Best Shift Points
 

I have been driving stickshift consistently for about a year (as long as I have had the Porsche ) and I am trying to find the best shift point (rpms) for my cars. It seems like I can easily shift the Porsche between 5000/6000 RPMs but when I switch to the VW it seems like I am lagging when I shift that high. Both cars are comparable in horsepower - torque I think is close. The VW is a six-speed - I am shifting a lot more in this car than in the Porsche. For cruising/high-speed driving - what are the best shift point(s)? I don't want to cause damage to my engine by shifting improperly. Any help is always appreciated.

You mean you can actually shift before the red line?

6000, 6400, 6400, 6400; respectively.

Are you serious about this? I been wondering if I'm doing my engine harm by driving a long distance at 4000 rpm. Going above that would mean exceeding the posted surface street speed limit too much.

Whilst I can "appreciate" the shift points being quoted above at or over 6000 rpm, I think a certain measure of "serious" reply might serve 84Porsche and Cantdrv55 better than the full tongue in cheek versions...

It is not remotely "necessary" to shift that high up in the revs!

When driving my Carrera in a "normal" fashion, which I would for the purposes of this discussion rate as the "legal vmax. 120 kph", I shift as low down as 3000-3500 rpm, which I consider "very leasurely", absolutely non-stressing and "quiet". It is, of course, another matter when I want to go faster: medium-fast, I'd shift at anything between 4000 and 5000, maybe 5500 and when I want to go full out (which is +not really+ usual on the street, of course there's no harm in 6000 'ish. But I think the benefit is just for the noise, because at 5000-5500, my guess is that all the torque is (or has been) there and, sure, go up a gear!

I mean, after all, I don't always and at all times drive "full out" (I'd have police fines from here to eternity!).

As to driving "all day at 4000 rpm", why not? In fifth gear, that's exactly 160 kph. And I am absolutely certain that the Porsche Carrera 3.2 liter can do that from full tank to empty tank without the slightest problem at all!

Thanks Paul. Exactly the advice I need.

Sure, but why would you want to? If you're simply cruising, and you don't need to accelerate quickly, then there's no reason not to upshift. Not only does it save petrol, but it's quieter and it will extend the life of the engine. The higher the RPM's, the faster the engine will wear out.

IMO, the only times the tach should go above 3k is during acceleration or fast cruising in top gear.

On my well-modified 3.4-liter 911SC, dyno runs have produced a torque curve that is flat from 4,000 to 5,000 rpm. Though the redline on this particular engine is 7,500, I can't imagine any point in revving higher than 5,000 before shifting even for max performance, unless I'm on the track and conditions--distance to the next corner, etc.--require higher revs.

And for brisk performance, why run it any higher than 4,000 unless you're absolutely intent on staying in that max-torque band? Also, I agree with posters who advocate even more leisurely shift points for normal driving.

Stephan

He asked for "best" shift points. To me (and someone who would buy a 911) that would be max acceleration.

Torque is what acellerates the car. Torque rises from low rpms, hits a peak and then falls at higher rpms. You want to shift when the torque level at the falling rpm point equals the torque of the rising rpm level at the next higher gear. You can kind of feel this after several experiments.

I guess the "best" would be between 3000 and 6000??? Jeeeeeeez!!!!

Now can someone tell me what's the best tire for my car???

No ... there is only one BEST shift point per gear.

Rick, I'm familiar with torque... In my car, torque doesn't rise to a peak and then fall. It rises to a peak at 4,000 rpm, stays virtually flat to 5,000 rpm and then falls. If I shift no later than 5,000 rpm, I am maintaining max torque and the revs will not drop below max torque if they don't fall below 4,000, which they wouldn't. (Granted, I'm not talking about a micrometrically ruler-flat torque curve, but the variation from 4,000 to 5,000 is in the single digits.

Stephan

I don't agree with that. I think that the only time you should go UNDER 3000 rpm is coming to a stop. I would never sfift into a gear while intending to go anywhere that would put the engine at 2000 rpm. That's just lugging it and that will wear out an engine.

FWIW, race cars are set up track by track to shift at the max torque rpm and into the next gear at the max hp rpm which is not always redline. This is always realtive to the track layout so you don't get caught in a situation where neither gear is right at any point on the track. Sometimes it is necessary to stretch it a bit at the top to get to the next corner. All set ups are a compromise one way or another.

So, for really agressive driving, shift at the torque point and move up at the hp point. The standard ratios installed are OK for this, but not perfect. My 914 901 short ratio tranny was on the money on this one. I didn't have to over rev the thing to get going fast enough to be up on the torque curve. YMMV

best for what? Acceleration? Gas mileage? Ticket avoidance? Making cell phone calls while sipping your latte?

Those are all slightly different numbers. My general rule is 3K until oil is warm, then typical street shift is somewhere between 4-6K depending on situation and mood. It is rare that I get to "cruise" on the freeway for non-traffic periods, but when I do then I'll usually sit at about 3200rpm or so. In general I like to be in the 3-4K range around town on in-town freeway, as you never know when you need to punch it to get out of the way of some crazed suv...and if you have to downshift becuase you're loping along at 2K, you're road kill ;)

Are you monitoring the "CASIS" indicator?

what Milt said...from my old VW Bug days my dad always told me "don't lug the engine, dammit."

From purely physical standpoint, you will obtain maximum accelleration by choosing shiftpoints so sum of swept areas under power curve for each gear is highest.

As torque (and thus power) curve isn't linear but highly irregular, this particular problem must be solved numericaly. You have to know gearing for each gear and have somewhat accurate graph of your torque vs RPM curve.

Give me that and I can probably hack something to find optimal shiftpoints.

All this gets even more complicated when using turbocharged cars which have delay factor.

Clear as mud? :-)

"I would never sfift into a gear while intending to go anywhere that would put the engine at 2000 rpm. That's just lugging it and that will wear out an engine."

You are kidding right?

"FWIW, race cars are set up track by track to shift at the max torque rpm and into the next gear at the max hp rpm "

How much racing have you done? If you shift at max torque then you are missing some high torque on the other side of the curve. You would be wasting torque considering when you shift to the next gear you will definitely have less torque at a lower rpm. I shift when I feel the power fall "off".

No, he's not kidding, and I agree.

Regarding my previous post, yeah it was a little tic, but not completely. I’m w/ nostatic on cruising rpm, 3-4k is a great place to be.

When I’m running hard (most of the time since it’s not a daily driver) I usually shift at the top of the power, which happens to be close to redline. Sure it may not be at peak torque anymore but that doesn’t mean that all the torque has dropped off. Don’t forget that hp continues to climb, it’s not one or the other, they go together.

I have hit the rev limiter a few times b/c I just never felt a loss in power. The 3.0 would drop off a bit depending on gear, but the 3.6 just doesn’t stop pulling, ever.

When I cruise on the freeway its around 3200 rpm at 70 mph. Thats 5th gear. My 79 SC is stock and doesn't have big power so I don't "race" people. When necessary I will have it in 4th and pull away from most people or pass cars with ease.
When tooling around the neighborhood I regularly see 2000 rpm. I don't want to attract attention and be seen as a racer through the hood. Lugging it is when you are in 5th gear at 1500 rpm. You can physically feel the motor and trans "shake". If you shift above 3000 rpm you won't have that problem. but I can't see running my car to 6000 every time I jump in it.