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DD2 BHP calculator
DarrenW - 24/2/06 at 09:18 AM

Does anyone know how it works? Or in other words how to set up the dash to get the most accurate estimates?

Ive set mine up to 800Kg (way over) and it has logged a 170bhp maximum! There is no way my car is over 130BHP at the moment.

Cheers,
Darren.

gingerprince - 24/2/06 at 09:27 AM

quote:
Originally posted by DarrenW
Ive set mine up to 800Kg (way over) and it has logged a 170bhp maximum!


Well that's why. Basically because you've told it your car is heavier than it really is, it thinks your car must be more powerful than it is because it would need more power to pull the acceleration you were making it pull, if you see what I mean?

But really I'd take the actual values with a pinch of salt from this sort of thing - I have some software somewhere called "road dyno" which basically records your RPM over time (pickup from HT circuit) and calculates your BHP based on input weight, CoD etc etc.

The best thing really is to use it as a "relative" term. Basically set it up so the numbers seem about right, then test at a known location. Do your mods, then do the same test. You can then compare near enough like for like. Good to see whether cutting that big hole in your Saxo zorst to make it sound faster has actually made it faster or slower

The actual calculations are about on t'interweb somewhere, I found them years ago when I was playing with building a car computer with realtime bhp calculation. In the end I just used the road dyno software instead, it was easier

DarrenW - 24/2/06 at 10:03 AM

Oh - i see. I thought telling it the car was heavier would have given a lower figure!!! ooops - wrong way round.

I take your point ref comparitor. Before tweeking timing and mixture i was getting around 130 - 140BHP Max. After setting it up managed 171BHP Max. I very much doubt i saw a 30BHP improvement but it was definitely pulling better afterwards.

Ill try resetting to approx 650Kg to see what happens (Car shouldnt be that heavy but im lardy!!!! Ive been on 5 salads a week since new year so my power to weight is improving now!)

I recall Alistair once made an informative post (he did the programming for DD2) so ill try and find his email and see what he says.

DarrenW - 24/2/06 at 11:17 AM

I have just recieved this from Alistair. Confirms earlier reply.


My mail:

"Hi alistair, A while ago you helped me with Speedo calibration of DD2 following my post on locostbuilders.

Since then i have had the car on road a lot and am really enjoying the DD2. Can you help me out please with some more background. I was wondering how the BHP calculator works and how best to set up the dash to get it kind of accurate. I realise it is an estimator but it does also give me some good comparative powers when assessing if tweeks are working?

So far i set the weight up quite high (800Kg) and get 170BHP Max. i know the engine isnt this good (old 2.0 Pinto with slight mods - should be approx 130BHP on a good day). I think car with driver will be around 650 - 700Kg. Will setting this higher give higher BHP figure?

Iam kind of guessing the only settable figure is weight for the BHP estimator? It will probably follow therefore that best way to get somewhere near will be to go for rolling road set up and then play about with the weight to get close to RR figure. iknow there are all sorts of variable that will affect this in the end (fuel in tank, weight of driver, passenger in car or not, accuracy of RR etc)."

Alistairs reply:

"Hi Darren, Yes the higher the weight the more power the unit thinks you need to achieve the acceleration values!

So by putting the correct weight in you will see a reduction in indicated power for your case.

The results are highly dependant on no other factors influencing the results and G sensors while doing the tests and you need to achieve max acceleration at some point! Also any other factors likes bumps etc need to be avoided!

Cheers, Al."

I hope this helps others wondering the same.
Darren.