Hot pipe diameter

smoke machine

smoke machine

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I've built a couple of twin kits lately and had a lot of fun doing it. Enjoy learning and figuring stuff out so I had a thought on hot pipe diameter. Most I've done have the primary out front so the hot pipe is longer than normal most out of 3.5". What I'm wondering is are there any benefits between using 3.5" or 4"? I know velocity is a good thing but is there anything to be gained by increasing the diameter for more flow. Thanks in advance and I hope this turns into a good discussion
 
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I always build my hotpipes with 3.5". I don't really see a reason to go up to 4" since 3.5" fits perfectly with the t6 foot.
 
There are a few threads about it floating around, the answer I found was that 3.5 is the perfect medium between flow and spool
 
Great, now this thread has got me wondering if doing my hot pipe in 4 inch schedule 20 is a bad idea. Any input on doing the charge pipe in 4 inch vs 3? sorry for the thread jack.
 
What are your power goals and setup? There is a big difference in volume between 3, 3.5, and 4"
 
newsmoke said:
What are your power goals and setup? There is a big difference in volume between 3, 3.5, and 4"
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Me or the OP? I'm doing a really weird build. S256 over a k31 with a batmo. going for quick spool, power goals are the same as what i currently have 550hp.
 
okish said:
Me or the OP? I'm doing a really weird build. S256 over a k31 with a batmo. going for quick spool, power goals are the same as what i currently have 550hp.
Click to expand...

I think 3" would work well for you. I had been looking into the s257fmw actually.
 
newsmoke said:
I think 3" would work well for you. I had been looking into the s257fmw actually.
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i think ill do the charge pipe in 3 inch, but the hot pipe will be 4 inch schedule 10 stainless since i have a 90 on hand.
 
I used 16ga tubing. In my peanut brain the smaller the pipe the higher the velocity but less volume. Mines already built with 3.5" but I thought this would be something that some of the big guys could come in and talk about.

I just towed 30k with my setup and I think 3.5" is perfect. No surging, barking, or any problems spooling even when I had to get off the skinny pedal then back on.
 
My hot pipe on my set is 4" and the charge are 3.5". Never any surging or issues towing up to 36k. Stocker over S475 with 90HP injectors and EFI tuning.

I am going to have to build a new set of pipes for the 6.7 when it goes it, I most likely will do 4" again with 3.5 for charge just like previously. The 6.7 is getting a S366 over S475 with same injectors and tuning.
 
Mine has a brace that comes off the T-6 flange down to two bolt holes on the block beside the oil filter
 
I bought a mount from source automotive. Made the hot pipe out of 3 1/2 exhaust tubing
 
3.5" hot pipe and 3" charge pipe here. The bends in 3.5" are still tight enough to work well when routing it out on the fender. My mount is 1/2" solid rod to the oil drain.
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I could be wrong, but I can't imagine a situation where you'd ever need more than a 3.5" pipe... maybe somewhere north of 2000hp?
 
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