Hitting Speed Limiter = blown engine?

Post by **MadSideways** » Mon Feb 16, 2004 3:05 pm

I don't know if anyone's asked this before, but can't hitting the speed limiter kill a boosted engine?

If you're at high rpm's & high boost and then cut fuel, (which i believe is what the speed limiter does), couldn't that cause predetonation and possible engine failure if your pushing high enough boost?

Although it probably retards/advances the ignition to compensate, but it doesn't seem like a very bright feature to add to a turbo engine...

Post by **Onizuka** » Mon Feb 16, 2004 3:05 pm

It probably cuts ignition as well, it would kind of be a really bad engineering desicion to make something that nukes when you miss a gear (which is guarenteed to happen a couple of times in a motors life) :pface

Im not certain though, maybe someone else can shed some light onto this.

Post by **Cyberkreig** » Mon Feb 16, 2004 3:05 pm

to my knowledge the SR computer only cuts fuel. (This is info from various internet sources so take it as you will)

IF this is correct, than yes, it will cause your car to run momentarily very very lean and possibly destroy your motor. Its more likely it will just knock. Think about it.. very very lean means very little fuel which means a weak combustion

Checkered-Member · Post by **Checkered-Member** » Mon Feb 16, 2004 3:05 pm

Cyberkreig wrote:to my knowledge the SR computer only cuts fuel. (This is info from various internet sources so take it as you will)

Where did you hear this?

It first cut off ignition at a certain levelthen if somehow you managed to rev your engine past that it will cut fuel.

Think about it, why would Nissan make an engine that will go lean every time you hit the speed limiter and blow

Post by **MadSideways** » Mon Feb 16, 2004 3:05 pm

Quote »Think about it, why would Nissan make an engine that will go lean every time you hit the rev limiter and blow[/quote]we're not talking about the rev-limiter, we're talking about the speed limiter....

Post by **Phax** » Mon Feb 16, 2004 3:05 pm

I've hit the speed limiter more than once. My engine is still fine. As soon as the limiter kicks in, you lose all of your boost. So it's not like you're still cruising along under boost, without enough fuel to compensate.

Post by **MadSideways** » Mon Feb 16, 2004 3:05 pm

I have aswell...it sounds horrid.

It must cut ignition and fuel at the same time in order for the boost to fall. I mean as long as the clutch is engaged the engine is still spinning, theres just no load, so I guess the CFM drops and the turbo slows down.

Although it still sounds like a hazard waiting to happen.

Post by **Phax** » Mon Feb 16, 2004 3:05 pm

MadSideways wrote:I have aswell...it sounds horrid.

That it does.

Post by **Cyberkreig** » Mon Feb 16, 2004 3:05 pm

checkered - sorry i cant source myself. thats just what i have read. I admit it could be wrong and welcome solid information.

Phax & madsideways - What does it sound like for you guys? I've hit it before and all that happened was a huge loss of power accompanied by an exhaust fireball

Post by **hokiruu** » Mon Feb 16, 2004 3:05 pm

Bah, I have hit the speed limiter about 4 times in five miniutes racing a 911 on the highway. Then I did it a bunch of other times and just because I am insanely addicted to speed. it sucked, but not because it sounded bad or I didn't win by as much as I would have liked, but because now I need to spend $ overrriding it.

Post by **RobDET** » Mon Feb 16, 2004 3:05 pm

If you CUT fuel you cannot get detonation becuase there is no fule to detonate. That's why it works.

Post by **Phax** » Mon Feb 16, 2004 3:05 pm

Cyberkreig wrote:Phax & madsideways - What does it sound like for you guys? I've hit it before and all that happened was a huge loss of power accompanied by an exhaust fireball

I can kind of make the sound, but I'm not sure how to translate it into text.

Post by **SpeedRacer1** » Mon Feb 16, 2004 3:05 pm

The car has a fuel cut off at high RPM's. Which is the same for your speed cut.

Its bad, but not horrible. An ignition cut would result in a fireball.

This should answer most of the questions...http://www.takakaira.co.jp/per...n.asp

Post by **IvoryJ30t** » Mon Feb 16, 2004 3:05 pm

RobDET wrote:If you CUT fuel you cannot get detonation becuase there is no fule to detonate. That's why it works.

thank you for mentioning that. it bugs the hell out of me when people say that you go lean when you hit fuel cut.

YOU DONT GO LEAN, YOU LOSE ALL FUEL!!!!

fuel cut doesnt make the motor lean out, its cuts it entirely. you cant have a lean condition if theres no fuel at all!!!

Post by **IvoryJ30t** » Mon Feb 16, 2004 3:05 pm

trust me, you would rather have fuel cut than ignition cut.

when the fuel is cut, the air just passes through the cylinders. no lean condition, no detonation, no knock, just nothing.

