Rev limiter in the P5
 

ok guys i know this has been discussed heavily that there is a rev llimiter on the p5 at 7100-7200rpm.... So i got my snow tires off today and the dunlops back on, and decide to take her for a nice spin..... so i got some room and im going 15 in 1st gear, so i leave it in first gear and floor it..... i wrapped it up to the top of redline (never done this before, and dont plan on doing it again).... to i guess itd be 8100rpm.... and there aint no damn revlimiter anywhere up there that i found.....

just a piece of info i thought you guys would like to know

hmm well ill have to do that..... lol

What will happen after you hit the rev limiter?

i guess the fuel will cut off, i guess killing the engine, but i dont know

Fuel cutoff. Stops your engine from going anymore, just in case you're wondering :D

it prevents the engine from revving any higher, not from going anymore. you'll know exactly when you hit it. just shift. ;D

i agree, doesnt it seem like it would be easier for them to make the computer skip ignition pulses like MSD does...

either way it kills the engine....now back to the original post...

do you really think it wise to take your p-5 out there and wind it up that tight just to see if you can get it to hit the limiter? come on dude! you are just asking for trouble....take someones word for it...there is one.

i wouldn't say it kills the engine. whenever i race (at the track) i hit fuel-cutoff atleast once since the tach isn't completely accurate during my time trials. i wouldn't sit in that gear and keep mashin on the gas, just shift quick and you'll be fine. i have yet to *kill* my engine by hitting fuel cutoff. i think that's the point of it.. so you don't. and i don't know if anyone else is getting the wrong message.. but you guys keep sayin it 'kills' the engine or 'stops your engine from going anymore.' makes it look like you're saying it's stalling out or literally shutting down. (that's what i see anyway)

I smacked the rev limiter in my Shelby Turbo a few times... quite the experience the first time. Here I was in first, passing & fingering:the finge the guy who just cut me off, wasn't paying attention and "click". There I was with my foot to the floor watching my tach sweep the wrong way! After the computer & head upgrade I was always hitting it, learned to shortshift 1st. quick enough.

Don

correct...that does NOT happen....it only kills it...or stops fuel delivery MOMENTARILY till the rpm's drop back below the specified rpm

ok so here it goes..... i took her out again today to test, so on to the interstate baby.

so i go up onto the on ramp, and max out 1st, no revlimiter, second all the way up to 8100rpm, no revlimiter..... 3rd gear, up to redline and kaboom i hit it, so i shift and keep going, it just feels like a brick wall or something i guess, lol.....

so it is there

I would say you have a problem, or you are going to have one. I know that the BP engines have no problems with 8000 rpm (CSP guys do that all the time), but I don't know about the F-motors. I'd assume the FS-ZE would do it, since the power peak is at something like 7600, but...

So, either your rev-limiter is incorrectly set (FS-ZE computer perhaps), or your tach is WAY off. The tach in my '90 Pro is off by 300 rpm at the cut-off. You might want to hav that checked out at the dealer, unless you want to be able to run to that kind of RPM.:)

That said, running against the rev limiter really isn't a problem. Autocrossers do it all the time. Some cars don't mind, but some do. My Accord had a particularly vicious limiter, that felt like you'd blown the engine. It would drop about 200-300 rpm before giving it gas again. But my Protege would run all day right on the limiter. Cars like the ITR do it all the time at autocrosses (one of the winningest has a license plate "REV LMTR").

well keep in mind, i wasnt staring at the tach, i was watching the road like i should, so i may be off on what i said by a bit...... all i know is that i was in the right ranges..


also i dont run those kinda rpms ever, i usually shift at a max of 6500rpm

I've hit a rev limiter in my Pro5 that was NOT a fuel cut. It was a soft limit that just killed ignition, around 7500rpm

[agreeing with pseudo]
IMHO, whoever came up with the idea to stop fuel delivery should be shot in the head. That is one of the stupidest things you can do to a car. It forces the whole drivetrain to accept a shock very similar to hitting a curb dead-on. Screw emissions it's not worth that. Besides, doesn't fuel act as a additional coolant and lubricant to the engine?

Anyone catch the Honda Civic Si project cars that appeared in SCC, Car and Driver, and Super (Stupid) Street. Three out of the four project cars had JR superchargers. Paul Tracy (IIRC?) was the test driver. He melted pistons on all three of the supercharged cars. Seems he was going through a particular turn on the limiter rather than shifting. But, Honda uses a fuel cut rather than ignition cut, so you had all these boosted cars hitting the limiter under boost, the computer cut the fuel, the cars suddenly went extremely lean, and BOOM!, there goes the engine.

Honda does use a much softer limiter on Acuras, at least Integras.

You still don't want all that unburned fuel getting into the air. Besides, whats a little more pain when we have already ran the car up to its rev limiter anyway (kidding)? I haven't hit the one in my new car but I have hit the speed limiter in a '97 Thunderbird (around 95MPH) and it was pretty bad. It slammed the engine hard and would not let the car have any more fuel until I was down at about 90MPH again. Maybe they could design a more comfortable way to cut fuel to the engine, trim back the level or something.

