kw at the wheels & on the fly?

[Nrage33]

lots of info to absorb here...ok so when it says a ferrari 360 modena is rated at 400bhp, how does one judge, according to the fixed loss theory, how much rwhp the car has?

Because it appears that alot of power is actually lost through the drivetrain. I mean, whether it be 30% of the figure or even at a fixed rate, it's alot of hp that gets absorbed.

[Steve]

Nrage33, it will vary from car to car. As sydneykid pointed out above, even R32 to R33 GTS varies.

[Sydneykid]

Hi Joel, I believe there is a case for a certain amount of the losses to be variable. Keeping in mind that there are no "losses" as such, they are really "transformations" into other forms of energy. A real world example would be where I have seen gearbox oil temperature increase slightly when a higher power engine is used. But it really is very minor. The problem is further complicated by the fact that some of the oil warming may be attributable to the extra heat from the exhaust and radiator heating up the gearbox case rather than the extra torque warming up the oil.

The other issue I find a lot of people get confused with is transformations of energy in the engine itself. The fact that a large portion of the calorific value of the fuel ends up heating the water and going out the exhaust pipe. This is of course irrelevant in comparing engine bhp with rwhp, any combustion efficiency transformations are in both numbers.

Hi Nrage33, I have no personal dyno (engine or chassis) experience of Ferrari 360 Modena, a quick look over at a recent race meeting (Bathurst 24 Hour) tells me that around 70 to 80 bhp in transformations would be logical. The driveline is fairly large in componentry however it is very well engineered for minimal transformations (eg; drive shaft angles are very small). So I would expect to see around 320 to 330 rwhp (250 rwkw) out of one on our dyno.

A point of interest, we had a Nissan on the dyno last week that was lowered excessively (IMHO). I adjusted the coil overs to raise it up so that the drive shafts were straight and the rear camber was close to zero (still a little negative). It picked up 8 rwhp from just doing this.

This is not the first time I have seen excessive power transformed due to driveline inefficiency. One of the race Skylines, a while ago, had a bad vibration under power and we stuck it on the dyno to find it. It turned out to be the tailshaft centre bearing. When replaced (along with the universal joints) it not only got rid of the bad vibration it also yielded an additional 5 rwhp.

Keep this in mind when drag racing or dyno comping.

Hope that helps some more

Only 1 more sleep till Santa comes

[browny]

Sydneykid, have you ever tested a stock engine on an engine dyno to double check Mr Nissans claimed figures?

[Sydneykid]

Hi browny, we tend not to engine dyno standard engines, there is kinda no point. I have had a production racing R32 GTR N1 engine on the engine dyno, it had been blue printed but was otherwise standard to N1 specs, except it had no exhaust from the dumps back. It made a heap more than 206 kw, more like 266 kw actually.

I have seen nothing to suggest to me that Mr Nissans quoted power outputs are excessively optimistic, they line up pretty well with other manufacturers. Except GTR's of course, they always seem to be conservative, along with many of the 206kw club.

Hope that helps