rolling road day this weekend

[kitch]

Originally Posted by MG mad

It's possible to measure the actual losses on run down to get a measured flywheel figure. Your first dyno run, with 189 bhp calculated from 150 would indicate transmission loses of 26%, which is quite high for a FWDer. On the other hand, the 5.8% of your second run is unrealistically low - 15-20% is more likely. That would put 150 bhp at the wheels at around standard 180 bhp, and 172 bhp at the wheels more like 200 at the fly. Of course different dynos on different days, it's almost pointless comparing the two.

You're slightly out there.

Basically, it's not possible to achieve a factual BHP figure for the engine from a chassis dynomometer. Not even mine! The only way you'll do this is by removing the engine and bolting it to an engine dyno.
A measured flywheel figure is purely an estimate. It's not a million miles out, but research has shown it to vary from the real figure by up to 10%. This is because though a rolling road dyno does its best to convert mechanical drag into a power figure, the simple fact is the losses measured on coastdown will be different on the pull because the behaviour of components changes when they have loads against them. The more accurate number 9 times out of 10 is the corrected figure. They're still not gospel, but they've been found to normally end up 5bhp either side of an actual measured output on an engine dyno. The corrected figure will take the measured figure and then apply a formula to it, which takes into account air temp, humidity, air pressure etc. So we all had (or most of us had) good WHP figures that day, but then it was ******* cold, meaning the air was dense. The wheel figure is absolute.....indisputable (provided the dyno has been operated correctly). But it's sensitive to the conditions, just as a car would be on the road. The corrected BHP or Torque figures take the temperature etc into account, meaning a result you got on the weekend should be very similar to one taken in the summer. This is why it's the preferred method for mapping and tuning, because it's the most stable baseline.
Quoted book figures also have a corrected formula applied to them.....otherwise manufacturers would have to quote one figure for someone in Norway, and another for customers in Mexico! The industry standard worldwide is now SAE J1349 (I think) but in Europe it used to be DIN (or PS) which is essentially the metric version. The ZS 180 is quoted as 177PS, or 174BHP. This is why. BHP is the imperial SAE unit.

I don't know the exact details of the run Ian's comparing at the top, but I agree 150WHP vs. 189BHP doesn't seem right. It's likely the 189BHP is a measured flywheel output, not a corrected flywheel output, which means it's essentially just a number written on a piece of paper that means **** all to anyone. Quite why he's only recorded 150WHP against his decent show on Saturday I'm not sure. Could be the temp conditions, health of the car.....could even be the way the car has been strapped down! I couldn't suggest anything concrete unless I saw the graph.
Regarding the second figures, or the ones I produced, the 182BHP is the CORRECTED figure. The measured figure was 189bhp (IIRC). There is nothing to say a FWD car will lose 15-20% through the transmission. There is no set rule....if you had to be REALLY broad and generalise you might be able to argue that around 10-12% on a sub-200BHP car is a rough guide, but it really does vary from car to car....tyres, gearbox oil temps....it all makes a big difference. Nearly all FWD cars I test lose around (what it believes to be) 20HP through the drivetrain.

You're right about different dynos, different days, but the information you're quoting is slightly misleading. As someone who's dynoed what must be over 200 cars or more, I can honestly say hand on heart that 90% of all the standard-spec cars we test come out pretty much exactly where you'd think they should.

[stamford]

Excellent post, very informative.

[kitch]

Originally Posted by Craig-ZS180

So what would others be looking to pay for the same session? I had to pull out a couple of weeks ago due to other commitments so dont expect to be in the same area of pricing but I didnt drop out at the last minute as said early on things had changed on my part.
Really am gutted I couldnt get there as the pics do look good and looks like was a good laugh there.
Well done Rich for putting the effort in to organise it.

Well normally (if you don't buy them on our eBay listing) runs are £45, which is still pretty cheap compared with the competition. I've held the offer for those who came down because they stuck to their word and two of them came a fair distance too. In the end we only dynoed five cars, one of which was mine and another two belonged to the same member! It was a bit of a let-down in terms of turn out, but the guys who did turn up were all good company for the day.

Appreciate some people had pulled out weeks ago, and its not a dig in any way to those who did....if you're busy, you're busy. It's more a reward/loyalty thing to those who did make the effort.

[talkingcars]

Originally Posted by kitch

Appreciate some people had pulled out weeks ago, and its not a dig in any way to those who did....if you're busy, you're busy. It's more a reward/loyalty thing to those who did make the effort.

