bore and stroke of a 73.5T?

911SCfanatic · 911SCfanatic's Garage

The 73.5T (911/91) is supposed to be a 2.4L, right? On page 201 of Wayne's Engine rebuilding book it lists the bore and stroke as 90x70.4 for the 73.5. But, for 72 and 73 2.4L the bore and stroke is listed as 84/70.4. I've got to be missing something. What?

Shuie · 08-27-2004, 07:32 PM

I dont have the book handy, but 90x70.4 is a 2.7

911SCfanatic · 911SCfanatic's Garage

It just must be a typo.

Jim Richards · 08-27-2004, 08:56 PM

84mm x 70.4mm is the bore / stroke for the 2.4L engine, Bill. For some reason I thought you had an MFI engine.

Henry Schmidt · Henry Schmidt's Garage

Jim is correct. One of a kind 2.4 8.5 to 1 comp. 70.4 x 84. They run like a 2.7 but a 2.4 never the less. They also have one of a kind heads. Like the MFI engine the injectors are in the head not the manifold. All other CIS engines have the injectors in the manifold.

911SCfanatic · 911SCfanatic's Garage

Jim, I do have an MFI enigine.

I have a 73.5T long block (engine code 911/91 and serial number 6134046 with a 7R case). The engine has MFI on it. Best I can tell, the MFI from the original '72 was installed on the 73.5 engine (MFI pump Bosch number 0408126015). Apparently, from what Henry has said I gather that the 73.5's special heads made the MFI swap easy.

Jim Richards · 03:24 PM

Very cool, Bill. MFI rocks.

And thanks to you and Henry for pointing out that.

Henry Schmidt · Henry Schmidt's Garage

The 2.4 CIS heads are not easily usable for MFI. They could be converted but it would be more trouble than it's worth. If you want to convert a CIS engine to MFI I suggest you buy the correct heads.
Guess what ? we have them of course.
We have almost any aircooled engine part instock.

911SCfanatic · 911SCfanatic's Garage

Henry, I'll be talking to you down the road as soon as I do some more research and map out what I think I want to do. Basically, the plan is similar to Jim's and many others in that I want to make this engine into a 2.7RS.

I'm guessing that these heads aren't the best to start off with because their ports are 30/33? Also is the combustion chamber shape different and are the valves oriented differently? What makes the 73.5 CIS heads any different? I wasn't sure, but I thought if it was possible to open up 72T heads, it would be possible to open up these. What's the typical cost to buy already reconditioned S heads compared to having these heads reworked? Thanks.

Actually, another question while I'm thinking of it: I'm going to use this 73.5 2.4L 7R case as the base. Any reason I shouldn't--this is the case that was used for the RS, wasn't it?