Having heard so many arguments regarding this subject, I have taken it apon myself to carry out my own little field test on my local rolling roads, namely Abbey\'s Dynapack and CPL\'s Dynodynamics.
Both systems have their merits, in my opinion CPL give you a more true indication of road power where as Abbey is so much kinder to your car [very good for tuning]
About 2 weeks ago I took my rex to CPL to carry out a power run, the weather was 6c and dry with low humidity, today I went to Abbey the weather was similar - just 8c and same humidity.
The car had not been altered in any way, same petrol was used [BP super] and as stated very similar conditions.
What was the results - well the only way to carry out any comparison is to convert the figures supplied back to flywheel, in the case of CPL divide the total by .85 and in the case of Abbey add 50hp:confused:
This gave me: CPL 315.7 = 385FWHP
Abbey 346.5 = 396.5FWHP
These convertion rates were supplied by the companies involved and both knew I was carrying this out.
My conclusion: If you want to know how powerfull your car is on the road use a rolling road, if you want to spend time getting the tuning right use the hubs.
Regards
John
ps - yes I know Fishy - it\'s all pub talk:cool
Congrats on another good result John :cool
In my opinion a Dyno is only ever good for seeing what effect tuning has had on the engine ... i.e back to back testing on the same device with modification/ tuning inbtween runs. And of course for tuning the engine under load and checking that its running right.
Power figures are really just for bragging rights ... knowing that a car makes xxx H.P doesn\'t make it any faster :)
Wow that\'s quite a Difference.
The main thing is though that your car is nice and healthy and will suprise quite a few single turbo\'s at rotorstock that\'s for sure.
rgds
that\'s only 11 bhp Brian, not bad, very consitent power from engine.
I will be at Abbey very soon myself so hope to have some numbers worth talking about in the pub:D
rgds
QuoteOriginally posted by g11ary
that\'s only 11 bhp Brian, not bad, very consitent power from engine.
The \'10%\' difference between \'atw\' v \'ath\' is interesting still, if not surprising.
Not sure how really \'comparative\' the numbers are to the fly wheel though; the \'divide by .82\' and \'add 50hp\' are hardly scientific methods of calculation are they! Looks like Danny will have to get his bench dyno built and rented out if any ones really bothered :)
As John correctly pointed out, it’s all pub talk. ;)
As for the bench dyno, I won’t be bothering as things are afoot and there is no point when they are only going up in a straight line. ;)
I wonder if wheel sizes effect speed? Will 15\'s make me go any quicker???
Fish
yes!
smaller rolling surface ie smaller wheels/tyres will surely improve acceleration but reduce top speed so depends on yer definition of quicker (http://www.stopstart.freeserve.co.uk/smilie/deal.gif) lol
Si
There are two schools of thought regarding drivetrain losses.
One is that it is pretty much a fixed figure which is a certain amount of HP.
The other is that there is a percentage loss.
I personaly go for the specific HP loss over the percentage.
Why should the losses go up just because the HP goes up?
It makes sense to me that the losses should stay REASONABLY the same.Obviously with a very hi HP you will get slightly more powertrain loss but only a few more HP than was originaly established as the loss in the first place.
Just my thoughts on the matter.
Kind regards
Carl
QuoteOriginally posted by MikeLMR
In my opinion a Dyno is only ever good for seeing what effect tuning has had on the engine ... i.e back to back testing on the same device with modification/ tuning inbtween runs. And of course for tuning the engine under load and checking that its running right.
Power figures are really just for bragging rights ... knowing that a car makes xxx H.P doesn\'t make it any faster :)
Mike is quite right about the way Dyno\'s should be used.
I have known on N/A engines to see as much as 30 hp difference between rolling roads.(160hp on one,190 hp on another)
What this means is that the best way to see how much power you have really got is to take it somewhere like the drag race strip and see how quick it is.
I know that this will open a whole new can of worms about all the other things that have been done to the car,like Tyres,gutted interiors,axle ratios,gear boxes,and the like but that to my mind is all part of the modification to make your car go quick.
What I am saying is get your car modded however you see fit and be quick up the strip.
Kind regards
Carl
QuoteOriginally posted by Carl
What I am saying is get your car modded however you see fit and be quick up the strip.
Agreed, theres no other way to compare cars, especially when modified from stock greatly. You cant account for weight differences, drive train differences and a 100 other variables by any other means accurately. Of course you\'re depending on the driver being able to get the most out of the car then too though!
Regards drivetrain losses, I think Chris Wilson said some thing along the lines of the further outside the original intended performance parametres that a drive train is taken the worse the losses will become - until breakage. I guess every one has their view, bit tricky to prove either way for certain!
Losses on rollers are proportional to RPM. I\'ve got some coastdown plots that show how it varies with speed.
If you want to win on a dyno day, put on narrower tyres and pump them up to 40 PSI. You will see 10-15 more HP on a rolling road.
Hub drive, used properly are a lot better, but always ask to see the cal certificate with a grin on your face.