Why do F1 cars have such high RPMs?

They did produce the limited-production NSR repli-racer superbike for sale to the public, with the oval pistons, not sure of the year, if memory serves it was around '94-96 in that time frame and it was I believe 900cc. It was more than Ducati expensive at the time however.

 

Downforce is not the issue here. it is more the drag bring produced by the tires out in the open that requires more horsepower from the engine. This is why you see aero devices like winglets, barge boards, and flipups near the tires. they are there to channel air away and to also to redirect air around the turbulance being produced by the tires. If a F1 car was able to place on a sports prototype car (Le mans) body onto it you would see a dramatic increase in straight line speed.

Take a look at the pictures for the front wing end plate on the F2003-GA. The secone picture is the same as the first with comments added in.

 

F1 engines close the valves with high pressure nitrogen instead of with springs. It seems that the mechanism of valve closure is limiting CART engines (ala 2001 before RPM constraints). The high pressure nitrogen has the property that the pressure between the cam follower and the cam is rather constant, whereas a spring has increasing force with increasing lift. The net result is that a pneumatic valve can A) open faster, B) close faster, C) follow the shape of the cam better, D) as long as you don't run out of high pressure nitrogen. The major reason this technology has not penetrated road cars is the leakage of nitrogen and the requirement for pressureizing the valve train before cranking the engine over at startup.

Then, of course, the valves are made of titanium, as are the retainers and the pneumatic cam followers. Before 2000, the engines used berylium vavle seats. These seats transfer heat better than other machinable materials, weight nothing, and are toxic to the machinists who cut the seats and lap the valves onto the seats.

Current valve timing for F1 engines hovers around 40/80-80/40 or 300 degrees of duration, and 80 degerees of valve overlap. In fact, the valves are only closed for 200 degrees of rotation out of 720 degrees, compression getting 100 degrees and the power stroke getting another 100 degrees.

Ok, The pneumatic valve springs got rid of the RPM limit from the valve train or at least moved it into the 22K-25K RPM range. So the engine designers sought to make use of the newly found rev range. This lead to a shortening of the stroke to keep the reciprocation motion from limiting the RPM reach of the engines. Shorter storkes lead to bigger pistons. The combination of bigger pistons and shorter strokes makes is harder to develop a combustion chamber that has both high compression and a fast flame front.

At this point (late 1980s), the valves were inclined in pairs of intake and exhaust in a roof-like chamber. If was found that arranging the valves in a squashed pyramid and adding squish at the ends of the combustion chamber, that the combusion could be compressed into the inner 70% fo the combustion chamber, resulting in the fast flame fronts necessary to burn a mixture at 18,000 RPMs and higher.

Compression ratio hovers in the 13:1 to 14:1 and is more limited by the specification of useable gasoline than by the ending designers and constructors. Current F1 race gas is a mixture of 112+ octane compoments (Tolulene, Xylene,...) and some 80- octane components (heptane) so that the mixture will look like 101 gasoline in terms of knock in the testing 'research' engine. If F1 engines were restricted to actual pump gasoline power outputs would be reduced 50-75 HP. If the fuel for the F1 engines were obtained randomly from a gas station in the town at which the race was to take place and everybody got fuel from the same tanker, F1 engines output would be have to be reduced by 75-100 HP just so that the engine would survive on the uncalibrated fuel.

As the RPM band gose higher, the size and weight of the intake velocity stacks and exhaust headers both get smaller and simultaneously it becomes easier to extract energy from the harmonics of pulsing pressure, giving a self-superchargin effect. At peak TQ a typical F1 engine is around 115% volumetricly efficient! Modern F1 engines have the velocity stacks on a servo mechanism in an attempt to move the TQ resonance in concert with the engine RPMs so the engine always operates at TQ approximately equal to peak TQ.

On the header size, the current RPM band of best header operation has header tubes that are so short that packaging all 5 tubes into a single collector requires a tube bending genius. The collector masquerades as the big tibe from the juction of the header pipes to the slashcut exhaust.

To recap:
A) pneumatic valve train
B) fast burn combustion chambers
C) excellent breathing
D) complete utilization of pulses of pressure in header and intake
F) expensive fuel masquerading as gasoline

 

Mitch - I've been looking for pictures of the head assemblies on ANY car with a Pneumatic valve train with not much luck. I would really like to see what the assemply looks like and how it works. Do you have any source for pictures, or better yet, exploded engineering drawings showing how it all goes together?

Anyone have anything like that?

THANKS!

 

pic of Marshals impounding a car - http://img.photosight.ru/2004/06/28/536300.jpg

 

Honda wanted to race & win in the 500cc GP bike class with a 4-stroke, and since a two-stroke has twice as many firing strokes (so even though it's not as efficient it produces more power per cc) decided that if they could get more revs and build a bike with a very light weight they would stand a chance, so they went for oval pistons so that the weight of the con-rods and valves would be less of a constraint on revs.

They were wrong. The NR500 appeared in 1979 and by 1981 had got to be as good as it could, and had a seriously fast rider in Freddie Spencer, but still couldn't cut it. It revved to 20,000 and had lots of torque, but was still heavier than a two-stroke and had only about 110 hp when the Suzuki and Yamaha were around 130 hp.

So then they did a 750cc version, which was raced in some endurance events where engines didn't have to be based on production bikes, such as the prestigious Suzuka 8-Hours (at Honda's own track), and since it made 155 bhp and loads of torque it was quicker than the ordinary v-four which had about 130 bhp. Then they did the NR750 road bike, but it was the priciest thing on the road so only sold to curious millionaires!

And they went to two-strokes for racing, and won the 500 and 250cc WCs with Fast Freddie.............but now Moto GP is all 4-strokes, currently 990cc with sliding weight limits for the number of cylinders, and the V5 Honda gives over 240 bhp, which is still less than the 300bhp/litre of F1 engines.


Paul M

 

When I started following F1, the engines were developing about 400 HP out of the same 3 liters, with peaks at about 10,000 RPM. So the more-than-double horsepower nowadays is due, at least in part, to those super-high revs.

But I liked the way the cars sounded better when the revs weren't so high. If they want to slow the cars down, a rev limit of not more than 14,000 RPM would do that, and the sound wouldn't be so painful!