Drive Pressure loss=HP gain?

JQmile

JQmile

Comp Diesel Sponsor
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Nov 19, 2006
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So I recently had some weak dyno results (332 with nitrous :doh:) despite being up from 36 pounds of boost to 54psi with my compressor upgrade. I talked to a few people, and I think with my stock turbine wheel and 3-inch downpipe, my drive pressure might be as high as 90-100psi with nitrous.

Now for the 64,000 question: if I lower my drive pressure to 45-ish with a wastegate, I may have less boost (hopefully--the turbo is off the map at about 45) but I think I should make more power due to having less of a restriction on the exhaust side. Not only will it divert pressure, but I think the lessened volume will also make my stock downpipe less of a restriction. What's your guys take on all this?
 
Yes high drive pressure kills power, and yes a wastegate would be a way to divert some air around the turbine. Usually the wategate leads back to the downpipe one way or another.

Three things that could help are a better flowing turbine, bigger housing, or better wastegating. I think the restriction at the turbine would be greater than the one in the downpipe.
 
Now for the 64,000 question: if I lower my drive pressure to 45-ish with a wastegate, I may have less boost (hopefully--the turbo is off the map at about 45) but I think I should make more power due to having less of a restriction on the exhaust side.
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volumetric flow rate should increase, assuming properly gated. why not a better turbo setup? project $$$?
 
Ypu should drop down to an Hy-9 and add more nitrous.
 
Thats how we do it out here, just keep adding nitrous until you get the # you want, then multiply that by 1.67 and you have it :nos:
 
You will most definitely pick up power. Probably a lot of power. I'd get a 38mm external wastegate and a bigger down pipe and I bet you pick up 75+hp.
 
I would shoot for more like 40psi with that turbo. What size exhaust housing do you have on it? And yes you will make more power with a wastegate of some sort. I have worked over 12 and 14cm internally gated housings that will flow more than you need, and much cheaper and easier to set up than an external.

FWIW, my 24 valve with stock hx35 ran quicker at 32psi after i modified the wastegate than it did at 38-40psi.
 
I believe Jason is trying to do what he can with what he already has, and you could probably pick up a wastegated housing for almost nothing.
 
Right, but it seems to me that turbo will never move enough air for those sticks, so I was thinking kill 2 birds with 1 stone by swapping out a bigger charger. Of course you did just upgrade the compressor...
 
No dought dumping a bunch of that nasty DP will free up a ton of ponies..... like already said if on a super tight budget pick up a gated housing and modify it for the max gate flow, then set the boost around 40# and spray away..... the bottom end will love ya for it too. JMHO
Ryan
 
I would look for a 16 cm wastegated housing. IIRC about $200. The smaller housing will help spoolup, and the wastegate will help control drive pressure.
 
No offense guys...but a stock wastegated housing won't cut it with spray...even a modded one will be close.

For what you can buy a housing for, buy a good 38-44mm external gate, and do it right;)


Once you go external gate, you'll hate anything else...tuning is so much easier!

Chris
 
you can just run a dump tube for the gate... it's ghetto, but it'll work and really help cut backpressure in the downpipe
 
Signature600 said:
No offense guys...but a stock wastegated housing won't cut it with spray...even a modded one will be close.
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You are wrong, that I know for a fact. I have first hand experience with a modded 12cm housing on a truck that was at 500-550hp with nitrous. Jason's truck is no where near that, he is just over 300hp, heck he could probably get by with an unmodified housing at that HP level.
 
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