Matt,

Please tell me about the throttle body and intake system on your 2.9. I haven't seen that before. It looks VERY intresting, as in VERY COOL!
Looking forward to you posting.
All the best!
Roger Grago
R Gruppe #27

Matt,
I'd love to see about 100 more pix of that car. Please post some or PM me.

Roger,

All I know about the intake system is that the previous owner spotted them in the workshop and told the mechanic that he had to have them! I'm guessing it's a custom intake system.

Hi Matt

What case is the engine built on - early aluminium or 7R?

Cheers - Ryan

Ryan,

It's built on a 7R case.

that's good news matt - i think that means it should be eligible for targa tas, classic adelaide etc... (as 7R cases were used in 74 right?)

i got my entry for targa tassie confirmed yesterday # 448

Ryan,

I think the 7R cases were introduced in '73. All the 911/83 2.7s were built on them.

Good luck with your '04 Targa campaign! I'll be keeping track of your progress online!

Speaking of aluminum, what about a 2.9L motor on an early aluminum sand cast case, or even more interestlingly, the same pistons in an early case w/ a 66mm stroke?

The main problem with the 2.9 conversion is with the cylinders not the case. The cylinder walls are too thin. If you want reliability then the 2.8 cylinders are a better option.

0.1L increase in displacement froma 2.8.... result is 3% more hp

That answers the whole thing, doesn't it?

Agreed. At what cost/benefit ratio is this upgrade? And at what strain on the case and componentry?

Alan, owner of the Stable in San Francisco seems to like the 2.9's. Has built a few for his customers. You should talk with him. We bought a '74 rsr clone that came with a 2.8 twin plug, but pretty mild compression as it runs fine on pump gas. Has been converted to a race car. I havn't taken the motor apart so I'm not sure what's in there. I notice a lilttle improvement at the track with 100-102 octane, but not significantly.
'74 rsr w2.8 (255 h.p. @ flywheel)

I don't particularly agree, but everyone has different experiences.

FWIW, the 93mm 2.9L Mahle pistons/cylinders that were developed by Andial were to alleviate case problems because at that time there were alot of people building 3.0L's from 2.7L's using a 95mm bore. When these 3.0L conversion motors were being built, the case spigot bores also had to be opened up from 97mm to 100mm which meant that casesavers were no longer adaptable. THAT IS WHEN PEOPLE WERE REALLY HAVING PROBLEMS WITH PULLED HEAD STUDS! These 3.0L conversions were just not smart to do if long-term reliability (like most street engines are built for) is a significant factor.

In response to these issues, Andial's solution was to just increase the bore to 93mm which meant that the case spigot bores did not need to be opened up and thus remained at 97mm. This allowed the use of casesavers which greatly helped with the reliability aspect. The only head machining necessary was a small chamfer for the slightly increased bore.

There is nothing wrong IMO with a properly built 2.9L. It will be just as reliable as a 2.8L will. YRMV I guess but we built alot of them at Andial back in the day and didn't have issues. Whether the cost difference (if there is one) versus power gain is justifiable is a different story and is up to the purchaser to decide. If I wanted to build a motor from a 2.7L rather than going the 3.0L/3.2L/3.6L transplant route, I would have no qualms building a 2.9L. To each his own.SmileWavy

Ralph

Cylinder wall thickness aside, the magnesium cases are a very weak design. They will never be able to handle large power engines. Not only do you have problems with head studs pulling out, but the entire case tends to twist and deform over time. The 74 RSR engines were aluminum for a reason. If you want to build up an engine greater than 2.7L, then don't waste your time - build it on an early sand-cast aluminum block, and you'll be miles ahead when it comes to longevity. These cases run about $750 these days. Be sure to get one with the intermediate shaft, as the shafts are difficult to find these days...

-Wayne

Gee, this kinda supports what I was saying.

The case is not the issue.

The cylinders, however, are thinner. They just aren't as strong and in some cases have failed.

If I had to have more than 2.8L displacement then I would sell off and buy a 3.0L to start with.

Good thread, and many good points were brought up here,...:)

Everyone has their own experience with these things and I would
simply contribute some of mine. Although there is far more to this than I have time to address, Please bear with me as I would make two points about large-bore, mag-cased engines.

1) 90mm-92mm-93mm cylinders are thin. Thin-walled cylinders do NOT maintain concentricity when hot and leakdown figures always show that. One gets compression loss and increased oil consumption.

One of my favorite ways to demonstrate this to a customer is to hand him a Mahle 90mm cylinder and have him hold it tightly between the heels of his hands. Then, I slip a piston into the bore (sans rings). The piston will not fall out the bottom until he relaxes pressure on the barrel and then, voila',....out the bottom in a flash. Not very damned rigid and thats at room temperature!

2) 2.7-2.8-2.9 litre engines operated continously over 7000 RPM develop cracks in the case around the main bearing journal bulkhead behind # 3. It doesn't seem to matter whether its all shuffle-pinned, line-bored, or not; its doesn't matter how precisely the crank, rods and piston assemblies are balanced. Its a likely occurrance and tough to swallow after you spent $ 2K in case prep and machine work. Maintain reasonable rev limits and you'll be fine. Run the things hard, and don't be surprised to find cracks after a few years of that. Its a combination of lack of case rigidity and crankshaft harmonics. The Factory figured this out in '73 and even made some (rare) 2.8 litre 7R aluminum cases. After that, all race engines used the special aluminum RSR case since they had the 70.4mm crank (and 95mm P/C's).


All of these cylinders are thin and so we all make compromises. IMHO, the 93mm (2.9) ones are just too damned thin and hot leakdowns always show the less-than-ideal ring sealing. Compression is HP and for my money, these ultra-thin things give away too much to the 90-92mm ones for power and durability. In short; its not worth it. (IMHO, of course)

Bottom line; its your money but I'll not build anymore 2.9's for these and other issues. There are MANY products made to satisfy a market-driven demand, but that doesn't make the purchase of such things a smart decision,....:) 2.8 litres is max for me.

For those with very deep pockets, one day I'll tell you about a 2.8 we made from an SC engine using custom cylinders with modified 935 heads that made 327 HP at 8200,....:)

I do hope this helps,

you tease...