Turbo back exhaust question

[sloLs1]

So on my '63 Chevy ll I have a 4.8l ls motor and plan on making 700-800hp.... I wanted to keep it somewhat of a sleeper look. I want to run two tail pipes out the back. Could I run two 2.5in pipes from the turbos back and not lose much hp or would I need 3in? Any Dyno proven results? I know people run cut outs but that's not something I want to do. Any help is always appreciated!

[Wagonbacker9]

this question has an easy answer.... cutout.

[BAD LS1]

Wouldn't parallel 2.5" trump a single 3"? I made 750 thru a 3" down pipe with allot of bends and an entire catback...

[sloLs1]

Wouldn't parallel 2.5" trump a single 3"? I made 750 thru a 3" down pipe with allot of bends and an entire catback...

Lol I think you answered my question! Ya I was thinking two 2.5in pipes would equal a 5in single pipe?!? And shit if you made 750 through a single 3in, ill be set for 1000hp haha

Thanks for the reply!

[sloLs1]

Just seems like a lot of build threads I read everyone has a 4in open down pipe or something else that isn't close to what I want to do

[Wagonbacker9]

Lol I think you answered my question! Ya I was thinking two 2.5in pipes would equal a 5in single pipe?!? And shit if you made 750 through a single 3in, ill be set for 1000hp haha

Thanks for the reply!
Doing the math, dual 2.5s are equal to a 3.5" single pipe.

[sloLs1]

Doing the math, dual 2.5s are equal to a 3.5" single pipe.

yaaaa i see what your saying, my thinking was defintly off!

[Josepy]

I am in for a video of when this is completed. Totally badass.

[FourEyedFord]

Turbos hate post turbine back pressure, so the more free flowing the exhaust can be after the turbo the better. Two 2.5s should be OK for your power goals, but two 3" ones would be best though. If you are doing tailpipes, you gotta remember how much length of tubing is involved too. Stick with a straight through type muffler also, not a chambered one.

[-stew-]

What does the length of tubing have to do with things?

[jbiscuit]

Why not just install dummy factory style tailpipes in the stock location and do a short route exhaust of whatever size/configuration you want

[Wagonbacker9]

What does the length of tubing have to do with things?

No idea how this plays into turbo, but here is a demo of why length matters. (Yes, thats what she said)

http://www.youtube.com/watch?v=1ywUEz5XtdE

[Lash]

The way I though it was for a full exhaust is that you want it as free flowing as possible without letting the exhaust gases to cool inside the pipe too much. Generally speaking, cold air is more dense than warm air. Dense air in the exhaust... Bad.

[SSLEVO]

A single 3" pipe is 7.1 square inches, a singe 2.5" pipe is 4.9 while 2 are 9.8. Duel 2.5" would work but 3" would be better. I am making over 500 whp through a 3" exhaust on my evo though. Also the length and number of bends of the pipe plays a role due to the flow at the outside of the pipe being almost nothing, this creates turbulence and restricts flow. The longer the pipe the less flow. Try breathing through a full size straw and then cut off an inch and try it again, same principal at work here.

[JOHN 86GT]

I would run 3 inch and the longest straight through muffler you can fit . It will be quiet . (at low rpms ..)

[Prince Valiant]

Turn the tips down a bit, and it'll be just a bit harder to tell the diameter of the exhaust.

[sloLs1]

Everyone makes good points.... If its a matter of robbing me of 25hp I might not be too concerned. Now if 2.5in pipes rob me of 75-100hp then I will reconsider! Totally understand straightest route is the best. Ill have to see how much room I have under there once it's all said and done. I don't want turn downs or anything like that! I want to be able to drive the car and not get annoyed! I'm thinking I might try 2.5in pipes at first, one that I can disconnect easily at the down pipe. Run it on the Dyno and see how much It gets restricted. I'd rather lose a few hp and save a headache later than make a few extra ponies and not wanna drive it!

On a side note.... I should be updating a build thread soon!

[jbiscuit]

2.5" won't be nearly enough on a twin turbo car. And turn downs aren't bad, have it exit just in front of the rear axle assembly. I have 3" on my car with it exiting like that and its not too bad

[The Shaolin]

On a side note.... I should be updating a build thread soon!

That's what I like to hear!

[sloLs1]

2.5" won't be nearly enough on a twin turbo car. And turn downs aren't bad, have it exit just in front of the rear axle assembly. I have 3" on my car with it exiting like that and its not too bad

Ill start with open down pipes, if that's to obnoxious ill do turn down before rear axle, if that's still too much ill go out the back ahha jus keep building it back! I think I'm gonna run 3in down pipes and 3in as far back as the axle. Then decied what to do after that. Prolly just end up running 3in all the way out the back lol

[sloLs1]

That's what I like to hear!

Yes sir! Still a littl too cold to be working in the garage!

[FourEyedFord]

My downpipes exit in front of the front tires, and I still drive the shitt out of it, lol. I have two 3.5" pipes that neck down to 3". It does get a little loud in the car sometimes, but to each their own I guess.

If it's a pretty mild motor like mine, it won't be that loud.

http://www.youtube.com/watch?v=YP-_RShiEfk

[sloLs1]

Thanks for the video, and yaaa I think that's sweet but not what I want lol and I've never been such a lame ass with exhaust so this is why I'm asking, normally I run open down pipes or dumped before the axle, that's fun and cool and all for about 30mins of cruising and then It gets annoying to me atleast. I kinda want to try 2.5 and see how it sounds/horsepower and such. Maybe disconnect at the down pipes and see how that is. 2.5in exhaust can't be to expensive seeings that ill proly only need two straight sections and a couple bends over the axle... If it sucks scrap it lol

[WickedSix]

small pipes rob turbine efficiency, the larger the diameter after the turbo the larger the delta across the turbine. The more you can do to get the temperature and pressure after the turbo low, the more efficient the turbine will work. Heat drives the turbine, the smaller tubing drives backpressure that results in a smaller temperature delta across the turbo. In the ideal setup the exhaust gases after the turbine are ambient temperature and atmospheric pressure.

[juicedimpss]

5"
/thread.

[JOHN 86GT]

single turbo

3 " down pipe to y to 2 1/2 " dual cat back

vrs

3 1 /2" down pipe to y to 2 1/2 " dual cat back


Is one better or is the exhaust only as good as the most restrictive part?

[juicedimpss]

i like to size the DP to match the turbo outlet,typically. also try to keep the first few feet as straight as possible.(45* bends instead of hard 90*s)
so if you have to use a tight bend 3 1/2" to fit,vs a gentle bend 3" the smaller tube MAY actually work better. I think there really is no textbook answer for real world application in some cases.

[sloLs1]

i like to size the DP to match the turbo outlet,typically. also try to keep the first few feet as straight as possible.(45* bends instead of hard 90*s)
so if you have to use a tight bend 3 1/2" to fit,vs a gentle bend 3" the smaller tube MAY actually work better. I think there really is no textbook answer for real world application in some cases.

With that being said.... When the time comes, I might be contacting you for exhaust work!