lperei02

Loren, maybe I did not express myself appropriately... the Official Porsche Centers in Portugal (three as far as I know) do not perform PPI’s. Nevertheless, I plan to do all the work in there :)

In Europe, some contries dont have the PPI concept. For instance, in Portugal, there's no PPI from official Porsche dealers... and TBH I dont trust non-official dealers to perform this kind of inspection. Cheers

Well, soon I'll be looking for a car away from home but it seems that durametric software/cable will only allow to read codes from 3 cars :( How can I "shop" for a car with just 3 tries? I decided I can't rely on this nice tool...

Did not know about this. :oops: Thus, I agree that Type I revs are kind of irrelevant upon buying a vehicle. Nice one about the 0W40 :lol: Despite all advances in engineering and lubricant's quality, engines are still subjected to great amounts of "friction" among all its moving parts. That's one of the reasons why high working temperatures are reached! Heat from friction is just being dissipated. Physics on the other hand, tells us that, the faster one part is being frictioned against another, the greater the friction and the wear. At high speeds friction is proportional to v2 or even v3. The non-linearity of this relation between wear and parts velocity means that doubling the speed can have a four-fold impact in wear!

I think you mean that you can have very serious type II over-revs and not so serious type II over-revs. I agree with you. I dont know the type II rev limit, but lets assume it is 7280 rpm. If you make 7281 rpm it wil be registered as a type II over-rev as would be a 9000 rpm, and I agree +1 rpm is not that serious. I think this is one of the reasons why Porsche decided to increase the number of intervals where over-revs are classified (6 types in 997 I think). So I would say that an abused engine has, for sure, type II over-revs. On the other hand, having type II over-revs does not necessarily mean that the engine was abused. Nevertheless, as a buyer with free will, I will not take risks and I prefer to reject a good engine than accepting an abused one. This implies rejecting cars with engines with considerable type II over-revs! So I think the procedure is correct from a buyers perspective, of course! In what concerns Type I over-revs, let's do this experiment: 2 perfectly equal engines run for 100,000 km. Engine 1 is pushed to the redline in each and every shift. Engine 2 has a more "calm" usage pattern and never reaches, lets say, 6.000 rpms. Engine 1 thus has 300,000 type I ignitions and engine 2 has zero type I ignitions. Which one would you choose? I've no doubts about it! Theoretically at least, engine 1 has been subjected to greater stresses and is for sure more weared than engine 2, or not? Just my 5 cents ;)

Well, although I have researched before asking these questions, I've been digging more and more and found out some things that could be useful for other potential buyers. So, I'll share it with you. 1. For a 996 3.4L Engine the compression should be ~160 Psi. For a 3.6L Engine it should be ~210 Psi (such a big difference, can anyone confirm this one?) I still dont have any idea about the loss of pressure that should be a deal breaker. I've also read that what matters most is the difference between cylinders, but I would say there should be some reference value to "reject" an engine. Someone would like to throw a number? 2. The maximum "acceptable" pressure difference between cylinders is 10%. As far as I could understand, a good engine would be <5% and a fair engine between 5 and 10% 3. Over-revs come in Type I and Type II. They are measured in number of ignitions, so a split second @ 7200 rpm will translate in several ignitions. 7200 rpm = 120 rps. In 0,1 secs we will have 12 engine rotations and thus 24 ignitions (I'm assuming one ignition for each engine block for each rotation, is this correct?). The engine working hour at which the last type I and II over-revs occurred are also registered. Type I's are normal, but an engine with tens of thousand of these will have a shorter life expectancy than other one just with thousands. What I mean is, the more Type I's the more the engine wear. What should be the type I threshold to turn around in a deal? I don’t know...maybe hundreds of thousands. Type II's theoretically mean there was some mishift. Recently there has been some evidence that one can build type II over-revs without actually mishifting (there's a post by wross996TT from August 2008 that gives some very interesting links about this issue). Nevertheless I would say that an engine with <50 type II ignitions is OK, between 50 and 100 be careful, although it shouldn’t be a deal breaker, mainly if the last type II ignition occurred many hours ago. Over 100 hundred I would seriously think about buying the car. Over 200 I would definitely not buy. I am being to tough on this one? 4. Some research would point to 30 to 50 km/h (~20 to 30 mph) but I guess these values are country dependant. These are OK in Iberia (Portugal + Spain). 5. I would appreciate to have some help on this one :) Cheers :renntech: Edit: Typos :blush:

Hi all! Since I'm about to buy a 911 996, most probably with a 3.4 engine, could you help me with some engine parameters that I will have to "decipher"? :rolleyes: 1. What are the engine compression readings considered normal for a 996 3.4 L engine (in Bar or Psi)? It could happen that I end up buying a 3.6L, so if you have the compression values for this engine, i would appreciate it :) 2. What is the maximum acceptable difference in pressure between cylinders (in percentage)? 3. What is the output information that one can get concerning the Type I and II over-revs? For instance, number of type I and II over-revs for all engine's life, or for the last x days? What is considered "normal" concerning type II over-revs? 4. If I'm informed about the engine working hours, what average speed ranges should one use in order to compare with the stated car's mileage (I know this depends on country/ region, but a range of speeds will help me anyway)? 5. BTW, would someone be kind enough to send me an example of a PPI report? If you wouldn't mind to send me one please PM me and I will give my e-mail address. Thanks in advance for your help! B)