Is there a way to mechanically rev limit an injected engine?

[Tommy]

Hi everyone

This year Chris and I intend to go racing with 'Little Blue' but she's too powerful for the regs. We don't want to detune or add ballast so I've been in contact with the organisers (Trackday Trophy) about fitting an electronic rev limiter. They say it's too easy to change but they did accept a mechanically rev limited car last year. I assume a mech. rev limiter can be made more secure against being changed. Anyone know how this could be done? I can understand limiting the throttle opening but that won't limit the revs.

[Harry]

I haven't read the regs so don't know the power limitations, where you set the rev limit will surely depend at what RPM in specific gears the output of the engine exceeds the regs I don't see how this can be achieved mechanically other than via some form of centrifugal force operated device. I am sure that the output can be regulated more precisely than limiting engine speed, this could be achieved through a simple restrictor but no doubt the scrutineer would want to see a sealed unit.

I wonder if this sealing could be applied to an electronic limiter, I am sure that there are other better informed members with a solution

[maff]

Maybe they mean like a centrifugal or pneumatic governor like they have on diesel engines? to controls the fuel supply?

Still doesn't directly control the revs though... Weird, no idea really. That was helpful. Do they recommend one?

edit: Great minds

[Tommy]

Thanks for the thoughts. I

[Daniel]

i may sound like a div saying this but can't you slide a barrell lock and grub screw onto the throttle cable at a certain point?

[warboys]

Yes, I would rather do something under the bonnet than in the cabin. Just a long bolt on the butterfly mechanism to stop it opening so far. Or a physical restrictor in the throttle body itself.

Does the car have a throttle cable or is it fly by wire?

[Tommy]

Thanks guys. We've actually rethought this and considering remaps are nicely resolved for full throttle openings but less so for part throttle openings, we think it is probably too great a risk for the engine that is in the car. It runs a carbon airbox and no MAF so is Alpha N mapped which, I am led to believe, means that the amount of air the engine is taking in is always an educated guess by the ECU.

Our solution? Two maps on separate OEM ECUs. We'll run one at around 315 bhp (fly) for the Trackday Trophy and the other at full power (currently 351 bhp on a map prepared on a similar car. It needs to go for live map tweaking and hope to extract 360 bhp) for trackdays and any rounds we may join of the Deutsche Marque series.

[Harry]

I reckon this is the sensible approach Tommy if it satisfies the Regs