Davard

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.

kc5zom

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.

jmauld

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:

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 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.

makeminemazda

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

kc5zom

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.

azrakain

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....

LooseCannon

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

Sir Nuke

OKAY guys....lets think a little more clear here....why do you think there is a limiter in the first place? just to **** 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.

jmauld

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.

Sir Nuke

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

kc5zom

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.

jmauld

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.

Sir Nuke

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!!

LooseCannon

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.

kc5zom

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.