Dastek - FAO all 4wd cars who attended the R.R. on Saturday 14th August
 

Hi Guys,

To make sure I draw your attention to Gerry's reply regarding figures for 4WD cars at the rolling road I have copied it below:

Hi Guys,

Andy F emailed me with a few queries, so I replied in length to him, & it would make sense if I stuck the reply up here as well, maybe explain a few things.

I spent a few hours on Saturday night (much to the wife's amusement) looking at all the raw data, & I spotted the problem.

Here goes the long winded tech explanation As you probably noticed we control the roller RPM per second per second rate on both roller sets, this we feel gives the car a more realistic load & extremely repeatable results (& hence the boost & torque curves usually match how the car performs on road) Because we have a constant acceleration of the rollers we know how much torque is required just to accelerate the rollers at this rate ( torque = polar moment of inertia * rpm per second / 9.5) thus we use a look up table depending on the ramp rate we are using & add it to the torque seen by the loadcell on the brake (which is controlling the ramp rate) this way the engine is always under load (unlike other systems that apply more load the faster the rollers go - so low boost & torque at low engine speeds, then a spike of boost & torque as the brake comes on, then a killer load at the top end) Anyway, in my eagerness to impress the Scoobynet fraternity, I worked very late on Friday night trying to finish the 16 channel data logger with the new software that provides the ramp rate, correction factor, temp, atmo pressure, peak figures, losses, etc etc, just like most people are used to, however I couldn't get it finished in time, so I swapped the software back to the old version, but I forgot to replace the 4WD look up table, so when we ran the 2WD cars, they were spot on, but when I ran the 4WD cars, they were looking at the wrong torque multiplier (the software basically thought it was to add the torque in for only accelerating one chassis only) so the power at the wheels for the 4WD cars would be down somewhere in the region of 20 - 40 bhp depending on roller speed. However at the time I didn't believe it could be wrong as I had dynoed & mapped quite a few 4WD cars during the week & they were all producing what I would expect (this was before I fecked about with the software of course) so a big bit of humble pie for lunch today

The above however, wouldn't affect the transmission losses, as we use another calculation for this. John Banks made an interesting observation in that, at circa 50 bhp, the M3 had almost identical losses to the 4wd cars. What he witnessed was that the M3 was run in 4th gear & the gearing is quite long on these cars, & as the transmission losses are related to roller speed (windage of rollers & retarders, parasitic drag on the bearings, deformation of tyres etc) the drag is higher with greater speed. What you probably would have seen (with the correct look up table installed) would be higher at the wheels figures (remember we run the 4WD 5 speed cars in 3rd) & much lower transmission losses, this is not just because of the roller speed being lower in 3rd gear, but also because our rollers are closer together (so the wheel doesn't get 'pinched' by the two rollers & thus the tyres deform less) & also because the finish on the rollers means we don't have the same slippage problems as other dyno's (providing we get the wheel base correct - but this is easy picked up on the run if it's not) we therefore don't need to pull the cars down hard onto the rollers (further deforming the tyres & reducing the power at the wheels & increasing the drag)

So apologies to all the 4wd cars for the wrong results, so my proposal would be either to get back all the 4WD cars & do them again (preferably when I've got the new software 100%) or refund the money to all affected.

Let me know what you think.

Cheers,

Gerry.

SO PLEASE VOTE ABOVE AND SIGN UP BELOW FOR WHICH YOU WOULD PREFER. COPY AND PASTE THE LIST PLEASE.

This will give Gerry a rough idea of the best way forward.

Cheers all,

Brian.

1. Sti-04!! (rerun please) asap though before the modding begins;)

1. Sti-04!! (rerun please) asap though before the modding begins;)
2. wrxmania - RERUN please

Brian :D

Sound fair and that explanation would certainly make sense! Lucky my wee just fully serviced Bimmer was there as a kind of benchmark to get heads scratching!!

Hopefully this will settle alot of worried Scoob owners!!! :)

Anyone who has big enough baws to admit a mistake in public is OK by me. :notworthy Not sure my wee non technical noodle understands any of the explanation though :confused:

Stiks

Good on Gerry for admitting he made a faux pas, well done mate.

If the boys opt for a re-run, I'd like to come along since I missed the one on Saturday?

