I was doing some numbers today and think I found something cool. Frist, assumptions: - The stock s/c lasts 100,000 miles - The 15% reduction s/c pulley is 15% smaller than a 100% (stock) s/c pulley, so 85% of the stocker's size. - A 15% diameter reduction would cause a 15% increase in rotational speed - The 15% reduction pulley causes the s/c to fail 15% faster than stock. Case 1: new car with stock s/c pulley, 100% of stock size. 0 miles, 100% s/c life left, new 50,000 miles, 50% s/c life left, half 100,000 miles, 0% s/c life left, failure Case 2: new car has 15% reduction s/c pulley added immediately, 85% of stock size. 0 miles, 100% s/c life left, new 42,500 miles, 50% s/c life left, half 85,000 miles, 0% s/c life left, failure supercharger life is 85% of the stock life due to the 15% higher rotational speeds causing failure 15% faster. Case 3, my case: Car had 15% pulley added at 27,924 miles, so at that point it had 72% life remaining, based on the 100,000 mile stock life span with the stock size pulley. Working with 72% life remaining, I then found 85% of of that life remaining to account for the accelerated declination effects of the smaller pulley on the 72,000 miles that were theoretically still in the s/c. So that is 72,000 miles*(1-.15). That yielded 61,200 miles remaining if I use the 15% reduction until failure. My car is at about 61,940 miles right now, 34,016 have been on the 15% reduction pulley. (61,940 right now - 27,924 installation = 34,016 mileage on 15% reduction pulley) So that means that I have 61,200(remaining s/c life with 15% reduction pulley) - 34,016(mileage on 15% reduction pulley) = 27,184 miles left until failure. Added to my current odometer, that means my s/c will fail at 89,124 miles. I know that the real world failures on these s/c is far from predictable, but I wanted a basic idea, and now, in true Star Trek fashion, I have the "exact time to failure." Any mathematicians or physicists out there please feel free to pick this apart.

Not precisely. I mean that is a good guess/approximation for warranty purposes, but more accurately the SC life is determined by revolutions as a first order variable, not miles. Miles happens to be easy to measure and easy for the consumer to understand. Carrying this to the extreme, you can stress to fail a SC strapped to a bench with a drill motor hooked to it, so no miles. You could also get one to last much longer than the 100K mile assumption if the vehicle spent 100% of the time in 6th gear at 50mph. To increase the accuracy of your remaining life calculations you need to understand the usage model utilized to calculate the 100K miles. This usage model will boil down to a specific number of SC revolutions. Then you need to compare that model to your driving habits and adjust accordingly. There are other operating condition parameters involved in the usage model like, temperature, engine load, boost levels, etc., but you get the idea. Yes, math can be fun.

OK, I am sure both of you violated some sort of site policy with all of that, so I am issuing strikes.

Hereâ€™s the first mistaken assumption, the 15% difference is only relevant to the pulley, not revolutions of the supercharger lobes; it only spins about 10% faster with a 15% pulley.

Yeah, that's very true. This thing was pretty much full of holes from the start. I had a feeling that was basically the case. I didn't know how to find out true revolutions. Most of my math skills are with percents, since that's what most the math in my business education dealt with.

Nothing is 100% mathematical with cars. If your car was built on a Wednesday, I would say the car will last 15% longer than a Monday or Friday.

Another thing... Wear isn't linear. To first order it goes as the square of the speed. First thing is that a 15% really "wears" not at 15% faster, but a bit more than 30% faster. This is just a "rule of thumb" and isn't absolute. I'd change "exact" to "Approximated" and it's a good start. Most comparisons like this though assume the driving profile in the two cases is the same, but you really need some estimate of what percent of the time things are at what RPM to do anything reasonable with this... It's such a mess of interrelated suff that most just do a very simplistic estimate of relative wear, then do a survey of the populations to look at how they really change. Things like this are "guides to the eye" more than anything else. Matt

Another thing to pick apart.... really this is an estimate with an accuracy of at best a few percent, more likely a few 10s of percents. That means you only need one or two significant figures, and can do lots of rounding to make the math easier. Now in the days of Excel and electronic calculators, it's easy to carry way more precision than is needed, but it doesn't really increase accuracy.... Also, the 100k mile lifetime isn't a failure distance, it, at best, is an average failure distance where individual units may last much, much longer, or sadly, much shorter. It needs to be biased by driving style, because, as on poster put it, rotational numbers and distance aren't exactly correlated. Here's an easier estimate of SC lifetime, I drive my car hard. Should expect problems any time after 50k-60k. I baby my car. I should expect little or no problems with my SC till well past 100k. Of course, with some of the early WP gear failures, none of these estimates are worth anything. Matt

Ummm, I got lost in the math. :arf: We had an 05 MCS on the Dyno Friday, it is driven hard and fast. We had limited boost and the prime suspect is SC failure in progress. About 82K on the MINI. Don

Is there any distinction in the failures of S/C between the early (02-04) uncoated and later coated S/C's? Is one tending to last longer than others? Show we create some sort of poll or survey to gather info on S/C failures?

Yes, let's poll the people on this one. Make sure to include the proper variables, and NOT just miles.

Well, you all bring up good points. Calling it the "exact time to failure" was sort of a joke, I referenced Star Trek up in the first post, you see. More information: (from Ex Astris Scientia - Star Trek ClichÃ©s) <-- awesome site btw, almost as cool as memory alpha ""Exact time to failure Exact time to failure In the real world, there are always more than sufficient safety margins for anything constructed by engineers. Most of all because of the inevitable measurement uncertainties and manufacturing tolerances that allow only a coarse extrapolation of the actual failure conditions, and also for reasons of product warranty and safety standards. Scotty would definitely confirm that. He himself told Geordi that he always accordingly modified the figures for the captain and for the technical manuals (TNG: "Relics"). Still, in Star Trek there are often absolute maximum ratings that denote a precise point of destruction or otherwise catastrophic malfunction of a device, as if the real ship or phaser behaved exactly like a simulation. For instance, there are always definite figures for failure of shields, structural integrity or life support. Spock and Data occasionally even go as far as giving a time to failure with a precision of less than a second! One particularly bad example is in TOS: "That Which Survives" where Spock is obsessed with the idea that the ship will explode in exactly "14.87 minutes" instead of 14 minutes. In "Star Trek Generations" the officer played by Tim Russ reports "45 seconds to structural collapse". In TNG: "Hollow Pursuits" Data reckons that the time to structural failure will be precisely "15 minutes 40 seconds". Only on few occasions reasonable safety margins and fabrication tolerances are taken into account. One positive example is DS9: "Paradise", where Dax tells Kira that if the builders had a good day, the runabout wouldn't break apart when trying to tractor another runabout at maximum warp. They did have a good day.""

Well great then, let me know if you need some help with alpha testing and traveling the learning curve road.