Got my latest results from Surrey rolling road meet.

It might as well be in klingon.

I do know that i ran with both O2 sensors and tps not working at all.,

 

Here are the 4 readouts, which is which??

 

Once the sensors and tps are replaced with new ones, will it make much of a difference.

Im only running a mongoose system and a blitz sus filter, what is a reasonable figure to aim for.??

 

1st: Flywheel power/torque

2nd: Wheel power/torque

3rd: Flywheel power/boost

4th: Flywheel power/AFR

Apart from the AFR you are match for match with me but i have 0.5 more HP than you :P Good solid results there bud!

how do those figures compare with how it came out of the factory? Are the factory figures that get quoted flywheel or rear wheel figures?

how do those figures compare with how it came out of the factory? Are the factory figures that get quoted flywheel or rear wheel figures?

 

They tend to quote the flywheel bhp as its higher than at the wheel, so sounds more impressive. Not to mention a lot of manufacturers actually lie about BHP!

Edited May 24, 200916 yr by Steams
spelling!

all the zeds seem to be the same hp at that place

Cars will announce the Flywheel HP so in the 300's case it was 300hp on the Jap so after losing a few HP each year then to regain the lost one's and gain an extra 30+hp is a good result!

was it 300bhp stock or 280?

Sorry for all the questions... but I've always wondered how you measure power at the flywheel on a rolling road?

280hp for the jap and uk spec. in the US its 300hp :rolleyes:

was it 300bhp stock or 280?

Sorry for all the questions... but I've always wondered how you measure power at the flywheel on a rolling road?

 

Some rolling road systems can try to work out transmission loss but on others they add an estimated loss depending on the transmission type - manual, auto, 4x4.

Either way it's not 100% accurate and is open to abuse.

 

Found this article that explains it quite well:

 

"What is transmission loss?

Well all mechanical systems suffer from friction and a proportion of the power fed into a system will get dissipated by friction and turn into heat and noise. Note the key phrase there - "power fed into a system". For there to be a loss there must be an input - simple and obvious yes but we'll see the relevance in a minute. When your car is parked overnight with the engine switched off, the transmission losses are obviously zero. When the car is running then some proportion of the flywheel power will be lost in the gearbox, final drive, drive shaft bearings, wheel bearings and tyres. For a given mechanical system these losses will usually stay close to a particular fixed percentage, let's say 10% for example, of the input power. So if the car is cruising and developing 20 bhp then 2 bhp will get absorbed as friction - under full power, say 100 bhp, then maybe 10 bhp will get absorbed. Now it is true that not every component in a transmission system absorbs a fixed percentage of the input power. Some components like oil seals and non driven meshed gears (as in a normal car multi speed gearbox) have frictional losses which are not affected by the input torque. These losses do increase with speed of course but at a given rpm can be taken to remain constant even if the engine is tuned to give more power. Finally, the biggest source of loss in the entire transmission system of a car is in the tyres - they account for half or more of the total losses between the flywheel and the rollers. Each set of driven gears, i.e. the final drive gear or the particular gearbox ratio that you happen to be testing the car in, only absorbs about 1% to 2% of the engine's power. Ok - so how do these software systems that supposedly measure transmission losses so as to "predict" back to the flywheel bhp work. The power curve at the wheels is taken in the usual way as explained above. Then, at peak rpm, the operator puts the car into neutral and lets the rollers slow down under the drag of the tyres and transmission. The software then measures this drag (or "coast down loss") as "negative" power and adds it to the wheel power to get back to the supposed flywheel power. BUT - and hopefully you've all spotted the problem now - the engine is not feeding any power into the drivetrain while the car is in neutral - in fact it isn't even connected to the drivetrain any more!! Whatever drag this is that's being measured it has nothing at all to do with the proportion of the flywheel power that gets lost as friction when the engine is powering the car in the normal way. The engine could now be an 800 bhp F1 engine or a 30 bhp mini engine for all it matters because it isn't connected to the gearbox or feeding any power into it. Obviously this "coast down loss" is something to do with the transmission and tyres but it is not the true transmission loss - in fact this coast down loss should never be expected to change for a given car at a particular rpm regardless of how much you tune the engine whereas a true transmission loss will increase as the engine power increases because it is dependent to a large extent on the amount of power being fed into the transmission. As the engine was tuned to give more power the "true" transmission losses must have also increased to some extent but these chassis dyno systems don't, and can't, show this happening.

