engine at high rpms for extended time - concern?

[Christien]

I'm commuting for work 2 or 3 days a week lately, just over an hour each way, open highway cruising at 120 km/h (75 mph). My transmission is only a 4-speed, so I'm at about 4000 rpm the entire way. It occurred to me on my way home the other day that it might not be great for the engine to run at 4000 steadily for an hour or more. Then it also occurred to me that it might even be beneficial for it.

What says the Pelican brain trust?

[Joeaksa]

Probably the best "Italian tune-up" you can do to a 911 or most other hi-performance engines.

[Packy]

RPMs kill engines, but usually at higher RPMs than what you're running. I've heard people say don't cruise at 5k or higher for extended periods of time. FYI, the forces on the connecting rods and the rotary assembly increase exponentially with RPMs.

[layzee]

Err - its meant to do that

I just drove to Le Mans from NW England with the tach always over 4k, probably 600 miles each way. That's about 140kph+ in my 4 speed Sportomatic.

[Gemballa2006]

I try to not drive below 4K haha. Thats where it works the best. These are Porsche's, aka street legal race cars. Drive it and enjoy it.

[WIL84911]

Coming from work just yesterday as usual on NY thruway... I turned off the cd player after downshifting to 4th so I can listen to beautiful tunes by way of 2/1 M&K. hehe

[ossiblue]

As previously stated, these engines were built to run at theses rpms. BTW, just because your car is a four speed isn't a factor--the final gear ratio is the same on the 72 four and five speed tranny. You also have a 7:31 ring and pinion which will keep you at high rev's at highway speeds.

[kidrock]

recently spoke with a trusted Porsche repair specialist who also races...he swears by keeping these motors in the 4K range. Says they stay "cleaner" this way. I usually don't like to go over 3.5K until she's properly warmed up...then pretty much anything goes.

[Gemballa2006]

I believe the manual for the 84-89 turbos states to start the car, get it on the road right away, no idling, and wind it out in first and second to blow all the crap out. If thats straight from Porsche I don't think driving at 4K is going to hurt any engine they build

[Packy]

They come on cam at about 3500-4000, that doesn't mean that it is better for the motor. They were designed for high RPM torque curves. Aluminum blocks should always be warmed up before driving hard otherwise the tolerances wont be correct and you can damage your engine. Stay out of the power band until your engine is warm. Let it warm up for a good 5-10 minutes before driving and take it easy until oil temps are up.

I always cringe when I see the cold engine Le Mans Starts.

[rnln]

are you saying sit and idle the car for 5 - 10 minutes, or drive slow for 5 - 10 minutes?

[tcar]

Originally Posted by Gemballa2006

I believe the manual for the 84-89 turbos states to start the car, get it on the road right away, no idling, and wind it out in first and second to blow all the crap out. If thats straight from Porsche I don't think driving at 4K is going to hurt any engine they build

Where does it say that in the manual.

That's generally a terrible thing to do with a cold engine. Even worse with a turbo.

I'll bet it says not to sit idling but to drive easily, not hard, not high rpm's until the oil is warm.

[Packy]

Originally Posted by rnln

are you saying sit and idle the car for 5 - 10 minutes, or drive slow for 5 - 10 minutes?

I generally idle the car but driving slow is fine. The idea is to limit the loads on the engine and aluminum block while it is still expanding from the heat it is absorbing. I've heard it is better to drive slow than to idle, probably because you keep the fluids flowing. Either way, definitely don't drive hard until the oil temps are up. Aluminum expands more than steel at the same temperature differential (the aluminum block expands more than the steel crank).

[Gemballa2006]

It was heresay from someone else. I have heard that letting these idle isn't good though

[Christien]

There's no need to idle the car to let it warm up. Easy driving is fine. The point is that until the metals are all warmed up and fully expanded, you can damage the engine at very high rpms. Many modern performance cars (eg BMW Z4) have dynamic redlines - the guage is orange-backlit on the hashmarks. When you first start the car the redline will be at, say, 5000, then as it warms up, the orange backlights go out one by one until it's at 7500, or whatever full warmed-up redline is. I regularly start the car and head straight for the highway (about 2 minutes from my house), but I'll keep it at 3000-3500 for the first few minutes.

My concern was driving for extended periods over 4000, and whether or not I should give the engine a break. I'm not at all adverse to high rpms, especially at the track. Usually my car will see redline every time I drive it, once it's warmed up.

[Packy]

Maybe when idling you get hot spots and can boil the coolant and get air bubbles? Anyone?
This may be okay for air/oil cooled engines but probably worse for water cooled. Hmmmm?

[JeremyD]

The cams need oiling / flat tappets - at Idle there is not enough oil pressure to adequately oil the cams/tappets.

Much better to drive - or idle at over 1500 rpms...

[Joe Bob]

Ummmm, it's a Porsche, flog the Bastard....just watch engine temps.

BTW, even though it's a 4 speed, the final drive is pretty much the same as a 5 speed.