rev limits

[RichardB]

I was racing at the weekend using WOT and part of the selector broke which meant i missed a gear and with 100% throttle the revs shot up to over 10500rpm and damaged the engine.

I currently have a revlimit of 8200

Rev limit mode: Inj Soft & Ing Soft
Rev limit range: 500 Rpm
Rev limit retart: 4.0 Degrees
Overrun TPS limit: 0.8 %
Overrun LOAD limit: 60.0

Is there any way to stop this happening again?
(This is a turbo engine)

[Ian]

Is this a rotary or piston engine?

[RichardB]

piston, 4g64 evo engine

[Ian]

Were you data logging or did the max rpm show in the telltale? As the ECU is calculating rpm from crank pulses the overrev could have occurred for less than an engine revolution.

What actual damage occurred? Soft fuel cuts should be carefully considered before implementing as fuel gets redistributed through intake manifolds with reversion pulses and may cause lean conditions. Even very short term lean-outs on turbo / supercharges engines can result in detonation occurring.

[RichardB]

logging data, i changed gear using WOT and there was a problem with the selector and it missed the gear, so the revs climbed up to 10500+ rpm in 0.3 sec I got off the power within the next 0.3 sec but the damage was done.

[Chris]

Even very short term lean-outs on turbo / supercharges engines can result in detonation occurring.

I had a 3.2L twin turbo Honda V6 on the engine dyno last year, Got on the soft fuel cut @ 4000rpm and blew the side off a piston. Luckily it was a stock engine we were using for testing the turbo kit setup.

Be sure to inspect the block main webs well, have seen a few carb/magneto race boat engines break the propshaft and pull the webs out of the block. What damage did your engine sustain?

[RichardB]

I will know more next week when we finish stripping it down.

so would any of the cut options have actually helped prevent this, or is fact that it went from load to no-load and up to 10500+ rpm in under 0.3 sec just too much for the ECU to handle?

[Chris]

In some cases inertia can carry the engine well over the rev limit. I think a hard cut might be a good option, and our Honda needed alot more rev limit retard.

[RichardB]

In some cases inertia can carry the engine well over the rev limit. I think a hard cut might be a good option, and our Honda needed alot more rev limit retard.

can I ask what settings youve got set on your honda?

[Chris]

I don't have that cal file saved, but from memory was set as fuel soft and fuel hard with 4 degrees retard, which is the default setting.I heard it det, but couldn't get the throttle off fast enough.

Using ignition soft cut has proved to be a bit deadly for the off road racers, if you have two or more cars in close proximity where the driver cant hear the engine. Dropped valves result and for a driver that is prone to hanging the engine on the soft spark cut limiter I often see worn valve collets on the remaining valves.

I now use hard fuel/spark and am looking forward to E throttle as a method of rev limiting

[Yequan]

Hat actual harm occur? Soft cut fuel, should be carefully considered as a fuel, the adoption and implementation of the reversed pulse redistribution of the intake manifold, and may result in thin conditions.