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.

I live in SF, there are many hills, small streets and lots of traffic.
If suppose I shift at 6000, and 2000 is a definite no no, am I supposed to stay in first gear the whole time?
I usually get to shift to second and that's about it until I find an excuse to hit a freeway.
I would probably spill my girlfriends cappucino if I stayed in first.:)

Well, since everyone on this board bought a 911, and there is widespread disagreement on this, then your assumption is incorrect. "Best" does NOT necessarily mean "fastest".

Best could also mean "least engine wear", or "best compromise between performance and fuel economy".

I shake my head every day when I read posts from you speed demons who are under the impression that these cars are made to be driven hard. They are not. They are made to WITHSTAND hard driving, but that does not mean that it is GOOD FOR THEM.

A Porsche engine and drivetrain has no special magic. The rules are the same as for all other cars. The harder you drive them and the higher you rev them, the more stress you put on them and the sooner they wear out as a result. FULL STOP.

Do I shift at 5-6k occasionally? Sure I do, because I'm willing to trade a little engine life for some fun. But 90% of the time I shift at 3.5-4k because I want my car to last many years and keep its value without spending an arm and a leg maintaining it. I am also perfectly happy with that level of acceleration. For me, the fun of the car is more in its handling than its speed, and I get a tremendous amount of enjoyment just leisurely cruising through the twisties at 3k rpm.

Do whatever you want with your car, but try not to assume that all 911 drivers are just like you. They aren't, thank god, or there would be far fewer 911s on the road today.

Racing? Enough. 2nd mechanic on a formula team, a stint at Mickey Thompson when they were in 3-4 types of racng simultaneously and karts for 30 years. Now, with karts especially, I understand torque and hp because there really is so little to work with and yet the things would regularly top 100mph at Willow with 16hp.

BeepBeep, clear as mud? Nope, I'm with you on that. We are sayin the same thing essentially.

Who would have thought so much discussion on shifting? You never know what is gonna take here and what will slide.

You and I will still be enjoying our original engines when the rest of these power junkies are on their second rebuild.:)

No, you'll just be praying that the B12 treatment clears up the carbon buildup. :p

From everyone I've talked to and everything I've read, going *slow* with these engines is just as hard on them as going fast. Will constant redline shorten the life of the engine? Probably, but I think that spending most of your time loping along at 2K will result in an unhappy engine, and is a waste of the car. I don't think babying these cars does them any favors...and frankly I don't enjoy my car at 2K.

ymbermv
(your mileage between engine rebuilds may vary)

If you have that "white mystery gunk" in your oil cap you shift at 2500-3000.

If you have powder painted or polished Fuchs you shift at 3000-3500.

If you have a powder painted fan you shift at 4000+

If you have 300HP then you shift when you see the other guy in the rear view.

Oh, what a load of crap you've been listening to. Can you provide a logical explanation why going slow is just as hard on the engine as going fast? You have to be careful who you listen to and what you believe. There's way too much snake oil mythology surrounding this cars. The rules of engine wear are governed by reason and common sense, not by German engineering or lead-footed hot shots who will believe anything that justifies their need for speed.

Secondly, I never lope along at 2k, nor did I ever encourage it in any of my posts. I merely stated that there's no reason to keep the RPM's above 3k unless you are accelerating or cruising at high speed. At cruise speed, you should be in a gear that is easy on the engine (want to maximize cooling don't you?) while still providing enough available torque to handle an emergency. I find that sweet spot to be between 2500 and 3000.

p.s. Sorry for the rant. I'm having a rare day.

Another "newb" probably with "white mystery gunk. :)

Same guy looking for his "performance springs"?? LOL

"Lugging" is a myth. It's in fact a very efficient way to run an engine. Our dads all told us not to lug the engine, but none of them who did were mechanical engineers.

Stephan

It depends on what you consider lugging. I'll quote a post by John Colasante:

I am definitely learning alot - please continue - I am the first in my family to even own a sports car so this is great. I added the short shifter in the car - but does it enhance better shifting points? I hope so. I started shifting with the light to learn and then pushed it a few rpms higher.

