Braked Dyno Operating Procedure

[brumster 135 1 Cars]

So I popped along to Sandwell College today in the rally car to make use of their facilities. Nigel Briscoe, one of the course leaders there, offered the use of their braked dyno to take a simple power run figure on the existing 8v 1.9 and then, when the mi16 is in later in the year, I could return and get another figure - and obviously see the comparison of before and after.

 

Due to my stature (5ft 7) being a bit different to Nigel's (6ft+ !!) and the requirement that competition cars have their seats bolted in, Nigel wasn't able to do the 'driving' so I had to do it myself. We got it set on the rollers then he explained to me how it works - basically the test starts at a set speed (39mph in this instance) so we get moving in 4th, approach the start speed, "boot it" when the test starts. You then feel the dyno brake load up the engine, revs drop as the engine fights the resistance, then we spin up to the redline and at my point of choosing we slip into neutral and let it coast down to determine the losses. Ok, all good.

 

We did a few practise runs but it seemed to brake the engine too much, dropping the engine to a stall a couple of times, and one spurious reading where I don't think I accelerated properly and we ended up with a reading of 182bhp (!!). Either way I did something daft.

 

Anyway, once I'd got the hang of it we did two runs that came up with figures in the 139/141hp region. Obviously bonkers considering this is a standard 1.9 8v lump, albeit blueprinted and built by Skip Brown on a K&N filter with some dizzy and AFM tweaks. We came away with some figures - which for comparative purposes will serve fine - and Nigel believes it's down to the dyno being seriously out of calibration. He says it's always read a bit high on some other cars (95hp for a 90hp standard car, for example) so maybe that's all there is to it.

 

I was just wondering if I was screwing up the technique in some way or had maybe skewed the results by doing something daft...? Flat in 4th at 30mph, why did the dyno brake so much in our early attempts enough to stall the car, considering the car was easily on the torque curve at that point (it's on a 1.6 box with a 4.8 final drive, so it's very short geared).

[Richie-Van-GTi 70 2 Cars]

Im pretty sure the dyno itself has to be set up before hand according to different types of engines etc. I know my mate has rollers at the college he works at and he has to do something with them before he uses them.