3" exhaust reducing down to 2 1/2" after x-pipe

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Mrpatel

Mrpatel

512Dart
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Will I loose any significant power by running a 3" exhaust and reducing it to 2 1/2" after the x-pipe? I will be making over 600hp and it will be difficult to run 3" all the way out to the back. I thought I saw something that mentioned that the first 4' matters most. Thanks Andrew
 
GMachineDartGT said:
I run 2.5 tails and 3" head pipes and mufflers. The restrictions are in the mufflers.
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^^^^^^^^^^^^^^^^^^^^^^ LOL. I built an approx. 600 horse sbc vega. Sold it and put the engine in a 92 gmc shortwide. I took it to a muffler shop and had tailpipes over the axle installed, coming out behind the rear wheels much like a Camaro. I had built the 3" w/ mufflers dumping at the front of the axle previously. I ran it for about a 1000 miles before having the tailpipes put on. The second I started it to back it out of the muffler shop, I could drastically tell the diff.,it was down on power. I drove it home and pulled the tail pipes back off and reoinstalled the turn downs. The power that I was well used to, was back. I still have those 3" tail pipes in the barn, if anyone wants them , they can have them for paypal fees and shipping > 406 sbc, w/ 17/8" headers, full 3" to the axle, flowmaster mufflers. My currant 505" 68 fastback has 2" headers w/ 3 1/2" done the same way, except for the mufflers, I made my own. Take this for what it`s worth.
 
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I've got TTI headers into 3" pipe w/dumps right after the collectors into 3" Magna flow mufflers with 2 1/2" tailpipes..sounds real nice loud but not obnoxious like so many others..
 
I agree that the best solution would be 3 inch into the mufflers and 2 1/2 out to the tailpipes.
 
Necking down a size has been done forever on Automotive exhaust. Some say it keeps the velocity up after the restriction.
 
S USED TO WAS BACK.
toolmanmike said:
Necking down a size has been done forever on Automotive exhaust. Some say it keeps the velocity up after the restriction.
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Ty removing the tail pipes and then tell me what u think. U will be able to tell the diff., unless ur car doesn`t make much power to star with.
 
famous bob said:
S USED TO WAS BACK.

Ty removing the tail pipes and then tell me what u think. U will be able to tell the diff., unless ur car doesn`t make much power to star with.
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It was probably the manufacturers saving money. LOL Tail pipes cancel the sound. I had a Super Bee with straight pipes off the collectors and turndowns out of Turbo mufflers. It was loud and sounded like crap.
 
I would just stay with 3" the whole way. Especially with 600hp
 
Mrpatel said:
Will I loose any significant power by running a 3" exhaust and reducing it to 2 1/2" after the x-pipe? I will be making over 600hp and it will be difficult to run 3" all the way out to the back. I thought I saw something that mentioned that the first 4' matters most. Thanks Andrew
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most say you should run 3" pipe and mufflers then 2.5" tail pipes.. say the gasses are cool enough by then that the 2.5" tail pipes will keep the gasses moving fast.
 
abodyjoe said:
most say you should run 3" pipe and mufflers then 2.5" tail pipes.. say the gasses are cool enough by then that the 2.5" tail pipes will keep the gasses moving fast.
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Try it w/ and w/o them ----------done.
 
Wife likes the dumps. Makes her happy and it's easy since I already have them. Thanks for the input. My 2 1/2" mufflers flow 450cfm. It's should work and the cut outs give me the option. Andrew
 
Hi Brian, dad's wagon dropped a little bit (.05 sec.) running 2.5" mufflers but he still runs 3" over the axle pipes. His 4100 pound car runs 117 mph so you can run the numbers to see what sort of power this takes.
It's always a toss up when you need tailpipes to fit versus getting every last hundredths of a second out of the car. Dad wanted quiet as can be so we worked hard to keep the sound levels very low and the performance very high.
Tom
 
.05 means jack.. 10.55 vs. 10.50. Big whoop.

I'd rather have a queiter car that's enjoyable to be in and doesn't throw dust everywhere and run the .05 slower. We're bracket racing anyhow.
 
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roccodart440 said:
.05 means jack.. 10.55 vs. 10.50. Big whoop.

I'd rather have a queiter car that's enjoyable to be in and doesn't throw dust everywhere and run the .05 slower. We're bracket racing anyhow.
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Mine isn`t exhaust loud, more motor loud. the 3 1/2" system doesn`t have any back pressure, don`t rack, or drone. No need for cut outs or dumps. 505" strokers have ample low end. No dirt roads around where I drive to stir up dust. Only problem I have is, it likes gasoline ! lol
 
Mine with the new exhaust was more engine loud to. I sound proofed in interior and trunk. It made a night and day difference.

I used Dynamat's products.
 
Interesting, my pypes 2 1/2" Violators flow 453 cfm, and straight 2 1/2" pipe is 500 cfm. What would 511 cubic inch motor need for flow?
 
When the exhaust leaves the manifolds (or headers), it's super hot gases, as it travels towards the rear it cools....this is a known fact. Any gas contracts as it cools, another fact. So as the exhaust gas travels towards the rear it needs less space because the same volume of gas gets smaller. Theoretically...your pipes could get smaller towards the rear and still be able to carry the same amount of exhaust. Of course smaller pipes (towards the rear) will also increase pressure (with the same volume). So if you use larger pipes as the exhaust goes towards the back of the car it will give the gases more room and decrease the pressure which should allow more flow!!


Theoretically speaking!!
treblig
 
Nice! I'm going to run the 3" x pipe to my 2 1/2" mufflers. I will have a 3" straight flow to my electric cut outs. Exhaust will run to the bumper. Street car and call it good. Thanks everyone for the input. Andrew
 
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