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-   -   minimum RPM's vs gear selection (https://rennlist.com/forums/993-forum/176764-minimum-rpms-vs-gear-selection.html)

2ndof2 12-24-2004 02:46 PM

minimum RPM's vs gear selection
 
Was wondering: is there a minimum RPM that I should keep the motor above when driving around town or on the freeway? Just under 80mph in 6th the revs are at about 2800 or so. Is that ok or is it too low and potentially bad for the motor? I try not to lug the motor so if I get to a section of road where its an incline or if I have to slow too much for other traffic I downshift before placing too much load at low RPMs (under 2500 to 2900 or so). In short, what is the general concensus on the best RPM level to stay above in general?

Tom W 12-24-2004 03:25 PM

I think there are diverse opinions on this topic. Mine is: For cruising down the highway in light traffic 2800 is fine. To briskly accelerate, 2800 is low. I find I typically drive at 3300-3900 in my commute as I have a lot of acceleration and slowing (and a LFW with close ratio gears). With the LWF, you get pretty substantial transmission noise if you "lug" the engine. After a couple years, I've been re-trained by the audible feedback to keep my rpms higher. It's worse for gas mileage but makes for a much more responsive car to keep the rpms higher.

kkim 12-24-2004 03:39 PM

I've had a difficult time, too, trying to figure out what gear I should be in. For me, I've found 2000rpm and above is fine for light duty driving and the engine doesn't "lug" if I keep it above that.

I've also found a quick and easy way to determine what gear I should be in to be above that minimum rpm. Look at your speedo... if your going 20, you should be in second, 50/fifth, 60/sixth. Remember, these are the lowest gear you should be in to be above 2000 rpm. The gearing in the U.S. trans works out so this method works.

Prior to me doing this, I would always be below 2000rpm when coming in from a high speed highway section into town and I'd end up leaving it it 5/6 and unknowingly lug the engine down to 1200-1500 w/o realizing it. Now that I use the speedo as my gear gauge, I don't have that problem any longer.

1999Porsche911 12-24-2004 04:12 PM

REDLINE for ALL shifts! Anything less am you're babying the car.

2ndof2 12-24-2004 04:31 PM

Ho Ho Ho! You guys from Chicago have a great sense of humor...Merry Xmas!!

1999Porsche911 12-24-2004 04:35 PM

Merry Christmas to all you guys in California. You should stop by and enjoy the BELOW ZERO temps we are enjoying here today!!

2ndof2 12-24-2004 04:54 PM

Dare to dream! Stay warm out there...its about 70 degrees outside right now...I have the window to my office open to let the mild ocean breezes in. :)

porscheralph 12-24-2004 05:01 PM

Here is my 2 cents - I've driven Porsche's for the past 36 years, from 356's to early 911's to my current 993. I rarely shift below 3000, mostly 4000 to 4500 and ALWAYS redline two or three shifts every time I drive(once the car is warm and the oil is in the "happy" place). It has been my expperince that Porsche's are happy and run better (and longer) at these rev's. Enjoy the car and it will make you happy. My Best for the New Year.

STLPCA 12-24-2004 05:27 PM

Prior thread.
I cruise @ about 3-3.5k & shift @ between 3.5k & redline depending on conditions. I rarely use 6th below 75 mph (~2800 rpm).

Carrera Mike 12-24-2004 06:52 PM

My 97 C2 manual states the following Minimum Upshift Points:

1st to 2nd...15mph or 2750 rpm
2nd to 3rd...25mph or 2600 rpm
3rd to 4th...40mph or 3100 rpm
4th to 5th...45mph or 2700 rpm
5th to 6th...48mph or 2300 rpm

So as not to remember all these nos., I just don't shift at a minimum 3200rpm, therefor I give the engine enough power to easily move a certain gear. If you're under 3000rpm(not below the min upshift point) and you shift, as long as you don't hammer the accelerator or you're uphill, the engine shouldn't lag. Lagging is when your hear the engine knocks because it's under powered to turn that particular gear.

My normal shifting habit, I don't shift 'till rpm is over 3500. Agressive shifting, minimum for me is around 4500 rpm.

Joel Reiser posted this(below) at PCA Tech Section:

Ideal for fuel economy is to shift at the lowest rpm you can, and don't accelerate hard. It is mostly personal preference, but generally for economy you are talking 3500 rpm, give or take. This is also true for highway driving in rush hour traffic.

Ideal for acceleration is to run it right up there. Close to the redline, but not to hit the rev limiter.

