N51

Tom,
The 300 to 280 is a ~9.3% loss. Thanks for the inclusion. It is always good to
see you here.

Geoffrey

First it would benefit you to actually use an engine dyno and experience an engine running through a proper test cycle before representing ignorant statements as facts.

Second, why do you think there is a new SAE certification test process (J2723) available where the Corvette Z06 was the first engine to be certified using the process? It exists because regardless of what you dyno you use, you need to have a consistent test process.

Thrid, I can manipulate an engine dyno result by the following ways:
- Use different correction factors - SAE J1995, SAE J1349, SAE J2723, BS 5514, ISO 3046, BS AU 141, DIN 70020, Standard Temperature & Pressure
- Lower the barometric pressure input by putting a vacuum pump on the probe
- Raise the intake air temperature by putting the probe next to the exhaust
- Remove all of the accessory belt drives
- Running the test when the engine is below normal operating temperature
- Altering the calibration of the engine dyno

You seem to think that every engine dyno produces a "true" number and that cannot be further from the truth. And that every chassis dyno is useless which is also far from the truth.

I do agree that dyno numbers on Rennlist are all over the board and are meaningless when compared against each other. Do I know what the drivetrain loss is on a 964? No. Do I know what some engines I've tested show on an engine dyno and then again tested on my chassis dyno - Yes. Can I make an inference as to the loss between the two that would be applicable to just that scenario? Yes.

Low 964

Mine has lost 18.4%

256.2 at f/w
209.1 at wheels.....seems engine is getting tired...

N51

Geoffrey,
Such a lather you've worked up, while the world burns. Make some use of it
and break out the razor.

J richard

Wow...time to roll off the meds...

ValveFloat

Amen, I never understand why people need to make up a %loss number after they see chassis dyno results. They could have saved some $ and just made up a number without the dyno run.

Not exactly. That negative curve shown on your graph is the frictional loss of your drivetrain in an unloaded state. When your accelerating the friction will be different, how much I can't say, might be negligible. The other loss missing in that curve is the energy your engine put into accelerating all of the drivetrain components.
Some chassis dynos claim to measure, or calculate, flywheel power, but they are estimations at best, IMO.

Tom W

Noah: Those were general numbers from the 3 engines I know the results for (on the two different dynos). My results were 295 at the flywheel on an engine dyno and 278 at the rear wheels (about a 6% loss).

VF: I agree that the frictional loss could be different, it's a question of how much different. While it's a stretch to compare results from different dynos, the 12 hp loss at a point where the "on power" figure is about 260 hp (12/260=5%) is in resonable agreement with the 278/295= 6% difference.

I provided my numbers as an alternative to the 12-20% numbers that get thrown around. Dyno numbers are fun to look at and great to use as an excuse for why you might be slower than another guy or gal, but not much help unless you can make the direct comparison. In my case, the shop that supports my car has built 6-8 engines for my race class. They all make about the same on the shops engine dyno. We all make about the same power on the same chassis dyno. That's a good enough comparison for me. What matters to me is when the engine gets built with different components and one of my competitors starts making 4% or 10 hp more power. When you are only 0.1 second apart on lap times, that starts to be something to worry about.

warmfuzzies

And herin lies the heart of the problem, it's a "new" SAE, therefore does any of the older testing fall under that remit, probably not would be my answer.

I'm an old engine on dyno type of guy, it was my bread and butter, albeit 4000BHP or so, but as long as the environmentals are the same, there is little if any opportunity to defraud Joe public. Whereas many's the time we all see huge gains quoted, and none of us have any certainty about the relaity of it all, unless of course everyone is playing by the rules of SAE J2723..

Kevin

JET951

i find it very difficult to believe that some of you guys are getting only 6% loss in power between the crank and the wheels. the problem is the fact there are so many optimistic dynos out there. We have six in our area and only one that we trust to give good enough reading.