Righto! Prolly just yappin' to myself again here, but the jury is back.

This concept has its limitations, mainly due to imprecise data collection (especially in 1st gear) but it does come up with reasonable numbers.

The dyno said 71.9hp (71-72 rwhp from 5300-6100 rpm) for my A-15.


In second I got 61hp @5750, 82km//h
In 3rd I got 49hp @ 5750, 130km/h
in 4th i ran out of road @ 4750; 46hp, 126 km/h

First was pretty much a write off, the tacho needle was moving too quick

These figures are 'net hp' so they are less than the dyno due to wind resistance.

Assuming a 'barn door' cd of .55 and a frontal area of 2.25 sq.m (1500*1500mm).... both rough guesses, According to the G-tech site at:

83 km/h- 12.2 hp loss
110 km/h- 28.4 hp loss
125 km/h- 41.6......

So, based on those numbers the technique works ok for low speed work (second gear over estimates by 1hp) but as you get faster the assumptions I have made about the CD and frontal area start to screw with the results (41.6+46= 87.6hp, 37% overestimate).

I have got this in an excel sheet along with a calculator for supercharger flow rates & pulley ratios, & i was going to put a gearbox calculater into it as well.

If people are interested in using this, I will put a decent front end onto it to make it a bit more user friendly. My bro is going to test it this weekend on his VTR1000, so we can see if it still works up the other end of the power/weight ratoi scale.

I can kind of get around that- either by just taking the Gforce approach and measuring net torque/hp or by calculating the difference between each gear AFTER the curve has been normalised for torque multiplication from the gearbox.

Just got some data to work with @ 15 frames/sec so that should be precise enough to get the numbers flowing.

And the best thing is if I run the vid at 1.3X i get to hear what it will sound like with a blower..... and at 2x it sounds just like a hypo 4cyl bike

when working all this out would you have to take into account the friction from the road and tire pressure? something you need not worry about on a dyno obviously...just a thought

That reminds me ... I have an original Gtech in the closet. I should pull it out and test my 0-60 mph (0-100kph) times.

Answering my own Q's here-from the G-tech site:

"The Gtech measures NET horsepower, which takes aero drag and the rolling resistance of the road into account. A dyno does not have to contend with aero drag but the Gtech does. This often accounts for a large part of the difference between a dyno slip and the Gtech results."

Feral- so kind of surprising that it was still within 2%??

Quote:

Yeah, a mate of mine is dynoing his XR6T on the weekend so I was going to grab his data for verification.

your theory sounds pretty good. however. you will ofcourse need sevral basline horspower ratings for the same vehicle that have already been dynoed for this method to work. if you take to of the same vehicles with the same gear box and tire size and engine. (engine mods not relevant on eigther) and have them dynoed, then do the time recorded in each gear recording on each vehicle you will have a basline and therefore a formula.

More time than money

How does the Gtech account for wind & rolling resistance? do you have to to estimate parameters for it?

Edit: That's a pretty impressive bit of gear

http://www.gtechpro.com/rr.html

Gosh thats good...I might consider getting one now!!

Yep,
It will work but is a very hard way to do it.

I use a new series Gtech pro RR and they are so close its not funny.

I did some runs on a friends car 3 weekends ago while doing some base level tuning and then we did 37 power runs at Melbourne performance centres dyno last weeknd and the difference was 2% between Gtech estimate and dyno RW Kw's.

Its an interesting and challenging mental excercise if you have the time :)