I got an average of 230 HPs from a Gtech (here in peru dont have a AWD dynos).

That quantity of HPs are at the wheels, and how do i convert to ENGINE HPs.

15% 20%? i supose the diference is higher in the case of the impreza because of the awd system.

thanks in advance.

LG

 

The difference between engine HP and wheel HP is due to loses through the drivetrain (from the gearbox all the way through to the tyres). Generally this cannot be calculated as a percentage, only on a 4wd rolling road. I have found my last figures 287 bhp at wheels 362 at the flywheel (calculated) this means 75 bhp lost through drivetrain as a percentage this is 21% so guess can be made from that. But you say it was not tested on a 4WD set of rollers. I believe that is another ball game which I have no idea on.

 

Rule of thumb that I use is :
ATW figure is about 74% flywheel figure.

So it works out you are around 310BHP at the flywheel

 

Hmmm. what does a typical 2wd car lose between fly and wheels ?

Any idea ?

 

It sounds logic for me. i am running a VF35 (19 PSIs) in my impreza gt 1998 in replace of orig td04l.

thank you very much!!!

A last thing. the HPs from a Gtech are at the wheels right? i suposse so.

LG

 

Gtech data is at the wheels but also includes air resistance and is variable if the road isnt flat. To correct for the fly you need to work all this out.

Handily I found this on the gtech forum.....


http://members.chello.nl/~r.herweyer/

This dutch guy has written some excel sheets with all the formulae in the them. Just import the data from the gtech pass software and input the weather details. He has even included a web link in the page to get world weather!

Have a play about with them. There is some useful info on the gtech forums aswell despite them not being updated for ages.

It is surprisingly accurate. This is from a standard wrx. It is very close to a rolling road run I had done before I started to mod the car.

Just need to get round to doing an up to date one to compare with my prosport print outs.

From the gtech before correction I think it was making about 172bhp so you need to add 30% due to drivetrain and air resistance.



Gtech recommend doing runs in second gear because this will minimize the drag effect. The problem is after modding I dont make full boost in second so I need to run in third. Not easy to find a suitable road!

Obviously if your power run was done in third or higher you will have more drag so you will need to add more than 30%. Using the above method air resistance doesn't matter anymore so you can get fairly accurate results that seem comparable to rolling roads. Ill try and get a newer one done and post the comparison with prosports rr run.

Chris

 

Had my car dyno'd yesterday and the transmission loses where quoted at 30 bhp?

 

30bhp seems a bit low.....

That give about 7.5% loss? Only going off all the other dynos people have on here.

 

yeah! i see that number a bit low too.

any other experiencie??

LG

 

Been on that dyno before but they've just changed the software to show both figures so nothing to compare it to.