I was talking to a friend a while ago and was told that most factory installed rev limiters pull fuel to the engine. This causes the mixture to go lean and you risk burning your valves. Do any of you know if this is how the C5 rev limiter works and is it therefore bad to hit the rev limiter?

 

Well, its not a good thing to do but you wont damage valves by doing that. Worst case you'll bend a pushrod which is a $5 part and easy to replace.

Now, hitting the factory rev limiter while spraying a dry shot of nitrous would be bad. :eek:

 

I believe it is spark controlled, not long enough to do any damage from unspent fuel.. That is what the rev limiter does..it protects the engine...

 

During an overrev condition the injectors are cutoff, so there should be no lean condition since no fuel is being ignited. Same with a coastdown condition.

 

Yes...and no.

I'll lead with there was some debate in here when I posted this last year, but I have no reason to BS anyone here,
especially with the seriousness of the results.
About the xxx's in some of the numbers - it's been long enough that I don't remember the exact figures.
Anyway...

I'm repeating what I was told by my dealers machanic, and what was told to him by GM TAN when they were discussing
what caused my LS1 to eat itself.

1. There is no rev limiter in a 2001.
2. There is a fuel shutoff, which is programmed to activate at 190 mph.
3. The fuel shutoff module begins to lean out the mixture at 180 mph
4. The fuel acts as a coolant w/in the cylinder.
5.When the fuel ratio begins to lean out at 180+, it causes the cylinder temps to rise - dramatically.

Based on consecutive snapshot data from the computer.
Speed: 180
Coolant temp: 21x
RPM: 5xxx
computer begins leaning out the fuel mixture

time span: 14 seconds later
Fuel shutoff activated
Speed: 192
Coolant temp: 24x
rpm: 67xx

Result: 11 bent & tuliped valves.

Cause of melted valves: High cyl temps as a result of leaning out of the fuel mixture.
(given the coolant temp, GM estimated cyl temp somewhere over 3000 degrees)
Cause of overrev: fuel shutoff not activating until 192 instead of 190 as programmed
The 700 odd rpm over redline is gainable within that 2 mph.

Conclusion: Engine failure was not a result of driver misuse, abuse, or overrev, but
because the computer did not perform as programmed.
Action: Warranty replace with crate motor

A few pictures: http://members.bellatlantic.net/~aj98/engine.html

AJ


[Modified by AdrenalineJunkie, 2:17 PM 2/15/2002]

 

If there is no rev limiter, what is that "funny " thing that happens around 6200 in first gear at maybe only 40-50 mph? (6600 rpm in the Z06)
Besides, if you are documented at 500-600 rpm over redline(you as the driver had that choice to rev that high), you are one lucky dude to have warrenty replace your engine.
You probably were lean, but more than likely due to lack of fuel pump/injector capacity.

 

:lol:

 

Adrenaline Junkie (this is not addressed to you).

Some of the morons at these dealerships never cease to amaze me.

Yes there is a rev limiter in ALL C5's.

From the 2001 GM Service Manual:

Fuel Cutoff Mode
The PCM cuts off fuel from the fuel injectors when certain conditions are met. This fuel shut off mode protects the powertrain from damage and improves driveability. The control module disables the injectors under the following conditions:

The ignition is OFF (prevents engine run-on)
The ignition is ON but there is no ignition reference signal (prevents flooding or backfiring)
The engine speed is too high (above red line)
During an extended, high-speed, closed throttle coast down (reduces emissions and increases engine braking)

The only reason manufacturers implement fuel shutoff for speed reasons is based on tire ratings. The C5 tires ratings are such that there is no need for a speed limiter.

And why would the fuel system "lean out" at 180+? Fuel delivery is based on engine load and RPM, not speed.



[Modified by kewlbrz, 2:37 PM 2/15/2002]

 

I know hitting the Rev Limiter is bad for NOS.
BUT, is it bad for a Supercharger??

I don't consider hitting it bad for a stock or H/C engine. No worries. I've lost track how many times I've hit it. Not sure why it would bend a pushrod!!? I don't think it'd have any effect like that.

Missed shifts to a lower gear is another story...

 

There are two different senarios.

1-When you hit the rev limiter, the engine only fires 4 cylinders, therefore detuning the engine so power is cut by 60-80%.
2-When you exceed red line (which can take a while at 20% power) the fuel is shutoff ie the injectors don't spray but you can damage the engine especially in a over-rev downshift condition.

So, hit the rev limiter all you want just shift when you feel it and you will be ok.


[Modified by RedLandRocket, 3:20 PM 2/15/2002]

 

Understand, I'm not taking shots at the messenger here, only the tech that gave out that goofy info. No stock C5 is capable of top speeds in the 180 or above range. I'm sure somebody will say they have done it, but I'm here to tell you that if you car is stock, you better have proof or I'm not buying it.

 

I live in Germany and have a stock C-5 exept, vortex ram air. 179MPH is the top speed. Can't make it past 180 even going down a long hill!!!

No speed limiter in a C-5, only a rev limiter.

 

Thanks for not flaming - I took enough of that last time.

The info provided is what TAN told my dealers mechanic.
Given the replacement cost was 15k incl labor, why would TAN lie to the dealer as to the cause?
Cascading the logic, why would the mechanic lie to me? (and why would I lie to the people here?)

My car was off-line for over a month waiting for resolution and the new engine.
I'm just trying to save someone else the stress and PITA of the whole ordeal.

Agreed, I was lucky, as GM initially declined the claim due to the overrev condition.
The dealer pressed the case, so GM asked for the computer, which was sent to them.

What I've posted is the data they told me had been captured/was extracted from the computer;
the computer should have stopped the engine before damage occured.
It didn't. That was their reasoning for warranty replacing the motor.

No wind resistance on a dyno...the above story is also why on several posts asking about what to do/not to do on a dyno,
I've replied with "do not do a top speed run."

Not that I stayed there long, but I have inadvertently passed 6200 in first w/o effect,
so I've not experienced that "funny thing that happens" someone mentioned.

Given time, I can search my videotapes...and provide a shot of the dyno computer screen showing the speed/rpm.

AJ

 

There is a "rev" limiter on the upshift. How it is controlled, you hint at, and in fact you got a new motor and controller because it did not function as designed. That being corrected, the rev limiter will not protect you on the downshift, (i.e., skip shifts from say, 5th gear to 1st - 3rd ).

Indeed more energy potential through your vette's system can be generated on the downshift that the upshift.


[Modified by ruking1, 10:14 AM 2/19/2002]


[Modified by ruking1, 10:19 AM 2/19/2002]


[Modified by ruking1, 10:22 AM 2/19/2002]

 

Ruking is right. The reason the engine cant control unintentional downshifting is that bascially the tires lock up and the engine overrevs. If the engine could somehow control an overrev in that sistuation, it would have to physically lock the motor (i dont see how), and would keep you in a tire skid.

Just to followup, there is NO speed limiter in the C5. Only a rev limiter.