"I think that spending most of your time loping along at 2K will result in an unhappy engine, and is a waste of the car. I don't think babying these cars does them any favors...and frankly I don't enjoy my car at 2K."

I don't spend most of my time at 2K. I just get through the neighborhood that slow. When I get to a main road I go to about 2.5 or 3K, maybe more. When I enter the freeway I'll see 4K or faster. I look at my plugs and they look fine, no carbon build up. Do you suggest I go to Wal-Mart at 6K or 5K?

I've read that for best acceleration you should keep the RMP between peak torque and peak power. In theory on my car that's 4200 RPM (peak torque) to 6000 RMP (peak power). Seat of the pants it certainly seems to pull strongest over 4000 RPM. I haven't dynoed the car yet so I'm not sure how flat the torque curve is.

On the track (which I'm very new to) I'm changing at a little over 6000RMP (red line is 6800) and the revs drop to just under 5000RMP before I'm accelerating again. Around town I typically change around 3000-4000RMP, unless I'm having a little fun, in which case I keep it over 4000.

Those are the shift points my car seems happiest with, I'll know more once I get it dynoed.

I will never claim to be a mechanic (nor play one on tv), so I'll defer to those "in the know". I thought there were plenty of examples of engines not being run hard, and having the valves/etc get carbon build up. Isn't this part of the 993 OBDII issue?

I would suggest you don't go there at all (I've never set foot in one and never will), but that's another rant/thread entirely...

hey, drive your car however you like.

As suggested by several listers, lugging is not just an engine speed-related phenomenon. I can drive at 1500 rpm without lugging the engine. Of course, I may be in 1st or 2nd gear, have very small throttle openings and the car speed might be only 12 mph, but the engine is not being lugged.

To put undue load on an engine by lugging, you must have a combination of relatively low engine speed with relatively wide throttle opening. Operating the engine like this puts the engine on the edge of detonation and creates excess heat.

As for the term "best", I think you should define what this means to you in order to arrive at the "best" answer.

Sherwood
http://members.rennlist.org/911pcars

I posted regarding this question not very long ago...

http://forums.pelicanparts.com/showthread.php?s=&threadid=152665&highlight=How+to +drive+a+911

My answer: Turn key, warm up oil, flog if you want, cruise if you choose, either way, enjoy.

As Sherwood said (and I asked early on), "best for what?" The Carreras have a shift indicator light that must be telling you the "best" shift point, but I believe that is calibrated to maximize fuel economy, as opposed to fun economy.

I'm interested to see what the experts say with regards to "best" for engine longevity. I thought that most of the wear takes place when first started. So I'll pose a specific question: assuming an engine in proper tune and properly cooled will running it at 3K make for a longer lasting engine than running at 6K? Is there a plot of engine life v. rpm? Assuming that 6K is harder on the engine, how significant?

Not that I'm going to quit spanking her regularly. But just for the record I don't race anybody, nor do I speed recklessly. I just tend to run at higher revs (staying in second as opposed to third around town) and like to get up to speed quickly. And as I said, being at 3500 vs. 2500 allows for quicker avoidance of latte-laden suvs or cigarettes tossed from careless cars ahead SmileWavy

Todd,
Running at a constant, steady speed will always produce longer engine life (as well as better fuel mileage) compared to accelerating and decelerating. That probably doesn't answer your question.

Not an expert, but lower engine revs is relative, but that equates to lower load on engine parts and bearings. To qualify that; as long as the engine is not being lugged, carbon buildup is kept to a minimum and the engine is at operating temperature, lower than max. engine revs should result in longer engine life. How much longer? Don't know. Putting miles on any engine will increase overall wear. However, if engine longevity at the expense of driving enjoyment is one's priority, then just park it and look at it. Plenty of owners do just that - saves the engine revs for the next owner.

Sherwood

High RPM's cause higher temperatures and higher gas pressures, which equal
poor fuel economy, higher bearing loads, and expensive rebuilds sooner.

There is a price for all this fun!