What's wrong with a 2.9?

[Matt Holcomb]

The consensus seems to be that increasing the displacement of an air-cooled 2.7-litre engine to 2.9 litres will yield to an engine that is too stressed, and which will tire of sustained, high-rpm use sooner than if it was a 2.7. According to Bruce Anderson, "... the crankcase has to be bored out even more, further weakening the material in the area of the spigot bases."

Wayne Dempsey doesn't like 2.9s, a few fellow members of the Porsche Club of Victoria think they're bad news, and Bruce Anderson warns against converting a 2.7-litre to a 2.9 unless you're using an Andial 2.9-litre conversion kit, which Bruce says "... addresses all of the problems ...."

So what's the deal? How does the Andial kit "address" all the problems? If I can't confirm whether a 2.9 has been built with an Andial kit, should I be worried? Can you make a 2.9-litre engine out of a 2.7 without an Andial conversion kit?

[mark 74 carrera]

Matt,

I don't know all the ends and outs of the 2.7 vs 2.9 but I did just have a conversation with a wrench about taking my 2.7 to a 2.8. One racing guy said "There is no substitute for displacement." After talking with the guy doing my machining he convinced me to stay with my original plan. A 2.7 RS specs P&C w/ webers.

The key to me was that my machinist listened to how and for what I was going to use the car. He said the jump from CIS P&C to RS P&C w/ webers would be big jump in HP and "a durable & fun motor". I got the sense that the racing crowd is a lot more comfortable dropping and repairing and spending on the motors. It goes with the territory. I want to experience a re-build and then take care of it and not touch it for years.

I plan on using mine for street, DE, & maybe a little track time. (after all it is a targa, and therefore kind of worthless )

See Ya, Mark

[Chuck Moreland]

I don't know how the Andial conversion differs.

However, the only 2.9 I've been exposed to was built by Andial. It lasted about 1 year before it pulled head studs. It was being tracked regularly.

I think Mark is giving good advice on this one.

[Randy Webb]

Is it the 2.9 that wound up with ultra high compression and could not run on any pump gas? BA discusses this in his book somewhere.

[74911s]

i can give you my experiance on the andial 2.9 conversion as the engine chuck is referring to was mine.

i had my 2.9 built for my 74 off the 2.7 and retained the cis. i built the car to be a fun street car and once the engine was complete it was very responsive and great fun to drive.

i did an auto cross with my local pca and got hooked hard and soon found my way to the track as often as i could. looking back, i made a huge mistake that i believe ultimately lead to the premature end of life of my 2.9. while every time i went to the track i came home and modified suspension, tires, racing seats, harness, etc i never addressed oil cooling. i regularly ran the car on the track with oil temps hitting 250 and the head studs started to pull from the case even though it had been time serted. i believe that if i had proper oil cooling i would still be running my 2.9.

in the end, andial took care of me big time and the andial built 3.0 that is in my car now has been bullet proof not requiring a single thing except regular service and it is drivven at the track 90% of the time.

my advise is you really need to know what you are getting into to make an informed decisions, be clear as to how you are going to use the car, know exactly who built the engine and if their reputation will back it up and never cut corners on oil cooling, even for a short time.

[Ho Hum 74]

Can I ask a STUPID question?

What the heck was Andial doing building you such a great motor and not insisting that you cool it properly?

When I bought my 2.7 MFI '74 my local mechanic told me to immediately put a spoiler mount oil cooler on because I was tracking the car so often.

[74911s]

as i said in my description the car was built to be a street car and with the 28 tube cooler in the fender i never had a heat issue on the street. as i spent more and more time on the track i made the decision to spend my money on other upgrades and a nose mounted oil cooler always fell to the bottomn of my list of to do's. as anyone nows that has started to track a car that is mostly stock you can't have enough money or time in the first year or two to make all of the upgrades most of us desire so somethings have to wait.

now that i have a good amount of track experience i see newbies come to the track all the time just like i did and not show any concerne for the temps they run, especially important here in california when most of our tracks are in the desert. i try to share my knowledge now to hopefully save others from making the same mistakes i have.

