Another Rolling Road Session, Turbo time

[nfcf]

IMO you cannot directly compare between different RR on different days.

There is a few percent error, and some sites are suspected of being overly optimistic, others less so. It is far easier to tell people what they want to hear. Happy customers come back eh?

Most k20 Atoms seem make around the published figures.

The Nomads are either held back by tyres and / or the k24. We have not yet seen a k24 Atom or Nomad make the published figures, but we have only tested 2 (1 Nomad 1 Atom). Hopefully Karl and Phil will confirm that they do usually too.

I had my Nomad on the dyno with the same 50/50 tyres Karl uses and it made 285bhp. I was there with a couple different makes of car which made around there factory figures so the dyno was probably fairly realistic.

[Peter255]

[mention]nfcf[/mention]

Thanks for that.

Whats the factory spec for a charged Nomad? Is it 290bhp (from memory) or was it 300bhp?

[phil4]

I think they call the SC'd ones Nomad 300, implying 300bhp, but I think it's actually more like 280... which sort of ties in with the above.

[Toilet Duck]

TDI (Torque Developments International, not TDI North) use a hub mounted dyno for all tuning work (they mapped my atom in its most recent tune). They are based just outside the M25 near the Dartford Crossing. Maybe do a dyno day there sometime in the future? Their figures are very accurate.

[Anon]

TDI (Torque Developments International, not TDI North) use a hub mounted dyno for all tuning work (they mapped my atom in its most recent tune). They are based just outside the M25 near the Dartford Crossing. Maybe do a dyno day there sometime in the future? Their figures are very accurate.

Yes I think the rolling roads lose a lot of power due to lack of grip. I am keen to try my car on a hub. Some say...you get another 20% more power from a hub.

[Toilet Duck]

Yes I think the rolling roads lose a lot of power due to lack of grip. I am keen to try my car on a hub. Some say...you get another 20% more power from a hub.

No, you don't get any "more" bhp on a hub mounted dyno, you simply get a much, much more accurate result as it doesn't rely on jiggery pokery "calculations" that a traditional dyno (with rollers) has to use to work out the headline figures.

You might actually end up with "less" relative to the often over optimistic figures calculated by certain dyno operator's. Its all relative, but a hub mounted dyno is simply more accurate (and massively more expensive).

[Anon]

Not convinced you would end up with less. Pretty much everyone that does hub dynos report a larger bhp number - but this does not mean you will get that to the wheels. A hub dyno from what I understand removes the wheels so you are effectively removing the inefficiency when measuring the power and this (from what I read read and been told) leads to easier and more accurate tuning. I say this having never used a hub dyno before but going on what hub dyno folks are saying and what my tuner has told me.

I found this video quite informative:

[Toilet Duck]

If you are comparing the results of a hub mounted dyno to a "rollers" dyno, then of course you can end up with less (or more). If you go on an "overly optimistic" roller dyno and then straight on a hub dyno, the (much more accurate) hub dyno will show "less" simply because its far more accurate. Likewise if you go on a "pessimistic" roller dyno then straight on a hub mounted dyno it will read more, again simply because it is more accurate. It's not rocket science, it's all relative. If the hub mounted dyno was set up by a spastic then that will be out, but all things being equal the hub mounted dyno is far more accurate than roller dynos, that's all I'm saying, nothing more nothing less. Comparing results on different dynos on different days is, to a large degree, pointless.

There is a reason hub mounted dynos cost so much, one of them is the accuracy.

You said above that you'd heard you get "another" 20% more on a hub dyno. That would mean if your car got 350bhp on a roller dyno you'd get 420bhp on a hub dyno, that ridiculous.

The best thing about dyno days is that it gives a comparison between a number of atoms (or whatever cars are running) on the same day on the same dyno. Whether you get 300bhp or 3000000bhp isn't (in my humble opinion) the point, its just to see how your car performs RELATIVE to others. What would pique my interest is if one supposed 350bhp atom makes the 350 and another makes 320 then I'd want to know why the difference.

As an aside, what a quick dyno run won't do is show you what the power output is after 20mins of hard track use when everything is hot and IAT's have a chance to rise etc. A dyno run might show XXXbhp on a couple of pulls, but in reality you might have "only" YYYbhp when your out on track on a hot day driving very hard for an extended period.

[robfitz]

It would be interesting to do multiple runs and see how much of a degradation you get as it gets hot.

I intend to go back to the one where my K20 Elise was mapped and do a comparison for my own interest.

[Anon]

Watch the video, it is quite interesting if you have not already there are many like it as well all saying the same. Seems this is the general consensus. The 20% remark is just a joke what people say please don't take it literally. In most cases a roller dyno will under read power because you lose traction and the rear end is strapped too hard. On my car they found it hard to get traction. Re heat soak, totally, this is one thing that concerns me on track actually that as you say you will not see on a dyno. And my car gets hot.

It would be fun to find a hub dyno and try it on there to see the results.

[Anon]

It would be interesting to do multiple runs and see how much of a degradation you get as it gets hot.

I intend to go back to the one where my K20 Elise was mapped and do a comparison for my own interest.

Most shops want to take reading when the engine is not piping hot under load for extended periods of time though.

[Karl V]

Ok, I MAY be tempted to put a bit more air in my tyres for this, but I'm not dressing up.

If I give the car a clean, do you think that will help? I swear I get 50+ more HP when the car is clean. The golfers at Walton Golf Club seem to agree as I fly by.

Anyway... Bump on this thread...

[Anon]

There was a chap on the facebook forum who had a problem with his 4 not getting above 4500 rpm - was it Dean - can't remember. Anyway just a heads up may want to check with the Surrey rolling road if they have seen anything like this before. Would be disappointing getting there and not getting a proper reading.

Karl, not sure if you are joking re: tyre pressures, but they normally mess around with tyre pressures especially if they struggle to get traction like they did in my case. Make sure you don't have any melted rubber from all those slides as well as this affects the grip.

[Peter255]

There was a chap on the facebook forum who had a problem with his 4 not getting above 4500 rpm - was it Dean - can't remember. Anyway just a heads up may want to check with the Surrey rolling road if they have seen anything like this before. Would be disappointing getting there and not getting a proper reading.

Steve from Ariel assures me it will work unless you have sequential.

[phil4]

There was a chap on the facebook forum who had a problem with his 4 not getting above 4500 rpm - was it Dean - can't remember. Anyway just a heads up may want to check with the Surrey rolling road if they have seen anything like this before. Would be disappointing getting there and not getting a proper reading.

Steve from Ariel assures me it will work unless you have sequential.

If it's anything like the old atom, it might have a "static" rev limit of 4-4.5K.... but that's for when the wheels aren't moving. As far as the car is concerned it's moving when on a rolling road, so no such issue. Unless it's broken.