[flash]

it's not whether i agree or not.  we have COUNTLESS incidents of failures.  i've been watching this particular issue closely for 12 years now.  this is beyond question at this point.  it's that common.

 

the issue is polymer cross-linking.  this is affected largely by heat cycling.  the SC produces LESS friction therefore less heat, at the same road speed, because generally you are spinning lower rpms to achieve that speed.  it's not about the pulling force, or strength of the belt, as much as the lack of elasticity due to polymer cross-linking.

 

you are free to do what you want, but it would extremely irresponsible for us, as the harbinger of potential issues, to do anything other than to firmly recommend heeding the experience of those who have gone before us, and learn from that experience.

Partial Post: Please Login or Register to read the full post.

[Kim]

I haven't a 968 now but, when I did, I replaced the belt often. So I am with the masses here.  And, for what its worth, I do miss driving a 968 as I no longer have a car, only my SUV.

 

One question though, Flash you said "because generally you are spinning lower rpms to achieve that speed".  Not sure I understand this.  I did not think that the SC changed the gearing in any way such that the relationship between engine speed and road speed in any gear would change. So I would not think that this comment could be true as I read it.

Partial Post: Please Login or Register to read the full post.

[flash]

obviously when cruising in top gear, you would be spinning the same rpm, but when you are accelerating and such, and driving through canyons, you would be in a taller gear than normal, due to the big increase in torque, which would lower the rpms

Partial Post: Please Login or Register to read the full post.

[wildcat]

Your logic escapes me, as it frequently does but what I find most interesting is that your views and approach apparently work for you and what I experience is frequently at odds with your perspective. I've gotten philosophical about it, as in "if it works for you"...

The idea that there's less friction due to the super charger is mind boggling, the belt has to power up faster to keep up with the engine revs and therefore the stress is definitely greater. I do not disagree with your basic principal that it should be changed per the intervals you suggest. But people also have a tendency to baby this car and its a lot tougher than many seem to believe. I think the SC changes the equation considerably in terms of stress on the engine and power-train etc. This is a well known fact in the world of super charged cars. By adding a super charger the design equation has been radically altered, and the belt is going to be under much greater stress.  The issue on the tire I showed is the fact that I do drive my car hard and the tread ware rated at 440 was burnt up in roughly 20 months. That's my evidence. Whether you agree or disagree is irrelevant to me because those are the facts. 

Partial Post: Please Login or Register to read the full post.

[flash]

well, i am not inclined to give lessons in physics, but basically it's about the speed of the belt.  lower rpms means lower belt speed.  that means lower belt friction.  it is NOT about how quickly it speeds up.  it is NOT about how hard it is pulled on.  it's purely rpm related.

 

i would be willing to bet that your premature tire wear was due entirely to a poor alignment and/or incorrect inflation.  again, friction.

Partial Post: Please Login or Register to read the full post.

[Bulti]

Theory is one thing, and physics indeed can't be argued with.


But, the thing is, when you put a device in a car which make it more powerful, that person will most likely use that extra power and torque. Especially with a linear power buildup, where the extra torque is easily accessible.


And IF you use it, my common sense says you will stress the engine and other components more, including the belts. If you would drive the car like you would have without the SC, I go with the lower rpm story. But no human being has the dicipline to not change its behaviour jn such a case. If that person somehow could resist temptation, remove the SC at once and send it over right now ;-)


My 2 cts.

Partial Post: Please Login or Register to read the full post.

[flash]

lol - actually, just driving around, i found myself loping along at 3k most of the time.  i was getting up to speed much more quickly with lower rpms to do it.  can only drive so fast around town and such.

Partial Post: Please Login or Register to read the full post.

[wildcat]

I agree with Bulti but more than that the idea that you're getting more power at lower RPM just doesn't figure. I talked to an engineer at Solar Turbine on the subject of "air monitoring" which is what the M.A.F. does and the idea that you get more air without having to change the MAF doesn't figure. That would mean that a M.A.F. designed for a 2.8 will work with a 3.00 albiet at reduced air intake. What happens in fact is the 2.8 M.A.F. burns out trying to regulate the expected increased air intake. This being determined by the computer and related sensors.  It may take a week or so but that's what happens. And there was no noticeable reduction in speed relative to rpms, (as determined by speedometer and RPM.) 

 

If you've dyno tested it, then that would show that the the engine is producing more power at lower RPMs per mph. But a chip can do that by increasing the fuel air/ratio without a super charger and the MAF doesn't need to be changed. It is increasing the amount of air intake relative to its max input capacity, which gives a performance boost but the rpm/mph ratio remains constant.

 

I am not a physics major but I have worked on jets, and you can control air intake or fuel mixture or both but the system is limited to air density (moisture) and fuel. Its true the engine works more efficiently with denser air which means less fuel required but it doesn't change its relative speed as a result. The fuel control just reduces the amount of fuel as result.