 

So is there any way of really measuring the true transmission loss of a car?

Yes - only one - by measuring the flywheel power on an accurate engine dyno, the wheel power on an accurate chassis dyno and taking one away from the other. There is no way of finding out the true transmission loss just by measuring the power at the wheels. So hopefully that's got you all thinking a bit more now instead of just taking for granted the "flywheel" figure you were given last time you took your car to the rollers. Even worse is the fact that some of these software systems allow the operator to just programme in the percentage of transmission loss he wants the system to add to the wheel figures. So if that isn't a nice easy way to show some big fat flywheel bhp then I don't know of a better one. It's certainly a lot easier than actually doing some proper development work to make the engine perform better - just dial in a bigger transmission loss and there you go - the same wheel bhp now turns into a bigger flywheel bhp - happy customer, happy dyno man - just a shame it was all sleight of hand. See the end of this article if you doubt that this sort of thing really happens.

 

So what should you do when you take your car to a rolling road?

Firstly, make sure you get printouts that show the wheel bhp and not just the flywheel bhp. Then at least you can see if they look sensible in comparison. If you have a desperate need to know the flywheel bhp then you will have to estimate it - there's no other way short of using an engine dyno. The corrections you need to make for cars with manual gearboxes are these: The average front wheel drive road car with between 100 and 200 bhp loses about 15% of the engine bhp as transmission losses. The average rear wheel drive road car with between 100 and 200 bhp loses about 17% of the engine bhp as transmission losses. The increase in % loss over front wheel drive is because the differential has to turn the drive through 90 degrees at the back axle which soaks up a bit more of the engine's power. 4wd cars will have higher losses because of the extra differentials and other power transmission components. A reasonable estimate of an average 4wd car's losses might be 22% to 25% of the flywheel power but it isn't a subject I have sufficient data on to be definitive. What your own specific car loses is anyone's guess - yours is as good as mine - but it shouldn't be far from the figures above. For sure though, no car in the world, unless it has flat tyres and a gearbox full of sand, loses anything like 30% of the engine's power in the transmission and tyres as many rolling road operators would try to have you believe. So take the wheel figure and divide by 0.85 for FWD or 0.83 for RWD and that will get you as close to the true engine bhp as you are ever going to know. In general though it is fair to say that low powered cars have higher % losses than high powered cars. For example, a 60 bhp Fiesta will have around 14 to 15 bhp total transmission and tyre loss whereas a 90 bhp XR2 will only have about 17 to 18 bhp loss - a smaller % obviously. By the time you get to RWD cars with engines in the 300 to 500+ bhp range, losses can eventually drop to as little as 12 to 14% or so. Another rule of thumb I use which is quite accurate is to treat the losses as being 10% of the flywheel power plus 10 bhp for FWD and 12% plus 10 bhp for RWD cars. This equation "loads" low powered cars more than high powered cars which is more closely like what happens in reality. Remember, these percentages are not "gospel" - they are good realistic averages."

Edited May 25, 200916 yr by ChrisC

Good results by the looks of things Stu, congrats mate :)

 

When you and the other fellas have got everything together and what not, start a thread in the dyno section with pictures of the relevant graphs etc and i will start adding you all to the leader board :)

 

Cheers,

Isaac :cool:

Good dyno, but I have some questions...

 

In this picture Fly/boost

 

 

You have full boost at 4500 rpm... much lag??, at 3500 will be at full boost no?

Thanks for that Chris, very interesting.