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-   -   Question for Mechanics: 2200-2500rpm or 2700-3000rpm, what is best??? (http://986forum.com/forums/boxster-general-discussions/47539-question-mechanics-2200-2500rpm-2700-3000rpm-what-best.html)

Meat Head 08-05-2013 12:43 PM

Question for Mechanics: 2200-2500rpm or 2700-3000rpm, what is best???
 
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 08-05-2013 12:47 PM

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 08-05-2013 01:01 PM

Quote:

Originally Posted by Perfectlap (Post 355750)
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 08-05-2013 01:27 PM

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 08-05-2013 01:56 PM

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 08-05-2013 02:40 PM

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 08-06-2013 06:20 AM

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 08-06-2013 06:45 AM

Quote:

Originally Posted by stephen wilson (Post 355869)
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.

tonycarreon 08-06-2013 07:35 AM

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

Meat Head 08-06-2013 11:27 AM

Quote:

Originally Posted by tonycarreon (Post 355888)
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.

Perfectlap 08-06-2013 11:33 AM

Quote:

Originally Posted by stephen wilson (Post 355869)
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 08-06-2013 11:59 AM

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

tonycarreon 08-06-2013 02:35 PM

Quote:

Originally Posted by Meat Head (Post 355975)
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 08-06-2013 05:20 PM

Quote:

Originally Posted by stephen wilson (Post 355988)
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.

Ian c 08-06-2013 06:57 PM

I thought it was all about the variocam kicking in around 4k ....

In all honesty , with learning on the fly ecu maps the best thing to do is unplug the battery for 30 minutes then drive it like you stole it .

Don't believe the snake oil , don't believe the Internet , don't worry , just drive :D

stephen wilson 08-07-2013 03:22 AM

I agree. Don't drive by fear of what may happen, it's about having fun!

Meat Head 08-07-2013 11:16 AM

Quote:

Originally Posted by stephen wilson (Post 356094)
I agree. Don't drive by fear of what may happen, it's about having fun!

This has nothing to do with fear :rolleyes:??? It has to do with wanting to do what is best for my engine when day to day driving. I don't understand why people have such a problem with Box questions when it has to do with driving them in a subdued way??? Does everyone that owns a Boxster drive it like a bat-out-of-hell 100% of the time LOL :eek:??? My Boxster gets plenty of play time action but every time I take it out for a drive I don't feel the need to attack the Road :cool:.

I'm just trying to find out (from those with real mechanical experience on the 986) what is the most healthy rpm range for our Boxsters when cruising :D.

:cheers:

stephen wilson 08-07-2013 11:37 AM

Sorry, these type of questions always seem to get side-tracked into an IMS discussion!

I think Topless already answered your question best.

southernstar 08-07-2013 12:25 PM

Pedro has suggested a harmonic inbalance to the engine at 3000 rpm's that can lead to vibration in the car. Frankly, I have never noticed it and 3000 rpms, at least in 5th gear in a 2.7, is right around my usual highway cruising rpm. I believe he also suggests that his re-engineered front engine mounts can reduce the effect.... In any event, I have read nothing to suggest that the engines should not be cruised at that rpm, nor that it will contribute to IMS shaft bearing failure, etc.

And for what it is worth, I am with Meathead on this. I have fun driving my car every day, even though I seldom take it to redline. I do not lug my engine, but I also don't drive it excessively hard. I will occasionally take her to 7000 rpm rather than the 7200 rpm redline in first and second gear (positively love the sound), but more often than not, even when driving quickly I will shift at about 6000 rpm's. Frankly, the torque curve has flattened-out by then and there is very little to gain by pushing the envelope if you are not tracking the car.

The same is true of shifting. I never hurry my upshifts as the rpms need a chance to drop a bit before engaging the next higher gear. This puts less strain on the synchronizers and adds to smoothness, all while acknowledging that it may reduce the acceleration times marginally. I also ALWAYS double-clutch my downshifts, not only because it is fun and because I love the sound of the blip of the throttle, but also because it is smoother and again, puts less strain on the drivetrain. Braking? I never intentionally leave my braking to the last possible fraction of a second on the street. Apart from wear and tear on the brakes, the risk of encountering an unexpected patch of gravel, dirt, uneven pavement, etc. that increases your required stopping distance can be ignored only at your own peril (and frankly, the peril of others using the roadway). Lets face it, even with a relatively conservative approach to braking and cornering, I have nevertheless on occasion found myself going too hot into some corners.

Simply put, I do not baby my car, but nor do I abuse it or operate it in a way that makes errors potentially more serious - i.e., over-revs, 'beating' the synchros, rushing shifts and hitting the wrong gear with potential over-revs that could destroy the engine, etc. To me 'performance driving' on the street is much more akin to driving an endurance car than qualifying a formula 1 car; 10/10's is not only harder on any car, it also leaves very little margin for error. Do I care that someone else could drive my car slightly faster over the same roads? Not one iota. Indeed, in my experience I am often able to keep pace with even potentially faster cars that are being 'over-driven'. Big slides requiring big corrections will inevitably slow your exit speed out of corners and, in a car without huge power and torque, that is a sure-fire way to go slower rather than faster over a given section of roadway.

Brad

Perfectlap 08-07-2013 12:47 PM

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.


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