3 out of 6 cylinders do not like 12.5:1 compression

[Walt Fricke]

Scratch one theory. The head photos suggested 2 and 5 were the only ones not having problems (though 3 were worse than the 4th), which suggested some kind of height issue, as in those two had taller cylinders and held up the others. Though one would think that would show up by the cam binding as you assembled the motor. I think a lot of us have had the experience of needing to loosen the head nuts and retighten on occasion to get the cam to turn freely.

On my 2.7 race motor I ran conservative ignition advance.

But on my 2.8 long stroke I see I was at 30 degrees by 3,000 rpm, 33 at 6,000, and back to 30 at 7,500. This motor I shifted at 8,200. Nominal Mahle 10.5 CR. When I pulled it down based on 125 hours the bearings looked like they could maybe go another 125, and nothing wrong with anything. No head seal issues. ARP studs. This based on what the previous owner of the motor did, and what a local shop and tuner did when we had it on his dyno.

My short lived 2.8 short stroke (pulled a piston in half) had measured 12 CR. Only had chassis dyno time (<1 hr), but no signs of head seal issues using the same ignition map. Supertec studs.

All these sand cast cases. Maybe a mag case is more sensitive? Certainly not as strong, but you said you checked torque before disassembly, and it was what it should be?

I'd have thought that the steel studs were strong enough. The special virtues claimed for aftermarket studs is that they have thermal expansion characteristics complementary with aluminum cylinders, and don't just break like Dilivar can. They are significantly stronger, but isn't regular steel strong enough? The change to Dilivar was due to studs pulling out of mag with the Nikasil/Alusil, wasn't it?

Not much has been said about expansion and Biral. The steel liner presses against the head, but nothing rests on the case at its base. The aluminum around it buts against both, so I suppose it has expansion much like the all aluminum cylinders? Just not as much force from thermal elongation because of a thinner aluminum section? You don't hear of issues with Biral like the liner getting loose from differential expansion.

[neilca]

I was thinking about the birals the same way. It is odd that the compression of the head studs is transferred by shear between the steel liner and the aluminum fins. I would think the expansion would be like the steel liner which is half that of the fins. It is amazing these do not delaminate under the compressive and thermal loads.