rolling road day this weekend

[redzed]

Just a reminder, rolling road day this Saturday in fareham Hampshire be good to see loads of zeds down there, look in event thread for more details,

[peterzs]

10.00 am start by the look of it.

Confirmed for 9th February@

Southways Automotive Ltd
Unit C, Plot 5
Fort Fareham Industrial Estate
Fareham
Hants
PO14 1AH

For the sat nav's

See you there.

[MickUK]

Gutted I'm going to miss this.

[peterzs]

Throw a sicky!!!

[Skillen]

You're all too bloody far away!
Nothing goes on round my way!

[Witnes$]

Want time RR mine but that's just too far.

[peterzs]

You're all too bloody far away!
Nothing goes on round my way!

Have to have a mini-meet with Loz.

:wave::wave::wave:

[stamford]

I'll be along sometime during the day but no zed as it is still sorned and will be for quite some time.

[Skillen]

Have to have a mini-meet with Loz.

:wave::wave::wave:

Haha 3 car mini-meet if sheldore comes as well!

[peterzs]

Might get a deal with a RR guy for 3 ZS's, must be somewhere up in the Lakes!!!

[Dan1971]

.....still sorned and will be for quite some time.

:cry: Would've loved to hear it on the rollers .....

Looking forward to seeing what mine's got left after being left a bit rough until I got her. Hopefully the service etc will have her at about 160-170 .... we'll see ....

[stamford]

I would have loved to have heard it as well Dan!

Reckon you might be surprised.

[Craig-ZS180]

I need to stop reading these threads as I am very gutted to not see what mines doing and as you say about yours hear it at full chat from standing almost next to it. :(

[Dan1971]

I would have loved to have heard it as well Dan!

Reckon you might be surprised.

Get the veccy on there !

[stamford]

Get the veccy on there !

I wouldn't want to embaress anyone with the enormous power it has! :laugh:

[Dan1971]

I wouldn't want to embaress anyone with the enormous power it has! :laugh:

Reckon you might be surprised....;)

[DuckFeet]

I want to RR mine but apparently this is not a suitable activity for babysitting a 6 month old. Pah! She loves the car.

Make sure you post some results and mods!

[stamford]

I want to RR mine but apparently this is not a suitable activity for babysitting a 6 month old. Pah! She loves the car.

Make sure you post some results and mods!

Rubbish! It'll make them sleep!

[peterzs]

Dont know where this is, Sat Nav will find it, but I'm dropping the wife off in Gosport and on the way, there is a forward pointing speed camera.

So just in case.. as you come off the M27 dual carriageway, goes to a dual carriageway, drop down and go under a viaduct with a roundabout. Views of the harbour, turn left to Gosport.

Then there is a small dual carriageway and the camera is about 100/200 mtrs on the fast lane, garage on the left. It always appears to be on, not that any one will be doing over 30, but just incase, watch out for it.

Hopefully wont go along that stretch but you never know, sorry its late, but hit me during the night............

[talkingcars]

Sorry guys, not going to be able to make this, got called out by work overnight to take some pipe to a burst water main in Reading and have only just got in and it's blinking snowing as well :(

Enjoy.

[Dan1971]

Just leaving - hope to be there 12-12.30 ish .....

[peterzs]

Good to see you Dan, Stamford and redzed. Not forgetting Rich.

Was a good day thanks Rich for organising and sorting all the cars.

Pleased with the derv, even if I have got to sort out a couple of injectors that wernt sealing properly.

137.4 hp at the wheels
151.9 hp engine (corrected)
241 lbs torque (corrected)

So pleased that it went well.

Roll on Brands.

[stamford]

Shame the numbers attending were poor, but well done for those that made the effort. Thanks to the organiser, Rich :thumbsup:

[Dan1971]

Hmmm....... work to be done for me.

Great to see you fellas.....

[stamford]

All fixable though Dan. Vis indicators would be a simple and effective addition.

[Dan1971]

All fixable though Dan. Vis indicators would be a simple and effective addition.

Simple for some mate......;)

I don't actually think it's just the vis motors. I think a new manifold is required to be honest. Although not rattling, 35 BHP down ain't right. Thread coming with the graph in a bit for the online diagnosis....

Thing is I'm not actually that sad about it..... It means it'll actually be even faster.... :)

[stamford]

:hmmm: I feel another 'do stuff meet' on the horizon! :D

[Dan1971]

:hmmm: I feel another 'do stuff meet' on the horizon! :D

Trouble is that I did a full tank to get there and back too, 261 miles, and that was sitting at 75 - 80..... Its running too rich apparently too.

