Dyno run today on 1989 3.4 liter Mondial t

Hey Gents,

Pal of mine runs the local dyno shop. He had an "open dyno" day today, so I rolled the Mondial t up on the Dyno Jet.

For those of you not in "the know," the Dyno Jet gives you real world data for Horsepower & Torque @ the rear wheels. You can than extrapolate mathematically to obtain "crank horsepower" for a comparison to factory figures.

Here are my RWHP (rear wheel HP) figures:

Best HP @ the wheels = 260.2
Best TQ @ the wheels = 200.6

Using a 15% conservative driveline loss those produce these crank power figures:

306.11 crank Horsepower
236 crank Torque

The subject car is my 1989 3.4 liter Mondial t coupe. Basically stock with a Borla exhaust upgrade. I am happy with the results. It looks like it is running up to par! (take a look at the flat power band)
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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.

 

I am sure mine is. Please note the side bar on my dyno chart posted. "SAE" is noted clearly for both figures - printed right on the chart.

Yes, I see that, but that "rule" does not apply in all cases. Oh, and as for hanging this chart on the wall... I actually have the 800HP 996TT dyno chart hung on the wall. This Ferrari run was just for giggles. I am still happy I did it of course, as its great documentation for the cars file.

 

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?

 

This is exactly what I have heard. The correction factor is the culprit. It makes little difference to me though, but I am aware of the 5252 rule nevertheless.

 

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.

 

I will ask the dyno gent, and get the scoop from him as he has told me previously. If someone has not posted the details by then - I will lay 'em on ya when I have the data.

I must say though... I have used many dynos (over 300 "pulls" to date), and while I like the Mustang dyno the most, the Dyno Jet machine is still a fine tuning tool.

I do however agree that we can all "race" dynos (some dynos will give different readings than others).

 

Look at how the chart has the HP & TQ numbers listed along the sides. You see how the HP figures along the side run from 0 - 300 & the TQ figures along the other side run from 0 - 225.

Well... If you take that TQ side on the right & shuffle the "200" down to equal the HP "200" line off to the left you will see that the two curves would have crossed at 5252. I think perhaps the "correction" he spoke of has to do with the layout of the page numerals.

Anyhow, that gives you your 5252 rule.

 

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.

 

Thats quite all right fine sir.

It took just a phone call for me to figure out what "correction" my dyno guy was talking about.

I told him to print me a corrected version just for the heck of it

 

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.

 

Nice call Mark.

The Dyno Jet does have a program to measure the loss, but as Mark pointed out, it is just the best calculation they can provide with the data inputted.

15% is a good number to use anyhow.

A 1970 Plymouth may be as high as 25%, and a late Porsche 911 could work out to near 12%. 15% is a nice comon percentage, and in my Ferrari's case, it is close to exact as I needed.