Westfield Posted January 10, 2003 Share Posted January 10, 2003 Browsing through some old receipts I have for my car I found two for rolling road sessions. One was when the car was first built in 1990 and gave a BHP of 109 at 6000 RPM and the second in 1997, which gave a figure of 112BHP, no RPM specified. The engine is a 1700 crossflow with a Piper 285 cam, and twin 40 Webers. I know little more for the specification of the engine. Given this was at the wheels, what would that be at the flywheel? Thanks Tony Link to comment Share on other sites More sharing options...
Alex Birtwisle Posted January 10, 2003 Share Posted January 10, 2003 I'm still quite new to all this RR thing so please put me straight if I have misunderstood... When we put S713 UMY on the rolling road (1998 1.8 k-series) she was producing 133bhp at the fly wheel and a smidge over 100 at the wheels (due to transmission loss) ...... so if that is anything to go by you could add about 30bhp to your RR reading. I could be talking out of my 🙆🏻 though ❗ Cheers Alex B S713UMY 1.8K Viper Blue and Black Link to comment Share on other sites More sharing options...
Westfield Posted January 10, 2003 Author Share Posted January 10, 2003 Thanks Alex If that turns out to be the case I will be a very happy man! 😬 140 BHP will suit me fine! Anyone else like to comment? Link to comment Share on other sites More sharing options...
stevefoster Posted January 10, 2003 Share Posted January 10, 2003 Many things affect this. Live axle is less resistive over the De dion. Narrow highly pumped tyres less resisitive over wide ones. Thinner transmission/engine oils. Cold dense air in to the inlet vs warm air. etc etc. The first one having the most affect. I believe the live axle to be around 15-20% loss. Don't know about the De dion but 30% seems high. It's hard to gauge. My 175 bhp at the flywheel De dion VX had the measure of 155bhp at the flywheel XF's on live axles on the track. With losses allowed for you would think there was not much between them. The old HP vs grunt again. Obviously there are many other factors involved too. /Steve My racing pics, 7 DIY, race prep. Updated often here Photo's of the year here Hants (North) and Berkshire Area club site here Link to comment Share on other sites More sharing options...
Nick Woods Posted January 10, 2003 Share Posted January 10, 2003 There was a huge thread about the accuracy and consistency of rolling roads and whether it was possible to calculate flywheel bhp using them. I cant find it at the moment because the search keeps timing out but I'm pretty sure the gist of it was that RR's are only useful for relative comparisons before and after a change to the engine and only then if the time between the two runs is kept short Nick P8MRA - bent 1.6K supersport which is nearly back on the road now Edited by - Nick Woods on 10 Jan 2003 13:56:24 Link to comment Share on other sites More sharing options...
Nick Woods Posted January 10, 2003 Share Posted January 10, 2003 I think it was this thread here, including a memorable quote from Roger King :- If you stop for a cup of tea on the rollers and then do another power run on the same settings, you will often see an improvement of 5bhp. This is simply due to temperatures cooling off Nick P8MRA - bent 1.6K supersport which is nearly back on the road now Edited by - Nick Woods on 10 Jan 2003 13:56:50 Link to comment Share on other sites More sharing options...
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