kbannon wrote: I had my old 320i on the rolling road in Enfield a few years back. Apart from a K&N panel filter the car was pretty much standard. It did However, need a good service. Factory bhp is 129, I got 128!

Hmmm, sounds like a dodgy rolling-road to me!

I've had my '94 standard E36 M3 done last year before i got an exhaust on it Dave, and it was spot on too  (285.??? can't remember )

Dave I've heard that some rolling roads are a bit dodgy but good ones will give accurate readings. The thing is the temperature and atmospheric pressure on the day of the test.

I know airplane manufacturers use a thing called the International Standard Day for quoting performance figures. Can't remember exactly but it's like 18 degrees C and 1013 pressure. So if they say their engine puts out 150HP at 2600rpm it will be exactly that in those conditions. Higher temp and lower pressure will reduce horse power but lower temp and higher pressure will increase horse power. Maybe it's the same for car manufacturers.

flyingalexf68 wrote:  Higher temp and lower pressure will reduce horse power but lower temp and higher pressure will increase horse power.

So what we need - if we want a graph showing wonderful BHP figures - is to find a rolling-road located in a very deep cave?

thepits wrote: flyingalexf68 wrote:  Higher temp and lower pressure will reduce horse power but lower temp and higher pressure will increase horse power. So what we need - if we want a graph showing wonderful BHP figures - is to find a rolling-road located in a very deep cave?

Yes. If you can't find one in a cave try go to one when the pressure is high (watch the weather forcast). Also this time of year is the best, ie cold.

I can help on the new M6 in this respect....

BMW quote 507bhp....yet a hell of lot of rolling roads are quoting stock output of 530-535bhp. 

Understatement.  Now thats cool.

On the other hand I know of someone who bought an E46 M3 Coupe and its 343bhp was actually 323bhp when they had it tested (they had suspicions something was wrong).

Then there is the Audi S4 owner with his 344bhp car...that was putting out 306bhp!!!!!

Most of the time they're accurate, but the definitely lose power with age unless you keep on top of them. 

My 6 came out at 339bhp as opposed to its 333bhp quoted - and I don't think I'll bother complaining about that - but they reckon its because I run it on V-Power (or formerly Optimax) - so it proves it works.

flyingalexf68 wrote: Dave I've heard that some rolling roads are a bit dodgy but good ones will give accurate readings. The thing is the temperature and atmospheric pressure on the day of the test. I know airplane manufacturers use a thing called the International Standard Day for quoting performance figures. Can't remember exactly but it's like 18 degrees C and 1013 pressure. So if they say their engine puts out 150HP at 2600rpm it will be exactly that in those conditions. Higher temp and lower pressure will reduce horse power but lower temp and higher pressure will increase horse power. Maybe it's the same for car manufacturers.

Any decent rolling road should correct the figures for pressure and temperature. I have a link somewhere that explains...

Edit: here you go:

http://www.dynamometer.fsnet.co.uk/automotive-dyno-correction-factors.htm - http://www.dynamometer.fsnet.co.uk/automotive-dyno-correctio n-factors.htm

Thats useful to know Peter. Nice one.

Dave, where are you going to get it tested? I want to get mine done soon too. And I guess you'll have to make sure they have a good rolling road with all the above corrections.

276 bhp for mine (standard apart from a k&n panel and always ran on optimax/v-power) on Falkland Performance dyno, Alpina says 280 bhp

My old e46 323ci got 191 bhp, book figure was 170, something wrong methinks

funnily enough that's what the man said at the time (same rolling road)

thepits wrote: kbannon wrote: I had my old 320i on the rolling road in Enfield a few years back. Apart from a K&N panel filter the car was pretty much standard. It did However, need a good service. Factory bhp is 129, I got 128! Hmmm, sounds like a dodgy rolling-road to me!

Westward Engineering, Its probably the most accurate rolling road in Ireland and the UK.

Hmmm interesting post. 

BMW quote the engine BHP which is (and I stand to be corrected) crankshaft BHP and not the BHP produced at the wheel which my understanding is what rolling roads measure.

So if you guys are measuring BHP on a rolling road you are measuring the BHP produced at the wheel, aren't you?

What my question is, how do rolling roads work back from wheel BHP to engine BHP?

Andrew

US M3 wrote: thepits wrote: kbannon wrote: I had my old 320i on the rolling road in Enfield a few years back. Apart from a K&N panel filter the car was pretty much standard. It did However, need a good service. Factory bhp is 129, I got 128! Hmmm, sounds like a dodgy rolling-road to me! Westward Engineering, Its probably the most accurate rolling road in Ireland and the UK.

That's quite a claim!

