Big bore and 2 liters Silumin anyone?

[parced@telia.co]

I just bought a 911/83 engine that has been given 95 mm high comp. cylinders. The engine was rebuild after the original case got cracks. I do not dare to run this one with the current magnesium case. I have a set of 90 mm Euro cylinders that I thought I would use but I have now learned that the head has been modified.

So my options is to take a 2.4 S case that I have, 04R/05R and get my self a set of 2.7 Carrera cylinder head and build a S/RS engine or, take the 95 mm and use a silumin case that has been used together with 95 mm's and has been modified so it has "feet" for the MFI and build a 3.0 "RS". Both options will make nice engines.

I have spoken to people here, that is in Sweden, with experience of engines built with 90, 92 and 95 mm and say it works fine for everyday applications. Reading Bruce Anderson one gets another understanding. He says it's wise to stop at 86 mm.

Anyone with experience of big bore on old Silumin cases?

[Bobboloo]

Is the 2.4S case you speak of the one for your 72'S? If so I wouldn't do it. It would require boring out your spigots and that will bring down the value of your car. Besides there are better cases to use in this application that aren't as valuable as your 2.4S case.

I would look for a 7R case to build your RS motor on. Either a 73.5T case, they used a smaller spigot bore 7R case that can be bored out, or get a 74' to 77' magnesium engine case. They are all 7R cases and have the proper spigot size for a 2.7RS motor.

As for your 911/83 motor with 95mm pistons it's not at all surprising the case cracked. Those cylinders are to large for that case. The spigot size for 90mm, 92mm and 93mm P+C's is 97mm which is considered the maximum. 95mm P+C's require a larger spigot and the mag case just can't handle it. Really 92mm P+C's are considered the "safe" limit for these mag cases.

So what to do?

Find yourself a 7R case. Use your Euro 2.7RS P+C set and move the parts over to the "new" case. The heads on your 911/83 motor were probably fly cut for the 95mm pistons so they may not be ideal to use in this scenerio. If that's the case then you'll need to find a set of heads. Preferably a set of 2.2/2.4S MFI heads.

A used 7R case will probably cost around $275 and the machine work for the case will be another $1000.


One more path for you to consider...

If this motor is to replace the motor in your 72'S you might consider just buying a 7R case. Use the 2.7RS P+C's set you have and move all your parts from your 2.4S motor to the 7R case.

A 2.4S motor is virtually the same motor as a 2.7RS in every way except for displacement.

This way you save your 2.4S case and then you can just sell off the 911/83 motor.


Edit: I just re-read the thread title and realized you were refering to the early 2 liter aluminum case (not the later 3 liter case. oops! I deleted the part about 3.0 case) in which case I have no idea if you could use the 95mm P+C set on one of those cases.

I do know that they no longer make the 95mm P+C set so when these are past there limit you'll end up with an earlier aluminum case with bored spigots and no cylinders to fit.

Still it's an interesting idea though. Maybe someone can offer some advice.

[Eric911S]

Hello: You can use the 2.0 aluminum case for the 95mm cylinders from the 3.0. It takes some machining and welding to make it work. These are the old cheater engines we used to run a while back in SCCA. Thanks Eric

[parced@telia.co]

Thanks for the input. I have a rebuilt engine for the -72 S and this "sport engine" is made my -73 E a little more fun. After some pondering I have decided to go for the Silumin case and the 95 set I have. Me engine mechanic, Micke at www.spezialmotorer.com says it will be fine and I have heard about engines with this configuration running many 1000 km's, even with R-cams.

Vincent, that is my -73 E, will get Turbo 3.3 brakes and 16" fuchs. I will use 7" in the front and 8" from the 944 Turbo Cup. That will enable me to run 225 in the rear while keeping the narrow body. Vincent will be, close to, a 3.0 RS in -73 dress :-).