Rally2 (ex-R5) News

[stefanvv]

What is given by the rules is rpm limiter at 7500 rpm.

do You know why such rule exists?

[stefanvv]

No, I may have written that in a confusing way. The top speed may be wherever on the curve but it can hardly happen that the power on rpm limiter is so small that it's can't be reached on top gear What is given by the rules is rpm limiter at 7500 rpm.

Now I am confused. The original post made more sense to me, considering You meant by the power - bhp, but not torque and there is actually someone who really believes the top speed depends on the power?!?

[Mirek]

Of course the top speed depends on the power if it's not limited by the gearing. Nearly every stock car under let's say 200 Hp is limited by power on it's top speed and You can reach higher speed driving downhill or with a wind from behind. Speaking about torque when considering top speed is very missleading and can be considered even irrelevant as torque values transform through gears while power not.

Torque is a lot harder to understand because there is no direct dependence between torque and performance. Without knowledge of the whole curve and the gearing You can't say anything about the car while the peak power says quite a lot. When driven on straight diesel car and petrol naturally aspirated car both with 200 Hp will accelerate same way (when they have same weight) while when You do the same comparison with diesel car with 300 Nm and petrol naturally aspirated car with 300 Nm the later would be a lot faster and most likely have even higher top speed. The reason is that it must have a lot higher power.

do You know why such rule exists?

Most likely to keep reasonable durability and reliability. It's same for WRC cars.

[stefanvv]

Of course the top speed depends on the power if it's not limited by the gearing. Nearly every stock car under let's say 200 Hp is limited by power on it's top speed and You can reach higher speed driving downhill or with a wind from behind. Speaking about torque when considering top speed is very missleading and can be considered even irrelevant as torque values transform through gears while power not.

Torque is a lot harder to understand because there is no direct dependence between torque and performance. Without knowledge of the whole curve and the gearing You can't say anything about the car while the peak power says quite a lot. When driven on straight diesel car and petrol naturally aspirated car both with 200 Hp will accelerate same way (when they have same weight) while when You do the same comparison with diesel car with 300 Nm and petrol naturally aspirated car with 300 Nm the later would be a lot faster and most likely have even higher top speed. The reason is that it must have a lot higher power.

Yes I know at some point the power will have influence on the top speed, but that seems irrelevant with the current WRC/R5 cars considering the dyno curves and limited RPM to 7500. In my understanding power overcomes the friction forces of the tyres with road, various bearings and stuff, which increase as the speed also increase, while torque is more relevant to the traction, as on low speed and cornering, thus torque is irrelevant at these high speeds, and seems this engine is well optimised about these figures. Anyway diesel car with same power probably would accelerate faster at low RPM as it would have higher torque, but that's just for a short period of time.

[stefanvv]

Most likely to keep reasonable durability and reliability. It's same for WRC cars.

Hmm interesting, In f1 there are no such restrictions I believe, at least while I was still following it, and that was long time ago. AFAIR back then Ford 8-cyl Ford engines reached the cosmic 18K RPM, now they could be above 20K, I'm not aware. But of course these are N/A engines, as turbo were forbidden soon after introduced in 70's. Were the same RPM restrictions applied also for the N/A S2000 cars?

[makinen_fan]

Hmm interesting, In f1 there are no such restrictions I believe, at least while I was still following it, and that was long time ago. AFAIR back then Ford 8-cyl Ford engines reached the cosmic 18K RPM, now they could be above 20K, I'm not aware. But of course these are N/A engines, as turbo were forbidden soon after introduced in 70's. Were the same RPM restrictions applied also for the N/A S2000 cars?

Yes it exist in F1 as well, the last v8s were capped at 18k RPM and now the v6 turbos they are capped at 15k. Not sure about other motosports

[Mirek]

Hmm interesting, In f1 there are no such restrictions I believe, at least while I was still following it, and that was long time ago. AFAIR back then Ford 8-cyl Ford engines reached the cosmic 18K RPM, now they could be above 20K, I'm not aware. But of course these are N/A engines, as turbo were forbidden soon after introduced in 70's. Were the same RPM restrictions applied also for the N/A S2000 cars?

You don't have steel con rods and valves in F1. It's not allowed to use titanium in WRC/R5.

[Mirek]

Yes I know at some point the power will have influence on the top speed, but that seems irrelevant with the current WRC/R5 cars considering the dyno curves and limited RPM to 7500. In my understanding power overcomes the friction forces of the tyres with road, various bearings and stuff, which increase as the speed also increase, while torque is more relevant to the traction, as on low speed and cornering, thus torque is irrelevant at these high speeds, and seems this engine is well optimised about these figures. Anyway diesel car with same power probably would accelerate faster at low RPM as it would have higher torque, but that's just for a short period of time.

You are right with WRC/R5 as the power is always enough to accelerate up to rpm limiter. The main contributor for top speed when limited by power is drag as it is a squared function of speed. Other contributors are very minor in comparison.

The example diesel/petrol car was of course simplified. Let's say to a situation when both use continuous variable transmission with which they operate all the time on peak power

[Jeppe]

Otherwise I managed to make over 190 km/h GPS even with 1.2TSI 63KW Rapid which I once got for a business trip

Nice!! But I hope that was at the Autobahn

[Mirek]

Ja, natürlich, es war an A6 zwischen Tsechische Grenze und Nürnberg

Yes, it was on A6 between Czech border and Nürnberg.