kmagnuss

I keep seeing people say that on here... to keep the revs over 2500.
Why?

redriderrick

Fun.


Assuming this is actually a serious question, there's been plenty written about how hard it is on any engine to be put under heavy load at low RPMs.

Rubik

It's not a general rule, it all depends on the road conditions. What, if I'm cruising down a hill and my RPM is at 1500 what would be the concern. On the other hand, if I'm going uphill and expect my car to climb at 1500 RPM, that's both not good for the car and it's stupid.

5CHN3LL

If you're settled in for a long cruise on the freeway, a nice low RPM is fine.

From a performance perspective - I'll leave the "lugging is bad" for someone else - shifting too early is a waste of time. True, peak HP is available well before redline, but delaying shifting until you get closer to redline keeps the car in the top end of the power band longer. Think about it - if you shift at 4500 RPM, the engine drops back down to a lower RPM, and HP falls off precipitously. You have to sit there waiting for RPM to climb as the car accelerates to get back up near peak HP. When you shift closer to redline, you'll still be at high enough RPM after catching the next gear to make good power. That's one reason why the plateau of peak HP at an extended RPM range makes for a great driver's car - if you shift fairly close to redline, the car is making gobs of power as you row through gears 2, 3, 4, etc. When you shift too early, you are struggling through the power band and never really getting to the point where the car makes power. You can hobble a race horse every time you ride it, but why would you?

If you prefer driving at very low RPM, with lots of torque, a diesel is the car for you.

dmw996

Also from what I understand is also be sure to get the oil temps up enough to boil off any condensation that can form in the oil to prevent any sludge formation.

gnat

No, that'll happen regardless. It's just a function of time. Higher RPMs = more heat though so the time would be reduced. You don't, however, run at high RPMs until the oil is warm though to make sure you have good lubrication going.

As to the question, high revs equates to a higher oil pressure which helps keep things lubricated as they should. It has also been a theory that keeping your RPM, and therefore you pressure, up is good for The Part That Shall Not Be Named.

At the simplest though, it's just more fun.

I personally stay in the 2.5-3k range for warm up and then stay in 3rd which keeps me in the 4-7k range, unless I'm cruising, then I'll use a few higher gears. Gas mileage sucks, but the audio is glorious and the jump it makes when you touch the throttle while in the middle of the band is fun

kmagnuss

Obviously from a performance perspective the hp peaks higher... maybe I wasn't clear with my question.
Why would I drive around town in 4th gear at 45 mph just to keep the rpms up over 2500... when I could use 5th gear at around 2000 rpms? I keep reading people say they drive around with the revs over 2500.... so why? I don't have hills here in Florida and the only time the car 'lugs' is if i'm under 2000 rpms and trying to accelerate.
In my mind if the engine is cycling an extra 500 x per minute that's 500 revolutions I just took off the engine's life. Am I thinking about this wrong? I've always been in the mindset to keep it around 2,000 rpms if I'm just maintaining speed and not accelerating... unless I'm out of gears.

aviography

Jake Raby mentioned in his session while in Toronto a couple of years ago that the Vario-Cam kicks in around 2,200 RPM (IIRC), keeping the RPM above that avoids the Vario-Cam kicking in and out, generating a bit of shock load to the mechanism.

kmagnuss

That actually makes sense... thanks avio.

Byprodriver

2,200 - 2,500 RPM depending on oil temp & viscosity, Jake Raby @ the 1st M96 rebuild class.

Byprodriver

Increases oil pressure & reduces side load on IMSB.

Paul Waterloo

If you read the manual, it's pretty funny that it says not to upshift below 2,900 RPM. I can safely say I NEVER shift before that.....I get terrible mileage, also seem to shift at 4,000 RPM or more. High RPM = low torque, which is good for the engine! At least it makes me sleep better at night.

RickMiller

Same here. Once she's warmed up, it's pretty rare that I shift below 3500.

Third-Reef

At low rpm you get peak volumetric effeciency, so even at 1/4 throttle you might be getting a full charge in the cylinder at 1500 rpm. This equates to full load on the pistons, rods and crank and for a longer period of time and with less oil pressure. It all sums up to more wear at high load at low rpms and no fun.

jj1

In most cars I usually shift according to the synchros. At above 4k it slides into gear nice and slick. So for me a touch over 4 for day to day driving. Just to add another reason not to shift early.