RPM shift points of economy cars vs. racing cars

[sugarwood]

This week, I was reading a some very old threads about RPM shift points on the 911.
I thought this topic would be of interest to new crop of owners like me who were not around a few years ago.
Based on those threads, all the power is above 3000 rpm, and many people are shifting at 5000+ since max HP for the 911 is at 5900rpm.

Well, that's quite a mental adjustment to make, b/c it feels like regular high revving as described would eventually lead to "Should I rebuild this one, or find a donor engine?" Bringing the RPMs to these (seemingly torturous) levels is counter-intuitive to the way we are taught to shift a typical car. To date, I have mostly shifted my 911 like any other car and kept it b/w 2000 and 3500rpm. So, I tried it for myself, and kept the RPMs above 3000. Yes, the throttle certainly was a lot more responsive.

Here is the thing I am curious about. Is this sort of high RPM shifting unique to the 911, or performance driving, in general? And, can this strategy also apply to basic economy cars that also generate peak HP at 6000rpm? Because I have never seen anyone shift an economy car at 5000+. What if they did? Does it react the same way a sports car does? The 911 seems like an entirely different car when shifting at high RPMs. Does every car transform into a different car when shifted like that? Are most basic commuter drivers leaving tons of performance on the table by keeping RPMs between 2000 and 3000?

[gliding_serpent]

I always shift my car at 3k rpm until the oil/tranny warms up a bit. I shift slow during this period. I avoid runs that are too short to properly warm up the car.

On the street my car probably spends most of it's time cruising in the 2-3k range. I often try to get up to 6k now and then because is is just too fun not to. I mind my manners however as going above 4k is loud in my car, and the speed/noise can attract the law. Still, on quiet driving roads i like to stay in fourth and give it a go! 3rd if things are tighter.

I focus more on smoothness and enjoyment than outright redline speed. My style is to carry as much speed as possible, and to keep the throttle pretty smooth, snd the gears high. Unless passing, i am generally not a heavy throttle kind of guy and i probably shift near 4-5k. I am not racing, but a lot of people get freaked out by the speed i carry.

At the driving course i was at this summer, i do about 4k shifts on lap 1, 5k the next, then 5-6, then once the car and my brain are warm, 6+ but i dont wait to hit redline to shift. I tend to be in as low of a gear as possible to maxamize rpm's and power, and i try to shift as late as possible, without running out of gear/rpm on corner exit.

As i get faster and more comfortable with carrying more cornering speed, smoothness becomes more essential. As such i end up using higher gears for many turns (but probably similar rpm's as i am getting faster). I still shift at max rpm's and stay high in the power band. In high speed turns i prefer the smoothness of power delivery that comes with a higher gear.

I always think of Jackie Stewart's higher gearing mentslity. Google "weekend of a champion". I think he discusses these things over breakfast. Very inspiring

[sugarwood]

Originally Posted by gliding_serpent

I always think of Jackie Stewart's higher gearing mentslity. Google "weekend of a champion". I think he discusses these things over breakfast. Very inspiring

Streaming it on Netflix right now
http://www.netflix.com/WiPlayer?movieid=70285687&fdvd=true&trkid=1467260

[Hnichols]

The 911 loves to rev; even though the redline isn't particularly high, it revs quickly -- and loses revs quickly, too. Maybe a lighter flywheel than other cars?

My old BMW also has its power up high, but it seems like you have to wring its neck to get it. That one is a four speed, and if you shift it like a newer car you run out of gears at 40 mph. Which tells me it was designed to rev high without blowing up. Same thing with the 911. The shifting is actually smoother at 4.5 K than at 3.

[Eagledriver]

The shift point depends on your objective. If you are not at wide open throttle there is no reason to go above 3500 or so. If you want performance and are at full throttle, rev to the redline.

-Andy

[Bill Douglas]

It all depends on what the manufacturer intended. Commuter cars sell well if their fuel efficency is good (and they have plenty of airbags), and they do this by having their driveable power down low in the rev range.

For Porsche this wasn't so much of a consideration. They wanted it to go fast. So they set the cam timing up to be most powerful around the 5,000 to 6,0000 mark. And the rest of it is based around this sort of driving too.

There have been a few 911s that have been too mamby pambed around and the engines have died an early death from carboning up.

