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MG Midget and Sprite Technical - Confused power readings

After having my engine rebuilt and completely balanced, I also have a KN filter and a free flow exhaust I took the car for a dyno check just for fun. They ran the car in 3rd gear and the print out showed the following.

Power 36.3 Kw @ 4818rpm
Torque 1746N @ 2936rpm

When I do the conversion it shows

Power 50hp
Torque 1287 lbs/ft

The horsepower is reasonable if not disappointing after the cost of the rebuild and the 2 minor tweeks.

The Torque is totally confusing so can I assume that the torque calculation downloaded is wrong. What are my readings in old fashioned speak?
Mark Wilson

Using the initial figures, your conversion are right. But the initial figures must be wrong, as you'd be at 719 BHP at 2936 rpm with that torque!!
S Overy

What are the units given for the torque figure as "N" is not a measure of torque.
David Billington

Newton metres?

-:G:-
Gryf Ketcherside

Sounds like the dyno hiccuped when it was taking readings. We canmeasure power against a power absorption unit or against flywheel acceleration(weight of the rollers acting as flywheel) or a combination of both. If the engine hesitates when we are commencing acceleration power testing the power shows a stupid torque spike. If your curves are smooth then the dyno is daft.

Did you pay for tuning or just power run? If just power run how can you be sure your engine is set for best power?

I attach a pic showing two power runs. Although they are near enough identical one run shows massive torque at 1700 rpm. Which is not existant in 'real' life, a hiccup in the system, that is why we do lots and lots of runs to ensure we are measuring the engine power not a ghost.

Peter

Peter Burgess Tuning

Why did they do the runs in 3rd gear?
Daniel Thirteen-Twelve

We used to run mostly third gear runs with our Clayton rolling road, this was mainly the performance envelope of the rollers, 90 mph was about it. Our latest rollers are happy to run to 160 mph. We do the 4th gear or nearest to direct top so we can get realistic coastdown losses to guesstimate flywheel power.

Usually a car will show higher wheel power readings in third gear rather than fourth gear. Some unscrupulous dyno operators do before and after readings in fourth/third to exaggerate gains (if any!).

Peter
Peter Burgess Tuning

Good explanation I think Peter.

As you say rolling road figures can be "fiddled" to suggest all kinds of gains and it is very difficult for the private individual to be sure of the true facts.

Of course it is always best to use the same operator on each ocassion when developing an engine and add ons so that each modification is evaluated correctly.

That simply means that those who visit the rolling road once in a blue moon can only come away knowing their car is set up as well as possible.

Thus that leaves the fact that benefit very often depends upon how well the owner can set up his engine prior to the visit, if he is a good owner then I would assume a very small gain will only be possible, if he is poor then higher gains will be seen.

I once went with a friend to a rolling road session, the engine wasn't too badly set up but the before and after figures were quite massive. The operator did not give the engine "Full throttle" on the first run and so after he tweaked it and did another run this time on full power then a large difference was observed. Pity really because he did not need to fiddle to get good results but fiddle he did! shame!
Robert (Bob) Midget Turbo

Gryf,

If that figure is 1746Nm then it would be in the right ballpark for a NA engine of around 30 litres.
David Billington

Hi team,
Thanks for the feedback and apologies showing appreciation a little late, PC went in for new graphics card.
To answer the question posed by Peter. I have just had the engine totally rebuilt, noticeably more power, goes like a dream. So for interest I took it to a well established tuning centre but looks like the dyno had a glitch. Out of interest 2 days later the half shaft snapped and I reckon it was the dyno test.
Mark Wilson

This thread was discussed between 04/02/2012 and 11/02/2012

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