Compound turbo hot pipe 3" or 3.5"?

superdutyfarmer

superdutyfarmer

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Sep 21, 2008
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I posted looking for info on my 4b previously and didn't get any response. Made up my mind and am building a he351/hx55 setup cause I have both turbos here already. Working on hot pipe now; my delema is I have a 90* discharge for turbo here that has a 3" downpipe flange on it that I'm either gonna go off that to build the short pipe to hx55 or going to buy another billet flange and build it 3.5" any opinions on what's better. Already have spring gate setup on the 351 and will just lighten the spring and port the wastegate to get more flow to the 55. Looking for some input
Thanks
Rodney
 
I think 3" is more than plenty, especially given the reduced flow of a 4bt and conservative compound setup
 
That's kinda what I was thinking, 3" would maintain velocity and I plan on wrapping it so it should keep heat in better too. Never got into this kinda project I'm learning as I go. Trying to get away from all the nitrous I'm throwing at it now
 
I have 3" on my duramax. Makes over 1100whp with no problems. I would like to redo it all this winter with 3.5" or 4" though. The 3" just looks a little dinky is all.
 
I run schedule 40 3" pipe, so it's 3.5" outside, and 3" inside diameter.
Most 3" tubing is 3" outside diameter, and pending thickness...usually 2.8x" inside diameter.

And since I'm not a professional welder...it makes it easier to weld, without burning holes through it.
 
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I would think as long as the pipe has the same cross sectional area or as close as possible to the throat of a T-6 flange you should be good.
 
I used the 3.5" because it was easier to shape into the T6 flange open spacer so I could weld inside and out. I also went 3.5" on my interstage pipe to match the v-band I used on my S475. I know that 3" is more than adequate but I do like the look of the 3.5" pipe and the ease of fabrication was nice as well.
 
Sorry did not get this done yet, got busy with farm work and brother in law wanted help to build a 4b engine and stick it in his 79f150. I have all the pieces to make it happen, most likely going to use the hx55 I have here. Engine is coming out to fix a machine shop error and when it goes back together it will be done.
 
If packaging constraints are an issue I think 3" would be fine unless pushing the 4b to the limit. Are you going schedule pipe or thin wall? I'm assuming based on the responses so far the hx55 is t6 inlet? Maybe something t4 inlet is more appropriate?
 
The inlet on the 55 is a t4i off a marine application m11, I found a 90* cast elbow for the 351 with a 3" flange on it. I have someone with a Cnc at home making me a cradle setup for the 55 I was going to make it with a flange on the elbow come forward to another 90 and weld it to the cradle adapter. Is it bad to have a connection in hotpipe? Also how much will regular 3" thin wall hold?
 
I like that, I think I'll order a couple of them instead and weld it all together and make it one solid piece. I was thinkig if putting a bellows in there to allow for slight misalignment but knowing most manufactured hot pipes are cast one piece maybe that will be better off
 
They offer a short radius version as well. It is a little more spendy but worth it if things are tight.
 
Broaner said:
If packaging constraints are an issue I think 3" would be fine unless pushing the 4b to the limit. Are you going schedule pipe or thin wall? I'm assuming based on the responses so far the hx55 is t6 inlet? Maybe something t4 inlet is more appropriate?
Click to expand...

You will never be able to push a 4bt past the limit of what 3" piping can handle.
 
My hot pipe is thin wall 1 piece 4" and long(Side by sides). As long as you support the primary you're good to go. If you found everything you need with thick wall then your good to go anyway. Seems like 3" will match up with T4i better than 4". You can have a 2 piece hot pipe if needed. It adds another leak point but also a bit of installation flexibility maybe. I've been debating adding an hx40 vband to the middle straight section of mine next time its apart. I have to take the oil filter off to get it out of there.
01821BCB-0594-4EA2-AADE-E1EB66BD8AE1_zpsnbkwlgwf.jpg
 
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