t.c.

Can someone explain to me how a dyno makes a difference between hp and torque ?
Thanks .

damcgee

t.c, that's a valid question, but i feel certain that if you searched the forums you would find an answer.
I'll give you a real quick answer and tell you that a dynamometer does not measure hp. Nothign does, really. Horsepower is just a calculation that we use. You calculate horsepower using engine speed and torque. If you're interested, the formula is

hp=torque x engine RPM / 5252

This is why on a dyno chart, you always see the torque and horsepower graphs cross exactly at 5252. Above that RPM, hp is always more than torque. Below 5252, horsepower is less than torque. OK, I wrote more than I planned. Anyway, I hope you find this informative

t.c.

Hey thanks damcgee ,
Also while i was talking to a friend today he explain to me that a dyno only measure the energy in watt, and, with a formula ( like the one you gave me ) it automaticaly transform the result in hp.
Is he right ?


Thanks again !

Gernby

It's ALL calculated. The only real measurements taken is the rotational speed compared to the load of the dyno. Each type of dyno has a different type of load. A dynojet has a large heavy drum under the ground that is turned by the rear wheels. The speed of the drum is measure over time to determine instantaneous acceleration of the drum. This is used to calculate torque.

swtazn97

In what gear do we dyno the s2000? 3 or 4?

Gernby

The North Texas S2000 Owners Club had a dyno day today, and we used 5th. Our last dyno day, we tried 3rd and 4th, and found that 4th gave better numbers. I have always believed (although many disagree) that you should use whichever gear is closest to a 1:1 ratio. The ONLY thing that makes me question this is Ultimate Lurker's recent statement that load time is more important than gearing. He said that you should use whichever gear will give a load time greater than 10 seconds (or something to that effect). He defined load time as the amount of time it takes to do the actual dyno pull.

There are many people on this board that I respect and trust, but Ultimate Lurker's word is law, as far as I am concerned.

ultimate lurker

Thanks gernby, but we're all capable of mistakes and bad advice here, so always seek a second opinion :-)

On the topics of dynos, how they measure depends on the type. The Dynapack I use in an absorbsion dyno which uses hydraulic pressure to measure power.

But in the end, everything has to go through a processing algorithm to get usable data, and that all depends on calibration. That's why its important to look at changes in reading vs. what the absolute reading is. Comparing across different dynos is generally a no-no.

I would recommend using 4th gear on roller dynos like the Dynojet, as it seems to result in a decent 10-12 second load time. 5th gear could theoretically show higher hp, but I think you'll start seeing heat soak losses by the time you reach the power peak. A turbo car may want 5th gear though as it makes significantly more power. On a dyno like the Dynapack, just set the load time to about 10 seconds (I use 10 seconds on a 3000-9000 rpm run).

UL

Gernby

UL, regarding the heat soak issue, On every S2000 that was dyno'd yesterday, every run yielded higher results than the run before it. We did 3 pulls each, and the 3rd pull was the strongest for all of them. I assume that this is because the cars were not fully warmed up during the 1st pull. It seems that if we had used 4th gear, the shorter load times of the 1st and 2nd pulls would not have heated the engine up as much, so we wouldn't have seen good numbers without doing more pulls.

Yellow Streak

My opinion on dynos is that if you always go to the same shop and your car is always tested the same way, you will have a good idea what gains/losses your modifications are achieving. I have gone to the same shop from the very start. My opinion is of course based on the assumption that the shop/dyno are capable of getting consistent results from session to session. In my many, many sessions on the dyno, I have found that results from session to session were within 2-3 HP when nothing on the car has changed. Where possible, I try to make mods while the car is on the dyno. That way, some of the variables are reduced/eliminated (the way the car is strapped down, temp/humidity changes, etc.). Also, I would theorize that even when a dyno corrects numbers based on atmospheric conditions, there is no way for it to know what effect it has on a particular car. That is, if it is 100 degrees outside and the humidity is 100 percent - the corrections the dyno makes can't apply to every car that it could ever see. A Z06 would probably be effected by those temps/humidities differently than a blown S2000.

-YS

ultimate lurker

Gernby,

Here is something to consider:

Intake temps. We often get the best results on a car under the following conditions:
- car has been sitting cool for awhile
- start car and quickly warm up coolant to normal operating temps
- begin making passes, being sure to monitor intake temps for consistency
- do not turn motor off between passes, just idle down to bring coolant temps back into spec.

What is happening here is that as the car heats up, the fluids (oil, tranny, diff) become less viscous and flow better. A warm engine generally has fewer frictional losses than a cold engine. But, because we've kept the engine running and not given it any time to heatsoak, the intake tract is still quite cool. Thus, you're getting cool air with minimal internal friction - recipe for good power readings. I too have seen this phenomena on several types of cars. Realistically, the only time you'll see that combination of conditions is if you cold start your car in the morning and start driving, avoiding stoplights and heavy traffic. The intake tract will stay cool and the car will feel great. Turn off the engine once, or be forced to idle for a few minutes in traffic, and intake temps will shoot up. This is where a Hondata gasket and CAI make a big difference. They keep intake temps cooler and allow them to recover quicker.

Generally, what you saw yesterday was _probably_ (I don't know) a cool car meeting these conditions. Did you monitor intake temps?

UL