 

So I'm saying more air density not really more air,  less fuel but rpms don't change for a given ratio. Because a 3 liter is a 3 liter and the entire system is built around that displacement. You can push the air in faster, if its cooler its more dense, but you're not getting more air. More dense means less fuel required to burn etc. And for me the fact that you don't have to change the MAF proves that its not getting more air, just air into the chamber faster, and so the cycle runs faster and the belt is put under more stress as are all the components, crank shaft, valves, pistons etc. 

Partial Post: Please Login or Register to read the full post.

[flash]

you are now wasting our time.  i have posted charts to show exactly the results.  however, once more for the cranially thick (yeah - i'm getting tired of this)

 

the issue is NOT related to power.  belt life is related ONLY to cross-polymer linking which is related ONLY to friction and heat cycling.

 

belt life has NOTHING to do with any other stresses in the engine

 

what you don't get is that in 90% of driving, speed is directly related to rpm which is LOWER with the SC.  the ONLY time it is not is in steady state cruising.  during ALL acceleration, you shift earlier, and travel in a taller gear, which REDUCES the friction on the belt, and therefore the heat, and therefore the stress on the belt.

 

continue on this line and suffer the consequences.  i'm tired of having this conversation when you just don't get it

Partial Post: Please Login or Register to read the full post.

[ds968]

I presume the engine in our Pathfinder ( and probably similar to other cars with belts lasting hundreds of thousands of miles ) produces considerably less heat and less friction than the 968, even in general , but when you factor in that 99% of its life it was driven by my wife, who unlike me is a very mild mannered driver , that belt has rarely been subjected to sudden acceleration and other high RPMs driving. Who the heck would drive a Porsche like that, lol ?! Maybe if we have a member whose profile indicates : small stature, senior citizen , female , located in Pasadena, commutes only once a week to place of worship . :-) :-) So 200 K miles on that belt transaltes to maybe 50 K miles in the 968 ...

Partial Post: Please Login or Register to read the full post.

[Bulti]

Threatening people with 'consequences' isn't exactly promoting discussion and will make people weary of joining in. I don't care who's right or wrong. Without proof any opinion is just an opinion, no matter who's the author. Like with most things the truth will be somewhere in the middle or there are more variables that are important.


I know the idea behind this forum is to get the correct information published and that is a good thing of course.


That is why I'm trying to contact an engineer of a reputed company that actually develops these belts, not to be hard-headed, but to get an opinion of somebody that puts some real weight in the scale.


I have no idea if I can get a person like that to take his time to share his thoughts, but at least I would have tried.


If I get some results, I will post them here. If I'm not permitted to to that because some of us are getting wired up, they can make me face the consequences twice for all I care.


Little rant but I had to get it off my chest.

Partial Post: Please Login or Register to read the full post.

[Uber968]

It's always disappointing to see threats and insults in an open discussion.

Partial Post: Please Login or Register to read the full post.

[Kim]

This has been creeping in for a long time, but I have not seen it like this before. I simply cannot believe that one person can simply know so much about so many things in such detail to the extent that all the offerings of others always just need to be wrong regardless of their experience, education or professional training.

 

Perhaps we don't need a forum, just an on-line course. A good professor and a mass of eager students.

Partial Post: Please Login or Register to read the full post.

[ds968]

I agree that threats are uncalled for in a public forum. When and if indicated or necessary, I think warnings can. and should be handled via PM between the moderators and the member . However, I honestly don't see many "insults" hurled around here . Granted, some people are more sensitive than others and could interpret a statement from someone as opinionated as Bob ( wait, lol, is that an insult ? ) as a personal attack, but I doubt that's ever the intent . However, both Bob and Jay have a responsibility to the content which is posted on this forum and I believe they always err on the side of caution ..they have an obligation to do that ( right, or wrong ) . Now, having said that, I personally find some of that caution and erring to occasionally be extreme , borderlining a " the sky is falling " opinion and also based more on pure theory than actual life , but again, I suppose that's a necessity and as always the adage better safe than sorry is something to heed.

After my timing belt broke I have conducted more research and have spoken to more experts on this matter than probably any other person of which I could think , ( ok, except the R&D engineers whose findings lead to the manufacture of the belts, lol ..) And tne conclusion was materially contrary to the conventional wisdom expressed here . But I never shared that info on the forum because at the end of the day it's not a predictor of, nor relevant in any other way to any given individual experience one might have with their timing belts . Some can fail at 10 K miles and others will last 100 K miles . Waaaay to many variables which come into play. However, it's pretty tough to argue with the probability of a newer , less mileage belt outlasting and older, higher mileage belt , in any or all driving scenarios . So again, YMMV, just as long as you realize it's a $ 6,000 + bet ( unless you do the head job yourself, in which case you'll save quite a bit ) . Believe me, I'm struggling with that dilemma right now ; with the SC in the way my mechanic was suggesting a belt change now may be around $ 2,500 ( parts and labor total ) so I'm seriously considering letting it go double or triple the life cycle and hedge my bet on it lasting that long, because just two belt replacements jobs will bring me to almost the same cost as a head rebuild ...which after an incremental 75K or 80K miles could be a good thing to do no matter what .. I know, you might consider that to be a very odd way of looking at things but for me, it's a consideration ..

