I recall hearing people say this. Since I drive granny style daily, I should try to rev the engine high, like at redline once in a while. It helps to break up some of the carbon deposits, etc, etc.

True or false?

If true, should it be done with no engine load, like in N?

I also read that over-reving can be bad for an engine. Like it can bent valves. One would also say, how can that be? Engine have electronic cut-offs. And yet, there are guys that miss a shift (like 6th to 3rd, instead of 5th) that would cause the engine to over-rev.

Educate me.

TIA.

 

a rev limiter is electronic (fuel and/or ignition cut-off). an overrev from a misshift is mechanical, which nothing electronic can stop.

 

As long as you're not FORCING the engine speed higher than fuel cut (just above red line) by going into a too-low gear at too-high speeds, you're not going to damage anything.

 

True.

Not necessarily "at redline", but it can be good to do an "Italian tuneup" once in a while.
http://en.wikipedia.org/wiki/Italian_tuneup

Make certain that the engine is fully warmed up first, and then do a full throttle from from a stop to near redline, in every gear you safely can, repeat a few times, then allow the engine to run in low load conditions for a bit (cruse) before shutting it off.

I've seen mixed opinions of taking an engine to redline without a load. I don't think it's the best idea to do it, but can't say for certain that it's bad for the engine. Either way, without load, it won't burn off carbon and just makes it a waste of fuel at best and a way to try and grenade the engine at worst.

You already have your answer there. Only missing the shift can over-rev the engine. You can't do it with just the gas pedal, due to the electronic cutoff.

Also, be careful trusting the fuel cut to save the engine. If it was purely a spark cut, I'd trust it more, but fuel cut could result in a lean burn condition, which can cause pre-ignition, which can hurt the engine... Lots of "can" use in that scenario though, and many of us bounce off the limiter without issue.

 

The stock rev-limiter isn't really that outrageous. Some of the cheap ECU chips you can buy will boost or remove the rev-limiter, making people think they're getting more power, and they end-up floating a valve because they didn't install better valve springs (not like it would make more power anyways without reconfiguring other parts of the engine).

More on-topic though, I hear people saying the same thing about revving your engine up is good for its "health." And then the same people put high octane fuel in their tanks saying that's good for the engine's health, too, when exactly the opposite is true (since it's not good for a low-compression engine and leads to carbon deposits faster), and say that it improves performance when the opposite is true (lower octane will provide more power). I don't trust what anyone tells me.

In one hand, it's not bad to rev your engine up, so long as the rotating assembly is in balance. I don't think it's an end-all solution to removing carbon deposits, though.

 

From the wikipedia article I linked to:
On it's own, it isn't a solution for much of anything, unless you have an RX-8.

I'd say it's only useful on those cars that are subjected to the abuse of short trips that never fully warm up the engine. These engines tend to accumulate oil sludge and carbon deposits from a lack of sustained full temp and high load operation.

 

Pretty accurate and just about sums it up. Reving the engine itself will have little ,if any ,benefit.(though having a "rotating assembly" out of balance is a moot point in todays cars. Unless there is mechanical damage the engine is balanced fine as is. )It is a WOT run the will help remove "some" carbon buildup. And yes high octane fuel used in an engine that is not set up for it, will result in increased deposit formations while yielding little to no gain in performance or fuel mileage.

 

Just dont do the famous moneyshift. 3rd redline to 2nd. No idea how much b18c1 survived that with only 8 bent valves and 0psi in cyl 3.
GL