am I lugging this thing?
 

When I'm doing my daily driving in my 04S, I like to accelerate briskly up to 4k rpm; 6k or more if I need to make a move. I'll usually shift from 3rd to 5th (missing 4th) at about 55 mph, and cruise between 50 - 55 mph in 5th on a level road. This puts me between 2k to 2500 rpm.

Is cruising on a level surface between 2000 - 2500 rpm considered lugging?

No.

Lugging an engine occurs when you push the gas pedal at that low engine speed to try to accelerate and the car either doesn't or barely accelerates.

It's perfectly alright to cruise at low engine speed. Just drop a couple of gears to accelerate or go up a hill.

Generally when I have questions about lugging I try to think about what an auto gearbox does in certain situations. Usually autos will cruise at 2-3k at highway speeds and when you need more power to accelerate it'll drop down a gear or two and give you more torque.

Obviously, this depends from car to car but I feel it's a good general guide.

No need to drop into a lower gear with my Saab Viggen, enuf torque in any gear...

My 2 cents? At least in my car, '03 base, 50 mph in 5th is borderline lugging. Not much happens when I step on the gas. Don't usually go into 5th unless I'm doing 60 +. Lugging and the effect on the IMS has got me sort of paranoid. I'm always in a lower gear than I probably need to be but I get a great response when I punch it. And I don't really notice it affecting my gas mileage that much.

The thing to remember is that your oil pump and your coolant pump are crankspeed dependent.

Drive at too low an RPM and you're not providing adequate cooling or lubrication. And, the oil functions as both coolant and lubricant. It provides 60% of your engine cooling, and from some of the most critical areas. As it lubricates the main and rod bearings, it also carries away heat. Same with other areas of the engine, such as cam journals, where the coolant doesn't flow.

2200-2500 RPM is fine if cruising (though I prefer staying at 2500 or above).

But, there is a difference between cruising and accelerating. The engine isn't lugging if power output exceeds demand (such as cruising). But, I wouldn't mash the wow pedal from 2500 RPM in 5th to accelerate, this is where you want to select a lower gear first.

There's an old addage which is good advice: "when in doubt, downshift".

Cheers!

+ 1, 2000rpm is fine on the highway.

Just a guess but I'm thinking that 5th in a 6sp is different that 5th in a 5sp.

Good point about the gas mileage. I wonder if 500 lower rpm when cruising makes that much dif, as I'm trying to save gas. Prolly a question for a different thread.

I didn't think about that. So as the temps go up, so should the revs.

Well, not really... if the pumps aren't nominal, the temps will go up, period. Once nominal, the temps will essentially stabilize. The pumps are certainly operating at a good flow rate by 2500 RPM. Too high, and the pumps can cavitate and actually reduce flow.

Your temp gauge isn't telling you what temp the engine critical parts are at, it's telling you what your coolant is at. On a Boxster, this is typically around 180 degrees.

But the temps at the crank and big end journals can exceed 600 degrees. That's OK, they're designed for this. But it is the oil and the oil flow which keeps it at this temp, and there's no gauge for this, except maybe extrapolating the Tach.

So far as Range (MPG) is concerned, there are many variables, such as weight (don't keep the Trunk/Frunk loaded with unneeded items), tire pressure, tire rolling resistance, make/model of tire, road surface, elevation changes (hills), time at idle (stop & go), weather, top up/down, windows up/down, even the prevailing winds (headwind = lower MPG, tailwind may increase MPG). Then there is that variable right foot.

But also, every engine has a sweet spot, and if you can determine it, you can take advantage of it.

For instance, I bought my E-30 (325is) in NC and drove it 1400 miles home. Borrowed a friend's V1 for the trip. So confident, I had the cruise set to 85 MPH most of the trip (3100 RPM). MPG was 32.4 - reported electronically and verified manually.

One week later, with a fresh oil change, I took a trip 400 miles. No major differences in road, elevation, weather, etc. No V1, so I reduced the speed to 76 MPH on cruise. I ran at about 400 RPM lower because of this speed, and got only 26.2 MPG. This engine just likes to run at 3100 RPM - probably reaches it's best volumetric efficiency in this range.

This is not going to be a Boxster thing, it's unique to each individual engine. They will all have similar MPG overall, but every engine is different for lots of reasons - miles, type and mileage of oil, quality of fuel, regional fuel differences, etc. And each will have it's own 'preferred' RPM to yield maximum Range.

It's not easy to determine, you need some long trips and a bit of luck to spot it (or lots of record keeping). But if you can find it, and can operate the car in this range consistently, you can maximize your Range.

Cheers!

Quote:

Originally Posted by Lil bastard Well, not really... if the pumps aren't nominal, the temps will go up, period. Once nominal, the temps will essentially stabilize. The pumps are certainly operating at a good flow rate by 2500 RPM. Too high, and the pumps can cavitate and actually reduce flow. Your temp gauge isn't telling you what temp the engine critical parts are at, it's telling you what your coolant is at. On a Boxster, this is typically around 180 degrees. But the temps at the crank and big end journals can exceed 600 degrees. That's OK, they're designed for this. But it is the oil and the oil flow which keeps it at this temp, and there's no gauge for this, except maybe extrapolating the Tach.

Good info! I should have clarified myself though. I was thinking that it would be a good practice to drive with higher revs on a hot summer day and lower revs would be ok on a cold day. Maybe an oil temp gauge would be a good idea.

Interesting... I wonder if you would have gotten better mileage at 76 mph by dropping a gear to get that 325 in its sweet spot? It sounds like it would be worth it for me to try driving with a tank in 4th at 50mph and compare the mileage with a tank in 5th at the same speed. A 6 mpg difference is worth the hassle of finding out.

I read a car mag article where the editor suggested you'll get better volumetric efficiency by basically lugging the engine. He said to accelerate as fast as you can to your cruising speed by using a large throttle opening and low revs. It's best done with a manual so you can short shift to keep the revs low. He said it worked better in a high torque engine like a V8, so it probably won't work on a box, although a box has way more torque than say a S2000. Too bad he didn't say what revs to use at cruise.

Not meaning to jack my thread as the topic is lugging, not gas mileage.