74.4 Carerra crank with 102mm Mahle's?

fastbacker · 12-17-2006, 08:43 PM

I looked at an engine today that was built with a 78 3.0 case using a 74.4 Carerra crank and Mahle 102mm p&c's. The engine uses twin plugs and electomotive engine management.

-The guy said the displacement was 3.7 something. Is this correct?

-Is there reason to worry the 102mm p&c's?

Thanks-
Craig Backer

YTNUKLR · YTNUKLR's Garage

Technically that motor is 3648cc.

Reason to worry? 102 is getting VERY thin on a 3.0/3.2 case. That said, there are some motors I know of running those, and they seem to be doing OK. I doubt they have the longevity of stock 3.2 P/C.

scott.

Facey · Facey's Garage

i havn't seen it, however with modern metals and fasteners i believe it would be reliable as long as your not going to add a power adder (turbo/super/NO2).

expecially if you just go ~9.5:1, with a front mount. Keep the other stresses low, and it should make a early car a real beast!!!

fastbacker · 12-19-2006, 02:22 PM

My mechanic who has built more than a few 911 engines (street and track) said to stay away from it. He said the cylinders were too big for a 3.0 case.

cnavarro · 12-19-2006, 04:39 PM

The 102 mahles for the 3.0/3.2 are too brittle in my opinion - at the bare minimum, they should be cryo'ed to reduce the propensity to crack. Just like what Facey said, with the cast mahles keep the compression down and keep it cool. That said I have done many Nickies in a 102mm with a 106.5 register vs the 107 register that I have seen done on the on the mahles from Andial, and our cylinders hold up just fine, but I too would say keep in normally aspirated, and really, you should twin plug or keep the compression down.

There is nothing wrong with the case, no different than when we punch out type 4's for 98-105mm bores or 356s and 912s to 88-91mm bores. The part most guys don't like are the marginal sealing surfaces left between the cylinder bases and cases, which I personally have never had a problem with, just using Curil T on the bases. The other issue is that the exhaust, heads, cam, fuel system, etc must be upgraded to complement the increase in displacement, otherwise you end up with a combo that isn't worth even the sum of its parts.