Dyno run today on 1989 3.4 liter Mondial t

87 328 GTS. Factor of .86/220 HP = 256 hp at wheels. Does that sound right? My Air/fuel running a little lean @ 14. Should be around 13.0-13.2. That should make another 4hp or so. Run is with test pipe and tubi and K&N filter.
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Uhm...? You car is making 220 on that dyno, which is a measurement of wheel horsepower. This means your crank horsepower would be ~256...not wheels horsepower -- that is the number on the dyno chart.

Additionally, I am not sure that either of the numbers you guys posted are SAE corrected. Do you know if they are?

 

Not directly related to your post, but I am suspicious that many dynos are moderately to wildly optimistic, especially those at motorcycle events like Daytona where they do runs for $25 a head.


Everybody is happy. The motorcycle owners have a big number to boost their egos and the dyno man has 25 smackers.

No evidence of the machines ever being calibrated.

 

This Dynojet in-floor chassis dyno was done at a nationally known Mustang race development shop
1988 Mondial 3.2, Weber 40 DCNF-12s (pre-airbox high flow & short stack mod ) :
Uncorrected: 244 rear wheel hp, 210 rear wheel torque
SAE corrected: 236 rwhp, 203 rw torque
DIN corrected: 245 rwhp, 210 rw torque
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The Dynojet dyno accelerates a drum of known weight. Power figures are calculated from the time it takes to accelerate this known mass. Therefore the unit doens't require calibration, except for the use of corrections for temperature and humidity) Dyno's are set and forget, you do not have to regulalrly have them re calibrated, the only thing to watch for is the 02 sensor going off and starting to show overly lean AFR's. Most of these portable units are Dynojets, particularly in the US, which are known to read around 10% higher than other dyno brands.

EDIT: Forgot to add that Dynojet seems to have changed it's software around the same time they intriduced the brake dyno version. The new software is extremely "generous" shall we say, where the old software was what you would more traditionally expect to see. I won;t get into an argument about the merits, but drivetrain loss figures used to be calculated between 18-22%, the dynos were calibrated accordingly, with drivetrain losses figured by most to be closer to 15% in a modern manual, Dynojet simply re calibrated it's software.
I would hazard a guess that the three cars shown here would all dyno with 10hp of one another on the same dyno.

 

I'm immediately suspicious of dyno charts where horsepower and torque don't converge at 5250 RPM.

But hey, it's something to hang on the wall.

 

I'm a little slow; I just saw the SAE marker on those dyno sheets. Either way Dynojet dynos are notoriously high on readings. I have been to a couple of different dynos, and even stock the Dynojet read a bit high. The most accurate I've seen are Mustang Dynos (made by a company called Mustang, nothing to do with the car)...

 

Deaky, why is that? I'm not knowledgeable about this.

 

Quick rundown:

http://www.revsearch.com/dynamometer/torque_vs_horsepower.html

and I shoulda said 5252. (mutton)

 

Not possible when numbers are corrected.

 

So how far off can they be and still be reasonable? Is that 7K graph reasonable?

 

I'm not sure how you can "correct" out the mathematical equation that derives horsepower from torque....sure you can, but the result you get will not be comparable to anything else.

horsepower = rpm x torque / 5252

Nothing else!

Sure, you can correct the numbers by taking into account barometric pressure, temperature and humidity, but anyone that tries to correct out 5252 gets the odd look.

 

Look at the scales. HP on the left, torque on the right. The lines MUST cross at 5252, corrected or not (both hp and torque get corrected by the same %) if the hp and torque scales are the same.

The graph that started the debate has the full scale hp at 250, but the full scale torque at 200. When that is the case, the lines could cross anywhere.

 

You beat me to the post.

 

Mormally when they talk about "corrected hp" it means corrected for standard temperature, pressure and humidity.

I don't know why they like to make graphs with mis-matches scales....I guess maybe it makes the lines higher up the paper so it looks like more power?

 

That's the opposite of what I've heard (from my mechanic) and experienced. I ran a car of mine on a Mustang, then later on a DynoJet (no changes made to the vehicle). The Mustange was 20hp higher than the DynoJet. I've also been told that the DynoJet produces numbers that can be compared to other DynoJet numbers because there is consistency between them. Mustangs don't have that due to the way the operator can set it up (I guess there are different ways). The Mustang is good for tuning a car, to see what changes affect the power output.

For consistency sake, I only run my cars on a the local DynoJet now.

 

But then, couldn't the drive train loss be calculated by the decceleration of the drum after pressing the clutch?

 

Yes, sort of, but not very well. You can measure the decelleration rate of the drop and calculate the the torque being applied by the drive line to cause that torque, but it is not really the driveline loss you would see under power. The true loss is a % of the power transmitted, but in the decel test, zero power is being tranmitted. You get a good feel for how much friction is in the system at any give rpm, but not really drive train loss.