Question for Mechanics: 2200-2500rpm or 2700-3000rpm, what is best???

[Meat Head]

OK, I want the opinion from the people that actually work on Porsches or have a very good understanding of the design and internals of the 986 engine. What is the best operating rpm for our cars??? Is it best to keep our engines closer to 3000rpm when at cruising speed or at near 2200rpm?

I enjoy spirited driving as well as the next guy but I want to know when I'm just cruising around, what is the healthiest rpm range for my 986?

[Perfectlap]

why did you choose 2,700 to 3,000?

I've yet to read an article by an engine expert that speaks of anything below 3,000 as being beneficial to this car on this particular issue.

[Meat Head]

Originally Posted by Perfectlap

why did you choose 2,700 to 3,000?

I've yet to read an article by an engine expert that speaks of anything below 3,000 as being beneficial to this car on this particular issue.

No particular reason. I'm actually just thinking around 3000rpm. I find it very hard to believe that running the car at a constant 3000rpm+ is good for the car. It may be better for the IMSB but I question if you are not stressing other key components of the engine.

I will admit that my car background is mainly American muscle cars (only owning 2 previous Porches before the Box) but running most engines at + 3000rpm constantly would not be healthy in the long run.

[Perfectlap]

lower rpm, less lubrication.

Engine is not going to fail because of high rpms. It's going to fail for a slew of other reasons that you can't address while driving.
Those have to be addressed before you get in the car.

[Topless]

Disclaimer: Not a factory certified Porsche mechanic.

I have been wrenching them for many years and have yet to toss a Porsche boxer motor.
I see very little in common with a pushrod V8 so that is probably not the best comparison benchmark. Every motor has a RPM sweet spot depending on engine load where the combination of balance, lubrication, cooling and wear are at their best. My personal choices:

No engine load- 800 RPM idle
Flat, straight highway miles with very low engine load 2-3K RPM
Moderate engine load for passing, hill climbing or canyon carving- 3-5K RPM
Heavy engine load for max performance or motorsport- 4K-redline

I see no reason to ever drive this car below 2k rpm. The motor design is such that it could cause excessive lateral loads especially on the timing chains and IMS bearing. It even feels ugly in that range when leaving from a dead stop. As long as you don't load the engine by passing or climbing I see no problem cruising straight and level at 2.2K rpm. Just downshift to climb hills. A pushrod V8 was designed to cruise at much lower rpm and has no ugly spot in the 1500 range. Apples and oranges.

YMMV

[Steve Tinker]

Didn't I read somewhere about a natually occuring harmonic vibration in the flat 6 engine design that happens at around 3,000 rpm?

I've always had it in the back of my head to drive either just below or just above the 3,000 rpm threshold - there again at my advanced years, I could be talking out of the back of my head too......
But the everyday sweet spot must be in the 3,500 to 4,500 rpm pulling through the gears - very addictive!

[stephen wilson]

IIRC Jake mentioned avoiding cruising @ 3000 RPM a few years ago, but haven't heard anything since. I'm at 3K all the time, since it equals my 75 MPH highway cruise speed.

[Coffinhunter]

Originally Posted by stephen wilson

IIRC Jake mentioned avoiding cruising @ 3000 RPM a few years ago, but haven't heard anything since. I'm at 3K all the time, since it equals my 75 MPH highway cruise speed.

I am usually just a hair over 3,000 since I cruise between 75-80 to work everyday. With the speed limits on US freeways being what they are, there would be no need for 6th gear if we couldn't drive at 3,000 RPM.

I do shift down to 5th if I am going to pass though.

The only thing that I have ever heard as being bad is driving at less than 2,000.

[Perfectlap]

Originally Posted by stephen wilson

IIRC Jake mentioned avoiding cruising @ 3000 RPM a few years ago, but haven't heard anything since.

Other way around. He instructs 3K RPM driving for his engine customers.

[stephen wilson]

He may now (and I think it's Above 3k, not At ), but at some point in the past it was recommended to not stay at that RPM. I'm not 100% sure it was Jake.

Here's one mention of it:
http://www.renntech.org/forums/topic/38120-3000-rpm-ims/

Another:
http://www.pedrosgarage.com/Site_5/The_Bad,_the_Ugly_and_the_Good,_part_2.html

[Perfectlap]

Originally Posted by stephen wilson

He may now (and I think it's Above 3k, not At ), but at some point in the past it was recommended to not stay at that RPM. I'm not 100% sure it was Jake.

