Reliability & Longevity -Stock vs Modified???
06-16-2003, 02:37 AM
#1
Racer
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Reliability & Longevity -Stock vs Modified???
OK, so everyone who has a 951, including myself, wants to go faster. Nuff said. A guy in my PCA club brought up an interesting point though:
"You don't get something for nothing."
With all the upgrades available and different techniques to go faster, how much are you sacrificing
1. Reliability
2. Longevity
What is the trade off point? Is there one? At what level of modification can I not expect to get 200,000 or 300,000 miles out of my 951. I don't necessarily agree that if "Porsche didn't include it, than it doesn't need to be there" but I think there is something to be said about the effect that aftermarket modifications have on our street engines. Most enhancements are inspired and developed by race shops. However, they are running race motors that require complete rebuilds more often than 911 owners call us “Waterboys”.
My point is: at what point when one upgrades their engine is one making some sort of sacrifice in one form or another. Where is the balance of speed vs. longevity? Is there one? I just don't know enough to know. Any thoughts or insights would be most helpful to this new 951 owner. BTY, this forum is helpful and it's members so incredibly knowledgeable, I honestly believe that together, minus myself, there is no question that can go unanswered. Bravo!!!
"You don't get something for nothing."
With all the upgrades available and different techniques to go faster, how much are you sacrificing
1. Reliability
2. Longevity
What is the trade off point? Is there one? At what level of modification can I not expect to get 200,000 or 300,000 miles out of my 951. I don't necessarily agree that if "Porsche didn't include it, than it doesn't need to be there" but I think there is something to be said about the effect that aftermarket modifications have on our street engines. Most enhancements are inspired and developed by race shops. However, they are running race motors that require complete rebuilds more often than 911 owners call us “Waterboys”.
My point is: at what point when one upgrades their engine is one making some sort of sacrifice in one form or another. Where is the balance of speed vs. longevity? Is there one? I just don't know enough to know. Any thoughts or insights would be most helpful to this new 951 owner. BTY, this forum is helpful and it's members so incredibly knowledgeable, I honestly believe that together, minus myself, there is no question that can go unanswered. Bravo!!!
06-16-2003, 07:37 AM
#2
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IMHO, Powerhaus is the way to go. I did a lot of research before going with them. I have a hell of a screamer, that drives perfectly docile in everyday traffic without a hiccup, and more pull than almost every supercar out there. To back up their work, David, the owner has the same motor in his car with over 90,000 miles on it. Oh, yeah, got a warranty as well. Just my .02 worth.
06-16-2003, 10:26 AM
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This is conjecture, but I would think about this in these terms:
Modifications resulting in significant power gains generally will reduce your engine's reliability, but won't necessarily reduce your engine's ultimate life.
First, what do we mean by "life"? Do we mean miles between total tear-downs and rebuilds? Then this is probably a function of some of the less stressed items on the motor, the rings and valves. (Less stressed meaning, less than the cylinder head, etc.).
So reduced life probably results from running the car only at 4000 - 6000 rpm while the normal car averages 35 mph and turns perhaps 2000/min on average. So your car will wear out faster by running it on the track, even if it is stock.
What modifications do is reduce the reliability of your motor. Mine is stock, so it is as reliable as it's going to get. If I upgrade to 1 bar boost and an MAF, then I get 35% more power. But at what cost?
The MAF isn't going to break tomorrow, although the higher boost pressure will stress the head gasket, and will also make temps higher, putting stress on the cooling system and probably lubrication system. So these items might fail more frequently. Not to mention the higher terminal velocities will require better brakes, etc. So reliability will suffer.
Metric Mechanic, a BMW tuning firm, had a few papers published which are probably out on the net, about the expected life of a motor designed to rev at certain rpms. Note that a F1 car revs to 18,000 /min, and is designed to last 300 km. Indy cars rev to 12,000/min and are designed to last 800 km. Winston Cup cars rev to what, 8000/min, and probably are used for several races, maybe a whole season, before needing to be rebuilt.
Your car is designed to rev to 6200/min + or -, so by tracking it you'll probably reduce its service life to 1/3 what it was designed for. That's why you don't buy used Porsches in Germany, since they've driven on the Autobahn at maximum revs for hours on end.
Modifications resulting in significant power gains generally will reduce your engine's reliability, but won't necessarily reduce your engine's ultimate life.
First, what do we mean by "life"? Do we mean miles between total tear-downs and rebuilds? Then this is probably a function of some of the less stressed items on the motor, the rings and valves. (Less stressed meaning, less than the cylinder head, etc.).
