[Grady Clay]

jasam,

OK, lets analyze the pro & con of three common “improvements” for a 2.2T: The longer stroke crank, larger bore P&Cs (with whatever CR) and cams/induction.

The OE crank is a non-counterweight 66 mm stroke cast steel part. The replacement is a 70.4 mm stroke counterweighted forged steel part common to 2.4 & 2.7 engines. The connecting rods are necessarily different and must be changed with the crank. The crankcase must also be relieved for piston clearance at BDC.

The longer stroke increases the displacement in direct proportion to the change in stroke. Conventional wisdom says the increase in stroke has slightly greater increase in torque compared to hp.


Without changing the case spigot bore (92 mm), about the largest piston is 86 mm using custom (modified) cylinders and new pistons. Your stock 2.2 pistons are 84 mm diameter. The larger bore increases the displacement in square proportion to the bore. Conventional wisdom says the increase in bore has slightly greater increase in hp compared to torque.

It is common for the case to be modified to accept the larger (97 mm) cylinders spigots. The bore can be increased to 93 mm max. Normally the conversion is to the 90 mm 911 Carrera RS (8.5:1) or the 92 mm 911RSR (11.3:1) Mahle Nikasil. There are also aftermarket (JE) pistons available.


The performance of the heads, cams, intake and exhaust can collectively be called “breathing.” All of these issues must be addressed in concert. Simply changing cams without addressing port size and carburetor venturi (and jetting) doesn’t work well. A 2.2T already has great headers (heat exchangers).

As an aside, twin ignition improves performance (and drivability) and slightly reduces octane requirements.


OK, that is the quick tour. There are other important issues.

Probably most significant is the crankcase. You should look at the casting numbers on both sides of the case halves. I suspect they are 901.101.101.3R and 901.101.102.3R. The crankcase strength increased over the years with the 7R being the final (and strongest) version.

The OE Zeniths do not have performance (or even adjustment) spare parts available but you can make your own. Appropriate replacements are Webers and even better PMOs.


If you start with a ’72-’73 2.4 911T MFI core engine you have the basics for a 2.8S. The greatest benefit is you can take your time building the engine while maintaining your 911 in service. You can also build another engine where it appears exactly (911E or 911S) period correct.


I recommend you study two important books:
Anderson, B.; Porsche 911 Performance Handbook
Dempsey, W.; How To Rebuild & Modify Porsche 911 Engines
These are available from out host.

While you study both of these books, write yourself a proposed plan. You can then discuss that with knowledgeable engine builders and post it here for discussion. By doing this you can turn a vague engine idea into an action plan, complete with all the technology, contract services and cost estimates. The best part is at this point you only have some time and the book cost invested.

Best,
Grady