Trick to commitment might be to take a deposit.

As I said before - sorry I had to pull out, unfortunatly work comes before play and in my case several 1000 peoples water supply.

[grimmy]

[Dan1971]

"Kitch" - You should have a pm from me re some potential work .....

[redzed]

Originally Posted by kitch

I don't know the exact details of the run Ian's comparing at the top, but I agree 150WHP vs. 189BHP doesn't seem right. It's likely the 189BHP is a measured flywheel output, not a corrected flywheel output, which means it's essentially just a number written on a piece of paper that means **** all to anyone. Quite why he's only recorded 150WHP against his decent show on Saturday I'm not sure. Could be the temp conditions, health of the car.....could even be the way the car has been strapped down! I couldn't suggest anything concrete unless I saw the graph.
Regarding the second figures, or the ones I produced, the 182BHP is the CORRECTED figure. The measured figure was 189bhp (IIRC). There is nothing to say a FWD car will lose 15-20% through the transmission. There is no set rule....if you had to be REALLY broad and generalise you might be able to argue that around 10-12% on a sub-200BHP car is a rough guide, but it really does vary from car to car....tyres, gearbox oil temps....it all makes a big difference. Nearly all FWD cars I test lose around (what it believes to be) 20HP through the drivetrain.

You're right about different dynos, different days, but the information you're quoting is slightly misleading. As someone who's dynoed what must be over 200 cars or more, I can honestly say hand on heart that 90% of all the standard-spec cars we test come out pretty much exactly where you'd think they should.

The two different test were different cars and not the same one! the 189 was a corrected flywheel figure on the car you didnt do. I know that the red one you tested was quick, hence a 172 @ the wheels is good considering they put that out at the engine from factory. ive always though flywheel figures were irrelevant now i know as i thought it was strange the first one wasnt quicker when it had a supposedly 190bhp. I would have thought the corrected figure should be higher than 182 though if the wheel figure is that high, but im not bothered the only figure i talk about is wheel figure if i talk about bhp at all as its nowt but pub talk.

great day again so thanks for arranging it. Also post the similarities between our two readings as thats an interesting one! be good to see it against another standard zed so i'll bring my saloon (completely standard) down in a few weeks.

[Craig-ZS180]

That's cool, least I know now. It is a 2.5 hour drive for me too which is not a short journey & wouldve done a tank easily or the day, with that once I've spent the fuel money getting there and back the extra £20 on the session would probably make it less viable for someone like me to do.
I do understand what your saying about keeping the discount for those that could make it but in reality of it when you work shifts as I do and it falls on the weekend that I'm working I unfortunately can't just drop it to go.
The mrs booking the pics was and added issue but could've gotten around that if had needed to but unfortunately it was a weekend where I couldn't get out of it.
Glad you all had a good day though and am really gutted I couldn't be there to take part in the event. Ill be waiting to see the next update on people's cars that were there to see how they go.

[kitch]

Originally Posted by talkingcars

Trick to commitment might be to take a deposit.

As I said before - sorry I had to pull out, unfortunatly work comes before play and in my case several 1000 peoples water supply.

Deposit would likely work, but I just hate the idea of asking for one. I'm a bit weird about money; I hate asking for it (yeah yeah I know, I run a business!) But yeah hear what you're saying.

Like I said earlier though, extending the £25 a run to those who attended honestly isn't a dig at those who didn't, it's just to show my appreciation to those who made sure I didn't come in for no reason! Normally runs are £45....only less on selected days.

[kitch]

Originally Posted by redzed

The two different test were different cars and not the same one! the 189 was a corrected flywheel figure on the car you didnt do. I know that the red one you tested was quick, hence a 172 @ the wheels is good considering they put that out at the engine from factory. ive always though flywheel figures were irrelevant now i know as i thought it was strange the first one wasnt quicker when it had a supposedly 190bhp. I would have thought the corrected figure should be higher than 182 though if the wheel figure is that high, but im not bothered the only figure i talk about is wheel figure if i talk about bhp at all as its nowt but pub talk.

great day again so thanks for arranging it. Also post the similarities between our two readings as thats an interesting one! be good to see it against another standard zed so i'll bring my saloon (completely standard) down in a few weeks.

Ah I didn't realise it was a different car. But yeah, flywheel figures are pub talk if your line is "my motah's kickin' out 190bhp innit!"" The flywheel figures are a good guide, but you have to use common sense too, which everyone did on Saturday. Doesn't always happen that way

I'll get the comparison graphs up soon. They're the best type.