New manifold, induction, decat on the shopping list....then back to you for another run and some vis indicators

[stamford]

Ouch, that is alot. It does need fettling then it'll be all good.

[redzed]

Shame about low numbers but I was very happy with my road zed doing 173bhp @wheels! Shame my track one couldn't be done. I was very impressed with the diesel run, good to meet you guys

[daytona365]

:hmmm: I feel another 'do stuff meet' on the horizon! :D I can come and get my gloves and rags back lol................ mmmm now what needs doing on mine??????????

[redzed]

been looking at results from previous rolling road sessions, amazing what different results you can get, that last session i did on a different zs was:

189bhp @ the fly (which is calculated)
and it was only 150bhp @ the wheels (actual measurement),

the one yesterday on my red zed which feels much faster was:
182 bhp @ the flywheel (calculated)
and 172bhp @ the wheel (measured)

Surely the only measurement which actually counts is bhp @ wheels as its the actual measurement rather than calculated which is at best just a guess, just some thoughts

[petet16]

@ wheels figures are more relevant imo, but the fly figure gives a clue to transmission losses which are interesting to use for comparison purposes.

[peterzs]

Some pics of the event, Redzed has a racing blue one as well, so start with his.

http://i297.photobucket.com/albums/mm214/peterzs/ROLLING%20ROAD%209th%20FEB/IMG_0027.jpg

http://i297.photobucket.com/albums/mm214/peterzs/ROLLING%20ROAD%209th%20FEB/IMG_0026.jpg

http://i297.photobucket.com/albums/mm214/peterzs/ROLLING%20ROAD%209th%20FEB/IMG_0031.jpg

Dans, such a improvement from when I first saw it, just after Dan picked it up, just shows, bit of TLC and its a different car.

http://i297.photobucket.com/albums/mm214/peterzs/ROLLING%20ROAD%209th%20FEB/IMG_0030.jpg

http://i297.photobucket.com/albums/mm214/peterzs/ROLLING%20ROAD%209th%20FEB/IMG_0028.jpg

http://i297.photobucket.com/albums/mm214/peterzs/ROLLING%20ROAD%209th%20FEB/IMG_0029.jpg

My one.

http://i297.photobucket.com/albums/mm214/peterzs/ROLLING%20ROAD%209th%20FEB/IMG_0023.jpg

http://i297.photobucket.com/albums/mm214/peterzs/ROLLING%20ROAD%209th%20FEB/IMG_0024.jpg

And Rich's and just cos they are cheap, can still suprise on how good they go and sound.

http://i297.photobucket.com/albums/mm214/peterzs/ROLLING%20ROAD%209th%20FEB/IMG_0025.jpg

And hiding round the side is Stamfords, mighty Vauxhall Estate.

http://i297.photobucket.com/albums/mm214/peterzs/ROLLING%20ROAD%209th%20FEB/IMG_0026.jpg

Was a great day, thanks againg to Rich and his colleague who did all the tying down and a bit of spanner work on my injectors, trying to stop a bit of a derv blow. Plus the tea/coffee/biscuits they laid on, kept us all going.

:clap::clap::clap::thankyou:

[MickUK]

Someone PM me next time!!

Good pics!

[peterzs]

Will do

[kitch]

Hadn't spotted this thread!

Thanks to all who came, and like I said in the events one - the £25 a run offer is a rolling one (geddit? rolling?) to those who attended Saturday.

Rich

[peterzs]

Thanks Rich, I'll sort the injectors and see when Dan is thinking of coming down in his mended red one!!!!

:clap::clap::clap::rambo::rambo::rambo:

[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.

[MG mad]

been looking at results from previous rolling road sessions, amazing what different results you can get, that last session i did on a different zs was:

189bhp @ the fly (which is calculated)
and it was only 150bhp @ the wheels (actual measurement),

the one yesterday on my red zed which feels much faster was:
182 bhp @ the flywheel (calculated)
and 172bhp @ the wheel (measured)

Surely the only measurement which actually counts is bhp @ wheels as its the actual measurement rather than calculated which is at best just a guess, just some thoughts

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.

[kitch]

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]

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]

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]

:book:

[Dan1971]

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

[redzed]

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]

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]

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 :closedeyes:

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

[kitch]

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]

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]

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.



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.


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.



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]

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.

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.


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!

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:

http://img.photobucket.com/albums/v291/kitch/graph1_zpse896eab5.jpg

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?! :unsure:

[Dan1971]

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

[kitch]

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.