Mustang Dyno results for GTR at 4,000ft altitude

[R33_GTS-t]

"As you may know, we’re NOT a fan of running a car at full load on the dyno until we’ve properly broken in the engine. However, we were constantly asked today what it did on our dyno so we succumbed to the pressure and we went ahead and made a few WOT pulls with only a scant 100 km on the clock.
OK, here are the results. A few things to keep in mind.

a) We use a Mustang AWD dyno and all power figures are at the WHEELS. Not the highest reading dyno out there, not the lowest.
b) Runs were made in 3rd gear due to the speed limiter coming on in 4th. Partial runs in 4th produced better torque but we hit the speed limiter before peak HP. Remember, this is a JDM model and thus has a 180 kph (~112 mph) speed limit…too be removed soon!
c) We’re at ~4000 ft altitude here in SLC. Thinner air, less power. Even with turbos. Hard to directly compare NA to Turbo but a brand new stock Z06 puts down 405 HP to the wheels on our dyno."

[R32 Combat]

How does altitude affect turbos? I though that the turbos will just spin slightly faster to get the same boost?

Any thoughts?

[hodgie]

I believe its the oxygen level tht will effect the efficency of the engine i believe.

[SteveN]

Higher you are, the faster the turbos have to spin for the aformentioned boost pressure, often making turbos run clean off the end of the compressor map, which in turns knocks down power significantly

[Chuck_H]

Some more info:

Blue Line is torque (peaked at 416 ft-lbs)
Red Line is HP (peaked at 419 HP)
Green is Boost (peaked at 13.8 psi)
Gray Line is A/F Ratio (dipped down to around 10.5:1)

We made nearly 440 ft-lbs torque in 4th gear since it could load the engine a bit more, and I’d suspect that with some time to properly break in the engine and removing the speed limit, we’ll see maybe ~450 HP (wheels). Not too shabby!

[R32 Combat]

I can see this being a problem but I would of thought that this level was within the turbos capability.

[ATCO]

Reasonably flat long torque curve given altitude, pity it stopped at 6500. AFR is real rich, height maybe? Boost less than 1Bar? Ripples in the curve suggest a little wheelspin? I also presume this was rear drive only and not 4? What's your thoughts Andy?

[R33_GTS-t]

Originally Posted by ATCO

Reasonably flat long torque curve given altitude, pity it stopped at 6500. AFR is real rich, height maybe? Boost less than 1Bar? Ripples in the curve suggest a little wheelspin? I also presume this was rear drive only and not 4? What's your thoughts Andy?

AWD Dyno.

a) We used a Mustang AWD dyno and all power figures are at the WHEELS. Not the highest reading dyno out there, not the lowest.

[ATCO]

The fact that it is an AWD is irrelevant.

GTaRT use a Mustang Dyno and we had to force the Garage Bomber into permanent 4WD as it constantly spun up the back wheels on the rollers.

If the R35 with its intelligent 4WD sends all power to the rear, the Mustang dyno still reads figures at the wheels just the same, you just don't get the same "transmission loss" (17% rather than 25%). IF you have assumed 4WD when its really RWD then any ATF figure is inflated, not that anyone would inflate there power figures of course................

[tyndago]

Originally Posted by hodgie

I believe its the oxygen level tht will effect the efficency of the engine i believe.

Some people like to say it doesn't effect turbo cars as much, but I have run cars back to back at 1/4 mile tracks at 2700 ft and 1200 ft, and I would see a difference of about 0.6 sec in the quarter mile. Same car, same setup, same fuel, different weekend. On and off the trailer. Palmdale and Pomona in the LA area.

The 4000 ft is probably why you see 13.8 psi peak on this car. I have been told the factory ECU does this, part of the anytime, anywhere Supercar thing.

[R32 Combat]

Odd looking curve indeed Dave.

It's either tuning itself or somethings slipping.

If altitude was a restricting factor, would it only effect the top rpms?

[paul cawson]

For info

The performance of the turbine improves at altitude as a result of the greater pressure difference between the virtually constant pressure upstream of the turbine and the lower ambient pressure at outlet. The lower air density at the compressor inlet is largely equalized. Hence, the engine has barely any power loss.

[tyndago]

Originally Posted by paul cawson

For info

The performance of the turbine improves at altitude as a result of the greater pressure difference between the virtually constant pressure upstream of the turbine and the lower ambient pressure at outlet. The lower air density at the compressor inlet is largely equalized. Hence, the engine has barely any power loss.

Your theory is great, the reality of it is that it is not true.

[SteveN]

Originally Posted by tyndago

Your theory is great, the reality of it is that it is not true.

Like 99% of "theories" regarding modified cars.

But people like to stick with the argument regardless even when testing/experience shows otherwise...

[paul cawson]

Originally Posted by tyndago

Your theory is great, the reality of it is that it is not true.

Turbos were first designed for gasoline powered aircraft that can fly up to 50000 feet because they can operate in thin air with minimum power loss unlike a NA engine.