Red lining
 

Hardly a topic for a hypermile forum, I grant you.

I googled the consequences of redlining an engine, and one forum response suggested that the occasional foray into the red actually helped the engine, preventing the build up of carbon deposits. Opinions on this?

I've never done it, and with a red line at 8K and an average rpm of 2K I'm not likely to, but I'm curious. Is it simply a case that incursion over the line simply cuts the engine until revs fall below, at which point the throttle reengages? Is no damage caused?

I would think that it is plausible.
It is as plausible as those Fuel treatment, injector cleaner and all those products in a bottle that promise 30% increase in fuel economy.

It may work a little bit, but it is not worth to even try.

I doubt it, but what does work is the long trip for the short commuting car to get it hot every once in a while.
When you only do short trips the engine never gets hot. Over time some water may get into the oil from the vapour in the exhaust gas escaping through the gap in the piston rings.
High water content wil turn oil into a buttery slush, raising internal resistance and possibly blocking lubrication.
Taking that long trip will effectively boil the water out of the oil. Use grill blocks to speed up the process ;)

It's perfectly safe to allow the car the redline occasionally. The redline is determined by where the engine develops its peak HP, and the mechanical limits of the drivetrain. Most cars employ a rev limiter, which cuts fuel beyond a certain RPM, usually a couple hundred RPM after the redline. This is a safety feature that will not allow the engine to rev beyond its limits to prevent damage.

As far as cleaning out carbon, I would argue that you don't really need to go all the way up to redline to accomplish the goal. A few brisk accelerations up to about 60-75% of the rev range will work just as well. There are plenty of products like seafoam that are designed to do the same thing, without potential damage to your engine.

I like to think it does good, that way i don't feel bad about hitting 65MPH in 2nd every now and then when i have a highway onramp to myself. :rolleyes:

My uneducated opinion is that it will do little good, but couldn't hurt. I've hit the rev limiter on my car a few times at around 7,500 RPM. Maybe I average once per year. There is never a need to go all the way to the limiter though, unless you're racing.

It is possible to go over the limit in a manual transmission by shifting into a low gear while traveling too fast for that gear. I've never done it, but I'm sure someone has. It goes without saying, this could cause catastrophic damage to the engine.

It doesn't hurt, but it's not necessary. Just a few runs up into the powerband every once in a while helps keep the engine clean.

So is constant relatively low revving actually bad for the engine? I rarely cruise beyond 2200 RPM, and almost never go beyond 3000.

I expect that if revving does get rid of deposits and such, there would be evidence around of engines that weren't revved and have that kind of buildup.
Anyone seen that?

I'm willing to believe that the occasional revving helps the engine, just want to understand exactly what's happening.

Actualy yess, I have seen it. There is a groove of carbon deposit at the top of the block cilinder. But it's there because the piston rings don't travel to the very edge of the block. Going 7000 rpm instead of 2000 will not bring the piston closer to the edge so is will not change anything.
http://www.ms-motor-service.cn/ximag...1708201211.jpg
I have found that picture online, it is not accurate since the rest of the block is just too clean but it represent where it is. Usualy the groove is smaller than that and form a powder when removed.