I think what they do is test on the wheel under power, then measure drivetrain losses with wheels turning but with no engine engaged, and extrapolate from there. I'm sure someone with more familiarity in the systems can tidy that explanation up a bit!!

the E46 M3 has a sissy fit on a rolling road unless its a 4 wheel one with the front rollers matching the speed of the rears. Otherwise the engine management detects a speed diff between the front and the rear and restricts output somewhat. I've seen 2 E46s and same thing on both: run up to 320-odd bhp and then nowt more

http://www.dynamometer.fsnet.co.uk/power-losses-flywheel-BHP.htm - http://www.dynamometer.fsnet.co.uk/power-losses-flywheel-BHP .htm

From the site previously given explains how flywheel is derived from road wheel figures.

Killian I am still enjoying that 127bhp you had measured on the 320

i used the lads in ashford or rathnew with the mazda and it was one little horse down on the manufc rating. from 110hp to 109hp at the wheels.

i did trust them but it was a strange feeling knowing that someone else is ragging your baby.

trackdayperformance i think was the name.

thanks TJ that explains it.

Andrew

I had mine in westward too, 288.7 bhp with a K&N panel filter, so imo its accurate.

Evo magazine has taken to RR the cars its tests and quotes the rr power alonside the quoted power iirc the tvr tuscan covertable was way off, as in less.

Don't forget that other way to increase efective horsepower

Weight

If a 1200kg car has 240bhp (5kg per bhp) throwing out your 80kg passenger is worth 16bph

At the track days, some might have noticed people evicting spare wheels, tools etc. to improve power to weight ratio

Daveco wrote: Lads had my '04 325 tested on Friday in Xtreme Autos Waterford-Came in at 200.3bhp! This was in 4th gear at 115mph. Torque also came in at 183lb ft, 3 above what BMW say. The guy who did the test said if he ran it in fifth he could have got up to 204-5hp but I didn't want to push it. The 325 is running on standard fuel with no mods. Pretty chuffed!

very few cars will hit the rev-limiter in fifth, it depends if fifth is a direct top gear or an overdrive, if it's an overdrive then i don't think there would be no point in changing up since maximum power is achieved in fourth, if it's direct then he should have changed up

Hi Stephen

On a road most cars will not hit max revs in fifth due to weight drag etc.

These do not apply on a rolling road so an indicated speed higher than what could ever be got in real life should be possible.

Maybe there is a limit to the maximum roller speed on rolling roads.

Theoretically, should maximum power be measureable in all gears, or is this another limitation of rolling roads rather than the car

I stand corrected, thanks Gerard

Will a 325 do 155mph? If so it will hit the limiter. My old 2.2 Z3 happily hit the rev limiter in 5th gear on the (empty) road. 139mph and still charging hard. It needed another gear.

Thats a very good result Dave. You can be sure your car is running right anyway. See you at the next track day no doubt.

Daveco wrote: Thought so too...In fact why stop at a GTi?? Clearly in 911 territory now!

Steady on there now. 911? Boxster territory maybe.

Hi Alex I was surprised to hear of a road car hitting the limiter in 5th. So I calculated 139mph back to revs using rolling circumference of tyre, 5th gear ratio and final drive ratio. I got  6550rpm which I guess would be pretty close the expected limiter value of Z3

In this economy/enviromentally friendly era, it is rare to come across such a designed for performance set of gear ratios with the added bonus of a direct (1:1 ratio) top gear.

Such design detail is one of the reasons we love BMWs

Evo Magazine had a run-in MkV GTi on the rolling road for fuel testing, and stock it was putting out well in excess of the rated 200bhp (I can't remember the actual figure).

Even if it was stock, the GTi has 144bhp/ton vs your 141bhp/ton. You'd have marginally better traction, but to be fair between both drivers a rolling start is what I'd use, which'd negate the traction issue.  

My money would be on the Golf.

have a look at http://www.fastsaloons.com - www.fastsaloons.com , they have a "compare and race" section where you can "race" various cars 0-60 and compare full tech specs and performance info

flyingalexf68 wrote: I know airplane manufacturers use a thing called the International Standard Day for quoting performance figures. Can't remember exactly but it's like 18 degrees C and 1013 pressure.

1013 Pa is standard atmospheric pressure it equals 1 bar

T.J. wrote: Evo Magazine had a run-in MkV GTi on the rolling road for fuel testing, and stock it was putting out well in excess of the rated 200bhp (I can't remember the actual figure). Even if it was stock, the GTi has 144bhp/ton vs your 141bhp/ton. You'd have marginally better traction, but to be fair between both drivers a rolling start is what I'd use, which'd negate the traction issue.   My money would be on the Golf.

I think Evo's Golf was running 210 bhp on Shell Optimax and closer to 220bhp on 105 Octane race fuel.  

Dave

The handbook with my 330 is actually for the 323, 328, etc.  It does have standing km times in (but not terminal speed).  I made a note of the times for you but left the piece of paper at home.  From memory a 328 was in the region of 30-32 secs.  I'd imagine that your 325 would be close but maybe slightly slower than a 328 (you've got the same power, but I think the 325 torque is slightly lower).

Just got a second look at the handbook.  Standing km time for the e46 328Ci is down as 27.0, the 323Ci is 28.9.  So much for my memory!