Let's Talk Porsche 911

Originally Posted by atikovi
Originally Posted by Cdn17Sport6MT
Originally Posted by wings&wheels
Oh, to the OP one final thought; Pre Purchase Inspection! Have fun.

And that PPI includes a cylinder leak down test, along with (or perhaps instead of) a conventional compression test.


Unless it's got a miss or is running poorly, why? And if so, a relative compression test with a scope would be much simpler, or you could check through the OBD for misfire counts. This isn't the 50's anymore.


The leakdown test has been specified by almost all Porsche specialists for a PPI for a long, long time. It is well recognized as being in some ways more valuable to have than a conventional compression test. I like having both. A leakdown test (that the OP may be familiar with as an Aircraft Mechanic) allows the inspecting tech to pinpoint the likely cause of an engine performance deficit - and allows the Purchaser to be able to negotiate on price, based on knowing the costs typically to put right a given fault. On an aircooled 911, up to at least the end of the 964 era (1994) each cylinder barrel is about $500 to replace. They cannot be bored and replated with any degree of success. Even "Scotchbriting" them and fitting new std size rings is tricky... They are Nikasil plated (or Alusil plated). That is $3000 for parts, right there. The leakdown test will discern, generally, whether it is piston rings / barrel which is causing lower compression, or whether it is an intake valve/valve-guide, or an exhaust valve/valve-guide, or whether it is (likely) a broken cylinder stud (causing a head gasket leak). Note that an aircooled Porsche has 6 individual cylinder heads... all are separate. A borescope investigation is also warranted. An easy test if you are already doing a Leakdown or a Compression test.

Leakdown tests are useful for both water cooled and aircooled Porsche's.

In having done leakdown tests, and comparing it to standard compression tests...as indicated, they are both valuable. I tested one car that had perfect compression by conventional compression test. When I did its leakdown test it was evident I had a dead cylinder as I had 25% leakdown in that one cylinder.

Compression tests often test for camshaft lobe profile general integrity, along with a visual of same to the degree that is possible. If a camshaft lobe is worn down, cylinder compression when cranking will be poor...

See attached FAA inspired Teledyne-Continental document about "Cylinder Differential" testing on aircooled aircraft engines.

Final point: the automotive trade cannot seem to get it's mind wrapped around the orifice size necessary to be standardized in leakdown testers... for any of this to be meaningful. Meanwhile, the FAA has it prescribed down to the gnat's eyebrow. Worthwhile looking at the FAA docs to really know how to evaluate engine health condition... at least this aspect of engine health.
 
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Note that the FAA prescribes a 0.040" dia orifice, 0.250" (axial) length, 60 degree angles of approach and departure.... for cylinders that are 5" in bore size or below... (obviously, cars fit into this category). For > 5" dia. cylinders, FAA spec's a 0.065" dia. orifice...

FAA also spec's 80 psi supply pressure... and a 25% leakdown, by definition, would be 60psi downstream, 80 psi upstream... i.e. 80-60 = 20.... 20 / 80 = 0.25 or a 25% leakdown.

A well built engine, with properly seated rings and with well-done lapping of the valves (and on-size guides) might be 2% or 3% leakdown.

Racers use Leakdown tests to affirm "good" engine builds.
 
A leakdown test is better than any "technology" ever could be! Don't bother trying to prove your stance on the subject, I've argued with seasoned mechanics for years over it!

Not that relative compression tests don't have their place, It's great for finding cylinders with NO compression. Ford has a test that will identify a low contributing cylinder via a scan tool with great accuracy!
 
Originally Posted by clinebarger
A leakdown test is better than any "technology" ever could be! Don't bother trying to prove your stance on the subject, I've argued with seasoned mechanics for years over it!

...


Haha, I have seen commercially-available leakdown testers, made for automobiles, without even orifice's in them... let alone a standard-sized orifice. Without this- (and without the standardization of the equipment) the test and the results are meaningless. Without an orifice (provided the two gauges are accurate) the indicated leakdown % would be zero (0) !

It seems like few people use- or understand this excellent diagnostic device.
 

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Not sure what your budget is but I would suggest a 997.2 2009-early 2012. Classic porsche design no IMS to worry about. You will be thinking about it as a rebuild is $$$$$$$$$ These cars are not cheap. Everyone talks about the air cooled cars but honestly they are expensive and I dont think coming from a modern car you would be happy with one. These cars are going on 25 years minimum, you will have issues. I would check overrevs if you get a manual, but quite honestly PDK is fantastic. Here is article on 997.2 and photo of my 991 Good Luck!
https://www.pca.org/news/2018-04-10...-carrera-porsche-we-should-all-be-buying

[Linked Image]
 
Sweet 997, Raaizin!

I'll check out that article when I get a chance.

So, you mention over-rev. I've heard it mentioned before. So, do these cars not have a rev limiter that would prevent engine damage from being over-revved?

I realize that the 993 and prior 911s are very dated in many ways. And that's one of the things I'm wrestling with. I realize that the later, liquid-cooled versions are, in so many ways, better cars, But there's just something about the feel, and the aesthetic, and the character, and the sound of those classic, air/oil-cooled 911s that make them so cool. If I ended up making the decision to get one of the air/oil-cooled 911s, it would be to enjoy the car for what it is - to be immersed in that vintage experience.

But, you're right - they're expensive.
 
I would go for that 997.2, for the model year range indicated. I read that article, some time back. The aircooled cars... they stink inside sometimes due to oil leaks. Heat exchangers can presumably either rot or become leaky. Naw, go for the watercooled, without the IMS issue.
 
Originally Posted by john_pifer
Sweet 997, Raaizin!

I'll check out that article when I get a chance.

