7R case ...
 

Hi, I am looking at using a 7R case for a 2.5+ SS. With early Turbo cases into realms of unobtainium ... this looks like the next best option. What is the largest size and / or recommended sizes that I can go on the 7R? Can I machine the case to fit a 95mm. Looking at the LN Eng website it looks like pistons could be an issue.

Thanks Chris

The biggest size bore you can safely take a 7R case to is 2.8 litres. Cylinder spigots are 97mm.

Hello Steve, Excellent information. Thanks!

2.8 is 92mm bore. The 90mm 2.7 already has the 97mm spigot? Spigot boring needed only on a 2.4 7R? Engines were raced with 93mm cylinders also. Was that achieved with just a very thin cylinder wall where it sockets into the spigot?

Carbster - how would you get a crank short enough to run a 95mm piston and still keep the displacement down to around 2.5? The SS 2.8 is 95x66. Custom billet crank?

Fortunately, you can't easily run a 95mm piston anyway because of the head stud spacing needed for 95s. The 2.8SSs are built on a very early 3.0 or Turbo aluminum case, which used the 6 bolt flywheel crank. To use a 7R (or sand cast) case with 95s, you'd have to relocate the head studs. Peter Dawe might be able to do that, or some other inventive engine builder could, with a whole lot of work and welding and so on, but it would hardly be economical.

Fortunately, you can use either a 66 or a 70.4mm crank, and pistons no larger than 90mm, to get to around 2.5. The 66 might be the best choice, because the factory 2.5 long stroke had problems shaking the flywheels off of the crank. That can be overcome with flywheel bolt torque of 150 lbs ft and some red Loctite, but I think the 66 would be better anyway.

How about a 66mm crank + 92mm Rsr PC? = 2.6L. With standard heads the compression ratio is a streetable w twin plugs.

66X92 mm
 

I think the compression is still a little high. Maybe a little metal is to taken off the tops of the pistons to get to 10 to 1 compression with twin plug. also it helps to use 1975 911S 2.7 heads with larger spark plug dug out. Chris

Hello Walt, You are correct I really need an early 3.0 case. The Turbo cases are just too much money these days. Back to the drawing board or maybe ebay :(

I think the early (6 bolt crank) and 3.0 turbo cases are the same. Could be wrong. I have the only case of that sort that I need, so haven't followed prices. Maybe the serial number on the turbo makes it more valuable?

Shameless plug: you should be on the preorder list for my 3.6 cases!

I found a 3.0 turbo case installed in my targa after owning it for about a year and a half. It was the only pleasant surprise I came across with my motor rebuild.

Its a shame that I had to pair it with factory '83 heads and cams. A 9k rpm 2.8 would be so much cooler!