zzkamikazezz

Hi

I found this performance calculator on the net that looks quite good, plus it even has a preset for the s2000, although I don't know if the preset values are correct:
http://vlsicad.ucsd.edu/~sharma/Potpourri/perf_est.html

It only seems to work in IE by the way.

I've been trying to compare my car to a standard one for fun, but there are two things I'm not sure on that could really effect what I'm seeing:

1. It wants you to add 'wheel torque' to work out the cars power (it mentions this in the documentation section). Now dynos don't measure wheel torque, only wheel horsepower from what I understand and that give power and torque at the engine. Should I be entering engine torque? Or should I be trying to work out the wheel torque? I looked at my at the engine power figures and at the wheels figues and saw they were 15% less on the same dyno run, so I took 15% off across the torque curve. Does that sound like the right thing to be doing?

2. Final drive gearing. I haven't been able to find a concrete answer on the net. I know changing the gearing does not change the torque the engine has or the power, however it does change how the car accelerates as it changes the torque at the wheels if I've understood it correctly. I've changed my final drive from 4.1 to 4.44. Are dyno readings affected by a change in the cars gearing? Looking at my dyno prints it just shows the gear the car was in but not the gearing. Some dynos appear to have the gearing showing as well which can be varied by the operator. Are all dynos configured for the final gearing? Wondering if my readings are perhaps higher or lower than they should be? It was dynoed on a dynoejet dyno if that makes any difference.

Any help clever people?

lovegroova

1. Dynos - read this as it explains all about power and torque. http://www.fjr1300.info/misc/torque-power.html
2. Final Drive - you need to multiply your 4.44 by 1.16 to get the actual final drive, as shwon here: http://www.turnzero.com/technical_re...ear_calculator Use the AP1 settings and adjust accordingly.

zzkamikazezz

Thanks, I couldn't find that number, I know you have mentioned it in the past I just played around on the site until I got a top speed of 155mph.

It looks like taking 15% off of the torque works on that site. That gives a chart showing 350bhb at the wheels which ties in with my dyno print out. This is from the site, my inputs vs the 'stock s2000' they have to select:



Regarding if my figures from the dyno are right though that I'm starting with. Looking at that article it suggests that they work out engine torque based off of the wheel torque the dyno measures and then work it out based on the gearing:

To convert the rear wheel torque to engine torque, you divide the rear wheel torque by the overall reduction ratio. The overall reduction ratio is found by multiplying together the primary reduction ratio between the crankshaft and the transmission's input shaft, the final reduction ratio between the transmission's output shaft and the rear wheel, and the transmission ratio that depends on the specific gear that was used during the dynamometer run.

Do they really setup the dyno for each car and its ratios though? I'm wondering, as my car has 4.44 gears, if something should have been altered on the dyno and perhaps my figures are too high or low... Just trying to validate the figures I'm working with are correct to start with.

zzkamikazezz

So far I have this. The speed intervals they choose aren't kind to 4.44 gears, they seem to fall right on gear changes!



Also a rolling 20mph to 120mph, mine, mine with standard gears and a stock car according to the site:


PS: my initial comment about dynos not measuring wheel torque was based on speaking to Hayes that did my dyno, they said they can give me wheel horsepower but not wheel torque, as the dyno doesn't measure that

s2konroids

Havent got time to read all this but when setting a dyno up for a dyno run you do input the ratio, as well as correction factor.

zzkamikazezz

I'll have a chat to Hayes tomorrow if I get the time about their dyno, and if they set it up for the gearing. If it was set for a 4.1 final drive and my car is 4.44 I guess my figures would be out

lovegroova

It's also really worth calculating what those power, torque and time graphs actually mean in terms of distance covered.

The stock car comparisons make interesting reading though:

zzkamikazezz

I was confused looking at your table above with the top speeds all being nearly the same, but it must be down to the calculator being clever with the drag i guess.

I think ive answered my owner question now with some more google. As it was a dynojet, they actually measure power at the wheels, not torque and then work it back to give engine torque, so that is why hayes cant give me torque at the wheels for the calculator. However torque being linked to hp means seeing 15% being taken off of the engine bhp to give atw bhp, i can then take 15% off the engine torque the dyno calculated should give me the correct 'at the wheels torque figure' then.

If i understand it correctly, this type of dyno takes the final drive out of the equation then as torque isnt measured? Time for bed, my brain is hurting

"the superflow dynos use operator entered info for much of its base figures to use to figure power.....

the most notable place for error being final drive gear ratio which tahes into account not only final drive trans ratios + sprockets + tire diameter + tire groth at speed from centrifical forces....... get anythig wrong entered there and all you results are skewed...that is the way trinity gets 52 hp on a stock trx with a pipe

The dynojet dyno directly measures all of its variables...from atmospheric to final drive...no input from operator, all direct readings

the final drive is calculated from tach measurements from the ignition which gives crank speed...the dyno jet then compares the crank speed to the rotational speed of the drum...which of course has a known diameter... this even accounts for tire growth and its affects on final drive gear ratio through the run

none of the other dynos do this at all... they let the operator enter all the varables and don't account for tire growth even if all else is dead accurate"

This talks about a dynojet - http://www.bristoldyno.com/info/whatis.htm

http://www.dynosport.com/autodyno.htm
And here dynojet is mentioned
http://forums.nasioc.com/forums/show....php?t=1478091

James Rae

Technically you can go to 9,200 rpm remember (if you really want to wring every last ounce of revs out of it that is).

Ultra_Nexus

Fuel cut is actually 8900.