Anders_WR1

iTrader: (8)

I've been investigating a noise from the car and booked the car in to a rolling road today, so I could pin point the sound. I had a power graph done, but the car produced a poor 295bhp and a feeble 255lb/ft.

The car wasn't holding boost well, peaking at around 1.3 BAR for a split second, before falling to just over 1.1 BAR. On the road the car pulls about 1.45 BAR accelerating in fourth through the mid range and tails off to 1.2 BAR at high rpm.

The guy controlling the dyno couldn't explain why I'm seeing a 0.3 BAR boost difference between the road and the dyno. He said a difference of 0.05 BAR between road and dyno could be expected, but no more than that.

The RR was a Dyno Dynamics and it had a decent industrial size fan in front of the car. The ambient temp was about 23 Degrees C. The test was run in fourth gear with the centre diff locked.

The lack of boost will explain the sh1te power figures but can anyone shed any light on difference in boost?

Cheers

Anders

p1mark

Its very common for cars not to achieve boost on the rollers. Have seen it at dyno shoot outs all over the place on dyno dynamics rollers.

Its all to do with how the rollers are loaded, if they dont mirror the load on the road it spools up very different. Then there is the potential heat issue as well that you have noted.

My own car has been on a dyno dynamics 3 times now. First time it was some .3 bar short of what it does on the road (at WRC technologies in 3rd gear which is what dyno dynamics recommend) and twice at G force in Aylesbury.

After some advice from Bob Rawle all the cars on the Gforce days were run in 4th and all were very close to mapped or standard boost, although even then the graphs showed maybe 500 RPM later spool than i achieve on the road.

Rolling road dynos are a pain for accurate and repeatable figures. We dont do any power testing etc at work any more on them and rely on closed cell engine dynos which are far more accurate. the RR's we keep for noise testing etc.

Anders_WR1

iTrader: (8)

It was a waste of 50 notes. The noise I was listening for was hardly audible compared to driving on the road, because of the low boost figures. I noticed the boost was coming in later as well.

So why can't rolling roads be set up to accurately load the car wheels? I asked the guy if more load could be put on, but he said it was on maximum for the dyno plot and any more would stop the car from accelerating?

Anders

TonyBurns

iTrader: (3)

Its probably to do with the PPP and its inbuilt ability to cut back boost when the temps are getting high, hence on the road with a good airflow your getting better boost figures.

Tony