Cheers

It is certainly a brave thing to do. The Scooby community are an understanding lot (?!?!? :D).

Dastek and Stars rollers may not be as far different as some originally believed?!

Brian ;)

I agree :) It would have been easy for Gerry just to keep quiet or blame it on the weather etc.........Respect :cool:

Andy

THANK GOD ITS NOT ME!!!.....pulled my hair oot all yesterday. I still have to remap as it was running rich but thats more like what i want!!!

RERUN RERUN RERUN!!!!!!!!

Stuart :)

PS I am feeling MUCH better today

Thought u would mate;)

Question - Would this affect the torque figure as well ??

Re-run suits me. :)

Gerry...Top man for letting us know mate.
Very much appreciated. :)

Hee hee...I feel a LOT better today too.

Although...now regretting setting fire to the car and rolling it off a cliff now. :p

Nevermind - at least you have one plus point about it going over a cliff -

It was a wagon - eh Dougster?!?!

Wagons rule (and drop faster over a cliff when on fire).

And another plus point - you will now save a FORTUNE!!!!

Group buy on cliff useage anyone?

Brian :D

Damn, could've put yer fmic to good use too :p

I'll go again:

1. Sti-04!! (rerun please) asap though before the modding begins
2. wrxmania - RERUN please
3. Hugo

Nice of Gerry to be so honest. Learning something as well!

Hugh.

Me too...

1. Sti-04!! (rerun please) asap though before the modding begins
2. wrxmania - RERUN please
3. Hugo
4. kart_man

Thanks Gerry :)

1. Sti-04!! (rerun please) asap though before the modding begins
2. wrxmania - RERUN please
3. Hugo
4. kart_man
5. Johnny50

West Lothian Bukkake probably has a set of Buzz Lightyear wings in his roofbox and would swoop round back onto terra firma.

Nah,

Doubt that - by the time he opened the door the car would have pounded off the ground due to the additional downforce and weight!!!

May be good for track use though if you bolt the box to the boot and make it out of Carbon Fibre?

Brian ;)

I'll maybe run my wagon if there is another day organised.

I will be willing to do it again in the future once everybody has re- run there car from this one.

Nothing to it (Except getting there on time :D). I thought it was going to be a nightmare.

Would be later in the year though.

Thanks Bats - minus the technical stuff the day went well.

Brian :D

1. Sti-04!! (rerun please) asap though before the modding begins
2. wrxmania - RERUN please
3. Hugo
4. kart_man
5. Johnny50
6. sti-zlv(matt) would love a rerun asap

Thats what I call an explanation, top man for being so honest. I supose I could hold my order on a new Evo MR340 until the rerun!

Yeah - hold the order!!!

You should now be hitting 300!!

Brian :D

1. Sti-04!! (rerun please) asap though before the modding begins
2. wrxmania - RERUN please
3. Hugo
4. kart_man
5. Johnny50
6. sti-zlv(matt) would love a rerun asap
7. Spooks - Rerun please

I would just like to say to Gerry that is an amazing thing to do, how generous is that, firstly to look into why we were all moaning and secondly admit " oops my bad ;) " Absolulety top blokes.
Spooks

as i said in johnny's thread.....

:rolleyes: and yet peeps still stood up for them!

1. Sti-04!! (rerun please) asap though before the modding begins
2. wrxmania - RERUN please
3. Hugo
4. kart_man
5. Johnny50
6. sti-zlv(matt) would love a rerun asap
7. Spooks - Rerun please
8. StevoWRXPPP - would love to come if its on a Sunday .. suppose its ££££ for Gerry


If not , then I guess I'll get the next one ..

Steve

Mmmmmmm,

Not sure if "your sort" are welcome at these events?!?

It is only for those with a large post count or SN+ members - not NEWBIES!!!

:razz:

[QUOTE=StevoWRXPPP]1. Sti-04!! (rerun please) asap though before the modding begins
2. wrxmania - RERUN please
3. Hugo
4. kart_man
5. Johnny50
6. sti-zlv(matt) would love a rerun asap
7. Spooks - Rerun please
8. StevoWRXPPP - would love to come if its on a Sunday .. suppose its ££££ for Gerry
9. Simon9 rerun please