996 Engine parameters

[lperei02]

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)

Edited September 17, 2008 by lperei02

[lperei02]

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:

Edited September 19, 2008 by lperei02

[1999Porsche911]

The over rev count is an artificial number as it pertains to the safe rev limit of the engine. Porsche established a limit to the engine rpms far below the safe and obtainable engine speed. The 3.4 can easily obtain rpm of 7800 if the rev limiter is by-passed. Additionally, I disagree with you when you state that the number of type 1 ignitions can be used to determine whether one engine is better than another. Bouncing off the rev limiter with every shift does nothing to harm the engine since it is an electronic limit and not a mechanical one.

[lperei02]

The over rev count is an artificial number as it pertains to the safe rev limit of the engine. Porsche established a limit to the engine rpms far below the safe and obtainable engine speed. The 3.4 can easily obtain rpm of 7800 if the rev limiter is by-passed. Additionally, I disagree with you when you state that the number of type 1 ignitions can be used to determine whether one engine is better than another. Bouncing off the rev limiter with every shift does nothing to harm the engine since it is an electronic limit and not a mechanical one.

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 ;)

Edited September 19, 2008 by lperei02

[1999Porsche911]

The over rev count is an artificial number as it pertains to the safe rev limit of the engine. Porsche established a limit to the engine rpms far below the safe and obtainable engine speed. The 3.4 can easily obtain rpm of 7800 if the rev limiter is by-passed. Additionally, I disagree with you when you state that the number of type 1 ignitions can be used to determine whether one engine is better than another. Bouncing off the rev limiter with every shift does nothing to harm the engine since it is an electronic limit and not a mechanical one.

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 ;)

The type 1 over revs would not play a part in my decision. Since the computer can only log a maximum number of type 1 revs before the counter resets anyway, how do you know the car that shows only 2 is not the beginning of the 3rd or 4th count cycle. :D

How hard a car is driven does not, by itself, translate into additional wear of the engine. That is, unless you are using Mobil 0W40.

Edited September 19, 2008 by 1999Porsche911

[lperei02]

The type 1 over revs would not play a part in my decision. Since the computer can only log a maximum number of type 1 revs before the counter resets anyway, how do you know the car that shows only 2 is not the beginning of the 3rd or 4th count cycle. :D

Did not know about this. :oops: Thus, I agree that Type I revs are kind of irrelevant upon buying a vehicle.

How hard a car is driven does not, by itself, translate into additional wear of the engine. That is, unless you are using Mobil 0W40.

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!

[1999Porsche911]

The type 1 over revs would not play a part in my decision. Since the computer can only log a maximum number of type 1 revs before the counter resets anyway, how do you know the car that shows only 2 is not the beginning of the 3rd or 4th count cycle. :D

Did not know about this. :oops: Thus, I agree that Type I revs are kind of irrelevant upon buying a vehicle.

How hard a car is driven does not, by itself, translate into additional wear of the engine. That is, unless you are using Mobil 0W40.

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!

That assumes that the engine's components are creating the friction without bearrier. Beleive me, if any moving part of your engine was touching another part, even letting the engine idle would destroy it in a short time. Hense, the need for a better oil and oil pressure than Mobil 0W40 can provide.

Using the formula above, where "v" = negligible, the result would be slightly less negligible.

[deckman]

"How hard a car is driven does not, by itself, translate into additional wear of the engine. That is, unless you are using Mobil 0W40."

What kind of oil do you recommend?

[Loren]

"How hard a car is driven does not, by itself, translate into additional wear of the engine. That is, unless you are using Mobil 0W40."

What kind of oil do you recommend?

There are numerous "oil" discussions here on the site - and many folks have their opinion on the best oil(s).

Contributing Members can view Porsche's Approved Oils TSB list (all 11 pages).

[RF5BPilot]

If I understand it correctly, Type 1 counts are the number of ignitions that were limited by the rev limiter. It seems to me that if that count is high, not only has the engine been operated at close to redline frequently, but the person was using the limiter as a crutch. I would be cautious if this number is high. I would not assume that it's a deal breaker. Unfortuately, it is neither good to have a Porsche where the owner was reluctant to rev it and just lugged it around all the time. Yet, it is also reasonable to think that someone who thought they were Kid Racer with a sloppy technique, also increased wear. This implies that some modest number of Type 1 counts, combined with reasonable mileage may be ideal. (if there is such a thing as "ideal")

Type 2 is where someone has forced the engine beyond the limits imposed by the electronic limiter. I have seen a couple of posts over the years where warranty claims were denied because there were ignition counts in this area, implying the car had been abused. I would not be keen to buy a car with rev counts in 2. (of course, I'm old, crabby and conservative. However, I am slightly less concerned about genuine engine damage than I am about overall care of the car. I have bought mostly used cars over the years, and many times, found myself cleaning up after abuse delivered by the previous owner. I think if you find revs in Type 2, there are other cars out there that have been treated better.)

