bhp per tonne

[californiacuda]

The Noble info provided by THATPHILBRETGUY got my thinking about power to weight. The Noble car listed, is at 430 bhp tonne( the English way of spelling, how sophisticated am I). A few other cars of interest-the Ultimate SSC Aero that recently tried to set a speed record is 963, 94 Maclaren F1 550, Veyron 529, Hennessey Viper Venon TT 643, Ultima GTR 720 650.

The Ford Gt (550 hp and 3400lbs) is 324. bhp tonne. But the GT hp is under rated. So, if you take say 530 wheel hp and multiply by 15% for drive train loss = 610, that gives 360. With the Whipple and say 725 whp X 1.15= 834 flywheel hp giving 492 bhp tonne. Using Torrie's car with a stock block and a 1000 wheel hp X 1.15 = 1150 flywheel hp and 678 bhp tonne. And last but not least Joe's car at say 1250 whp X 1.15 = 1438 flywheel hp and 848 bhp per tonne.

This analysis is not the end all be all, but one of many ways to look at performance and to compare different vehicles.

 

[ThatPhilBrettGuy]

My Noble has I flywheel power of 506bhp so @ 1070KG's that's 473bhp/tonne more or less. But, that's not the whole story.

The Noble is really good at getting the power down. There's very little turbo lag, and the torque is basically a flat line @ 430ft/lbs from low down (I'll dig out the curves) until over 6,000rpm. So it's really easy to drive. Some of the cars I see with massive power outputs have horrid torque curves, so whilst the numbers may be big, I bet it's a PITA to drive.

But, the Noble has the aero of a brick. So, over about 130mph I'd expect the GT to walk away. That said, with that sort of power it still hits the limiter in 6th at a GPS verified 180mph. Also at that speed it's out the back of the power band so if I changed the gearing.....

 

[911teo]

On paper 2 cars with equal power to weight ratio should have similar performance.

But the reality is a lot different.

For example I would bet my house the GT walks away from the Noble past 100mph. Once the car gets rolling the power to weight ratio becomes less important when comparing acceleration and speed. It becomes a HP vs Drag race. And the GT is more powerful and has less drag...

But this is only one side of the story...

In any other performance comparison you want to take the lighter car. A lighter car will be easier on tires, brakes and any other component. It will change direction much more quickly. And the weight transfers (lateral and longitudinal) will have less impact on the balance of the car.

So the GT will smoke the Noble in a straight line speed contest but I am sure on a race track the Noble will walk away.

On the street is all a different matter. I will say that gearing (which in theory it has nothing to do with how well a car should do) has a big impact.

As PhilBrett noted above sometimes it does not matter if you are putting down 600hp if the torque curve is very steep. Evem with a short gear ratio transmission you will always lose out to a torque monster with long gears.

The GT is the perfect street car... even in stock form it is basically the ultimate weapon. No shift to 60... 100mph in 2nd... 150 in 3rd... Basically you are always in 2nd-3rd gear.