[psalt]

sugar wood,

If the goal is max performance, the rpm shift point(s) are simple math problems based on the gear ratios, rpm drop and torque curve. Many times it is advantageous to exceed the hp peak because of the rpm drop.

If the goal is max mpg, light throttle and early shifting is not the optimum. In an SI engine the throttle plate restriction is a waste of energy and accelerating with wider throttle opening has proven to be more efficient. The vacuum in the intake manifold is energy that does no work. Also steady cruising at light throttle is not the optimum, pulse driving with acceleration and coasting around the target speed has proven to be more efficient.

Most people drive a 911 for enjoyment and running the engine up to redline is enjoyable. Unfortunately the shifting at high rpm is not so great because of the location of the engine.

[Driver_X]

Completely depends on engine design. For instance, we have 2 manual cars on our fleet that we drive daily. One, a Mazdaspeed 3, completely runs out of breath above 5,000 rpm and pulls like a freight train from 1,500 on up, so the shift points would be lower than our other daily driver a Subaru BRZ. This motor has a 7,500 rpm redline and will pull strong all the way up there. Anything below 3,500 rpm and the motor is a total slug.

I always tried to shift the 911 in the 3,000rpm range until fully warmed up, and then would regularly shift in the 4,500 rpm range, no matter how long it took me to get there as that's where the motor seemed happiest. Of course, a couple of pulls in the upper 5,000 rpm's was a must just about every time out. You know, cause it's good for the engine :-) And fun....

[Josh D]

The 911 boxer six is an over square motor (bore>stroke) with a relatively short rod. With very good flowing heads with large valves for displacement, this makes it a "fast" motor. It's power curve is also dictated by valve timing as well as intake and exhaust design.

A square motor, or an under square motor (stroke>bore) with a long rod are low revving torque "slow" motors. Torque comes on early, but they run out of breath early. Good for a truck or a heavy car, not so good in a sports car.

Back in the seventies when the fuel crisis hit and fuel economy become important, everyone started to slow down there motors by installing taller gears in the rear end and add overdrives to the transmissions. They also changed intake port designs for higher velocity at low engine speeds and cam timing to build bottom end torque. In the american V8's, this actually had a detrimental affect. In many cases, the oiling systems weren't designed to run at these lower rpm's for extended times and camshafts would go flat at around 100K miles. Tearing apart one of these you would also see a ton of carbon buildup on the pistons and combustion chambers. Due to this, a lean burn calibration, vacuum leaks from way too many emmissions control devices, and crappy gas, many of these engines failed due to burnt exhaust valves. Anyone remember exhuast valve rotators? That was a band aid.

The 911 engine has a fairly sophiscated oiling system, so I don't see that being a problem with low rpm running. But the carbon buildup would be. Drive it hard. That's what it was design to do and will live longer for it.

[TheSt|G]

Simply put, if you want to shift at 3k while toodling about, perhaps you should consider other cars. These engines come alive over 4k, with not too much below that.

[911pcars]

Originally Posted by gliding_serpent

I always shift my car at 3k rpm until the oil/tranny warms up a bit. I shift slow during this period. I avoid runs that are too short to properly warm up the car.

On the street my car probably spends most of it's time cruising in the 2-3k range. I often try to get up to 6k now and then because is is just too fun not to. I mind my manners however as going above 4k is loud in my car, and the speed/noise can attract the law. Still, on quiet driving roads i like to stay in fourth and give it a go! 3rd if things are tighter.

I focus more on smoothness and enjoyment than outright redline speed. My style is to carry as much speed as possible, and to keep the throttle pretty smooth, snd the gears high. Unless passing, i am generally not a heavy throttle kind of guy and i probably shift near 4-5k. I am not racing, but a lot of people get freaked out by the speed i carry.

At the driving course i was at this summer, i do about 4k shifts on lap 1, 5k the next, then 5-6, then once the car and my brain are warm, 6+ but i dont wait to hit redline to shift. I tend to be in as low of a gear as possible to maxamize rpm's and power, and i try to shift as late as possible, without running out of gear/rpm on corner exit.

As i get faster and more comfortable with carrying more cornering speed, smoothness becomes more essential. As such i end up using higher gears for many turns (but probably similar rpm's as i am getting faster). I still shift at max rpm's and stay high in the power band. In high speed turns i prefer the smoothness of power delivery that comes with a higher gear.

