Retard Timing On Columns N17, N18 To Achieve To R&r Condition Possible On Powerfc?

[Dose Pipe Sutututu]

Hey guys, this might sound far fetched, but don’t flame me on this, and n00bs, keyboard warriors, school children, dreamers who they have Skylines need not reply.

Hypothesis

Okay, most not all of us are faced with a fuel cut rev limiter, which is fine if you rarely rev bash the motor, but say this car was used for drifting on the track and the occasional motorkhana then that fuel cut becomes a concern for lean out mixtures and motors going kapow.

PowerFC Standard Edition only provides us with fuel cut, the stock ECU also does fuel cut, but on high knock will also rich and retard.

Being a PowerFC user, and taking into context the stock ECU’s ability to rich and retard timing when high knock is detected, would it be safe to retard the timing 1~2 map points before the rev limiter?

Method

We take column N16 & N17 and set them ALL to ‘0’ and by the time it actually hits the rev cut, it would be insanely rich from what I gather. That would be, from what I gather, safer than a direct fuel cut which leans out as many have stated.

Another method could be create a module which essentially is a BeeR rev limiter and connect it so it cuts out just before the normal fuel cut. I was thinking of using a shift light to trigger a relay which will cut all power to the coil packs once a desired rev point has been reached.

Relays have 2 circuits, either always on or always off until power has been applied. I propose that the coils are always powered, until the shift light triggers the relay to open the circuit, therefore cutting power to the coil packs, which essentially would simulate an ignition cut module for a fraction of the price.

So what do you guys think?

[paulr33]

when fuel cut occurs, no fuel goes into the cylinders, combustion isn't possible without fuel

no fuel, means no bang

if you accidently hit rows 16/17 or higher and via your method

the engine is on full load and all the timing gets taken out of it

it would probably blow the exhaust wheel to pieces, doesnt sound safe under full load

[paulr33]

the idea of the fuel cut is to stop the engine running, not lean it out

leaning out shouldn't occur

[Dose Pipe Sutututu]

Hi Paul,

Thanks for your reply, I've read from alot of sources that fuel-cut rev limiters will cause a lean out condition on cut out and will destroy motors, hence people say ignition cut is the way to go.

I do plan to eventually take this car to a drift track for some fun and the occasional skidpan/motorkhana day and fear if I rev bash it, I might destroy the motor.

If in your opinion, fuel cut is safe, I will not worry too much about it then.

I have just been lead to believe that ignition cut was safer to rev bash, also the factory RB25DET ECU incorporates a rich and retard functionality on detection of high knock/excess air readings, exactly how much ignition is pulled out to achieve that?

[urtwhistle]

Hey I would have thought it would be more critical to worrry about the oil pump getting minced when bashing the limiter than lean outs

[femno]

Well when you think about it, despite putting more fuel in, and taking timing out just before the rev limit, you still have no fuel going into the engine at the rev limit. Thats if you were to attempt this R&R function using just the PFC.

The BeeR rev limiter isnt much better for the engine either, causing excess wear and turbos and so on, through mass explosions from cold fuel hitting extremely hot parts. So you cant really win.

And yes the oil pump will probably go before the pistons or rings do.

I wouldnt bother.

[GTR1993]

the idea of the fuel cut is to stop the engine running, not lean it out

leaning out shouldn't occur

But this is not always the case.

[swanny180]

But this is not always the case.

No?

What might you be basing that on exactly?

When you hit a fuel cut rev limiter, there is no fuel going into the engine.

You *can't* cause detonation when you dont have any fuel. Otherwise, what exactly is supposed to be 'detonating'?

[GT-RZ]

The problem of running lean with a fuel cut limiter is real but most likely not with 99% of the quality systems available, more theoretical/old crappy systems once upon a time?

If you think about the speed at which an injector must operate and spray it's fuel in to the chamber then you can understand that a fuel cut system must be very efficient to be able to stop 100% of the fuel being injected in to the chamber to prevent combustion... It can't. but most will cut >50% of the fuel which is enough to create a fuel/air mixture that is too lean to ignite. the only scare you could have with this is that something stuffs up but then thats with every part?

spark cut systems can cause more problems really. you have unburned fuel travelling out the chamber through your turbo and down your exhaust which can cause overheating problems. if you have a cat you could potentially melt your cat sitting on the rev limiter... (probably not an issue for most drift cars )

All in all a good quality fuel cut in good working condition is the way to go IMO. End of the day you shouldn't intentially be sitting on the limiter anyway. and a few cuts here and there wouldn't be much of a problem either way... hopefully.

[R31Nismoid]

Its not the fact of lean/rich near the limiter that should be a problem in terms of the limiter, so honestly im not really sure how you have come up with this theory.

The problem with bashing the limiter is the oil pump and/or drive etc.

If you are worried about bashing the limiter, just pull heaps of timing out from 500rpm before your RPM limit. It'll make the car feel lazy, and then you'll slowly tell yourself to change before this happens... and if you do happen to hit the limiter it wont be as hard... still not idea either way to be bashing the limiter.