Okay, so instead of unburned fuel falling to the ground (It is liquid) we can take up space in the landfields with blown engines, and broken parts. Sounds like a good trade to me.

Quote:

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Besides, whats a little more pain when we have already ran the car up to its rev limiter anyway (kidding)? I haven't hit the one in my new car but I have hit the speed limiter in a '97 Thunderbird (around 95MPH) and it was pretty bad. It slammed the engine hard and would not let the car have any more fuel until I was down at about 90MPH again. Maybe they could design a more comfortable way to cut fuel to the engine, trim back the level or something.

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Okay now assume you were in a curve, do you feel that it would be appropriate to have the car being unsettled at that speed. What if it broke something or just spun the car and you hit a tree (or a wall, hopefully you were on track since you were going 95mph) and died. Would it still be a good idea? :-)

Taking your suggestion a little farther, I think a better idea would be to kill the ignition while reducing the amount of fuel given. Not cutting it off completely. That way the emissions freaks can be happy.

Hey guys,

Since we're a little off topic anyway. I think you are missing the point a bit with your talk of rev limiters, fuel cut-offs, ignition cut-offs, etc., etc. Frankly, I don't plan to get there at all on my P5 just to see what happens.
But if I did IMHO Mazda has had this problem taken care of in its RX-7s since at least 1984. My 88 RX-7 turbo redlines at 7000 rpm. But at 6500 you hear the engine rev warning buzzer. It's a great feature. It sounds just like the horn going off and tells you you had better shift soon if you like your rotary engine, (and I love mine).
I still remember the writer from Road & Track that test drove the "new" Mazda RX-7 GSL-SE in 1984 (first RX-7 with larger 13B engine) wondering how the heck he hit the horn button while he was winding out the car. Once he realized there was an engine rev warning buzzer he didn't have to watch the tach any more at all. He simply put the accelerator to the firewall until he heard the rev limiter scream, grabbed the next gear and did it again! That's how I drove my '85 RX-7 GSL-SE and that's how I drive my 88 RX-7 turbo. Keep your eyes on the road and let your ears shift for you. That's also one of many reasons I've been driving Mazdas with a big grin on my face ever since 1988. Great idea! Great little cars. Zoom zoom:)

You are forgetting that the fuel has already been atomized by the injectors. So what is actually coming out the tail pipe is nothing more than fuel vapor. Even if it was liquid gasoline actually evaporates very fast. If you don't believe me put out a tub of gasoline for a minute and then light a match a foot or so over it (don't really try this please!). I don't think something as small as a fuel cut off is going to totally destroy the engine when you hit it. A smart "track" driver would have a dash mounted tach with a shift light to keep him from hitting it. And I was not on the track going 95MPH. I was on a 20 mile, almost straight stretch, of lightly travelled road out in western Texas. Of course it did not take me 20 miles to get a 4.6L V8 up to 95.

Those pistons were not all melted. SCC drove theirs away to the car show (SEMA or something) and it got stolen and striped there. I know that a blue SI that has Jesses favorite Force induction method (Vortech Centrifical Supercharger) on it melted pistons. There was another magazine in the contest as well (Popular Mechanics; if my mind serves me right). Back onto the topic....please don't run your protege up to 8000RPMs again, because you will be on here in a week bitching about how shitty mazda is and that their engines suck because you just blew your motor. Be more intelligent please....

ok i'm sorry if i'm repeating someone
 

but i don't have time to read everyones post

if you are talking a stock P5 to it's limiter, than you are shifting too late, power drops off before the limiter and these engines love 4-6000 rpms (torque bets)

that is all

thanks for listening

OKAY guys....lets think a little more clear here....why do you think there is a limiter in the first place? just to piss you off? NO, to keep you from blowing up your STOCK motor....to keep people from damaging their engines and costing MAZDA money to replace them under warrentee. THAT is why they are there....

as far as you hitting this limit in a corner....all I have to say about that is IF you were ever to be driving that aggressively and hit it and do any damage do to a spin out......I believe the LAW, as in the police, would be giving you a ticket anyway for reckless driving....for if you are diriving within the limits of any public street....you will NEVER get to that point...

don't get me wrong......I throw my car into MANY a corner and power out of them...and yes, exceeding the speed limit....but at NO TIME have I EVER seen the need or advantage of doing it at those RPM levels.....as stated already....your power and torque are dropping off WAY before you ever get to the limiter.

Did you read my post? I actually mentioned being on track. Believe it or not, some people do take their cars to autocrosses to learn how to drive correctly in a controlled environment, instead of driving aggresively on the street and risking people's lives. Last time I checked "the LAW" doesn't hand out tickets at sanctioned events.

This past weekend, I autocrossed and my car (not a protege at this event) was bouncing off the rev limiter for nearly 25% of the course. Why don't I shift? Because it slows your time down. This particular course actually had a sweeper that you could go fast enough to hit the rev limiter in 2nd gear.

