On the rollers!

**Geir** · 28 December 2005, 15:23

The braking should be done in the gear that is closest to 1:1 so i believe thats in 5 gear for your car .

**stevieyid** · 28 December 2005, 19:05

So with that being taken in 5th gear what do u reckon my top speed would be? Must at least 160? what do u think?

**Geir** · 28 December 2005, 19:22

something around 160-165 should be in range (i have heard of 280 hp cars that have done 280km/h (175 ) but i dont think that is 100 % correct , maybe the speedo was showing 280.

**topsparky** · 29 December 2005, 19:23

Originally posted by Geir

something around 160-165 should be in range (i have heard of 280 hp cars that have done 280km/h (175 ) but i dont think that is 100 % correct , maybe the speedo was showing 280.

had mine off the clock when she was over boosting because of split diaphram
aby 6 speeder

**stevieyid** · 15 January 2006, 01:27

Just been looking through some other dyno graphs and came acorss an s3's graph. He only lost 46hp from the flywheel to the wheels but i lose about 90. Why do u think this is? Also im going to get my exhaust fitted in a a couple of weeks and my graph was done when i had collapsed a cat, do u think the new exhaust will get me nearer 290 and more torque? cheers

**S2central.net** · 15 January 2006, 16:12

Originally posted by Mikes2

Something not right with that graph. Power and torque should always cross at 5200 rpm

They should cross at 5252rpm for bhp and lbft - different measurement units will have a different crossover point.

The 5252 figure comes from 33,000 divided by 2 * Pi ......... Don't ask !

Paul

**S2central.net** · 15 January 2006, 16:21

The rule of thumb for quattro transmission loss is 25% but it's not an exact science.

Also its not appropriate to compare tranny loss to an S3 - they have a totally different 4WD system (Haldex) than our quattro (Torsen).

A better flowing exhaust should indeed release some more power - turbos hate any form of restriction in the exhaust.

AFAIK - most of the roller runs I've seen done before are in 4th gear. Collectively we should be able to compare transmission losses.

However - never forget the really important number is the one at the wheels - its the only one they can actually measure. When I dyno'd my S2 at 280bhp it was 210bhp at the wheels - that was done in 4th... And so my 70bhp 'lost' was bang on the nominal 25% expected pain.

Paul

**dan_b** · 15 January 2006, 20:13

Originally posted by Geir

something around 160-165 should be in range (i have heard of 280 hp cars that have done 280km/h (175 ) but i dont think that is 100 % correct , maybe the speedo was showing 280.

But on a rolling road, there is no air resistance for the car to overcome, so wheel speed can surely attain a higher indicated speed on the rollers with the same engine power as what you could ever see on the road?

**S2central.net** · 16 January 2006, 08:26

Gotta agree with Dan's musings on this one......

At high speeds there are significant aerodynamic losses. A quick google should find lots of info on the subject. I have some calculations for this stuff to help estimate things like maximum velocity for a car weighing 'N' kg with 'X' amount of power and an aero efficiency of 'E'. Estimations for frontal surface area are required from memory.

Its all in a spreadsheet somewhere.....

Paul

Paul

On the rollers!

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