2.2 or 2.7

[mikl911]

I have tried searching this question and also spent as much time as I could just scrolling thru the forum to find a thread, that I'm sure is here somewhere, with no luck.
I have a 1967 911 that has been modified as an RS clone with a 1970 2.2. The motor needs a rebuild as the rings are worn so it smokes and burns oil (compression test and visual inspection verified this). I have the option to change to a 2.7 (7R case) but have been told that the 2.2 may be a better option. The 2.2 does have Mahle aluminum cylinders, that I've been told might be able to be refurbished, where as the 2.7 would have JE cylinders and forged pistons and case savers installed. Either motor would get upgraded cams, new timing chains bearings, valve guides etc. Neither would get crazy high compression, no twin plug. The car weighs just under 2000 lbs. and will only be driven on the street (I have a 1978 SC for track days) My plan is to enjoy the car and hand it down to one of my kids, Although I love HP I'm willing to go with dependability, longevity and value. I don't want to leave them with a money pit so I'm willing to spend the money now to make either motor right.
So my question is what would the advantages or disadvantages of building a 2.2 over a 2.7? So far I have one opinion 2.2 and one 2.7

[targa72e]

Both the 2.2 and 2.7 are mag case engines. The case in the 2.2 is one of the weakest of the mag cases. The 7R case for the 2.7 is one of the strongest. Both cases will probably need some work to use. Case savers for head studs, inserts for some of the other critical case threads, oil bypass mod (2.7 case may already have this). Mains checked and case machined as needed. Cylinder mating surfaces decked as needed. The work to make either case usable will probably be about the same.

Are the 2.2 cylinders Biral cast iron with aluminum outer fins (this is factory) or late piston and cylinder set with Nikasil cylinders? If Biral they can be bored larger and new pistons used.
JE does not make cylinders only pistons. Factory 2.7 cylinders can be reused if Nikasil and in spec or re-plated for use the JE pistons.

Since you have two engines to pull parts from you could make a 2.2, or 2.4 or long stroke 2.5 from the 2.2 (larger displacement needs crank from 2.7) with final displacement dependent on bore. With the 2.7 you could build a 2.5 short stroke (use 2.2 66mm crank) or 2.7-2.9 depending on cylinder bore choice.

I assume you are using Carbs to day so they should be able to be repurposed for use with any of the above combinations.

I would vote for 2.7-2.9 with Mod S cams. I have had a 2.4 E spec motor and a 2.7 RS+ with Mod S cams in my 914-6 conversion in the last year and the 2.7 wins hands down.

There are several similar thread in the engine rebuilding forum you might want to check out.

john

[Matt Monson]

Why not just do a top end rebuild on the 2.2? Maybe new pistons, with the cylinders refreshed, along with some headwork if needed, and cams to suit whatever compression you decide to run on the pistons?

[mikl911]

Thank you for your reply John a lot of great info and lots to think about.

[Uwon]

John, do you know what a ‘71 2.5 ST variant would entail?
Johan

[targa72e]

not sure what was used in 71. Porsche built a short and long stroke 2.5 race engnie. Long stroke uses 2.4-2.7 crank. This crank has RPM limits due to harmonics so 7500PRM max (harmonics cause flywheel to come of at high rpm, BAD) . Short stroke 2.5 uses 66mm crank (use counterweighted) and 90mm cylinders (same as 2.7). These engines because of short stoke crank and big bore can rev much higher than longer stroke engine. Cams, heads exhaust etc all come into play. comes down to what you want to buile, Plenty of info on engine building forum.

john

[lrodri64]

A 2.4 with a combination of parts from both engines is a very good alternative in my opinion.