I always think of Jackie Stewart's higher gearing mentslity. Google "weekend of a champion". I think he discusses these things over breakfast. Very inspiring

+1. I think Gliding_Serpent has the right idea. i remain mystified by those who red-line between stop lights.

Sherwood

[Eagledriver]

Originally Posted by psalt

If the goal is max mpg, light throttle and early shifting is not the optimum. In an SI engine the throttle plate restriction is a waste of energy and accelerating with wider throttle opening has proven to be more efficient. The vacuum in the intake manifold is energy that does no work. Also steady cruising at light throttle is not the optimum, pulse driving with acceleration and coasting around the target speed has proven to be more efficient.

Most people drive a 911 for enjoyment and running the engine up to redline is enjoyable. Unfortunately the shifting at high rpm is not so great because of the location of the engine.

I'm usually more diplomatic, but this sounds like gibberish. What does the location of the engine have to do with anything? Anyone with the slightest understanding of physics knows that accelerating takes more energy than steady speed.

-Andy

[porwolf]

In the early days of the Volkswagen the saying was "it must sing" meaning keep the revs high. One reason is that the air engine cooled engines need higher RPMs for the cooling fan to do its job, especially at load and going uphill. The same goes for air cooled Porsches, of course. The air cooled cars are designed to run at those speeds. I always was gentle on the RPMs and throttle before my Porsches were warmed up to operating temperatures, especially in winter time. Always stayed pretty much below 3000 PPMs. Once warmed up I rarely go below 3000 RPM.

[psalt]

I'm usually more diplomatic, but this sounds like gibberish.

Andy,

Maybe to you, but "pulse and glide" (PnG) is more efficient because of the BSFC at part throttle. Your "slightest understanding of physics" ignores the efficiency of converting the chemical energy of the fuel into work (70% loss). In a SI engine, peak efficiency occurs at WOT at the torque peak. Part throttle cruise is a much poorer BSFC. The increased efficiency of energy conversion and coasting more than offset the energy needed to accelerate.

BMW did the initial study into this in the 90's, publicized it widely, and it is used in all the record making mpg attempts. A 2009 SAE paper by a team from Virginia Tech and Argonne National Laboratory found that a simulated PnG driving strategy in a Ford Focus delivered 33-77% fuel economy improvement depending on different speed ranges and acceleration times. The fuel economy results of a 2004 Toyota Prius from simulation and testing showed 24-90% fuel economy improvement with PnG drive cycles compared to steady speed results.

If you are ignorant of this subject, I suggest doing a little research before being rude.

[wayner]

Originally Posted by sugarwood

Here is the thing I am curious about. Is this sort of high RPM shifting unique to the 911, or performance driving, in general? And, can this strategy also apply to basic economy cars that also generate peak HP at 6000rpm?

As others have said, it has to do with engine design.

Think of a horn without valves. It has one resonance frequency (engines have a narrow ideal RPM).

Take that horn and turn it into a trombone. Now you have a variable horn, good at many frequencies. Engine manufacturers use variable cam shafts now for the same effect on engines.

Air cooled 911 engines are from a era when there was no variable valve timing. Truck engine manufacturers designed engines for low RPM grunt (torque). Sports car manufacturers designed engines for high RPM horsepower.

If you have an economy car with variable valve timing, why rev it much?

If on the other hand it was designed to make lots of power out of a very small engine like the mini with its 1.6, you have to rev it to get any power (and fuel economy) because it just doesn't like to run at low RPMs.

[javadog]

Originally Posted by psalt

If you are ignorant of this subject, I suggest doing a little research before being rude.

I think he could have been more diplomatic but there are a few statements that you made that don't hold water.

"The vacuum in the intake manifold is energy that does no work." I get what you are trying to say but this just isn't correct. Obviously, a throttle plate that is less than fully open diminishes the full power potential at any given rpm. The higher vacuum that is symptomatic of this isn't 'energy'.

"Unfortunately the shifting at high rpm is not so great because of the location of the engine." This is completely false. One really has nothing to do with the other. A 911 actually has a pretty simple and direct shift linkage. The rear engine layout actually helps in this regard, as compared to a mid-engined car.

