rolling road day this weekend

[kitch]

Originally Posted by 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.

Not a problem, and I can only stress again that £45 is the normal price.....it's not anybody being penalised and in a normal situation it would only be £25 a run on special occasions. I was just grateful to those who came and have decided to extend that offer to show my gratitude. £45 a run is still a very good price, but I admit that mixed in with a full tank it's gonna mount up. I'm sure we'll do another day soon enough so unless you need a run it'd be worth waiting for the next one.

[Craig-ZS180]

Originally Posted by kitch

Not a problem, and I can only stress again that £45 is the normal price.....it's not anybody being penalised and in a normal situation it would only be £25 a run on special occasions. I was just grateful to those who came and have decided to extend that offer to show my gratitude. £45 a run is still a very good price, but I admit that mixed in with a full tank it's gonna mount up. I'm sure we'll do another day soon enough so unless you need a run it'd be worth waiting for the next one.

That's cool, I understand what your saying so dont get me wrong from my post. I was only meaning that once you take the tank & a bit of fuel it would probably use as really over fuelling at the mo and then £45 to put her on the rollers I can't really afford to do it. It then loses the "cheap" rolling road experience for me at least.
I really would love to get mine on the rollers so I can see what it's doing and to find out if the money I spent in modding it has actually paid off or was a waste of time and money. So I suppose its not a major issue but its one of those things that I would love to do it but as with most people and with now planning our wedding my money is very limited especially when it comes to not 100% necessary things being done.
I will see what happens the next time you organise something as was looking forward to coming down, going on the rollers and meeting you guys at your place too.
Thanks for responding to me though Rich, I was only saying that it was something out of my control as to not being able to be there as I didnt get out of work until 2pm otherwise I would've been there too.
Have to see how it all unfolds for the next events I suppose

[MG mad]

Originally Posted by kitch

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.

Depends on the dyno, specific chassis dynos have been shown to be very good, within 2% of engine dyno values. A measured figure, by definition, is not an estimate, however what I presume you are meaning is that it is subject to error - of course it is, every measurement is.

Originally Posted by kitch

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).

For a given dyno on a given day. Go to a different dyno or come back a different day and that measurement will change - sure you can correct it is using the same dyno but as a means of accurately comparing readings it's not without its drawbacks.

Originally Posted by kitch

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.

I totally agree, it's also the best way to measure the influence of particular modifications but it's always best to do it on the same day.

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.

I agree that bhp at the wheels is what matters and is most reliable. My point here was as much that 189 at the fly from 150 at the wheels is a significant over estimation, as many dynos don't measure the drag on run down and just guess. I also doubt that any car will only lose 6% through the transmission, that is exceedingly low, even for modern cars (note the use of the word doubt - I have no idea how you calculated or measured that to make a proper assessment of it). The figure of 15-20% is, or at least was, fairly commonly accepted as approximate losses in transverse engine/transmission cases, of course with modern cars the losses do tend to be lower than what they were even 15 years ago. If you understand the point that 5% range is quite a lot of variation you would understand that I am not referring to a hard and fast rule, by any stretch (and is also much broader than your quoted 10-12%, if we want to be pedantic).

It's also worth pointing out that the run down measurement is quite useful as it can high light differences in where the engine is making peak power and where that is being delivered to the wheels - ie that as revs climb the efficiency of the transmission can drop. I've seen this more in longitudinally-engined cars but it can occur in transverse ones too.

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.[/QUOTE]

It would be fair to say if the majority of the testing you've done is on the same dyno you'd get fairly consistent results, particularly if you have a good correction figure. I've also been involved in dyno testing and tuning cars several times, and have used a number of different dynos and have never got the same reading twice, even at the same dyno.

[kitch]

Originally Posted by MG mad

Depends on the dyno, specific chassis dynos have been shown to be very good, within 2% of engine dyno values. A measured figure, by definition, is not an estimate, however what I presume you are meaning is that it is subject to error - of course it is, every measurement is.

