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Turbo exhaust tube diameter questions???

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Old 12-23-2007, 05:58 PM   #1
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Default Turbo exhaust tube diameter questions???

I have to fabricate headers for my twin-turbo LS1 and i need feedback about tubing sizes. i had planned on running 1 7/8" tubing, but was told that that small of a diameter would choke the engine. It was recommended for me to run at least 2 1/4" tubes to the merge collector. The engine will be force-fed by two Turbonetics 62-1's. Any help, advice, suggestions and or feedback would greatly be appreciated. Thanks all!
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Old 12-23-2007, 06:35 PM   #2
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What kind of power you looking to make. I think you will be fine with the 1 7/8 pipe. I have truck manifold's and they are pretty small diameter also!
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Old 12-23-2007, 09:52 PM   #3
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What kind of power you looking to make. I think you will be fine with the 1 7/8 pipe. I have truck manifold's and they are pretty small diameter also!
Well hopefully, if all goes as planned, the engine will be in the 900-1000hp range. Looking to run a max of 18-20psi, it will be intercooled, yad, yada, yada...
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Old 12-23-2007, 09:59 PM   #4
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I have done them with great sucsess in 1 5/8".
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Old 12-23-2007, 10:19 PM   #5
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I'm a little confused? Do you mean the tube from the flange at the head to the collector or from the collector to the flange on the turbo.

I have seen good success with 1 5/8" from the flange at the head to the collector. Many people are using stock manifolds and I doubt they are bigger than 1 5/8s to the collector. However I have never measured because there are 7 second cars on the stock manifolds.

From the collector to the flange on the turbo you will want 2.5" tubing. The stock manifolds measure right at or just under 2.5" at the collector.

Good luck on the build.
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Old 12-24-2007, 12:17 AM   #6
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I personally would go 1 7/8", but that is the maximum your motor can really use at those power levels.

I don't know why there are people comparing stock manifolds to your header. The stock manifold is what you want to replace, so improve upon it. Just because it works doesn't mean it can't be better, making more power at lower boost, and spooling quicker.

I would go 1 7/8" primaries, into dual 2.75" pipes into the two turbochargers. 1 5/8" to dual 2.5s will work great as well, but I think at the specific outputs you'll be nearing you should go at least 1.75".
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Old 12-24-2007, 12:44 AM   #7
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Everyone that I deal with says to use 304 stainless steel material to build the exhaust system out of. Any comments or suggestions about mild steel vs. 304 stainless?
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Old 12-24-2007, 12:45 AM   #8
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I personally would go 1 7/8", but that is the maximum your motor can really use at those power levels.

I don't know why there are people comparing stock manifolds to your header. The stock manifold is what you want to replace, so improve upon it. Just because it works doesn't mean it can't be better, making more power at lower boost, and spooling quicker.

I would go 1 7/8" primaries, into dual 2.75" pipes into the two turbochargers. 1 5/8" to dual 2.5s will work great as well, but I think at the specific outputs you'll be nearing you should go at least 1.75".
Are you kidding me?!?!?! Stock manifolds, running 7's?!?!?! I need proof and pics! Please.
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Old 12-24-2007, 01:47 AM   #9
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I was referring to 1 5/8 tubes for my Turbo headers. I use 2.5" from the header to the Turbo Flange.
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Old 12-24-2007, 02:36 AM   #10
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I think 1.75" would work great. Isn't the exhaust port on the head only 1 5/8" and ported ones around 1.75" for most heads?

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Old 12-24-2007, 03:18 AM   #11
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1 5/8" with 2.5" logs on my truck. good for 1050rwhp thru a 4l80e and tcase.

i think the 2.5" logs are a little on the large side. we are steping down to 2.25" logs on our next project and are hoping to see ~1500rwhp eventualy.

here is a pic of a header we made today.

Click the image to open in full size.
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Old 12-24-2007, 05:24 AM   #12
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Are you kidding me?!?!?! Stock manifolds, running 7's?!?!?! I need proof and pics! Please.
search for Ohio Boys

Pretty sure both cars are on truck manifolds and in the 7's. But they have got to be getting close to the limit

FWIW, Tom's radial car has been going high 180's on 1 3/4" primary into 2.5" crossovers. Even with the header shrouding the port pretty badly it's still making power
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Old 12-24-2007, 06:09 AM   #13
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search for Ohio Boys

Pretty sure both cars are on truck manifolds and in the 7's. But they have got to be getting close to the limit

FWIW, Tom's radial car has been going high 180's on 1 3/4" primary into 2.5" crossovers. Even with the header shrouding the port pretty badly it's still making power
Tom running AllPro heads? Just wondering because of the shrouding as I know they have 1 7/8" ports on their 6 bolt heads.
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Old 12-24-2007, 07:48 AM   #14
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Quote:
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Everyone that I deal with says to use 304 stainless steel material to build the exhaust system out of. Any comments or suggestions about mild steel vs. 304 stainless?
Mild steel is cheaper and easier to weld and work with,it works ok too but it will rust and look terrible in no time.Even if you have it coated it will rust from the inside.Best to bite the bullit and use stainless even though it cost more,its harder to work with at least in the average home shop.It will have to be tig welded also.
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Old 12-24-2007, 08:46 AM   #15
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Tom running AllPro heads? Just wondering because of the shrouding as I know they have 1 7/8" ports on their 6 bolt heads.
ET canted valve. They have 2" ports, so we're not exactly ideal. Since the headers were made for a different car, we just dealt with it.
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Old 12-24-2007, 08:59 AM   #16
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Quote:
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Mild steel is cheaper and easier to weld and work with,it works ok too but it will rust and look terrible in no time.Even if you have it coated it will rust from the inside.Best to bite the bullit and use stainless even though it cost more,its harder to work with at least in the average home shop.It will have to be tig welded also.
how are they going to rust from the inside if you have them coated.
they will be fine if coated.
some of my junk has been ok, also check out klyes green TA that stenod built looks fine to me.
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Old 12-24-2007, 10:00 AM   #17
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Quote:
Originally Posted by SUPERBOOST View Post
Mild steel is cheaper and easier to weld and work with,it works ok too but it will rust and look terrible in no time.Even if you have it coated it will rust from the inside.Best to bite the bullit and use stainless even though it cost more,its harder to work with at least in the average home shop.It will have to be tig welded also.
that pic of a header i posted up above is 304 stainless scheduel 10. cheap and easy to work with. should be very durable too. you can mig or tig the stainless just like steel.

the little elbows are $7, a 2.25" elbow is $11. that entire header has $132 in parts and we burnt up $22 in holes saws. that includes the t4 flange and header flange all in 304 stainless.
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Old 12-24-2007, 02:55 PM   #18
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Hey Parish, did you notice a difference in spool when dropping from 2.5" tube to 2.25" tube?
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Old 12-24-2007, 03:03 PM   #19
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we are just now puting the 2.25" combo together and it will be completely diferent so i wont be able to say even once it is running.
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Old 12-24-2007, 03:30 PM   #20
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i used 1 3/4" stainless for my header material, and then a stainless works collector and 2 1/2" stainless for my crossover from the merge to the turbo, and from the turbo all the way to the back of the car is 4" stainless downpipe. and all my cold stuff is in aluminum 3 1/2" and 4"
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