A thought has sprung into my tiny little mind! I know - shock horror

Anyway - there is always lots of debate about rolling road comparisons, especially UK v STi v P1

My question is this - a well respected rolling road man persuaded me that RR results will vary based on the gear ratio being used - and typically cars are tested in 4th gear.

BUT - I suddenly realise - don't the three main categories of car mentioned have very different ratios for 4th and so ENTIRELY negate any real comparison between them, even on the same RR on the same day?

So the only real way to do it would be to get a bunch of volunteers for a BENCH DYNO day - who's up for it - £1,500 per head and it'll only take 6hours per car.....

Rannoch

[This message has been edited by Rannoch (edited 22 August 2000).]

 

Rannoch.

If what you're saying is correct then it is pointless comparing ANY cars with different 4th gear ratios to the Scoob on ANY dyno, which completely defeats the object!
I take it you're still pi55ed off about getting stuffed by the UNICHIP brigade?

Stef.

 

Stef,

contrarily it hadn't even crossed my mind until you mentioned it

However on real world driving it's torque that counts and I think my car is pretty strong in that area - after PS I modified my advance and on the hallowed PS rollers I got around 8ftlb of torque for each degree...

...now how many degrees did I do?

And the result is that I don't need to artificially raise my boost - if I calibrate to Harj's car at PS, my Link would have to be pushing out 1.6 bar, which doesn't seem like a good idea to me - I prefer to reserve my peak boost for dynamic conditions on the road - and the Link lets me do that without having to show off on the rollers

Anyway - your post doesn't answer the question - although the challenge is absolutely spot on!

Rannoch

 

Ay, forget the Unichiper's. At the next PS rolling day, you Scoobs are gonna have to beat REAL POWER.......My Cossie.

And I think we all know who's gonna win that battle!!!!!!

Shaun.

 

The rollers is the ONLY place your heap will ever beat my Scoob you logger!

Stef.

 

I have to second what the Cossy Killer is saying

Harj...

Im up for a Possum Vs my Car

 

Hi David, you are absolutely correct in saying that the gearing of a car cansignificantly affect the rolling road result. UK gearing is consistant, STi has at least two variants (or three as Wagons are a bit different again) and those with centre diffs are yet another scenario.

Try doing back to back runs, one in 4th and one in 3rd ...

Bob

 

Bob,

now the interesting comparison is to whether the shorter gearing of the STi will give and impression of less or more power, therefore dealing with the sometimes closeness of STi v UK cars.

The more obvious of course is how to compare P1 and STi back to back, which is the one people are looking at, as far as I am aware - and I am not sure of this one - P1s have a longer final drive then the STi.

Thanks for bringing us back to the original question

R

 

Put me down for the Bench dyno if im allowed, I only have a 97 WRX which should be 280BHP standard in Jap form.

Harj...

 

Harj,

That's 280 PS you numnuts

The day somebody buys your twisted heap , will be the day you beat my car

Shaun.

 

Cant wait for the next rolling road day

Hopefully Jonathon will be there? in his P1?

Rannoch - we'll have to meet up to compare cars - but then you've only got the standard turbo on

 

Cant wait for the next rolling road day

Hopefully Jonathon will be there? in his P1?

Rannoch - we'll have to meet up to compare cars - but then you've only got the standard turbo on

And what the he*l is flood control - stoppin gme from posting - now I'm getting miffed

 

Don't worry about bigger turbo's, it the gearing you need to alter to get better figs.

 

Steve,

Flood Control stops you posting the same thing twice to stop you looking like a ****. guess it didn't work this time eh?

SimonM

 

From memory PE put in the different gearing for each model to compensate.

I hope to make it to a RR in the near future. Cancelled the S3 today as I couldnt bear to part with the P1

Might have to upgrade it to full WR spec now or order a new STI.

Jonathan

 

SimonM

I only tried to post the once not twice - so your talking bollocks

 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by steve McCulloch:
<B>
I only tried to post the once not twice - so your talking bollocks
[/quote]


Strange how two messages appeared then eh?

SimonM


[This message has been edited by SimonM (edited 23 August 2000).]

 

Jonathan,

glad to see that you are staying within the fold

It would be interesting to see how the gearing compensation works and do they all do it? We wouldn't want there to be any reservations on the back to back test.

It's almost worth converting my car back to standard if we can't find a standard STi

Cheers,

R

 

What would be interesting, would be to get a bunch of us together, and use a "Road Dyno". This would be just as accurate as any RR, and cost us zip.

We would just need to know the various gearings of each car model. Temps, atmosphereic pressure, etc', would be the same. Would be fun anyway, and you can still have your graphs etc'.

Mark.

 

SimonM

I did not post twice! not my problem it appeared twice

Ah whats the point of this idle banter - back to some serious discussion

 

part of the operators job on Rolling Road setup is to enter an rpm figure for the plots to be accurate - this is normally done by running the car to 60mph on the rollers and then recording the tacho reading - this will then make sure that the plots are correct.

vis a vis gearing - what is important is that the power at the wheels figure is not affected - this is what the software will use to back calculate the power at the crank - usually by measuring the resistance to the rollers from the car's transmission on the 'run-down' - some problems can occur when type-r + ra cars with shorter gearing are tested in that the rollers 'slip' and a false reading can result - this is why testers have been known to make someone stand in the boot or get 3 or 4 people to hold the back down - the 70/30 torque split seems to exacerbate this problem too. It may be a better idea to test type Rs in 5th gear - but the figure for rpm at 60 mph would then have to be re-entered of course.

I would expect the transmission loss to be greater the higher the gear selected so the 'hokey' calculation used to assess power at the crank would be less accurate at higher gears - if this innacuracy bothers you, then you are best off going by the power at the wheels figures only - its just that they don't sound as impressive when bragging in the pub ;-)

I do however see no problem in comparing cars tested on the same rig on the same day - but in order for the plots to show the correct rpm against the curve, the correct rmp/60mph figure must be entered for each type of car (uk,sti,wrx,type r, ra, etc.)

paul w

 

All,

Paul is bang on with regards to it not really mattering for power at wheels figures. It is the at crank figures that can be more tricky. More important things can affect the figures such as whether you have any air in your tyres etc.

Not sure about this 60mph/match rpm biz though. At Powerstation the rolling road has an inductive pickup that you clamp onto a HT lead for rpm signal against power at the rollers. I haven't seen a rolling road requiring what Paul talks about.

The gear that is run in (normally 4th) is purely dictated by the need to have a reasonably long run without wheel spinning. Mega powerful cars have to run in 5th to stop them breaking traction.

Cheers

Ian

[This message has been edited by IWatkins (edited 25 August 2000).]