Low 964

I assume standard 250 is flywheel....how do you calc wheel hp from flywheel and visa versa?

demonfish

its about 12% loss i think... 220 at wheels...

Steven C.

Add somewhere between 15 to 20% to chassis numbers. I think I remember 17 or 18% was accepted for 964? You asked what mine is so here is a chassis chart on mine.

N51

It depends on the tuner's integrity.
I trust engine dynos, only.

JET951

you just hit the nail on the head!

tony.t

try trusting car v car

Steven C.

I trust that I am not taking the motor out of my car.

Geoffrey

Noah, it has less to do with integrity as it does the tools that are available for common testing.

N51

Geoffrey,
For those of us who have attended this forum for some time, we've seen the
creep. The percentage of rear wheel loss. Now at 15%. Correct me if wrong.

I stand by my original statement. Engine dynos are true. They remove variables
that only serve the tuner and not the customer.

Geoffrey

I resent the implication that tuners who use a chassis dyno have integrity issues. In fact, an engine dyno has an equal access to a tuner's ability to manipulate dyno numbers. I think it comes down to how the results are presented and what the test parameters were.

FWIW, a completely stock 964 will be between 225 and 230whp on my dyno.

Steven C.

BTW My tuner did not run my car. Actually I don't have a tuner as I bought the car as it is and just drive it. The shop that ran my car is Lou Gigliotti's shop from World Challenge and Corvette racing. We run our race cars there also and find all of their results to be in the "range" of what we expect. They do not tune any of our cars we just rent the dyno from them.

www.LGMotorsports.com

I completely agree with Geoffery. Use whatever % you want.

N51

The issues are in your mind. Not in any engine dyno. Yet they, engine dynos, are true.
It is good to see you drawn in. I enjoy your work.

Yes, is does come down to how results are presented and what the parameters
were. It goes back to my original thought.

J richard

I'm a bit confused by this, and even more confused as to why anyone really cares about the conversion of chassis dyno numbers to engine numbers. what use is it? bench racing? The only thing that matters it litterally where the rubber meets the road...

N51

When money enters in, there must be no confusion.
To no one else but Geoffrey, I've submitted my build. He is smart and understands
it. A great asset to me and the forum.

Some of us reach beyond. Allowing our failure or success to point others in a more
perfect way.

Tom W

You can measure the drivetrain loss on the newer dynos... Mine shows about a 12 hp loss at 100 mph (where I get about 275 rwhp). That's at about 6000 rpm on my car in 4th gear.

The engine dyno at the shop said about 295 hp at the flywheel but they don't calibrate it as they only care about general numbers on it. A couple other engines built by the same shop that all showed 300 +/- 5 hp on the engine dyno, measured at the flywheel, at the shop during break-in and tuning showed 280 +/- 5 hp on the chassis dyno at Thunderhill.

This is a run in 4th gear up to about 7k rpm and then putting the car into neutral (no clutch) to monitor how the wheels slow. (I have a /32 6-speed transmission and an engine built to rev to 8k.)