How many powers is norm?

[vipergts]

Had my old 3.8 donkey set up today on a rolling road

208 BHP and 247 lbs torque

Is this normal...good...bad?

[Heuer]

At the wheels or corrected at the flywheel? If at wheels add 18-20% transmission losses = 250bhp and 296 lb/ft at best. Jaguar quoted 265bhp and 260 lbs. Not bad at all. If the figures are already corrected for transmission losses then not good at all!

[christopher storey]

True, David, but the Jaguar figures were gross bhp ( and therefore gross torque ) to the old SAE standard i.e. not installed in the car, without filtration , dynamo etc . If those are at the wheels figures they are splendid, particularly if they are the DIN breed of horses . However, IMHO since rolling roads are notoriously inaccurate in the setup, they are better regarded as a means of tuning the car up to its best potential rather than taking the figures for comparative purposes against other cars done on other rolling roads

[PeterCrespin]

True, David, but the Jaguar figures were gross bhp ( and therefore gross torque ) to the old SAE standard i.e. not installed in the car, without filtration , dynamo etc . If those are at the wheels figures they are splendid, particularly if they are the DIN breed of horses . However, IMHO since rolling roads are notoriously inaccurate in the setup, they are better regarded as a means of tuning the car up to its best potential rather than taking the figures for comparative purposes against other cars done on other rolling roads

Agree with Chris. As a ballpark number it's pretty healthy. Torque is what they measure. Gee gees can only be calculated, not measured.

[vipergts]

Figures quoted as at flywheel.

I was quite pleased with the torque and as stated this is what counts.

Car feels quick enough

[Heuer]

If at flywheel then theoretically the car is down on power, at least compared to the figures Jaguar quoted. But as Christopher says their figures were gross so you can add 10% for the exhaust system (unless it is already straight through) and 6% for the air filter (unless you are using an after-market foam one). For comparison my car has been measured several times on both rolling road and on-road dyno - it consistently comes out at 280bhp and 340 lb/ft. This is with straight through exhaust, ITG Maxogen filter, EDIS/Megajolt, 9.5:1 head and higher lift cams. And, yes, it is very quick.

Torque is King on the road. As my Dad used to explain it to me "Horsepower is how fast a boxer can punch, torque is how HARD he punches".

[christopher storey]

It would be interesting to see the shape of the torque curve. Incidentally, the first thing I always check with rolling road figures is that the power and the torque figures are exactly the same at 5252 rpm . If they are not, then the calculations ( and indeed the measurement ) are suspect

[PeterCrespin]

.. the first thing I always check with rolling road figures is that the power and the torque figures are exactly the same at 5252 rpm . If they are not, then the calculations ( and indeed the measurement ) are suspect

True, but not always, as that only applies when using hp and ft-lbs, which we do here of course. Once you stray into DIN/metric it gets sticky comparing old plots with new.

[Heuer]

My car's readings 'at the wheels':


We never took the revs beyond 5,000 but you can see the two would be coming together at that point.

[vipergts]

[Dave K]

I posted mine before but for comparison:

Corrected power 222 BHP
Engine power 226 BHP
Wheel power 177 BHP
Drag power 49 BHP

Torque 249

Dave

[Heuer]

Lee

Your torque curve is far smoother than mine because you have standard cams. Just shows Jaguar knew what they were doing on producing a drivable car.

[vipergts]

Yes David.

The car runs really well...smooth with no flat spots as the graph confirms

Noisy bugger though under full chat with foam ITG and mild steel system minus rear boxes.

Smelly car though.....sitting here now and my globber stinks of old donkeys

Or could that just be my natural aroma??