Fortunately this particular car has an ignition kill type limiter instead of a fuel kill limiter. That way I don't have to worry about riding on the limiter and blowing the engine. If it were a fuel kill setup then I would not even consider riding the limiter.

Autocross and you will see the light.

You are COMPLETELY correct about the purpose of the rev limiter. If they thought 7200 rpm was dangerous for the engine, then they would've put the limiter at a lower rpm.

okay jmauld, I wasn't thinking in terms of AutoXing....I was thinking of on the street...as you noticed....and unfortunately for those of us that DO like to AutoX.....that is NOT what Mazda is selling the car for.....sure it can be used there...and OBVIOUSLY THEY have a racing program too.....however.....if that is where you want to go.....well after all...that is why we have an aftermarket! thank GOD!!! IF you need to raise that limit....and if there is a outcry for that....SOMEONE will figure out a way to change the settings, and probably charge you big bucks for the priviledge of using their equipment. :{D

I haven't seen a dyno of the 2.0L but it stands to reason (from other vehicles whose HP and torque curves I have seen) that the drop off after the horsepower peaks is pretty steep. So instead of being a jerk to the car and running it way behond the spec'd redline just upshift the frickin thing and get in the meaty spot on the next gear. Has anyone else tried to find the rev limiter in their 2.0L? I find it a little ludicrous that it would be set much higher than 7000RPM. As to blowing the engine with the fuel kill I don't really see how you could. Things inside the engine don't just stop rotating because there is no fuel. The power from the wheels will keep the engine rotating (and the cams turning) until the fuel is kicked back in. All you are doing is breathing in air and pushing out hot air. No big whoop. The systems computer just tells the injectors not to fire (I know that sounds wrong, maybe I should have just put inject but that sounds lame too) until the engine comes back down under the rev limiter setting.

Please go research the purpose of gasoline in the engine. Then come back and we'll discuss. Here's a hint, it's not just for making power.

A good place to start is http://www.sdsefi.com . Look at the bottom, read everything in the tech section. That would be a good start.

true....the fuel does more than just make power....it actually acts as a coolant...and a lubricant (from its additives) and its not a good idea to starve an engine of those things. NOT to mention its just a shock to the entire drive train from power ON, to power OFF back to power ON....it will actually mechanically shock the system...and stress levels peak when that happens...and things break when stress levels peak to high.....BAD JU JU!!

well remember me saying i got 16.7 in the 1/4? If you take the engine to almost the rev limiter - low 17's (like everyone else) My 16.7 was short shifting using the engines torque. I dropped my time by half a second! Now my secret is out. :p

But you are not losing the coolant and lubricating (more cleaning than lubricating) for more than maybe a second. Just long enough for your car to lose some RPM. Without any ignition happening the engine temperature would drop anyway. The cooling effect is more so that the next ignition does not go over the heat limit. Since nothing is really going on in the engine except for friction the air and water circuilating through the system are more than enough. As for the harshness it is nowhere near as harsh as a downshift or just dropping the clutch in general (putting a large load on the engine all of the sudden). I think the pain is more experienced by the driver as his inertia carries him forward and suddenly that big push is lost. But if you think Mazda or any other manufacturer is going to release hydrocarbons straight into the air without even attempting to burn them then you are nuts. The government would throw a fit. Just thank the great Mazda God for putting that thing in there so that people don't blow their engines. Its a not so friendly reminder that you are doing something Mazda does not really want you doing.

A lean condition is one in which ignition is actually taking place and there is not enough fuel present. It is not one where there is no fuel present at all. The systems in the Protege do not create a lean condition unless the air where you live has enough combustibles in it to actually ignite from the spark (if there even is one, if I worked for Mazda as an engineer I would have shut off the spark too, no sense wasting power). All your engine is doing is moving air. Air comes in the intake, cools off the cyclinder, and leaves the exhaust. I have had an '83 F-150 for years and I happen to understand the necessity to maintain a proper air fuel ratio. And I happen to have taken enough courses in automotive technology and chemistry to understand the principles of combustion. Please understand someones posts or ask questions before you snap off on tangents.

I think you're missing the point though... the point was, if you are AutoX-ing, and for 3 seconds you have a choice between shifting up to third and back down again or bumping the rev limiter... you're going to be a lot faster if you're bumping the rev limiter.

Sure, if you're accelerating in a straight line, shifting the torque range will lower your time, but if you're choosing "to shift or not to shift" you'll be faster by not shifting.

Running an engine without proper fuel for 1-2 seconds is not good. Running an engine without any fuel at all for 1-2 seconds (I only said 1 second to describe the delay between the fuel being turned off and back on) is fine. Now when you say "proper fuel" if you were referring to the no fuel at all condition I can think of no plausible way that doing that can damage the engine. All that little controlled explosion under your hood is doing is providing force to keep the crankshaft rotating. Allowing the crankshaft to get its turning power from the wheels is not going to hurt anything. As long as that crankshaft keeps turning the drive belt and turning the alternator you will not have any problems.

Hey Jesse, these shift points are for what car and motor?

Just curious.

Don