reliability of air cooled 911 engine

[wkbergman]

Which of the aircooled engines over 2.0 are the more reliable?
Conversely, which have the self-destruct built-in?
Thanks
Bill Bergman
9110210590
wkbergman@gmail.com

[Dpmulvan]

Any interference motor has self destruct built into it. 3.0 is a reliable motor but pricey to add more power.

[silverc4s]

I would nominate the 3.2 Motronic Carrera engine as the culmination of air cooled flat six reliability development. Conservative power ratings in the low 200 bhp worldwide, only fault of note seems to be some era of valve guides showing excessive wear, many cars with well over 100K miles still on the road, roaring around curves on sunny Sunday mornings.

[Henry Schmidt]

My vote would also be the 3.0. They have zero case challenges, better valve angles than previous models and the first of the aluminum 908 style oil pump.
Except for the Dilivar head stud issues and a random assortment of faulty valve springs, these engine regularly see/saw 250,000 miles.
The rod to stroke ratio in the 3.0 is deficient but it is better than the 3.2 and the rod journal configuration [IE: smaller journal allows for larger rod bolts] is better suited to higher output and longer life.
As for the CIS injection: it lacks performance but is incredibility reliable and easy to maintain.

[Tippy]

If you compare the amount of bearings and wear surfaces (contact surface area) between a 911 motor and say American iron even up till today, the engine is incredibly robust. The rocker faces to cam loves are incredibly wide and being OHV, the valvesprings are extremely light

[silverc4s]

The thing that stood out most to me was that the quality and performance level of every part in a 911 engine was the equal of the best high performance aftermarket parts that I was accustomed to in my American car hot rod experience.
I wont even go into British cars and motorcycles that I knew pretty well in their day.

[MichaelSJackson]

3.0 w/CIS or 3.2 w/EFI? Duh.

Not to mention the choked exhaust of the 3.0 or the chain tensioner upgrade in the 3.2.

But I will state, my 3.0 has been very reliable.

[faapgar]

The last generation of the SC produced the best 3.0.The second half of the 83 model year received the 1st 3.2 case with no sump plate.Much stronger.Pressure fed tensioners were also part of the changes.The heads had the provision machined for the cylinder head tempurature sensor.Top studs were steel and bottom studs were black powder coated.

[MichaelSJackson]

faapgar,

What about the larger ports on the early SC heads?

This is an interesting little thought experiment, because we have no real idea of Bill's goal. Is it a simple swap or the base for a performance project? Not to mention his willingness to upgrade to a 915 to handle how much of an upgrade?

Or is it just a thought experiment? I've often heard the 3.0 referenced as the first bulletproof 911 engine.

MJ

[faapgar]

The 83 ROW had the large port heads and higher compression.9.8 to1.Also 204 hp.

[safe]

I'd say the 3.6 engines are the best air cooled engines. Most powerful too. I would take a 3.2 EFI over any 3.0 kjet engines.

The downside with a 3.6 is the initial cost, slightly more involved in a swap, might be too much torque for a stock 915.

[Dpmulvan]

The original question was reliability engine wise. Not talking fuel systems, power output et.

[safe]

Originally Posted by Dpmulvan

The original question was reliability engine wise. Not talking fuel systems, power output et.

I think fuel system is a large part of the reliability. K-jet is just a time bomb in waiting and basically no one except specialist, far and few between, knows how to fix, diagnose issues or even want to touch it.
In reliability terms a 3.0 (or 3.2) is only reliable if they have been rebuilt with new head studs.

[MichaelSJackson]

Dpmulvan,

The question was which "aircooled engines over 2.0". That sort of implies a swap? And also implies a 901? But other than that, it is an open-ended query?

How can "reliability" be addressed without more context?

Also, what does built in self-destruct refer to? A specific design fault, or a list of design faults/weaknesses through the evolution of the air-cooled engines.

I don't believe there is a single answer for the question, as stated. I'd thought it was an interesting opener for a discussion.

[ahh911]

Safe,
Why is the Kjet a bomb? waiting to happen?

With the O2 sensor, 81 and later, set FV to 45% to achieve mixture, dial in the idle, keep all stock parts. Fuel economy is very good, no surging, smooth as silk to redline, and I can easily spin the wheel in back during summer with a rolling start (81 u.s. stock everything). Sometimes for the first minute treat the gas gently or let it warm up, but I always drive right off. Easy and fun to work on and diagnose, lots of info out there. Once you start modifying and removing stuff, then I don't know. Is it bad gas you're talking about? Because I don't really hear anyone having issues that aren't in the end, very basic, like the last gentleman didn't have 12V at his wur, the previous gentleman didn't have his O2 relay (fv relay) working, for so many Kjets out there, I don't hear much on this board.
Phil

[faapgar]

The best long life motor comes the best owner.Start car drive away easy & do not jump on it until you get to 180 oil temp.After driving like you should go easy for 5 minutes before shutting down.Change oil per schedule and do not miss a shift.Happy motor makes long life.Ciao Fred

[Speedy Squirrel]

These are all great comments. I can see the attraction of the 3.0L. If I was buying a used 911 I would have to go with a 964, especially after the head gasket fix. The larger stud spacing allows for thicker cylinder walls, it still has the larger valve stem diameters, and the chain tensioners are better integrated without all the little tubes and fittings. A very durable engine. You don’t see too many in pieces.

[faapgar]

Rev happy and reliable has to be 76-77 3.0 Carrera.Aluminum case & light crank.26 lbs. versus 35 lbs.Due to weight of the crank a low stress environment.To each there own.

[Wizoftk]

Just learning more about these engines. Which ones would be easier to work on and have better part availability?

[Trackrash]

Originally Posted by Wizoftk

Just learning more about these engines. Which ones would be easier to work on and have better part availability?

Depends what you mean. For normal maintenance my vote would be for a carbureted car being the easiest to maintain.

Now for motor rebuilds the mag case motors are becoming problematic.