So, you mention over-rev. I've heard it mentioned before. So, do these cars not have a rev limiter that would prevent engine damage from being over-revved?

I realize that the 993 and prior 911s are very dated in many ways. And that's one of the things I'm wrestling with. I realize that the later, liquid-cooled versions are, in so many ways, better cars, But there's just something about the feel, and the aesthetic, and the character, and the sound of those classic, air/oil-cooled 911s that make them so cool. If I ended up making the decision to get one of the air/oil-cooled 911s, it would be to enjoy the car for what it is - to be immersed in that vintage experience.

But, you're right - they're expensive.

Nothing will prevent overrev in any manual car.
 
I have a 1979 VW van, 2.0 litre aircooled engine. The rotor in the distributor has a centrifugal, spring-loaded element in it... and it limits the revs of the engine to around 5400rpm.

I also have heard/seen cars run into their rev-limiters... where fuel or ignition is cut. Sometimes, in the lowest gears, a novice driver will not anticipate how fast the revs rise (under full throttle) - and they fail to time their shifts (BEFORE) the max rpm / cut-out point... and they sound like fools running into this rev-limter.

So I'm not sure whether over-rev events are actually charted, but the PCM can chart out, say, how many 6000 rpm events occurred, how many 6200 rpm events occurred, etc... up to the actual rev-limit.

Please, Others, correct me if I have this wrong.
 
Originally Posted by Cdn17Sport6MT
I have a 1979 VW van, 2.0 litre aircooled engine. The rotor in the distributor has a centrifugal, spring-loaded element in it... and it limits the revs of the engine to around 5400rpm.

I also have heard/seen cars run into their rev-limiters... where fuel or ignition is cut. Sometimes, in the lowest gears, a novice driver will not anticipate how fast the revs rise (under full throttle) - and they fail to time their shifts (BEFORE) the max rpm / cut-out point... and they sound like fools running into this rev-limter.

So I'm not sure whether over-rev events are actually charted, but the PCM can chart out, say, how many 6000 rpm events occurred, how many 6200 rpm events occurred, etc... up to the actual rev-limit.

Please, Others, correct me if I have this wrong.

Until you're slamming gears and do a 3-2 because of weak or sloppy factory biasing...
 
Ah, I see, now. Thx...

Yes, in my Mazda6 once or twice, instead of 6th, I hit 4th instead.... was so smooth, it went in, like butter. Luckily I did not wring it out in 5th. So I did not rev too high.
 
Originally Posted by Ws6
Originally Posted by john_pifer
Sweet 997, Raaizin!

I'll check out that article when I get a chance.

So, you mention over-rev. I've heard it mentioned before. So, do these cars not have a rev limiter that would prevent engine damage from being over-revved?

I realize that the 993 and prior 911s are very dated in many ways. And that's one of the things I'm wrestling with. I realize that the later, liquid-cooled versions are, in so many ways, better cars, But there's just something about the feel, and the aesthetic, and the character, and the sound of those classic, air/oil-cooled 911s that make them so cool. If I ended up making the decision to get one of the air/oil-cooled 911s, it would be to enjoy the car for what it is - to be immersed in that vintage experience.

But, you're right - they're expensive.

Nothing will prevent overrev in any manual car.


Oh, you mean, like, if someone downshifts into too low of a gear going into a corner at high speed, then lets out the clutch. Yeah, I can see that being a problem.

I'd hope that the owner of a car like a 911 would already be experienced enough to avoid doing that.
 
There is no Rev limiter on a 964, and the PCM/ECU does not cut the fuel pump at any redline. I would have found the limit cause I have beat the daylights out of a couple 964's, they were extremely durable, and very well built, and strong. The chassis are extremely ridged, you can't jack one wheel off the ground, two wheels, or one side jacks whether jack is placed near front tire or rear.

A very good friend of mine for 25 years owned an indy Porsche, Ferrari, Lamborghini, sports car dealership and a very successful Porsche salvage yard. I had easy access to parts and Porsches, otherwise I would have been a lot nicer to them! They can take a beating like no other vehicle I have drivin, and I have drivin or owned most all makes and models.
 
Originally Posted by KneeGrinder
There is no Rev limiter on a 964, and the PCM/ECU does not cut the fuel pump at any redline. I would have found the limit cause I have beat the daylights out of a couple 964's, they were extremely durable, and very well built, and strong. The chassis are extremely ridged, you can't jack one wheel off the ground, two wheels, or one side jacks whether jack is placed near front tire or rear.

A very good friend of mine for 25 years owned an indy Porsche, Ferrari, Lamborghini, sports car dealership and a very successful Porsche salvage yard. I had easy access to parts and Porsches, otherwise I would have been a lot nicer to them! They can take a beating like no other vehicle I have drivin, and I have drivin or owned most all makes and models.



Rev limited rotor arms are cheap, available and common.
 
Originally Posted by KneeGrinder
There is no Rev limiter on a 964, and the PCM/ECU does not cut the fuel pump at any redline. I would have found the limit cause I have beat the daylights out of a couple 964's, they were extremely durable, and very well built, and strong. The chassis are extremely ridged, you can't jack one wheel off the ground, two wheels, or one side jacks whether jack is placed near front tire or rear.



That's cool to know!
 
But that's for a 911 Carrera 3.0 1974-1977, back when they were still 911's

How would that work on a C-2, 3.6, 964? It seems to me as something is missing... Fishing expedition...
 
This will always and forever be my dream car. My childhood neighbor in Wyoming bought an early 80s SC Targa when I was 14, and I've been enamored with these phenomenal cars ever since. I was thrilled to see Porsche reviving the true targa layout on the more recent 911s. They look great.

930.JPG
 
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