I agree with Sherwood, in that many 911 drivers, especially those that are relatively new to the car, or to performance cars in general, tend to use more revs than they need in normal driving. I define normal driving as going from point A to point B, with some regard given to the speed limits and driving at a similar pace to other traffic. In that case, you don't really need even half of the acceleration potential of a 911, and it is capable of driving in that fashion without using a lot of revs. I can keep up with normal traffic and not lug the engine and generally shift anywhere from 3,000 to 3,500 revs.

The key is to understand that the more power you need, the more revs you want to use. There are times that shifting at a higher engine speed is warranted but crusing around at small throttle openings in the lower gears is just a waste of gas and harder on the engine. Those that think that you need high engine revs for increased engine cooling around town ought to experiment with that a little bit. You might be surprised to find the opposite works better. Also, keep in mind that you are measuring oil temperature and not cylinder head temperature, which is probably a more useful thing to measure in an air-cooled engine. You should think about what hard acceleration or high revs does to cylinder head temperature...

Earlier 911s with less displacement or more radical cam timing often need more revs than the later cars. That's pretty simple to understand. If you need X horspower (or torque, pick one) to accelerate at a certain rate or to maintain a given speed, in general a later car will need fewer revs to deliver that amount than an earlier car. That's because the engines in the later cars are larger and Porsche increasingly tuned them for a fatter, flatter torque curve.

JR

[psalt]

"The vacuum in the intake manifold is energy that does no work." I get what you are trying to say but this just isn't correct. Obviously, a throttle plate that is less than fully open diminishes the full power potential at any given rpm. The higher vacuum that is symptomatic of this isn't 'energy'.

Nothing is free. If you can create a 16 in/hg vacuum in a 2 liter box without using any energy, I will recommend you for a Nobel prize. It does take energy to create the vacuum in the intake manifold and it is energy that does no work in moving the car. It is a completely different issue from cylinder filing and the crappy BSFC at part throttle. It is part of the pumping losses of a SI engine and fully described in Lumley's text on fluid dynamics in engines if you want to learn about it. It is one reason for the higher efficiency of the diesel engine.

I have owned and driven many 911's for 30 years and in my opinion they do not shift as well as front engined cars at redline after WOT. It is also my opinion that this is partially due to the longer shift linkage and the movement of the engine on it's mounts. I have several cars where the gear lever goes directly into the box and the shift at high speed is much better. Perhaps you've had a difference experience.

[javadog]

Originally Posted by psalt

if you want to learn about it.

Haha,

I could teach classes on that subject.

The point that I was trying to make is that what you said, meaning how you worded it, was the reason he likely called your statements 'gibberish'. You have to admit, there's a better way of getting your point across.

I've owned more than my share of cars, with about every combination of engine and transmission layout known to man. Their respective shifting attributes had more to do with the linkage design and the condition of the components. Engine position really wasn't a factor.

When I hear people complain about how poorly a 911 shifts, two things come to mind. Either that person doesn't know how to shift properly (at least half of the poplualtion, I'd guess) or their 911 could use some work (way more than half of the owners).

A new 911, shifted properly, was a joy to use. I also have a 914-6, with a freshly rebuilt gearbox, and it has a shift linkage that was considered by most people to be the work of the devil. It shifts like greased lightning.

JR

[psalt]

OK, so now you agree that manifold vacuum represents wasted energy that does no work ?

You just didn't understand what the word "is" means ?

Just like Bill Clinton ?

I drove these cars new and their high rpm shifting sucked compared to Alfa, Ferrari, BMW and Japanese sports cars, but that is my opinion.

[javadog]

Originally Posted by psalt

OK, so now you agree that manifold vacuum represents wasted energy that does no work ?

Any idiot knows that throttling an engine reduces its efficiency. Perhaps you should drive a diesel and quit worrying about throttles.

Originally Posted by psalt

Just like Bill Clinton ?

Really? Come on...

Originally Posted by psalt

I drove these cars new and their high rpm shifting sucked compared to Alfa, Ferrari, BMW and Japanese sports cars, but that is my opinion.

How did they suck, exactly? What problem did you have shifting at the redline that you didn't have at, say, 4,000 revs?

Study this sentence a while and see if you can figure out what's wrong with it:

Originally Posted by psalt

The vacuum in the intake manifold is energy that does no work.

JR