BHP ATW vs ATFW

[philip]

other than always benchmarking improvements on the same RR (and thats impossible in my countrywide chase for decent mods), what is the most reliable way to compare power after mods. Obviously the only true measurement is bhp/torque at the wheels, but even that will fluctuate from RR to RR. is there some sort of calibration process an RR has to go through, e.g. they put a "metric-standard" 100bhp through the RR and calibrate it? Basically how do I make sure Im getting my £££s worth if somebody tells me their mod will add xxbhp. Also, is the relationship between power at the wheel and at the flywheel linear, i.e are transmission losses a fixed percentage or do they vary with external factors?

 

[BenR]

rolling lossis are not linear, they increase with BHP.

ATW is a known amount, but its up to the general quality of the RR operator to keep it calibrated. All it does is measure a known torque moment, so you put in a known torque through a lever on the measuring arm.

Well, not that simple, but getting a known amount in and you can calibrate it.

ATF measurements is where all hell can let loose, corrected outputs are a gamble in some cases.

Best way to measure it, see if you can get roung a track any faster, if not....the mods are no use....of course, weather permitting.

 

[Chris_H]

corrected outputs are gamble in some cases...Ben thats crap its a gamble in all cases.

Load of cack atf measurements, I have seen 1 litre novas with 120bhp at the fly and only 30bhp at the wheels for example.

atf are useless, also so are the losses they say, 20% loss through the transmission, aye in a 4wd, if any fwd box lost that much they shoudl take the sand otu and put oil in it.

Wheel figures are only of use. Compare them. Thing is due to atmospheric changes its never the same twice.

 

[BenR]

Chris, im trying not to offend that much, as some RR operators do try.....lol.

our synical and more realisitc world would depress almost everybody, we can just accept the truth, people need figues or they sulk.

 

[philip]

Thanks for feedback guys. Ill go with atw figures. cant go wrong with that. And Ill continue doing a before and after RR (on the same RR) for each mod phase. What it means ATF I couldnt care less. My goal is to reach a nice ride 200hp/ton in time for the summer track season - Ill live with a +/- 5% uncertainty around that quite happily.

 

[paddymph]

when i went to my first RR, they gave me a figure of 152 @TW, they didnt give a fly figure, i then went to another would say Fly figures were the ONLY way to go, and said i had 163 (atf i think)? WTF? RR are all bollox..id gradually loosing faith in them

 

[Nick Read]

Chris is right. The only comparable benchmark is at the wheels, and even then you need to stick to the same RR every time and try for similar weather etc.

Best way is like Ben says, test it in a different way, either round a track or up a quarter mile.

 

[philip]

Many thanks for the feedback. Ill be testing the car on track all summer..