Dyno results

Put my car on a rolling road dyno today at janspeed in salisbury. Pulled a 369.54BHP at the wheels so the thor one of 395 at the hubs isn't that far off really.

They had a bit of a problem there as the car kept wheel spinning on the dyno lol. They said that it was very unusual to have a car powerfull enough to do this. Plenty of low end power see heh heh.

Nice figure.

Using Ian C's favoured figure of 8% drivetrain losses would put the flywheel figure at 401.67 BHP

Well that can't be right as I have lost 25 hp just from the hubs to the road. So I am therefore only losing 6 hp through the entire drivetrain from the hubs to the fly? I find that a little difficult to swallow.

I do agree that the estimated figure of 19% losses from the hubs to the fly is a bit excessive but I actually think its not that far off. Powertrain losses are horrendous. Some vehicles lose 25% from the fly to the road.

You cannot really compare the run you had at Thor with the new figure.

You really need to stick to the same RR/Dyno to compare..

I did the run on the dyno at janspeed to see how a rolling road compared to a hub dyno. Bear in mind my profession used to be testing turbine engines in a test facility I know the ins and outs of engine testing. I have no doubts that both the rolling road and the dyno's at thor get regularly calibrated and as such are going to be fairly accurate.

I also am very much aware of mechanical and thermal losses across a transmission and if I got my old text books out could probably work out most of the generic transmission losses and how much heat those losses produced.

So in a way yes I can compare the results I got today to the results I got on Thors dyno. I lost a bit of power today as he had a hard job putting my power down on the rollers as the wheels kept spinning so there was quite a large loss there straight off. The air temp was lower today than it was at JAE when I got the thor dyno done but the humidity was higher at JAE than today. I also felt that since my speedo converter has lost its signal that my car isn't running as strong as it has been. But on a whole I think the reading that I got today is an accurate portrayal of my cars power. 370 at the wheels is reasonable. With a general 25% transmission and tyre loss (which isn't that unrealistic) adds up to circa 460 hp. 395 at the hubs with a 19% calculated loss (again I don't think is that much off the mark) gives you 474 hp. All in all given different days and conditions 14 hp differences is not a lot and gives me a real idea of the ballpark my car is operating in.

PS how is running the same car on the same dyno without further modifications or some alterations going to produce any kind of comparison? All that will do is prove that the dyno puts out consistent results.

I just assumed that you had some further mods done, my mistake. I agree 14 hp is not a lot of difference.

Nice figures at any rate.

Oh don't get me wrong I'm not being an ars*y pr*ck because someone questioned my power figures lol. Just explaining my reasoning

If I factored in a 25% power loss from my wheels figure I get 775 crank horsepower which seems frankly daft to me... Would you agree?

-Ian

Did they do it at the castle street place? if so how much? if u dont mind my asking

If I factored in a 25% power loss from my wheels figure I get 775 crank horsepower which seems frankly daft to me... Would you agree?

 

-Ian

Unless the parts you have fitted have raised the efficiency of the drivetrain then quite possibly that is correct. Once you start taking components out of their designed operating range they become more in-efficient. The more power you put through a component the more heat will be generated by the friction of gear tooth on gear tooth and bearings will be forced harder onto races obviously if you do nothing then this will generate more heat. Heat generation is obviously going to result in power loss. Thats why squeezing even a bit more power out of a set component without redesignwork is so difficult. If you've uprated your diff and gearbox then it is possible that you have reduced your transmission losses by a significant enough amount to drop your losses overall to less than 25%.

PS I'm not trying to teach you how to suck eggs here just explaining my reasoning to people that might not be as engineering minded as your good self.

Have I got mixed up here or are you talking about an Auto (DB's) and a Manual (Ian's)?

Straight off the losses are gona be completely different right?

Don't think I'd wana use 25% or 8% to be honest.

When we went to G Force Im sure they worked on 20% losses for Auto cars? And they were no idiots.....

IMO all the RR is good for is:

Is the car running correctly ie not lean etc

And after a performance mod take it back to the same RR to assess any improvement in HP.

Ah I didn't mean all cars were 25% just up to 25% loss's are to be expected. I think that the figure I'd had bandied about was 19% for auto supes would be in the correct ballpark. No 2 transmission systems are the same, quality of the oil and condition of the parts won't be the same on any 2 cars that have been out of the factory for any length of time.

The fly power is IMHO a useless figure unless you calculate it on a fly wheel dyno and use it to actually assess how much you are losing through the transmission system. The power you lose in the transmission is wasted energy and could be a million % its not going on the road so it just doesnt count.

I agree that rolling roads main use is to assess the condition of your engine in comparison to previous runs on the same test bed.