upgrading from 66mm crank worthwhile?
 

Hi all,

I'm getting relatively close to starting to put my 2.2 back together. One thing that keeps nagging at me is the idea of upgrading to a 70.4mm crankshaft. I have a set of good used mahle 2.4s pistons and barrels (I know I'd need rods too but will cross that bridge if and when I come to it) and like the idea of being able to use those, and also the counterbalancing and extra .2 liters of displacement, but am not sure it'd be worth the hassle of buying a new crank and selling my old one.

This engine is for my long-term '69 912 project, which has gone on long enough that I've decided to just make it a 911. It'll probably never be tracked, just a fun driver.

Any thoughts would be greatly appreciated. Thanks!

The 2.4 S is 8.5/1 cr over a 2.2 T, you’re not gaining much
2.2 pistons and the longer stroke would be a better combination.
Bruce

thanks, so just to clarify you're saying that if I used the 2.4s pistons with the 66mm crank I'd be at 8.5/1?

Yes.

No, you’ll be below 8.5 because of the shorter crank. It’s 8.5 with the 2.4 crank and rods.
Bruce

Gotcha, thanks Bruce

Couple thoughts as some one who always wants a little more. Sounds like you have a 2.2T engine. If you plan on using the T cams you could use the 2.2T P&C with a 70.4 crank and have a little more displacement and a little more compression. Using the 2.2 pistons with 70.4 crank will get you about .5 increase in compression over the 66 crank. If you want to use more aggressive cams (E,S, Mod solex or Mod S) then the 2.4 P&C would be a better choice as you have the valve clearance with the pistons for the hotter cams. 70.4 cranks are pretty easy to find.

john

Thanks all, I think I'll source a 2.4 crank and use the 2.4s pistons I have (I don't have the original 2.2t pistons). Thanks for all the advice and info!

Its a slippery slope. Time and money ... stay with the stock 66 crank if you don't want to shell out alot. I had a 914-6 made into a 2.4 .. what a joy of an engine; but it would not be cheap to build now; 2.2S pistons, 2.4 heads .. a crank. Cams etc. .. fun car.