senseiturtle

A friend of mine, a dyno shop operator, has posted the following and would like everyone to take notice.

This is why I firmly believe that comparing dynos across time, space, and dyno brands is stupid.


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There is a love affair in this country with obtaining the highest whp numbers for the added mods that one installs in the cars.

There are many factors that can contribute to the added of higher numbers as well as one machine reading different than another one. From the mods that each magazine advertise, one has to take those numbers with a grain of salt. Marketing departments of these aftermarket parts do a great job of finding the highest outputing dynamometers to reflect these gains. So when one sees these number gains, they should not be set in stone since there are many factors that contributre to +/- numbers when these parts are installed in ones car.

There are many dynamometers brands out there and some estimate the whp close to another brand of dynamometer. Also there are some dynamometers that display significantly higher whp numbers when compared to a different brand.

One good thing to remember is, when ever you get a baseline, try to stick with that shop for all your future mods. If its a good machine and a good dyno operator, the results are/should be repeatable in the future.

In order to understand why one machine reads different than another is the way they read/calculate power. There are two main types of dynamometers, Inertia (DynoJet) and load bearing dynamometer (Dynapac, Dyno Dynamics, Mustang and many others).

The way these two types of machines read and figure out WHP are slightly different. Both apply formulas to calculate the whp. Physics formulas are applied to each machine to calculate the whp.
The main difference btn a Inertia is the way power is measured (F=ma) and a puff factor added to the formula based on mass rotation. A Load dynamometer (Hp = Trq * 5252 / RPM) uses this figure to calculate whp. This is usually why you are going to see higher #s on a inertia dynamometer than a Load dyno.

Because of this puff figure that is added to a dynojet figure is why the numbers in those machines are going to be higher than a Load dynamometers

There are other benefits found in eddy current (load) dynamometers than a Inertia, but I wont get into to those at this time.
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Therefore, a person who hits 135 on a mustang dyno with full boltons might be just as powerful as one who hits 160 on a dynojet. The only way to tell is to run the 1/4 mile and compare trap speeds, with the NHRA correction factor if need be.

I can further explain what he's posted if necessary... but the point is, do not get discouraged if you run a baseline and don't get the figure you think you should get. The dyno is a TOOL, which should be used for measuring your gains through tuning... not comparing cars throughout the country.


I hope I can begin to clear some things up around here... please let me know if you have any questions.

ScionDad

Great info.

Yeah...I have one question. What exactly was the relationship between trixie and speed racer?

aarontrini85

thank you although this has been explained be for no one ever took the time to express it in sutch a masterfull way lol


thanks for the post

senseiturtle

Sciondad... I have no clue whatsoever. If I was him, I'd do her.


Not a problem, aaron... I just get tired of all the dynos and lack of 1/4 racing done around here.


If you'd ask me which was "better,"... I'd say a load-bearing was much more accurate. It'll read lower numbers, but it'll reflect what your car does under stress much better, since you'll always be under load while accelerating.

ScionDad

Fushyuguru

Thanks for putting this in one place.

Myself and others have mentioned this when we see people arguing, but then posts die and people's memories get erased and they start the same argument over again.

peteyd

umm i think they were boy friend/girl friend if i remember correct. but other then that great info....or was speed having an affair with chimchim?

engifineer

I think speed is all over that girl......

But great info! Its good to see people addressing these types of things. This, among the many variables in between the engine and wheels adds to the reason manufacturers specify BHP on thier engines. Well explained as well. I would like to see more of the math going into it.. but I am just a geek

Fushyuguru

Same.

Thats one thing I resent about the ScionLife boards, not too much technical discussion.

I may do some writeups on calculating proper intake runner length to maximize VE. Then throw in a dash of exhaust acoustics to get people thinking how much goes into these designs, not just cutting some pipe (they snake for a reason). Then if I throw in some Helmholtz resonance effect in tuned plenums... someone's going to crash their scion or stop reading.

ack154

iTrader: (7)

peteyd: Not sure yet about a sticky on this. Might be something for the FAQ or Tech section though - cause it's more of an "everyone" thing.

peteyd

i forget about the tech section! my bad.

senseiturtle

I'd be honored to have my posts placed in the faq section.

I just went on a giant speil about HP vs. TQ, which I'm going to search here and also post for potential movement to the FAQs.

DynomyteSW

sweet info thanx 4 the post