Thread: Max Hp numbers from a T-25 - T-28

It is what it is. I prefer a different torque curve but if you know what you're doing it's not too bad. It's all about compromises.

Just a question out the blue ben not to go off topic, is it possible to alter Hp & Tq numbers just by exhanging the exhaust wheel, or the intake wheel on the turbo. For example if I want more torque and less HP and vise versa or are those only altered by the choice of cams that you use. If that's true which side of the turbo do you alter for the change to take place.

I'm rebuilding my engine in the coming weeks, based off the information in here, do you think shooting for about 270hp is reasonable with stock DE (freshly rebuilt), GTi-R T28 & intake manifold (with 444cc's), a ported/polished head, and around 12lbs of boost?

I'm not really sure what kind of numbers to expect from the ported head, and how much the GTi-R intake mani will change the curve as well.

Rest of the car has full 3" exhaust, Calum Basic, N60 MAF, and a wide-band so I can tune my AFRs fairly well.

Your thread, you can go off topic all you want.

When you change an exhaust wheel (and exhaust wheel housing to match) from a smaller exhaust wheel to a larger exhaust wheel you're going to have boost onset a little later which will slow your power production early and likely lessen your peak torque output or at least move peak torque later into the rev range. You will gain peak power (up top) because you've "uncorked" the exhaust a bit. The same thing happens if you go to a larger A/R ratio on the exhaust housing.

Same thing basically with a larger compressor wheel for slightly different reasons.

When you change a compressor wheel (and compressor wheel housing to match) from a smaller compressor wheel to a larger compressor wheel you're going to have boost onset a little later which will slow your power production early and likely lessen your peak torque output or at least move peak torque later into the rev range. You will gain peak power (up top) because larger compressor wheels are intrinsictly more efficient than smaller ones*.


*A larger compressor is more efficient because the ratio of the area of the compressor wheel to the area of the gap between the wheel and the housing is larger. There's always a gap between the compressor wheel and the housing. Through this gap pressure can escape and basically bypass the compressor. This area makes up more of the total area on smaller compressors so they are less efficient.

Fun fact: this is also why the power potential of one large turbo is always higher than from a twin-turbo setup using two turbos that are "half" the size.

that torque thing is interesting...
In my case in my setup with the GTi-R @ 12psi I made 270whp and 242lbs/tq, then the next run was done same tune but at 14psi and made 283whp and 264 lbs/ tq... I gained 12hp and 22 lbs/tq... that was interesting...

Ben your the reason I still log in the forums.

Yeah, the disco is a great turbo. I ran it for a year with 21psi of boost and never had a single issue. It made great power and was stupid responsive.

I sold the car to another guy who blew the transmission, put a B15 in, and the turbo is still going strong running 12-14psi daily. Garrett bb turbos are beasts!

I can add a bit to the discussion of turbine wheel sizing. The turbine wheel size must be kept within a small range of the compressor sizing. You see a lot of people putting a large compressor wheel on a small turbine, but this can create issues with turbine speed and compressor surge. Pick too small of a turbine, and the compressor may surge as it tries to force air into the engine in a region of instability on the compressor map. Picking too small of a turbine is spinning the shaft up too quickly, yet restricting the exhaust flow and lowering VE.

A larger exhuast wheel doesn't always mean more lag. Though the moment of inertia is much higher, the volumetric efficiency of the engine can be drastically improved with the right turbine/housing size. This increase in VE can improve spool by making the engine breathe and perform like a bigger version of itself. Precision and Borg Warner make large turbines for their power output. A small SC61 has a much larger ex wheel than my GT3076r. Pick an exhaust wheel that flows too well, and the setup can be sluggish and not want to spool.

There are other reasons for not wanting to mix turbine/compressor sizing too much, but I figured I would touch on that basic understanding first.

I wish Garrett made a GT3576r, or a 76mm compressor on a larger turbine. This would cure all of my surge issues

The disco is at peak power delivery at 340whp, and should be reasonably reliable at that power level. Keep pressing the boost though, and it may live a short life.

DET, S4 cams, Disco potatoe on GTIR manifold, JWT ECU, 740cc injs, 300zx MAF, Fidanza flywheel JWT clutch and full 3 in exhaust.

16 PSI 370 WHP and 330 LB Ft torque.

car ran 11.8 @ 122 MPH

Owner of car Marty.

.......speechless keep that great info coming guys I read every word you say.

yes that was on stock W10 DET block. a stock DET motor can make 450 WHP with no problem.