Taking the 2.7 to 2.9L

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Hi guys – before I assume this is a Y not want to ask if this is a path worth going down? I had low compression on one of the cylinders on the 2.7 L original engine in the 74 Carrera so I pulled it and had it stripped down. Bottom is fine, Case actually looks good, but of course I’m going to get that all appropriately machined etc.

I’ve had a couple conversations with the shop that’s doing a rebuild and bumping it up and displacement is really a function of cost of parts because the labor is going to be the same, so if I’m not a stickler for originality is there any reason not to do this?

I assume the power bump of the larger displacement along with a slightly hotter cam will be noticeable but not earthshaking, is that the right expectation?

I intend to run the original CIS on it

Thanks!

[Walt Fricke]

With CIS, I suppose you have read the discussions here about the 3.6 cam? But you can't use that stock cam - journals are larger. With the CIS and stock compression ratio, I'd not expect much of a gain from a cam, but there is no replacement for displacement.

The 2.7 CIS pistons have tops contoured especially for the CIS injection characteristics. Those aren't available off the shelf, I suspect, in the aftermarket for 92 or 93mm cylinders. The 93mm cylinders always seemed to me marginal because the part which sockets into the case is so thin. SCCA allowed them in a class, but that's racing where costs kind of go out the window. You might see if J&E could cut you pistons with the CIS swirl tops.

I've got to wonder why, owning a 911 with a 3.2, you'd want to upgrade a 2.7. My first 911 was a 2.7, and it had all the power I really needed for driving to work or taking trips.

This is a US Carrera, right? Don't those command a premium, at least over the 2.7S of that year?

[stownsen914]

2.9L 93 mm cylinders are really thin walled as Walt said. So much so that the standard 2.7L CE style head gasket doesn't work well. The cylinders also distort easily due to being thin. You get most of the punch going with 2.8L 92 mm and avoid the above challenges.

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Originally Posted by Walt Fricke

With CIS, I suppose you have read the discussions here about the 3.6 cam? But you can't use that stock cam - journals are larger. With the CIS and stock compression ratio, I'd not expect much of a gain from a cam, but there is no replacement for displacement.

The 2.7 CIS pistons have tops contoured especially for the CIS injection characteristics. Those aren't available off the shelf, I suspect, in the aftermarket for 92 or 93mm cylinders. The 93mm cylinders always seemed to me marginal because the part which sockets into the case is so thin. SCCA allowed them in a class, but that's racing where costs kind of go out the window. You might see if J&E could cut you pistons with the CIS swirl tops.

I've got to wonder why, owning a 911 with a 3.2, you'd want to upgrade a 2.7. My first 911 was a 2.7, and it had all the power I really needed for driving to work or taking trips.

This is a US Carrera, right? Don't those command a premium, at least over the 2.7S of that year?

Thanks for the thoughtful reply and information.

My 1974 "regular" 911 has a 3.2, I am asking about my 1974 Carrera (different) car that needs an engine rebuild.

Sounds like a 2.8L approach is better for longevity, so will go that route after reading about the 3.6 cam consideration. That is new info to me.

Thanks!

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Originally Posted by stownsen914

2.9L 93 mm cylinders are really thin walled as Walt said. So much so that the standard 2.7L CE style head gasket doesn't work well. The cylinders also distort easily due to being thin. You get most of the punch going with 2.8L 92 mm and avoid the above challenges.

Good coaching, thank you.