You can't apply a blanket 'within 2% of engine dyno values' to a particular dyno, because different cars affect the coastdown losses differently. The fact is you cannot measure the power of an engine at the flywheel on a chassis dyno. You can only measure within certain parameters and the rest is down to guesswork, however close it may be. For the measured figures, there's almost no point in reading them.

Originally Posted by MG mad

For a given dyno on a given day. Go to a different dyno or come back a different day and that measurement will change - sure you can correct it is using the same dyno but as a means of accurately comparing readings it's not without its drawbacks.

Different dynos will differ in their readings, yes I agree. It's almost pointless drawing comparison between different dyno recordings if they have recorded very similar readings, if not exactly the same. You could do 4 or 5 pulls one after the other, and on many cars the results can very by 2-3hp there and then.

Originally Posted by MG mad

I totally agree, it's also the best way to measure the influence of particular modifications but it's always best to do it on the same day.

It is, but that's the whole reason for correction values....so that you stand a chance of being able to tune on different days. Although that said, it always makes me laugh when someone says they've fitted a "high-flow" panel filter and want to come back to do another dyno run.....the differences you notice with parts like these doesn't even register on dyno runs. Even those on the same day!

Originally Posted by MG mad

It would be fair to say if the majority of the testing you've done is on the same dyno you'd get fairly consistent results, particularly if you have a good correction figure. I've also been involved in dyno testing and tuning cars several times, and have used a number of different dynos and have never got the same reading twice, even at the same dyno.

Different types of dyno can affect the results as you say. I can only speak on behalf of mine, and in all the times I've been testing it the only people who've ever questioned it on the day have been talking out of their arse. It's rare but it does happen! "Your tranmission losses are too low, they should be 60-70bhp. That's why my graph doesn't show the 240bhp I was promised by the makers of this resistor I fitted in my fuel rail."

Sad I know, but it happens

[MG mad]

Yes there are all sorts of weird things talked about by those that know little in regards to dynos and dyno testing. It's one of the reasons I tend to talk about increases when considering mods and seldom give a precise number when asked what my car makes etc.

The only thing I would say is the particular dyno I know of that claims +/- 2% has done a lot of testing and comparisons with engine dynos (I can't recall exactly how many but enough to get a good statistical basis to justify their claims).

[kitch]

Here's the 'interesting' graph we mentioned earlier:



The red plot is my 2001 120k mile battered, beaten-up ZS 180 which I've taken a hammer and chisel to the VIS power flaps on.
The black plot is redzed's mk2 ZS 180, in much better condition with (seemingly) working VIS flaps (to the point we removed the motor to check out the operation of the rail).

The numbers aren't important so much - Ian's car has a decat which from experience I've found to be one of the more effective cheap mods on many cars. His engine is also likely in better health and I would bet he's running it on some expensive 99RON fuel (which I've found on certain engines sometimes produces 1-2bhp more, but on some it makes no difference at all), though I don't want to knock the ShedEss as it's clearly running happily enough. Someone will need to convince me that removing the power flaps reduces TOP END power, and until that happens I'm sticking by my theory that it only effects low end pick-up.

This does raise a question though....the interesting bit is the comparison between the graphs. Given that one has no power flaps at all, and the other has seemingly fully functional VIS, look at how similar the curves are! There are even kinks replicated at certain points in the rev range!
If Ian's car does indeed have fully functional VIS........what on earth does it do?!

[Dan1971]

Fair enough when putting the pedal all the way down, but what about in normal town driving .... Smoothness, economy effected maybe ?

[kitch]

Originally Posted by Dan1971

Fair enough when putting the pedal all the way down, but what about in normal town driving .... Smoothness, economy effected maybe ?

I think economy is affected, because mine's pretty juicy and unless everyone who's told me the ZS180 can achieve high-20's is spouting bullshit, I think it's down to the flaps.
Mine's perfectly smooth at lower revs, but I would have expected there to be a massive lack of low-down grunt compared with a car with working VIS. What surprises me is that there isn't.

[MG mad]

What's interesting to me is that both curves appear to get the increase in torque at ~3500rpm from the VIS system working. Very odd, as you say.

It really depends on what state the manifold defaults to I guess, long or short runners, as to what will be lost and where.