Post by **Supafly** » Mon Feb 16, 2004 3:05 pm

ignition cut with big injectors=bad juju (hydrolock in some cases). cutting all fuel just makes your engine lose power temporarily then come back when fuel is reintroduced. it would be bad if it cut to 1/4 fuel flow or something to slow you down, but cutting all fuel stops the burn.

Post by **Cyberkreig** » Mon Feb 16, 2004 3:05 pm

I'm sorry but you guys are wrong. Fuel cut only can be dangerous. Fuel cutoff is instant and can interupt an injector pulse. Read this. And this is not the only place i have seen this information, I'll find other sources.

"Why fuel and spark must BOTH be cut.

Old style spark only rev limiters where designed to operate on old fashioned carby and dizzy type engines. They operated by intermittently grounding the negative side of the single ignition coil to cut spark.

A rev limiter designed for a modern EFI motor needs to cover a few more bases.

1/ A spark only system on an EFI car will allow raw fuel straight through the engine and will rapidly contaminate the catalytic converter and destroy it. Excess fuel will also wash the bores and contaminate the engine oil system risking long term bottom end damage. 2/ Most modern EFI cars have multi coil ignition systems which bare no resemblance to old dizzy and points systems so you can't simply ground a coil to the same effect. 3/ A fuel cut only system runs the risk of leaving small amounts of fuel flowing through the engine which may ignite risking lean burn and engine damage. The most effective and safest method of reducing power output independent of throttle position (i.e. WOT) is to stop fuel supply and simultaneously cut spark activity to eliminate any possible lean burns situations. On an EFI car, it's the only safe way of rev limiting. "

sourced from: http://www.rev-lite.com/flat.html

http://www.johngauto.com/P/HN.HTML

Post by **RobDET** » Mon Feb 16, 2004 3:05 pm

it isn't hard at all to start the cut at the begining of an injector pulse... If fuel cut really worked like that you would hear audible detonation when you hit the limiter... That doesn't happen.

Post by **Cyberkreig** » Mon Feb 16, 2004 3:05 pm

Can you PROVE, no hearsay or theorys, PROVE that the Nissan sr20 uses a fuel cut that starts before the injector pulse?

Can I PROVE that it doesnt?

I dont think either of us can.

Does anyone have any proof that the SR uses Fuel cut only? Ignition cut only? Both?

No one seems to. I have only hearsay (and as stated above i welcome hard information.)

I say that Fuel cut can be dangerous. Several of you disagree. I have two links to back me up. Also most Standalone ECUS offer both kinds of speed/rev limit. (reference HALTECH). Again I welcome any information that shows fuelcuts to be safe.

Dont get me wrong, I am not saying that hitting a rev limit or speed limit will grenade your engine. I am saying that having both F&I cuts is the preferable way to go.

Post by **RobDET** » Mon Feb 16, 2004 3:05 pm

I have the fact that i hear no audible detonation on revv limit/fuel cut. I also have the fact that only cutting spark is definately bad because of the washdown issues stated earlier.

I have the fact that nissan engineers get paid the big bucks to think about thinks like a lean burn causing detonation on a brand new SR20 could mean paying for several motors under warranty.

I also have the fact that starting the fuel cut at the beginning of an injector pulse would be absolutely cost free to program into the ECU and it would not have ANY adverse effects.

I'll go out tomorrow and revv my motor till it blows up. O wait i can't the nissan engineers made sure of that.

Relax man it's not an attack. I agree that there is no substantial evidence presented here to vote either side. My only point was that fuel cut alone is not a big deal if you do it right which isn't difficult.

BTW if i reply to this thread any more i'll be guilty of a message board ettiquete violation so i'm going to refrain for saying any more here.

Post by **SpeedRacer1** » Mon Feb 16, 2004 3:05 pm

There is a fuel cut gaurenteed mentioned in the service manuals.

There is no ignition cut at all, the ignition map on the SR is only changed from standard ignition during: Start up, warm up at idle, low battery voltage, and knocking conditions. There is no mention of an ignition cutting situation.

The fuel cut results from deceleration or operation of the engine at *excessively high speeds*. Sequential multiport injection is the norm on the SR, simultaneous injection is used when starting the car and during ECU safe mode.

So, there is a fuel cut, no ignition cut. Its straight out of the SR20 FSM's.

Post by **loudbay** » Mon Feb 16, 2004 3:05 pm

GO! SPEED RACER.... GO! SPEED RACER... GO, SPEED RACER... GO!!!!

Hitting Speed Limiter = blown engine?

Hitting Speed Limiter = blown engine?

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