How do "you" accurately measure "your" cars power output?

[Zenith]

I have been looking at alot of information relating to cars power output. Now most people say well on the dyno it did 200hp but on this dyno it did 300hp so therefore it must have 300hp, but as we all know differnt dyno's read differently and other factors come into play.

So how would you measure your cars power accurately, i have read allot about MPH at the track as in general around 120mph mark will put you in at around the 400hp mark. once again lighter cars will have less power but still do around that MPH, Could you possible meaure engine output by means of injector flow, ie, 440cc injectors at 100% duty cycle will flow enough fuel to make 88hp each at 11:1 AFR or something like that, so therefor these injectors at 100% will flow enough fuel to make 88hp x 6 = 528hp at the engine. but it is too hard to equate what it has at the wheels due to unknown loss through the drive train into heat. say for example we do loose around 25% that equals around 400rwhp

now i have tried to make sense of it all, and it does kinda work, just say that a gtr, does 450hp on a dyno at a proper ramp rate, but the standard 440cc injectors and standard AFM's are maxing out, now at the track the car actually does do 120mph or there abouts, does this mean that the car actually has 400rwhp, cause the injectors cant flow enough fuel to create over the 528hp, and the Afm's can only measure enough air to allow enough fuel to be burnt to create 528hp, factor in the given 25% loss it does equal around 400wrhp,

Now can this equation acutally be used, like does it work in your minds. And how much do you think is actually lost via heat in the drive train. 25%? so which would be right, the dyno or the calculations as they are reasonable similar?

Corret me if im wrong on anything, as thats what im hear to do is learn of others.

Cheers

Zenith

[switch]

if it puts me back in the seat, and i enjoy driving it or it breaks traction in 4th gear, then its fast

[paulr33]

i think the most accurate way is a shootout mode dyno, such as a dyno dynamics. it calculates what ever power the car makes at the wheels and rounds it off to 25 deg ambient temp. so that when you compare your cars run in brisbane in summer at 40deg abmient temp to another skyline run in shootout mode in tassie in winter on a 10deg day the results are comparable as the dyno rounds it up from 10deg ambient to 25deg. it also factors in humidity and so forth. so the output you have is comprable to the one in tassie despite completely different ambient temp.

[nmcmahon83]

the problem still remains that a well looked after dyno is going to be somewhat more free rolling that a poorly maintained one... dyno's are good for competitions and comparisons on the same dyno (ir tuning purposes)... other than tha they dont hold much cred IMHO.