twins piping size?

My hot pipe is 4" since that is what the factory charger pipe was and mated it to a T6, although it is some fancy bending to get it there. Other piping is 3.5 between chargers on the compression side and 3" into the intercooler. I went with a big of piping as I could get into the space and what mated up the best with the chargers.
 
Primary to the secondary is 4in. Air filter pipe is 5in or 6in, cannot remember which.
 
Thanks for the pics sharp looking engine! How do you go about bending the pipe to fit the t6?
 
If the discharge of the big atmosphere turbo is 3", I see no reason to run anything larger on the interstage charge pipe.

Unless of course you want more lag from the big charger because it will have more space to fill before it makes positive pressure. (Don't know why you'd want more lag...)
 
Big Blue24 said:
If the discharge of the big atmosphere turbo is 3", I see no reason to run anything larger on the interstage charge pipe.

Unless of course you want more lag from the big charger because it will have more space to fill before it makes positive pressure. (Don't know why you'd want more lag...)
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I will be changing my 4" to 3" for the reason listed above.
 
That a good point blue24 that I didn't really think of that. I'll be ordering the piping soon so I'll go with 3"
 
Big Blue24 said:
If the discharge of the big atmosphere turbo is 3", I see no reason to run anything larger on the interstage charge pipe.

Unless of course you want more lag from the big charger because it will have more space to fill before it makes positive pressure. (Don't know why you'd want more lag...)
Click to expand...

I'd be very curious to see what (if any) difference there would be between 3 and 4" piping, considering the air these turbos move. We're talking 1000+ CFM, and even with it being a little less than double the volume, I'd bet there wouldn't be much difference in time to pressurize the pipe.
 
Tate said:
I'd be very curious to see what (if any) difference there would be between 3 and 4" piping, considering the air these turbos move. We're talking 1000+ CFM, and even with it being a little less than double the volume, I'd bet there wouldn't be much difference in time to pressurize the pipe.
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Now you're just trying to justify your fancy 4" pipe... :shake:
 
This thread has made me contemplate buying 4" mandrel bends to re-do my coldpipe so I can make back to back passes at the drag strip and see what if anything changes.

I do admit, the 1000+ CFM is huge relative to the difference in volume between 3" and 4".

I believe in fluid dynamics, you learn that energy is lost everytime you expand and then compress a gas/liquid. If the discharge is 3", then you let it expand to 4", then compress it back down to less than 3" as it goes through the second stage turbo's small inducer, it would seem like there would be reduced efficiency which would equate to lower peak HP capability.

The coldpipe on the He351/Ht4B twins on my Junker Drag Truck have a 3" discharge ID, to 3" coldpipe, that actually runs into to bevel on the silencer ring on the He351 inlet. The throat of the He351 is 60mm just like the inducer or 2.36", so it does compress a little before going through the turbo's inducer.

It's about $60 in mandrel bends to test the difference, between 3" and 4", I might have to undertake that research project next spring when the track opens up every other weekend.
 
dvst8r said:
Now you're just trying to justify your fancy 4" pipe... :shake:
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More square inches of Candy Blue under the hood is justification enough!


My twinset, as I'm sure most peoples are, has a 4" inlet on the secondary. It has MWE, so you can't neck it down and feed it directly into the impeller. So if you use 3" piping, you're going to use a 3-4" adapter (be it pipe or coupler boot), and then the secondary takes it from there. Even the GT35 without MWE is still a 4" inlet. So the compression issue is a moot point. I know its a dynamic system, so pressures aren't going to be constant in all points of the pipe, but I'd think the turbulence of size changes would be a bigger issue. My GT42 has a 3.5" discharge, to a 4" pipe, to a 4" inlet, down to a 2.4" impeller. 3" would have more transitions in sizes than 4", in my application. Now if the primary had a 3" discharge, I would see more merit in the 3" pipe.

Now for the math part. Figure a hot pipe is 3.5 feet long, give or take on design and layout. 42" long has 297 cubic inches of volume. 4" is 527 cubic inch. So roughly 1/6th and 1/3rd of a cubic foot, respectively. Large difference relative to each other, but in the scheme of things, a drop in the bucket.
 
Big Blue24, do it I think it would be pretty interesting!
 
It would be interesting to see the difference from just that one change blue. I think the I let on the 80 is 5.5. So how well would that be going from 3" to 5"?
 
I had a few beers and wasn't thinking last night lol the outlet on the 80 is around 3" not 5.5. So it should match up nicely to a 3" pipe
 
I have two things that I think will contribute to this thread, first being this spreadsheet I made probably a year ago to evaluate the optimal hotpipe:
pipevsflange.jpg

It would appear from this basic chart that a 3.5" I.D. pipe would work best for making a hotpipe out of when using a T6 primary as most do. 3" would be better for a T4 primary.


The second contribution is this quote that a little searching turned up: (note: Brad is talking about the coldpipe here)
Bponci said:
I have used 3'', 3 1/2 and 4''. The only difference i did see is the amount of room and the boost response time. The 3'' is quicker to move the gauge between the chargers but i saw the cool down time and top end heat up. Down low in the rpm range it seemed better than the 3 1/2 and 4''. Between the 3 1/2 and 4'' in all instances i couldnt see a difference.
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Pulled from this thread if you're interested.
 
Anyone ever tried a primary turbo with a v band exhaust inlet? Or do they not go large enough? It seams this would be ideal for twins
 
newsmoke said:
Anyone ever tried a primary turbo with a v band exhaust inlet? Or do they not go large enough? It seams this would be ideal for twins
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Unless I'm drunker than you, the exhaust inlet is a t3, t4, t6.
 
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