Rolling road power figures.

[DaveEFI]

My SD1 is quoted to have 190BHP. What would I expect at the rear wheels? It's a 3 speed auto.

[RoverP6B]

Hello Dave,

If i recall correctly, that power figure is the gross figure with the engine void of all ancillaries.

The P6B had a gross output of 186HP, whilst at the rear wheels running via the 3 speed auto, anywhere from 60HP to say 110HP would be expected. Mine had 93HP, so anywhere between those boundaries.

Ron.

[DaveEFI]

IIRC, they changed the way the factory BHP figures were quoted between the P6 and SD1. IIRC, the carb SD1 was 155BHP - despite better heads etc than the P6.

[Darkspeed]

Typically the TP Vitesse although described as 190BHP seldom did better than 175BHP and more typically 168BHP at the fly - At the wheels through a slush box I would reduce that by 20% so estimate 135BHP ish on a good one.

[DaveEFI]

So 20% is roughly the loss you'd expect at around 5000 rpm? That was the sort of ballpark I was after.

[r2d2hp]

Is it possible to get an accurate reading on an automatic on the rollers. I recall my friends old ford v6 auto and due to the torque converter the figures could only be used as a ref point for before and after comparisons.

[Darkspeed]

20% is very much a glass half full approach to the likely losses especially on a box that has done a few miles.

http://www.carcraft.com/techarticles/cc ... tests.html

[JP.]

Is it possible to get an accurate reading on an automatic on the rollers. I recall my friends old ford v6 auto and due to the torque converter the figures could only be used as a ref point for before and after comparisons.

It is possible but you need the exact specs of the converter and recalculate the numbers. Below stall speed converters almost triple the torque numbers and there's where dyno math goes wrong.
Horsepower = torque x rpm : 5252. As the torque converter by its nature multiplies torque from the engine the math goes woos.

On a non lock up system about 90% is driven energy and 10 % is loss by slip of the converter itself.

In practise without true converter specs, dyno readouts above 3000 rpm on a stock converter can be "pretty" accurate. Below 3000 rpm the torque numbers are worth nothing.

[kiwicar]

Hi
"Horsepower = torque x rpm : 5252. As the torque converter by its nature multiplies torque from the engine the math goes woos. "

Or you just measure the revs at the output of the transmission as well as at the engine and do the calculation of torque times revs for the system using this revs figure to get the power output figure for the engine and transmission. Plot that against the engine revs and save yourself a whole heap of calculations and approximations, which is actually what happens on most rolling road dynos. It has it's own problems because everyone wants as big a number as possible so on the deceleration from the measured run you coast down with the throttle closed to give "losses" and calculate an engine out-put corrected figure. Fundamentally though there is nothing special about a transmission using a dyno with a converter on a rolling road.
Best regards
Mike

[stevieturbo]

My SD1 is quoted to have 190BHP. What would I expect at the rear wheels? It's a 3 speed auto.

Depends on the dyno, the operator, the weather, tyres...etc etc

[kiwicar]

My SD1 is quoted to have 190BHP. What would I expect at the rear wheels? It's a 3 speed auto.

Depends on the dyno, the operator, the weather, tyres...etc etc

how many pints it is since you entered the pub
best regards
Mike

[DaveEFI]

There's surely not that much torque converter action at 5000 odd RPM?

[kiwicar]

Hi
non clutched converter with about 150 bhp at the input on a converter and above stall speed and allowed to "unwind" assuming the converter is intended for the power range and weight of your car it should be designed to give
8 inch converter about 5%-6.5% slip
9" inch about 4%-5.5% slip
10" converter about 3%-4% slip
For small changes in power. . . . as a rough guide,

double the power across the converter and the slip goes up by 40%

half the power the slip goes down by 40% (but don't do this calculation twice because will still slip more than half as much)

The converter on the slingshot (8 inch converter 5200 flash stall) is intended to give 10 to 12% slip as I cross the line full throttle at 7800 revs. . . . well that is what I was recommended to gear it for.
best regards
Mike

[ged]

Also add in the fact that your engine has done 180,000 miles as I seem to remember you stating somewhere.

[DaveEFI]

Also add in the fact that your engine has done 180,000 miles as I seem to remember you stating somewhere.

Yes - it's beginning to loosen up nicely. However, only some bits of it have done that mileage...

It was more of a hypothetical question. Wanting to know what sort of losses there would be through the transmission.