Ideal for the track is a mix between the two if you are running low on fuel, or high on engine temps. Otherwise downshift before entering the corner, balance the car with the throttle to the apex, and floor it from the apex on out, and all down the ensuing straightaway to the next braking zone. Practice and build up to it, don't jump in over your head.

Optimal for general city use is probably around 4000 to 4500 depending on traffic. Optimal for the highway is dependent on cruising, which is more like the economy case above, or passing, which is more like driving on the track, you want to downshift when you need to get the best acceleration. But now where do we send the check for that annual renewable speeding license?!

Bouncing off the rev limiter probably doesn't do any damage, not until the dealer's tech reads the totals out with the computer.

In another write up, Joel Reiser wrote this too at PCA Tech Forum:

...Everyone is different, and different traffic moves differently, but the most common shift points are around 3500 to 4500 rpm in every day driving; 2000 to 3000 rpm for slow economy driving (best fuel mileage); and 4500 to 6500 for sporty driving. Shifting at 7000 and up is really for the race track, e.g. PCA Driver Education at any of North America's race tracks, and/or emergency high speed driving given suitable training and safe practice.

mr_bock 12-24-2004 07:25 PM

Drive it like you stole it..... :p :p :p :p

1999Porsche911 12-24-2004 07:51 PM

There is NO break in period for a car. Every car I have ever had has been redlined off the showroom floor after it is warm. A car is NOT a woman and therefore needs no training to learn how you are going to treat her.

msch 12-24-2004 07:59 PM

For me, I always keep it under 4k until the engine is warmed up (when the oil temp reads close to 9:00). Until then I drive over 2800 rpms to 3900.

mrsullivan 12-24-2004 11:10 PM


Originally Posted by 1999Porsche911
There is NO break in period for a car. Every car I have ever had has been redlined off the showroom floor after it is warm. A car is NOT a woman and therefore needs no training to learn how you are going to treat her.

Come on...this varies depending on the type of engine you are talking about, right? Although bench-tested, many new car engines have specific requirements regarding properly seating pistons, rings, seals, etc.... In many cases it is good to vary speeds, gears, shifts, RPMs, etc. with these new engines, but is not always good to drive off the lot redlining... (?) For example, I know in my BMW E46 M3, there were very specific recommendations from the factory regarding the engine break-in. These were substantiated by technical BMW motorsport articles and other sources as being required...

1999Porsche911 12-25-2004 01:03 AM

It is my belief and my experience that there is NO NEED to baby any engine during the so called "break in period". Over the years you have heard people say things like "you have to properly seat the valves and the rings and the pistons", etc. etc. Believe me, It's as if all these componants have just been thrown in the block and its the new owner's responsibility to get them to fit properly. If these things were not properly seated, fitted, installed, etc, your engine would immediatley come to a stop.

All materials used in the engine are properly machined and hardend prior to assembly and further driving of the car will not change that. It appears that some people think that an engine is assembled with parts that are ALMOST a proper fit and need final fitting during the operation of the engine. I wonder if these same people break in their new tires the first 3,000 miles to make them rounder?

I have rebuilt many engines, and believe me, if the componants are not built and installed with tight tolerances, even a low rev of the engine will throw them through th block or intake. On the topic a varying the speed....why? What happens to the engine when you drive for awhile at 5,000 rpm and then drop to 3,000 rpm? What happens if you simply drive at 4,000 rpm all day long? The same thing happens at all speeds. The engiine operates as it is designed. Oil continues to lubricate and the engine coninues to maintain a constant temperature. So once again, what changes, other than engine speed, by decreasing the revs once in awhile? Absolutely nothing. All moving parts are constantly lubricated by either water, oil, grease or fuel no matter what speed the engine is at.

In my opinion, the only requirment to increasing the life of a properly maintained engine is to let it get to full operating temperature before the abuse begins.

I have read that many Porsche owners have taken the first 3,000 miles to break in their new toys, yet they only drive the car 2,000 miles a year. What a waste of the first 1 1/2 years of ownership of such a nice car.

Drive the car and enjoy it. But if you insist on following the recommendations of Porsche for the break in period, make sure you use only Porsche Oil, Porsche coolant, Porsche replacement parts and you'll also have to eliminate all the non Porsche mods that so many of us have. There may also be a recommendation to use official Porsche air in the tires too.

Why is it that many will disgard the recommnedation from Porsche that only genuine Porsche parts be used, yet they use an after market oil filter or air filter? I mean if Porsche recommends something, it must be critical that we follow it, isn't it?

I think as we become more knowledgeable about something and develope an understatnding of its function, we grow more confident in making modifications. Those of you who insist on following the breakin period need to get a better understanding of the working of a combustion engine.

IMHO.


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