Rolling Road Setup

[andybj8]

Guys
Had my rolling road yesterday with Peter Baldwin a 68 year old whiz who races Mini Miglias.

While his road is not the newest and shinest, try finding someone who still deals with carbs and knows su's. He had just worked on a multi million pound ferrari last week.

A lotus cortina was before me.

I was not really bothered about the dyno run just trying to get the car set up properly. After spending an hour tuning the carbs and setting the timing / dwell correctly with a Crypton Cruise Mate and checking the individual plugs on the oscilloscope, we went for dyno run floored in 3rd gear, before checking the final mixture settings in 4th gear on the Bear gas analyser.

His dyno measures bhp at the crank, and final reading was 150bhp at 5000rpm, 150 was full scale on the standard setting so we had to go up x2 to double check on the next scale (0-300bhp)

Head has hardened valve seats for unleaded, no bottom work, and still running rebuilt standard 25d6 dizzy.

Readings were:
3.78 c02
2.20 hydrocarbons
1.06 lamba
780 idle speed
30 dwell angle
forgot to verify timing angle (started on 15 degrees)need to check with gun
150 bhp at 50000 rpm in 3rd

she is now running like a swiss watch, except for an extra spring needed to return the throttle shaft and have not got full choke (need to slightly adjust cables)

We had to outrun the rain on way home as she was on the back of a trailer with no hood fitted yet, but the scooby flew!

cheers Andy

 

[HealeyPassion]

Excellent results Andy! Generally our rolling roads (or "dynos" as we call them in the colonies) measure the hp/tq at the rear wheels. If memory serves, solid axle cars are said to loose about 15% of the crank hp to driveline loss (more for independent rear suspensions)... which would mean your car put down about 137.5 HP at the rear wheels. That sounds very strong for a stock engine. The fact that you measured 150 hp at the crank is also surprising since that was the advertised hp!
Excellent!

Thanks for sharing!

I recall Lin Rose shared some dyno numbers for his slightly modified BT7 (the Bloody beast) a while ago... at least a year ago. I think I'll try to find them.

Cheers,
Steve

 

[Genos2]

Andy, how does what appears to look like a chassis dyno,I used to run a Dynojet unit ,measure bhp at the crankshaft(flywheel).Looks like rear wheels are on rollers,am I right? cheers Genos2

 

[andybj8]

Genos

https://www.sun-diagnostics.com/uk/RAM3000.asp

Its a SUN road-a-matic an old explanation (they appear to be part of SNAPON now):
In order to make any sense of rolling road power figures you must measure the rolling losses and add them to the power at the wheels. When you do that you can run in any gear and get the same result on the power graph – almost. Several factors prevent you getting exactly the same result in every gear. First off a lower gear means more torque at the wheels and hence a little more tyre slippage than when you run in a higher gear. The run also takes less time, so the engine accelerates faster and gives you more of a "flash" reading. Our Sun RAM12 rolling road allows you to alter the acceleration rate so that you can adjust it for different power outputs.

The software in our system uses the road speed, measured by the rear roller, to obtain engine rpm in order to scale the power curve. You take an rpm reading at 60 mph and the software works out the revs at any given road speed from there. What this doesn’t take into account is tyre growth. As the revs increase the centrifugal force makes the tyre grow – which alters the gearing slightly, putting the rpm out by a tiny amount.

When you take all these "fudge factors" into account, it’s a wonder the rolling road is as accurate as it is. But it can be accurate, and more importantly, repeatable. With careful setting up of the acceleration rate to match the engine power, and accurate setting of the engine rpm, (dashboard tachometers are often out), you can get a meaningful number from a rolling road. I know that when trying to improve the engine in the Red Shed our rolling road is depressingly accurate enough to give the same power curve time after time – despite my best efforts to increase the power output!

I always call our final figures "simulated" flywheel figures but they are close enough to engine dynamometers judging by the comparisons we have available. Ken Snailham at QED recorded 218 bhp on his dyno and the same engine showed 220 bhp on our rollers. We’ve had similarly close results to the Lotus Service Centre dyno and J.E. Engineering’s dyno. We also see close to factory quoted power outputs - on most standard cars that we have run in the past

cheers Andy