Pros and Cons of rebuilding '73 2.7L to 2.9L

[AlfaGTA]

For a numbers matching '73 RS going into a restoration, I'd appreciate hearing opinions about the benefits and risks of building the engine as a 2.9L instead of 2.7L. Opinions about changes to it's "originality" also welcomed. Thanks.

[RSTarga]

Originality aside, the magnesium cases really get stressed with larger displacement. You could probably achieve almost the same power by raising the compression to 9.5.

[obrut]

i heard too many stories about 2.9's failing - although it is hard to separate fact from fiction.

if you want to go a little bigger, a 2.8 is much more battle proven, and has the 2.8RSR cachet to boot.

[69Sman]

I would leave the 2.7 ALONE. IF you want more power/displacement/etc., build a new engine, put it in the car, and put the original 2.7 on a stand somewhere.

[kenikh]

Don't do a 2.9L. This is the definition of pushing your luck. You might get lucky, but why try?

[a911s]

Don't do it.

[parced@telia.co]

Don´t go over 90 mm on a mag case, these days even 90 mm is on the bigger side. There is a big risk that you will be sorry when you are taking the engine apart, not many cases has survived without cracks. A friend looked at 10 used 07R cases and all had cracks! He then rebuild his original 73 RS engine around a sandcast 65 case. I'm rebuilding my 911/83 around a sandcast 65 case as well, stretching it though. I had a 95 mm RSR P/C set, it's the 2.8 upgrade set, and I thought it could make a fun engine.

[Steve@Rennsport]

2.9's have issues and those 93mm P/C's are not known for longevity & durability.

The biggest I'd go is a 2.8 and they run VERY well if properly done,...

Keep the revs reasonable and they last a long time.

[72targa]

I would leave the 2.7 ALONE. IF you want more power/displacement/etc., build a new engine, put it in the car, and put the original 2.7 on a stand somewhere.

+1

The original should be put away and properly lubricated for long-term storage. Build yourself a play motor and have fun!

[fryardds]

I would leave the 2.7 ALONE. IF you want more power/displacement/etc., build a new engine, put it in the car, and put the original 2.7 on a stand somewhere.

Unless the rebuild is done by Ruf to 2.8.