Boost/Drive Pressure numbers with 74+mm turbo's

TARM · Jun 9, 2011

You can run it across the front of the engine then you do not need the coils in the tubing stil not a bad idea to do either way. The only way the temp is going to carry back to the gauge is thru the heat conducting thru the metal as the air in the tube is stagnet.

Gearhead · Jun 10, 2011

powerstrokenstang said:
drives seem good there, it doesnt try to snuff or anything.

The cam profile is doing some of that too.

powerstrokenstang · Jun 10, 2011

indeed, it is def helping that.

TARM · Jun 10, 2011

I could be wrong but didn't you put the cam in with no other changes so you have direct results isolated to only the cam?

powerstrokenstang · Jun 10, 2011

correct at the time, pulled 4 times last year after only a cam swap.

TARM · Jun 11, 2011

What were the differences you saw? Its still in so I can assume their were at least no large negatives

powerstrokenstang · Jun 11, 2011

ill put it this way, i changed it in the middle of the season. pulled one sat, pulled the motor, swapped cam and went pullin the next friday and it was def worth it. spooled faster stayed on top of it better which made the low end much better at the end of the track plus now my intake pipe doesnt get soot in it. i had a 2500 stall and could take it there w/ no prob but w/ the new cam i could barely get it to 2400 cause it pulled through the brakes so bad, just wanted to go. the idle exhaust sound sounds cool too lol.

TARM · Jun 11, 2011

Thanks that's what I was looking for.

Powersmoker · Jun 12, 2011

Charles said:
It used to make no sense to me that opening up the gate around the 38R and letting the 47 work harder produced worse boost:drive ratios. I thought maybe all the devious plumbing angles I was forced to use in routing that gate was causing a lot of drag or something. Even though I still didn't quite buy it. I never dreamed that 88mm charger with a 1.32 turbine housing would have been the problem. But after talking to some guys in the gasser world I realized the turbine in the 47 becomes a bottleneck in big displacement applications. And with a second stage charger pumping up the dispalcement, that's exactly what was happening, which is why I decided to up the first stage and leave the 38R with the gate alone.

In fact, If you look at it by the numbers, I picked up exactly 89.5rwhp, best gain at 3000rpm. Which is obvioiusly crap, because it should have picked up a bunch on the top, but with the crap my truck is pulling lately it just can't make anything up top, yet that big ass charger still picked up right at 90 wheel at 3000 rpm, where it was barely loafing. And that was starting at a dismally low 538.49rwhp, and pulling it all the way up to 628.

In terms of percentage gain, that represents 16.6%. Assuming I had swapped to the 55 back when my truck still worked, and I pulled 644 on the 47 with the 300% nozzles, that same gain would have put me at 751rwhp.

Point being..... something like this 55 under the hood of a truck that actually works... would make some hellacious power for a Heui 7.3 on fuel. These 400's, by the numbers should make 689 on fuel on my old setup, when my truck used to work, and Brian proved it by pulling 687 IIRC on dunbars running them. You slap that 55 on that, and you might be looking at 803rwhp on fuel.... again, by the numbers.

Needless to say, it's killing me to have to see such potential being squandered by some bs problem that keeps plaguing my truck, and I would love to see some of you guys running similar setups on some of these engines that actually function properly in all other areas.

Send me your setup

Powersmoker · Jun 12, 2011

S480/83 T4 1.25 a/r. 42psi Boost / 42psi Drive Pressure.

Two .080 Jets brings boost up to 60psi and drive pressure to 75psi. Gates were set to barely open. (This setup ran the 10.55 @ 129mph) Basically, you could run this turbo with nos and would not need any wastegating......but it would have to be strictly used for nitrous. This turbo at 40lbs of boost is the biggest POS. Fuel only it surges after each gear change, but with two stages of spray boost pressure and drive comes right up and works great.

S480/92 T4I 1.15a/r .

55psi boost & 60psi of drive. Fuel only, This turbo also surged after each shift (rpm drop)but wasn't as bad as the s480/82. You could bring the shifts points up quite a bit and it would prolly be fine. This turbo required a lot more gating to keep drive pressures in check with nitrous.

So you would think smaller turbine wheel would make more back pressure and spin the compressor faster but it doesn't work like that. From what i've been told from Jose over at Forced Induction, the turbine is the limiting factor, it just doesn't flow the air as the larger 92 turbine wheel... kinda causing it to be "choked down" making less boost and drive. The smaller turbine wheel does spool way quicker than the larger one but it doesn't have any top end.

Charles · Jun 13, 2011

Powersmoker said:
S480/83 T4 1.25 a/r. 42psi Boost / 42psi Drive Pressure.

Two .080 Jets brings boost up to 60psi and drive pressure to 75psi. Gates were set to barely open. (This setup ran the 10.55 @ 129mph) Basically, you could run this turbo with nos and would not need any wastegating......but it would have to be strictly used for nitrous. This turbo at 40lbs of boost is the biggest POS. Fuel only it surges after each gear change, but with two stages of spray boost pressure and drive comes right up and works great.

S480/92 T4I 1.15a/r .

55psi boost & 60psi of drive. Fuel only, This turbo also surged after each shift (rpm drop)but wasn't as bad as the s480/82. You could bring the shifts points up quite a bit and it would prolly be fine. This turbo required a lot more gating to keep drive pressures in check with nitrous.

So you would think smaller turbine wheel would make more back pressure and spin the compressor faster but it doesn't work like that. From what i've been told from Jose over at Forced Induction, the turbine is the limiting factor, it just doesn't flow the air as the larger 92 turbine wheel... kinda causing it to be "choked down" making less boost and drive. The smaller turbine wheel does spool way quicker than the larger one but it doesn't have any top end.