Fuel flow restrictor

[Zac]

Does anybody have a record of any motorsport classes using a fuel flow restictor in the same manner as an air restrictor?

I think this was very very briefly considered for formula 1 in 1994 in the desperate attempt to slow f1 down (with the safety excuse) after imola.

But that is not the point, I was just wondering if it has ever been used. Having thought about it, it probably wouldn't do that much different than a typical air restrictor that is almost standard in motorsport regulation now. The best engines would still be big slow revvers or turbocharged. Engineers would hate running the engine so close to a lean out.

Thoughts, comments, etc..

[mondo2000]

This was proposed a long time ago by Cosgrove and/or Duckworth. I think towards the end of the F1 turbo era when there was a ridiculous fuel limit for Grand Prix.

AFAIK it has never been used in any motorsport class.

I think it is the best way to limit hp. In a round-a-bout way it imposes an unobtrusive rev limit. Direct injection would be necessary, which would be good for the manufacturers involved.

[Zac]

Then you might have to limit fuel pressure in some way too. Maybe all the regulating bodies decided it was easier to just limit the air entering the engine instead.

How do you figure it limits rpm any differently to an air restrictor?

[Ben Wilson]

It's a more logical way to limit performance, but, a lot harder to build and police, it would need some sort of pressure compensation and would probably wind up fairly expensive.

[mondo2000]

With airflow restricted engines, the power curve is flattened very dramatically. For example the power curve might climb steeply to about 5000 rpm, then it will be almost totally flat to 7000 rpm. It would feel like the engine is choking, it could be revved more but just refuses to make more power. This is not normal. Engines, and especially race engines, will usually make more power as you rev them harder, until the conrods say hello to the outside world.

A fuel flow restricted engine is different. For a given engine there is an AFR enforced rev limit. If you rev the engine any higher it will lean out, so that is where you set the rev limiter. However, up to that rev limit it would behave as you would normally expect that type of engine to behave.

As for limiting fuel pressure, that would probably be a good idea for safety reasons. It doesn't need to be difficult either. You could have a "control orifice", supplied by the racing body, at the inlet to the fuel rail with a "fuel pressure relief valve", also supplied by the racing body, as part of the same assembly and situated upstream of the orifice.

[Zac]

Yeah that makes sense. Still no sign of any racing series around the world that have implemented this!

I thought you would have to limit fuel pressure to circumvent engineers from just pushing more and more fuel pressure through the restrictor.

[Ben Wilson]

As for limiting fuel pressure, that would probably be a good idea for safety reasons. It doesn't need to be difficult either. You could have a "control orifice", supplied by the racing body, at the inlet to the fuel rail with a "fuel pressure relief valve", also supplied by the racing body, as part of the same assembly and situated upstream of the orifice.

Whats going ot stop peple running fuel into the manifold via vacuum hoses, or running it backwards through the return line?

That's just off the top of my head, I'm sure there are many other ways to cheat it.

[Zac]

Ben, maybe that is why the common engine restrictor is an air intake restrictor - it is easier to police and scrutineer, at the detriment of engine flexibility.