So reduced life probably results from running the car only at 4000 - 6000 rpm while the normal car averages 35 mph and turns perhaps 2000/min on average. So your car will wear out faster by running it on the track, even if it is stock.
What modifications do is reduce the reliability of your motor. Mine is stock, so it is as reliable as it's going to get. If I upgrade to 1 bar boost and an MAF, then I get 35% more power. But at what cost?
The MAF isn't going to break tomorrow, although the higher boost pressure will stress the head gasket, and will also make temps higher, putting stress on the cooling system and probably lubrication system. So these items might fail more frequently. Not to mention the higher terminal velocities will require better brakes, etc. So reliability will suffer.
Metric Mechanic, a BMW tuning firm, had a few papers published which are probably out on the net, about the expected life of a motor designed to rev at certain rpms. Note that a F1 car revs to 18,000 /min, and is designed to last 300 km. Indy cars rev to 12,000/min and are designed to last 800 km. Winston Cup cars rev to what, 8000/min, and probably are used for several races, maybe a whole season, before needing to be rebuilt.
Your car is designed to rev to 6200/min + or -, so by tracking it you'll probably reduce its service life to 1/3 what it was designed for. That's why you don't buy used Porsches in Germany, since they've driven on the Autobahn at maximum revs for hours on end.
06-17-2003, 04:57 AM
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H Dog, could you give some web site addresses for those rpms/engine wear -studies?
I personally believe there's a lot more to what causes engine to wear than simply how many rpms it turns. In fact, I always used to think that as long as the engine is warmed up and you've got fresh oil in it, the difference in wear driving between different rpms is pretty much non-existant.
Modifications that add power will increase wear whenever you use that extra hp; more air/fuel in the cylinder -> bigger booom -> more pressure on the piston/rod/crank/bearings ... I'm not sure how big the difference is, seems to me that as long as you're not boosting insanely much you're pretty much safe.
I personally believe there's a lot more to what causes engine to wear than simply how many rpms it turns. In fact, I always used to think that as long as the engine is warmed up and you've got fresh oil in it, the difference in wear driving between different rpms is pretty much non-existant.
Modifications that add power will increase wear whenever you use that extra hp; more air/fuel in the cylinder -> bigger booom -> more pressure on the piston/rod/crank/bearings ... I'm not sure how big the difference is, seems to me that as long as you're not boosting insanely much you're pretty much safe.
06-17-2003, 11:51 AM
#7
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Velvet951, you've had some very thorough responses here. From what has been said thus far, I think the moment you do anything that modifies the stock setup, you're compromising reliability/longevity of the car as it was intended to perform.
As a case in point, it's been incredibly hot in Southern Europe lately. Driving my bone stock '91 951 at high speed (over 140 mph) in high ambient temperature, kept the temp gauge right above the first mark. In stop and go traffic, it crept up to about the middle and I could hear the cooling system kicking in to bring it down to the first mark.
Needless to say, when you increase the boom Sami mentioned, the operating temperature has got to increase and you're going to get greater wear on the engine internals. Probably marginal, yes, but enough to reduce longevity of the engine unless major modifications are made to it (e.g. Powerhaus, Under Pressure, etc.)
Scott Gomes had some really informative posts about "bolt ons" vs. proper engine modifications and overall engine reliability. Check them out.
As a case in point, it's been incredibly hot in Southern Europe lately. Driving my bone stock '91 951 at high speed (over 140 mph) in high ambient temperature, kept the temp gauge right above the first mark. In stop and go traffic, it crept up to about the middle and I could hear the cooling system kicking in to bring it down to the first mark.
Needless to say, when you increase the boom Sami mentioned, the operating temperature has got to increase and you're going to get greater wear on the engine internals. Probably marginal, yes, but enough to reduce longevity of the engine unless major modifications are made to it (e.g. Powerhaus, Under Pressure, etc.)
Scott Gomes had some really informative posts about "bolt ons" vs. proper engine modifications and overall engine reliability. Check them out.
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06-17-2003, 01:13 PM
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velevet951. I recommend a chip upgrade only and that's it! This will increase your power - real world 20-30bhp. You will feel it big time and the car will retain its reliability and longevity. One thing though - if you do high speed autobahn driving 120-160mph for prolonged periods of time the head gasket will blow guaranteed - mine did - watch that temperature gauge - our cars are not great when really hot in stock form! On the hot day here in Europe if I drive it 160 mph the temperature goes right up to the final line - that's when you must back off! You will however get used to the power and will want more, well....we all do but I think if you want 200mph car and to be reliable buy 996 turbo which was designed that way. I will stick with my 951S, a chip and no MAF's!