The good news is that you can get the Durametric tool & check this easily on site before the cost of a PPI.

Edited September 22, 2008 by RF5BPilot

[lperei02]

If I understand it correctly, Type 1 counts are the number of ignitions that were limited by the rev limiter. It seems to me that if that count is high, not only has the engine been operated at close to redline frequently, but the person was using the limiter as a crutch. I would be cautious if this number is high. I would not assume that it's a deal breaker. Unfortuately, it is neither good to have a Porsche where the owner was reluctant to rev it and just lugged it around all the time. Yet, it is also reasonable to think that someone who thought they were Kid Racer with a sloppy technique, also increased wear. This implies that some modest number of Type 1 counts, combined with reasonable mileage may be ideal. (if there is such a thing as "ideal")

Type 2 is where someone has forced the engine beyond the limits imposed by the electronic limiter. I have seen a couple of posts over the years where warranty claims were denied because there were ignition counts in this area, implying the car had been abused. I would not be keen to buy a car with rev counts in 2. (of course, I'm old, crabby and conservative. However, I am slightly less concerned about genuine engine damage than I am about overall care of the car. I have bought mostly used cars over the years, and many times, found myself cleaning up after abuse delivered by the previous owner. I think if you find revs in Type 2, there are other cars out there that have been treated better.)

The good news is that you can get the Durametric tool & check this easily on site before the cost of a PPI.

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...

[Loren]

If I understand it correctly, Type 1 counts are the number of ignitions that were limited by the rev limiter. It seems to me that if that count is high, not only has the engine been operated at close to redline frequently, but the person was using the limiter as a crutch. I would be cautious if this number is high. I would not assume that it's a deal breaker. Unfortuately, it is neither good to have a Porsche where the owner was reluctant to rev it and just lugged it around all the time. Yet, it is also reasonable to think that someone who thought they were Kid Racer with a sloppy technique, also increased wear. This implies that some modest number of Type 1 counts, combined with reasonable mileage may be ideal. (if there is such a thing as "ideal")

Type 2 is where someone has forced the engine beyond the limits imposed by the electronic limiter. I have seen a couple of posts over the years where warranty claims were denied because there were ignition counts in this area, implying the car had been abused. I would not be keen to buy a car with rev counts in 2. (of course, I'm old, crabby and conservative. However, I am slightly less concerned about genuine engine damage than I am about overall care of the car. I have bought mostly used cars over the years, and many times, found myself cleaning up after abuse delivered by the previous owner. I think if you find revs in Type 2, there are other cars out there that have been treated better.)

The good news is that you can get the Durametric tool & check this easily on site before the cost of a PPI.

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...

I certainly would not judge a car on just reports readings from the Durametric Software or a PST or PIWIS tester. What you describe is not Durametrics (or the other tools) main purpose.

You would need a proper PPI on any car you care seriously considering.

[lperei02]

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

[Loren]

I would look for a reputable Porsche shop to do the PPI then. If you can't find one then you may have trouble doing any non-DIY work on your car.

[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 :)

[RedRidge]

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 :)

I believe Loren is saying to use a reputable independent Porsche shop (not official, but reputable)....

[rrspikemarty]

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 :)

I believe Loren is saying to use a reputable independent Porsche shop (not official, but reputable)....

The PPI report i received from a very reputable Porsche shop in So. Cal. stated 250 at all 6 cyls on my 2003 3.6L C4S. Is this reconcilable?

[wrljet]

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 :)

Leakdown tests are more useful than compression readings.

[pjalexandre]

Just because the Portuguese Porsche dealers don't have a PPI concept doesn't mean that you can't ask them to perform the service. It would be no different than say asking a dealer to do a track day inspection for your car when they don't routinely do them. You pay.. they do.

My father purchased a late model car last spring in Portugal and most of it was done from here in the US. And the dealer did the equivalent of a PPI for us. I just got on the phone and explained what I wanted them to check for and how much they would charge.

Cheers,

-Paul

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