I'm wondering if a good staring point might be squareport heads and 91mm Nickies with 105mm OD?

Do they have more meat behind the combustion chamber or are stronger?

http://www.shoptalkforums.com/viewtopic.php?t=74388

Mahalo guys, I appreciate all your generous sharing of knowledge. I'm learning a lot.

78.8mm x 91mm = 1997.9cc
69.1mm x 91mm = 1797.6cc

Nickie cylinder O.D. Top = 114.8mm
I.D. Bore = 91mm
Cylinder wall thickness = 11.9mm. Will this work? Thanks again Everyone.

That's a pretty good idea. 91mm is as small as you can go with Sq Ports chambers but that's what we want. With 105 nickies that's a lot of contact area.

The Sq Port offers more support under the chamber than the oval. It will still be the weak spot, but it will be stronger for sure.

Were square port heads only on (some of) the 2.0 Type 4's? We were saying before that the 1.7 heads are a good start for a small bore turbo. Just trying to understand ...

Had another crazy idea while sitting in traffic...take Type IV head and from the bottom side machine away the combustion chamber and ports, figure something like a 4" diameter hole a few inches deep.

Grab some 6061 billet and rough machine the combustion chamber and ports, press fit into head. The billet alum has a thermal expansion that is slightly more than the cast alum so the fit will be even better once warmed up. (from what I can find online)


cross section of 911 showing more "meat"

Click to view attachment

Just the vanagon Type4s had square ports. But oh the joy of having a normal exhaust flange and gasket.

I like the idea of the sq ports normal flange and the slight increase in chamber strength from the added material in that area.

Ten years ago I did a lot of R&D on sq ports. What I found was that to match the flow of a oval port head with 36mm ex valves, the port wall had to be opened up a fair amount. This wasn't a huge deal, but in the final analysis we determined that the heads would not be a good fit for 38mm valves, so they would not be a good fit for larger engines.

Eventually we stopped working with them for anything but Camper Specials and our stock Blueprint Specials.

For a small bore turbo engine with 40mm intakes and 36mm exhausts they might be worth a revisit, though be prepared for the potential for heat related cracks in the port runners. We saw a lot of that with O.E. heads. Not much air flow around that area, and the runner will have a not so thick cross section.