space but filling the same diameter pipe: velocity slows down... It's possible that it could get to a point where so much velocity is lost that the air will stagnate; this is counterproductive since the engine has to work harder to get that air moving again and out of the tail-pipe. Because of this, it's not logical to increase the exhaust pipe diameter the further you get away from the exhaust manifold/header/turbo.
Dynomax claims a single 3" exhaust pipe should support 700HP in a naturally aspirated engine. Given those are "aftermarket" horsepower numbers (i.e. highly optimistic), I would say anything under 600hp would be fine with a single 3" exhaust pipe. Anything 4" is overkill and IMO just for show (and it also weighs more). Going from a 3" pipe to 4" pipe equates to the same (i.e. illogical and potentially counterproductive overkill).
Dynomax claims a single 3" exhaust pipe should support 700HP in a naturally aspirated engine. Given those are "aftermarket" horsepower numbers (i.e. highly optimistic), I would say anything under 600hp would be fine with a single 3" exhaust pipe. Anything 4" is overkill and IMO just for show (and it also weighs more). Going from a 3" pipe to 4" pipe equates to the same (i.e. illogical and potentially counterproductive overkill).
04-10-2008, 04:21 PM
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what do you mean when you say 4" "track" pipe? did it go from down pipe and run the full length?
any more opinions anybody??? does a turbo exhaust(after turbo) rely on velocity like a good n/a exhaust?
any more opinions anybody??? does a turbo exhaust(after turbo) rely on velocity like a good n/a exhaust?
04-10-2008, 04:29 PM
#7
This is what my setup will be, 3'' to 4''. Its actually already done, jsut have to install. It go's from 3'' to dual 2.5's shortly after the k member than back into single 3'' about midway under the car than from there the 4'' and magnaflow 5'' muffler. One thing I am doing to help out the situation even more is an electric 3.5'' cutout right where it comes out above the k member dumped straight to the ground. The reason it changes so much is b/c its the PTK kit but I think it will still work great.
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04-10-2008, 11:14 PM
#10
The quote you referenced sounds like BS Al Gore internet logic. It takes a small amount of truth and incorporates it into a crock of ****. You want the biggest possible exhaust after the turbo for the most power. AFTER the turbo, exhaust scavenging and velocity are meaningless. It is entirely down to reducing backpressure.
04-11-2008, 01:34 AM
#11
The quote you referenced sounds like BS Al Gore internet logic. It takes a small amount of truth and incorporates it into a crock of ****. You want the biggest possible exhaust after the turbo for the most power. AFTER the turbo, exhaust scavenging and velocity are meaningless. It is entirely down to reducing backpressure.
04-11-2008, 02:52 AM
#12
The quote you referenced sounds like BS Al Gore internet logic. It takes a small amount of truth and incorporates it into a crock of ****. You want the biggest possible exhaust after the turbo for the most power. AFTER the turbo, exhaust scavenging and velocity are meaningless. It is entirely down to reducing backpressure.
And yes, N/A cars are much more reliant on exhaust gas velocity, where as turbo cars can't blow that **** out fast enough!
04-11-2008, 09:56 AM
#14
I agree...i have a 3 1/2 DP until it gets to the floorpan and steps up to 4" .. i am not 100% hiv positive but it really seems like the turbo kicks in a little earlier than when i had the 3 1/2 " DP just exiting the engine bay. I personally do not see why a turbo system wouldnt benefit from a stepped DP as long as its already an effiecient size coming out of the turbo. Just my opinion.
Turbos need NO restriction in the exhaust, put the biggest you can fit.
04-11-2008, 10:33 AM
#17
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thanks for the help guys. i agree totaly. i think that is why when turbo guys with say 3" exhaust pick up big power when they open a cut out where as n/a guys may get couple hp if they are lucky.
here is another qoute for ya. this is comeing from the same thread but on pt.net.
here is another qoute for ya. this is comeing from the same thread but on pt.net.
Well... a 3" diameter pipe has less area for flow than 2 2.5" pipes. Formula here is: Area = Pi x Radius^2
So a few examples for area of pipes:
So, at first glance a single 3" has .19 fewer square inches for flow. But there is another factor not being looked at here which is the frictional losses between the exhaust flow and the tube sidewall. So in that case a single 3" pipe would have less sidewall to impose friction compared to two 2.5" pipes. I think at that point we're splitting hairs between which one is better. BUT! A single 3" will definitely be LIGHTER than dual 2.5" pipes.
More pertinent to this discussion I'll point out that a 4" pipe has almost 5.5 square inches MORE than a 3" pipe. This is a case where we're going from smaller to bigger and there will certainly be a loss in velocity as the 3" pipe tries to fill the 4" pipe (I realize this is an exageration, but imagine a garden hose trying to fill a fire hose).
I did ALOT of thinking about this subject before I built the exhaust for my last car... When I see the 5" exhausts on the big diesel trucks it just seems like ridiculous overkill when you consider they probably only have a 3" or 3.5" outlet coming off the turbo. And I can't forget to mention the ridiculous exhausts and tailpipes on the riceboy cars. In terms of efficient flow: bigger is not always better.
So a few examples for area of pipes:
So, at first glance a single 3" has .19 fewer square inches for flow. But there is another factor not being looked at here which is the frictional losses between the exhaust flow and the tube sidewall. So in that case a single 3" pipe would have less sidewall to impose friction compared to two 2.5" pipes. I think at that point we're splitting hairs between which one is better. BUT! A single 3" will definitely be LIGHTER than dual 2.5" pipes.
More pertinent to this discussion I'll point out that a 4" pipe has almost 5.5 square inches MORE than a 3" pipe. This is a case where we're going from smaller to bigger and there will certainly be a loss in velocity as the 3" pipe tries to fill the 4" pipe (I realize this is an exageration, but imagine a garden hose trying to fill a fire hose).
I did ALOT of thinking about this subject before I built the exhaust for my last car... When I see the 5" exhausts on the big diesel trucks it just seems like ridiculous overkill when you consider they probably only have a 3" or 3.5" outlet coming off the turbo. And I can't forget to mention the ridiculous exhausts and tailpipes on the riceboy cars. In terms of efficient flow: bigger is not always better.
04-11-2008, 12:35 PM
#18
hmm...i dont get at all what you are sayin lol...i have seen numerous tests on this matter and have to disagree..when you have hot exhaust gasses coming out of your turbo into ,say a 3" pipe, and the gasses start cooling off, they start to shrink very rapidly and that alone creates a suction of air from the turbo. now adding a stepped pipe to a larger pipe will further create this suction. sorry but it is nothing like a waterhose going into a firehose. simply , there is always a point to where it is overkill, but its all a matter of the right setup to benefit from it. somebody correct me if i am wrong.
04-11-2008, 04:19 PM
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no, wasn't me. but i agree with what your saying. there only seem to be a few people that disagree with going to a 4". now just to order some pipe and hope my big azz magnaflow will fit under the tahoe like it did the silverado.