3.5L upgrade reliability in turbo application?

[JMA-RUF]

As I understand it, when going to a 3.5L big bore kit (from 3.2L Carrera), the case needs to be machined to accommodate the larger jugs.

Does this introduce a weak point in the engine when considering this upgrade for a big HP, turbocharged application?

Are there any ways to minimise this weakness, perhaps by using stronger ARP/Raceware fasteners?

[89turbocabmike]

James from what I've been told by a number of experts, including Steve@Rennsport, is that the 3.5 cylinders are just too thin for turbo applications and are definitely not advised if your interested in reliability regardless of fasteners. Your better off staying with 98mm (3.4) cylinders and running 8:1 with efi(autronic is in your neck of the woods) and perhaps even stroking with a 964 crank for extra displacement. That's what I'm collecting parts for myself. Of the 15 or so turbo owners I know from the boards who have rebuilt their motors in the last year or so, no one has risked it with the 100mm units.

[JMA-RUF]

Thanks Mike. I just received confirmation of this from Steve@Rennsport.

What would the displacement be with a 964/993 crank?

[Jim Dorociak]

you would be better off as I understand it with the 964 crank as the standard rods are used from the 3.3 and 3.6 engine. The small end that attaches at the piston is the same size as all 911 engines before. The 993 crank uses a different size small end of the rod. I believe your displacement would be 3.5 you will just get there differently. Jim

[Carrera3.5L]

When I worked for Andial 15 years ago, 3.4L & 3.5L motors were commonplace for normally aspirated applications and worked very, very well in these cars.

A few 3.5L 930 motors were built using 100's, but the vast majority were built 3.4L using the 98mm Mahle's. Andial generally did not have a problem using 100's in these instances, but they ran conservative boost and there are other variables at play as well. Many customers wanted adjustable boost and that as you know generally means an engine rebuild is sooner rather than later.

Andial also developed a 3.6L kit using the standard 3.2/3.3 case as the basis, 100mm Mahles (tops specially machined) and the 964 crank. They also developed a long stroke 3.5L using Mahle 98's and the 3.6L 964 crank that also proved popular for those wanting a larger displacement motor but not wanting to use the 100 piston/cylinders.

Ralph