[JP911]

Jim- Beyond the pistons, cylinders and case work were there any other modifications necessary to run the 2.9 with CIS? For instance, did it require twin-plugging the motor? Could you run on pump gas? I've been contemplating going to a 2.9 and am curious as to what is involved.
Thanks,
Jon

[Matt Holcomb]

I'm going to buy this car as soon as I sell mine. It's a '74 RS replica with a twin-plug, 2.9-litre MFI engine. My father bought it last week to tie it up for me.





The engine in this car was built by a legendary Melbourne-based Porsche wrench -- my late mechanic, John Gregory. It's a great engine; it's done less than 15,000km since it was rebuilt.

I plan on participating in a few club sprints per year with this car. It has a front-mounted, horizontal cooler, which, I suspect, will provide more than adequate cooling. If this 2.9 doesn't run hot, should it last as long as the 2.7 that John built for me?

[Ho Hum 74]

Matt,

Sounds and looks like a great car. Maybe there's more comfort in your car becuase you know exactly wha twent into it. The only other thing I've heard about the 2.9s is that the cylinder walls are very thin. I would guess that they could go out of spec easier than the 2.7.

Either way, you have an interesting experience on the horizon. Why was the car sold in the first place? Assume the PO put a lot of Aussie-backs into it.

Tristan

[Wayne 962]

You might as well find a Euro Carrera case and make a short stroke 2.8 or a 3.0 for the money you'll spend on a 2.9. With the aluminum cases, your engine will be bulletproof...

-Wayne

[Matt Holcomb]

Tristan,

The previous owner spent over $200,000 building this car. He's selling the car because he has to sell off some assets.

Out-of-spec cylinders = increased oil consumption, yes?


Wayne,

The '74 RS replica (check the above photos) that I'm going to buy is powered by a twin-plug, MFI 2.9. I'm just trying to determine if I should leave the engine alone or reduce the displacement.

[Adam]

I'd leave it alone until you know for fact that it's a problem that needs work.

With that big oil cooler, I doubt you'll have any issues. I was astounded at the difference my fender-mounted Carrera cooler made. Realistically, it doesn't get very much airflow compared to that center-mount unit. Your car probably won't be doing much heavy traffic grind, either.

Even off the track, imagine the efficiency with roughly 2-3 times the airflow!

[Ho Hum 74]

Adam,

I love the look of you car. Very sweet. Can I ask you about your Fuchs? After you took off the paint (as you show on your site) how did you re-paint? Thanks and sorry Matt for hijacking but I thought I'd squeeze that one in

Matt: Get a black ducktail for that 2.9 and it'll be one grumpy, bad-arse looking 911. Nice.

Tristan

[Randy W]

Of course, you could always use an early aluminum case ('67 vintage) for your 2.9, and it would also be bulletproof. That's what I'm doing with my current 2.8L racing engine rebuild.

[Adam]

HoHum,

Thanks! I just sent you a PM.

[dd74]

Originally posted by Ho Hum 74

Matt: Get a black ducktail for that 2.9 and it'll be one grumpy, bad-arse looking 911. Nice.

Tristan

This is good advice as a ducktail will also aid airflow toward keeping the 2.9 cooler.

[Matt Holcomb]

David,

Yes, a ducktail is mandatory for this car! Having said that, the IROC tail is as good as having Robert De Niro riding shotgun with his don't-f-with-me expression.

[dd74]

Originally posted by Matt Holcomb
David,

Yes, a ducktail is mandatory for this car! Having said that, the IROC tail is as good as having Robert De Niro riding shotgun with his don't-f-with-me expression.

LOL Matt - I like to think Mr. White from "Reservoir Dogs."

[Matt Holcomb]

David,

Yes, a much better deterrent!