RPM's- what's the deal?

[tdorsey835]

I have seen several times on this board- most recently on trader220's oil pressure question- that driving at to low of an engine speed is not good. Now I understand that 'lugging' the engine in 5th gear up a hill at 40 is no way to drive these cars, but I'm hearing (or deducing) that you guys are driving 65 in third gear and rarely if ever using fifth gear. What is the deal with the RPM situation? Incidentally- and to the other extreme- I've got that dumbass up shift light that constantly tells me to shift at 2500 !! Damn is that annoying.

[JTO]

Hi Troy,

I think in general we tend to drive our cars pretty agressively. As far as cruising, I will stay in fourth if I'm cruising at 65 mph. My impression is that for older cars like mine, revs help keep the carbon buildup to a minimum. When I'm cruising above 65 mph, I'll put the car in fifth.

My $0.02.

Troy

[Dave Ploss]

First, ignore the upshift light.

I'm not sure if this is the best way to drive but this is what I do.

Until the Oil Temp gets to approx 180 degrees, I don't go above 4000 rpm. I'll keep the rpms between 3k and 4k.

When it is up to temp. I'll typically cruise on the highway around 4000 rpm. In 4th gear, 4000 rpm is ~ 80 mph. On Massachusetts highways I have Kia's, 1987 escorts and various other cars pass me like I'm standing still. Now, if I'm on a twisty road or an on or off ramp, I'll shift between 5k and 6k. I'll cruise on twisty roads around 4500 - 5000. That's where the car is fun.

Basically I keep the revs below 4k before it's warm and anything up to the red line when it is...with the usual disclaimers about safe driving.

my $0.02

Dave

[Tim Walsh]

I ussually keep me car between 3-4500 rpm unless I"m have a "spririted" drive and then she sees between 4500 and redline (6500rpm)

I only use fifth for cruising on the highway, it keeps the engine between 3K and 4K.

[masraum]

Ignore the shift light (a loophole for fuel mileage issues), and don't drive around at 4500 rpm. It'll blow your mileage and cause extra wear on your engine. Yes the cars can do that, but they don't HAVE to, just be aware that the owner's manual does list minimum shift points for each gear, and they are something like this:
1st 2600
2nd 2500
3rd 2400
4th 2600

I drive my car pretty hard, I shift at 5 or 6K when the car is warm and I love to rev it up, but I cruise in 5th at highway speeds. If I had a '67S I may drive at 4 grand all of the time, but there is no need with a 3.2, 3.0 or 3.6. The reason they kept going to larger engines was to create more power and more torque so the things didn't have to run the really high rpms that the early small bore cars did.

IMO Running a 3.2 in 3rd or 4th at highway speeds is for people who don't want to shift. When I want to pass someone I drop a gear or two depending on my mood and go.

[stomachmonkey]

Under 4k till warmup then let er rip.

I basically try to keep the car in it's powerband all the time. For long stretches of cruising I'll use 5th.

Scott

[Superman]

A substantial portion of the heat generated by an engine is generated in the bottom end (main and rod bearings). If you ask a Porsche engine to make torque at low RPMs, you're asking it to make a bunch of heat at a time when oil flow and air flow are low. Lugging these engines can hurt them with retained heat. By raising engine speed, you are moving more oil (which cools the engine) and more air (which also cools the engine). In fact, raising RPMs while the load on that (Porsche) engine is low (coasting or cruising for example) will lower oil temperature. Apparently, a cylinder heat temp gauge will illustrate this clearly. You can watch CHT rise during high-load, low-rpm situations, and then fall when you downshift, even if load level remains the same.

Okay, enough technical talk. German air cooled engines simply have always been designed so that the more you flog them, the better they like it. Porsche engines in particular are legendary for their longevity under extreme conditions. and I mean EXTREME conditions. You can drive 100k miles in a 911, at the track, without ever letting rpms fall below 4500. Again, you can do this for thousands and thousands and thousands of miles.

I generally keep rpms between 3000 and 4500, in regular driving (mine is a daily driver), and I am more likely to cruise with rpms at 4800 than 2300. I could keep RPMs above 4000 constantly (after warmup) for years and probably not cause any wear problems.

[Yargk]

At 65, I cruise in 3rd.

[Rot 911]

Personally I would never advocate high rpm's or driving over the speed limit!

[trader220]

Troy,

Good point. I was loafing along in traffic on the freeway at 65 or 70 miles an hour and the question just poped into my head last night. I suspect that most people here tend to drive on the more agressive side. I love winding em out. For the life of me i could never find a use for the 6th gear in my 993 c2s. I understand that it allows for different ratios in the first 5 gears but 6th was such a dog. Take a look at the crew here.... you think anyone here is going to tell yaa they baby their car? We all know that in real world conditions the majority of the time you're in traffic and you're not ripping around like a banshy.

[trader220]

Bye the way dont forget this is the internet. Everyones smart, rich, good looking, and drives their cars at the limit all the time. I used to drop by some of the market chat rooms to discuss options but people did not want to chat about reality they all wanted to talk about how they beat the markets ever single day.

[rs911t]

Personally I would never advocate high rpm's or driving over the speed limit!

Except when you're working on threshold braking technique for Type 2 corners. That is, turns at the end of a long straight, as in your photo.



Me? My car is geared low, so 4k in 5th only gets me about 75mph. And, I like the sound.