Partial Post: Please Login or Register to read the full post.

[flash]

i'm just sick and tired of going around and around about BAD advice.  we have repeatedly asked NOT to go there.  we know what happens all too often. we know why.  we have talked about this time and again.  it's pretty basic stuff at this point.  you can't get an answer from calling an engineer, unless you are willing to take the tests and measure the elasticity.  it's all about polymer cross-linking, and the causes of a loss of elasticity.

 

that being said, i don't care what any individual chooses to do about their own car.  i do care when they continue to try to make people think that those things are necessarily a good idea, when we have ample proof otherwise.

 

as for "threats", i am getting very close to closing down the site.  i've spent over 12 years in the 968 realm, and i don't think there are many that have been more devoted to it.  this site has been a labor of love, and i would rather crash it than let it go the route of pelican or RL, with rubber band and bubble gum repairs too often being the norm.  there are only a couple of people who have ever been a problem here, and for the most part, discussions have always been good.  but when this kind of thing goes on, with absolutely no support of empirical data, sound physics, or the least bit of engineering proof, a stop has to come.

 

if somebody else wants to run things differently, the site is for sale.  if you think you can do better, it's all yours.  step up or shut up.

Partial Post: Please Login or Register to read the full post.

[wildcat]

I have never implied or stated that your advice shouldn't be followed. That accusation is way out of line. You have implied and stated otherwise which is just not the case. I will drop it because further discussion becomes obviously irrelevant. But you do imply a threat and that is uncalled for. I think it is important that people realize that there are different experiences which is not an attempt to refute good advice from a safety standpoint, but also to realize that the SC does make a major difference to a cars longevity and to the particular care required when owning one.  If that's not fair or you consider it out of line, then this is not a forum for open discussion and once again I've crossed the line. I don't think its fair to other individuals who realize the theoretical limits are not written in stone.  A doctorate in philosophy is just that "philosophy".  Philosophy is a way of thinking, not a hard and fast truth.  Einstein's theories are just that "theories", they are not laws like Newton's. Even math which is considered a hard science is offered as its highest merit a PhD. There is practiced wisdom which I believe you condone. I do not refute your "practiced wisdom" but when I experience something which is unusual relative to conventional wisdom, I feel it is important to share it. Your opinion about my intent is biased. You must re-read my posts to appreciate that my intent is not and has not to refute "practiced wisdom", but to show that there is latitude beyond which the 968 is certainly capable. 

Partial Post: Please Login or Register to read the full post.

[flash]

there you go again.  all things being equal, THE SC DOES NOT REDUCE LONGEVITY, AND IN FACT LIKELY INCREASES IT!!!  you are wrong wrong wrong.  rpms are what wear components.  the SC reduces the need to run the engine at those same rpms.  the engine runs cooler.  the loads are reduced.  no longer are you wringing the neck out of the engine to get to speed.  you are just not getting it.

 

philosophy has nothing to do with this.  this is pure hard fact.

 

a key indicator of your "philosophy" though, and how poorly thought out it is, is the shot above of the tire.  what kind of thinking would let that tire get to that condition in the first place?  it should have been changed long before that ever got close to being a situation.  that is exactly the kind of thing we do not want to see here.

 

as each day goes on, i get closer and closer to shutting this site down, due entirely to having to deal with ludicrous things like this.  i just don't have a place for it in my life, and i am not inclined to see the site get run down by being populated by this kind of inane ridiculousness, and the people who spout it.

Partial Post: Please Login or Register to read the full post.

[wildcat]

http://www.bimmerforums.com/forum/showth...eliability

 

opinions vary but over the years it has proven that super chargers do add additional wear and tear, Renault fan 4 cylinder

engines against Ferrari twelves within Formula 1 guidelines for displacement and constantly blew up engines.

 

Sure if you drive a super-charged car factory built that's one thing, but building a car for improved performance is definitely

going to add additional wear and tear and potentially blow up the engine. But don't take my word for it or Flash's for that matter

there is plenty of literature on the subject... check it out for yourself. 

Partial Post: Please Login or Register to read the full post.

[wildcat]

As for the tread ware on that tire, if I had taken other pictures you could see that the wear is more or less even especially considering how worn the tires are. The alignment is typical for a porsche and was done before the tires were installed. What happened here was a result of extremely hard breaking and the fact that the boat anchor did not balance that portion of the car.

The other tire showed the same wear, and in fact I didn't find the tear in the tire which I check regularly because the rest of the tire showed no sign of excessive wear consistent with the rest of the tire. 

Partial Post: Please Login or Register to read the full post.