Flat6 say 3K. At least once, in response to a forum member asking about Pedro raising the issue of harmonic vibration in the m96.

[BYprodriver]

Originally Posted by Steve Tinker

Didn't I read somewhere about a natually occuring harmonic vibration in the flat 6 engine design that happens at around 3,000 rpm?

I've always had it in the back of my head to drive either just below or just above the 3,000 rpm threshold - there again at my advanced years, I could be talking out of the back of my head too......
But the everyday sweet spot must be in the 3,500 to 4,500 rpm pulling through the gears - very addictive!

75% of my driving is on LA freeways with the cruise control set @ 73mph & 2900rpm.
After rebuilding my engine & balancing all recipricating parts & flywheel & pressure plate, I was amazed at how much smoother the engine feels & sounds. So much so that it seems tamer & a little boring. That was the 1st time I was motivated to buy a louder muffler.

[tonycarreon]

if the car couldn't handle higher RPMs, it wouldn't go that high. the limiter would kick in earlier.

[Meat Head]

Originally Posted by tonycarreon

if the car couldn't handle higher RPMs, it wouldn't go that high. the limiter would kick in earlier.

You can't be serious??? Trust me, NO car is going to stand up to constantly bouncing it off the rev limiter LOL. Just because something can handle it doesn't mean it is good for it.

[tonycarreon]

Originally Posted by Meat Head

You can't be serious??? Trust me, NO car is going to stand up to constantly bouncing it off the rev limiter LOL. Just because something can handle it doesn't mean it is good for it.

that's not what i said at all. i said if the car couldn't handle 5k rpm (for instance), the limiter would kick in before it hit that. i never said to go down the road bouncing off the limiter.

[Perfectlap]

I think the problem is that people get very used to driving passenger sedans which are usually very quiet and docile. They start to think that this is 'normal' type driving. \
When they get into a car with the engine directly behind them, and one that makes quiet a racket when it is operating in its version of 'normal', it leads them to think that they're 'over-doing it' or that they are inviting an engine problem by getting the revs up. For starters, while these aren't derived directly from race engine like on a GT3, they are still engineered to 'live' in the area of the rev counter that is nothing like that of a street car whose slush box is constantly short shifting.

It's somewhat counter-intuitive, a Boxster that is getting poor gas mileage (relative to an econo box) and making its passengers annoyed that driver can't ever hear them, is probably an engine that is running EXACTLY the way the engineers intended. And one reason why GT3 drivers always have a second car.

[The Radium King]

I think ian c hit it. you want to avoid driving around at the variocam roll-over points to keep from having the flappers and cam knocking back and forth. cams actuate at 1500 and 5500 rpm, and resonance flappers at (I think) 4000 rpm.

regarding resonance, I don't think there is anything definitive on that which I have seen. pedro is a nice guy but not a mechanic so i'd take that with a grain of salt. I think the 3000 rpm thing most likely comes from the vibration that some folks experience at that rpm range. I get it in my car and, depending on what you read, have heard that it is due to exhaust resonance, failing dual-mass flywheel or failing motor mount. ie, some sort of overall vehicle vibration and not a driveline/bottom end issue that will result in the engine rattling itself to death. the dmf is there to address any potential engine harmonics and it's a whole other argument as to whether cars with lw flywheels have any excessive vibration/harmonic resonance issues (that result in broken cranks, etc.).

to southernstar, I would suggest that gentle braking is harder on your brakes than hard braking - more heat gets introduced into the system if you brake for a long time vs a short time.

personally, I do everything to keep the tach right of vertical at all times. mechanic tells me its the strongest 3.2 he's ever seen and oil filter consistently returns a clean bill of health.

[southernstar]

Radium King, if late and hard braking reduces brake wear, why do cars that are tracked have to replace their pads and fluid more often? Theoretically, I suppose if you locked your brakes they would no longer generate any heat, but otherwise...

Brad

[The Radium King]

well, work = force x distance, so you can brake lightly over a long distance or hard over a short distance; same amount of work done in either case. note that brakes convert kinetic energy into heat, so high performance braking becomes all about heat management - the longer you are on your brakes the less opportunity they have to dissipate heat. I guess it only really matters in a racing environment, though.

[The Radium King]

some timely talk re low rpms and bore scoring:

http://986forum.com/forums/general-discussions/47812-3-8-replacement-motors.html#post358261