wheel hp into crank hp ??

[Nik0las]

Can someone tell for sure howmuch are the losses from the crank to the wheels in our cars? Also for the torque?

[Henkjan]

nothing's sure about that, also the rolling road pro's disagree on how to determine that ...

[j dog]

my mitsubishi evo 9 is 407bhp at the fly and 341bhp at the wheels. I think it's generally around the 20% mark for awd cars.

[Henkjan]

here are 2 measurements of my S2, one on a Maha, the other on a Superflow; both use the same method to calculate crank HP from wheel HP: after the run let the car slow down with the clutch in
rollenbank_resultaat_S2_Superflow_bank.jpg

rollenbank_resultaat_S2_Maha_bank.jpg

[prj]

Then there is a question if the WHP was "correctly" measured in the first place

The dyno is generally understood to be a tuning, not an exact measuring tool, and the main goal is to get a measurement you can repeat, rather than getting an exact number.
The only application I have found for one until now is for dialing in the timing map.

As for measuring engine output - nothing other than a very well calibrated engine dyno is going to do that for you.
Plus, it's all pub talk anyway. 100-200 times are a much better indication of how fast the car is actually going to be on the road.

The key word is weight - that is why a bike with "only 100 horsepower" is so fast.

TLDR;
I just tend to divide by 0.8...

[Rocco]

Then there is a question if the WHP was "correctly" measured in the first place

The dyno is generally understood to be a tuning, not an exact measuring tool, and the main goal is to get a measurement you can repeat, rather than getting an exact number.
The only application I have found for one until now is for dialing in the timing map.

As for measuring engine output - nothing other than a very well calibrated engine dyno is going to do that for you.
Plus, it's all pub talk anyway. 100-200 times are a much better indication of how fast the car is actually going to be on the road.

The key word is weight - that is why a bike with "only 100 horsepower" is so fast.

TLDR;
I just tend to divide by 0.8...

Also aerodynamic counts.... And how wide the tyres are? Yes on the road...the same as the weight around the hub hehe.


Also Dmitri,please check your inbox.......................

[EspenW]

here are 2 measurements of my S2, one on a Maha, the other on a Superflow; both use the same method to calculate crank HP from wheel HP: after the run let the car slow down with the clutch in
[ATTACH]34553[/ATTACH]

[ATTACH]34554[/ATTACH]

Were both dyno pulls done with the same setup/state of tune?
If you look at the whp measured, it is 239whp on the Superflow but only 167whp on the MAHA. If they just added an unloaded coastdown value to that, the MAHA estimated crank number would be much lower than the Superflow number. What they do is to apply an algorithm that takes coastdown values, whp values, etc. into consideration and use that to estimate the flywheel power. This is why you will see higher loss values on higher powered cars. The coastdown value would be the same if there were a 2CV engine or 6000hp Top Fuel engine in the car, so the fact that bearing losses, etc are higher under high power is taken into consideration by the software to produce a decent estimate for crank power.

[will20v]

it does no work on % as your drivetrain does not have more drag if you have more bhp
eg 230bhp car say looses 60 bhp if it was 700bhp it would still loose 60bhp not any more or less as long as it was the same as before

[EspenW]

it does no work on % as your drivetrain does not have more drag if you have more bhp
eg 230bhp car say looses 60 bhp if it was 700bhp it would still loose 60bhp not any more or less as long as it was the same as before

That defies the laws of thermodynamics, so it is probably wrong, at least in this universe.
It would mean that the drivetrain would transfer the energy of the additional 470hp at 100% efficiency. An engineers dream, but impossible, unfortunately.

What would happen if we reduced the 230hp output to 55hp?

Some of the loss is static, and some is load dependent, this means that a part of the loss will not change with increasing input, while another part of it increases with increasing load. A simple % conversion is thus inaccurate, since that will overstate the static component.

[Henkjan]

Were both dyno pulls done with the same setup/state of tune?.

only different in exhaust, the one on the Superflow was with my new exhaust (Supersprint dp, sportcat, no center muffler), on the Maha it was the std exhaust but without cats. And on the Maha I had the winter tyres on the car.

[prj]

I am pretty sure a loss constant can be plotted as a function of RPM for a given car.
So loss % = f(RPM). Determining f is the problem.

[speeding-g60]

i asked Javad, of 034MS, this same question a while back, as i know he had done back to back testing of the race car a while ago.

this is what he said:

ME: So Javad what is the current consensus on drivetrain loss for the Quattro drivetrain? HP/whp...
January 24 at 9:35am ·

Javad Shadzi: Best data point we have was the Castrol Top Shop engine, made 700whp here on our dyno and 848 crank on the engine dyno, so about an 18% loss,. For a car in this power range (like yours), that would be a very accurate figure to use. Drivetrain loss is made up of a static loss and a percentage loss, so there is a set amount and then on top of that a growing amount based on the power that goes through the components. I'd say at the 3-400HP level its closer to 22% and above 1khp its going to decrease into the 15% range and lower as power builds.

[Nik0las]

so recording to Javad 400whp car will be 488hp on crank? I'm asking because most of the info arround the web is 25% losses for AWD.

[EspenW]

so recording to Javad 400whp car will be 488hp on crank? I'm asking because most of the info arround the web is 25% losses for AWD.

Depends on the type of dyno used, since measured whp will vary wildly between brands. The lowest reading by far is the MAHA, and the whp off those should not be considered whp at all, as it is much lower than true whp. Next is Dyno Dynamics and Mainline, they read somewhat lower than the Mustang, which reads true whp (ie. the whp that the car in question will put down on the road in that specific gear).
You can do acceleration runs like 1/4 mile and FATS on a Mustang and the results will be pretty much spot on with what you see on the road/track.
The Land & Sea dyno that 034 Motorsport use reads pretty much identical to a Mustang. Then comes the Dynojet, which has a fudge factor built in that overstates whp. The highest reading will normally be hub dynos like Dynapack and Rototest, since they eliminate rolling resistance and wheel inertia, and that makes a sizeable difference. They don't measure whp, but most folks don't realize that and gladly quote hub power as whp.

Use the dyno as a tuning tool and use acceleration times for the relevant speed intervals to judge setups (remember to take weight into account), as it is the average hp over that interval that determines the outcome, not the peak number.

[speeding-g60]

Espen, do you have a link to any calculators that you could put 1/4 mile results into for that info?

i have a couple 1/4 mile slips, and some dyno sheets.... would like to see how they compare.