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Re: Engine Power Measured at the Wheels?

Hi - the ones I have seen were 'at the wheels' - but either would interesting... Colin

Re: Engine Power Measured at the Wheels?

The power loss in the drivetrain is very variable but the figures I have seen are in the region of 15% to 20%. I think some modern designs can improve on this quite a lot. With old worn gears and loose bearings the losses will increase considerably.
The only two figures for power output I have seen are for tuned supercharged engines. Measured at the flywheel on a dyno they were 70bhp and 90bhp. ie VERY non-standard!!

Re: Engine Power Measured at the Wheels?

Hi - I was also thinking that the engine might not be putting out quite as much as we might hope. Being aware of this might then prompt a review of the state of items that might make a difference - especially ignition components - Colin

Re: Engine Power Measured at the Wheels?

Having spent many years on dynos with my other cars the only advice I can give is if you are trying to arrive at a combined comparison, then have a dyno day at a local tuner, that way you are all being measured on the same rollers. The power output is so low a few % could be dramatic across different sets of dynos. They all read different levels in my experience. Measuring both at the flywheel and the wheels will give you a good power loss figure and give you scope for improvement. Likewise ignition and exhaust setups will make a difference. Merry Xmas everyone. James

Location: West Sussex

Re: Engine Power Measured at the Wheels?

Dyno's are notoriously inaccurate and many quoted figures need to be taken with more than a pinch of salt.
The only one I have ever used was Stuart Rolt's, which was an old Froude that had been used to test many known engines over the years. My Shorrock blown Austin 7 engine produced 32.5 bhp at 5000rpm (a boost of 5psi) which I think was very accurate
The benefit of a dyno is really to look at how changes affect the power output rather than the output per se.
I have a nice long 1 in 4 hill nearby that steepens to 1 in 3 which is useful for testing power output!

Re: Engine Power Measured at the Wheels?

I agree with that Malcolm. There's nothing like driving over a known course to test the power output or lack of it. The Austin is capable of huge differences in performance for very small alterations to set up. The power output is very academic. The brakes may not be considered very good but they can certainly slow you down if they have a problem!!

Re: Engine Power Measured at the Wheels?

Hi - I agree that the power output number is academic, but not the power output itself! As mentioned,I have used performance on a local hill to check that my Ruby seems right, but how would I know if it has always been low on power? I tend not to want to test it by seeing how fast it can go flat out! I agree that binding brakes can make a significant difference - but this can be checked by touching the wheel centre after a run to see if they are getting unexpectedly hot? Regards, Colin

Re: Engine Power Measured at the Wheels?

I would have thought for std cars the flat out test on a still day with flat road is as good a yard stick as any. A Ruby flat out will only be running a little over 3500 RPM, perhaps 4000 for a really good one, so not too much risk unless you are going to ask it to do this all day every day!
As stated earlier dynos are hopeless for comparisons unless everything is tested on the same machine. One of my cars produced 35 BHP on one dyno, then with further modifications and significantly reduced lap times produced only 30 BHP on another....nuff said!

Location: NZ

Re: Engine Power Measured at the Wheels?

If you intend developing an engine over time or wish to compare different engines the key is to always use the same dyno. I'm presuming most will use a chassis dyno.
If its an inertia type make sure it has atmospheric compensation, most do. Brake types with load cells should be recalibrated but many are not.
Never try to compare inertia with brake type figures if you happen to have used both types for the same car. If you are setting up an engine and wishing to make adjustments over time and forced to use different dynos you can only work on before and after runs on the day to guage improvements.

Paul N-M

Location: Midlothian

Re: Engine Power Measured at the Wheels?

Over many years of racing I have learned many things from dyno testing

It not only comes down to the type of Dyno but the operator as well. I've seen several people standing and looking on. The operator would run the engine up and then bang the throttle asking even "What did you see?" and average the lot

We consistently beat people that calmed far more HP than we ever did.

The higher one tunes the more a dyno becomes necessary. Compression, timing, carb jetting can make the moment between power and burning a hole in the piston.

I would always use a dyno to develop an engine model along with the flow bench.

I almost always found that after than keeping a close look at the spark plugs at the track was needed to correct for weather changes.

On or off the dyno and racetrack Plug checking is VERY IMPORTANT .... With a lot of timing, compression, and very lean carb settings you need to watch for the dreaded black flecks on the porcelain and cement boiling out of the tip. Then depending on the competition level back off or just leave it on "KILL"

Lastly, Most drivers confuse torque for HP since that is what kicks you in your seat.

A very Merry Christmas to you all from The Eastern Front

Location: Poland

Re: Engine Power Measured at the Wheels?

Having tested many large diesel engines, up to 20,000 BHP, engines on mainly 50 year old Heenan & Froude dynamometers we had to be able to provide a calibration certificate for the dynamometer. Essential if the power and fuel consumption figures were to mean anything. A purpose made lever was bolted to the dynamometer and loaded with calibrated weights, it is also important to check the calibration in both the increasing load and decreasing load as any discrepancy indicates a problem in the trunnion bearings. With these dynamometers you could run the engine at any steady power within their range for as long as was required, provided the dynamometer & engine cooling systems could cope. We had one customer who wanted a 168 hour non stop endurance test at full power under the ambient conditions found in the Middle East.