Motor geeks,
Here are the main specs of the engine I am building:
70.4mm crank
circa '72 S Heads.
'67 Alu case
Solex Cams
'71 911E P/Cs, 84mm (slightly higher compression, stock, than 72/73 ones)
Questions/Observations:
1. This engine SHOULD BE a bolt together correct?
2. When we got the long block mostly together the chain box was about 1.7mm too high and so the seal/plate around the cam didn't fit. Then we discovered the shoulders of all the Cs had been cut down about the same 1.7mm, same as we were off on alignment. This was done by PO on a 66mm crank engine with stock "normal" heads, I guess to increase the compression with those heads.
3. We then checked the old chain boxes (the ones the Cs came off off) and sure enough they had been cut on the bottom the same 1.7mm.
4. We have checked and for combination we are building the Ps do clear the heads.
5. What would be the estimated resulting compression ratio using the stock combo above WITH a\THIS further reduction of 1.7mm (liner travel of P) up into the head, any estimates? It is already going to be higher than the stock 2.2E (9.3:1 I think it is) due to longer stroke. I've forgotten at the moment what factor one applies but as I recall it was, like, up to say 9.5:1.
6. Finally, this is elementary but just want to check. IF a P is at top dead center and the intake valve was so mistimed as to be at its maximium extension into the cylinder there would be a collison. Correct? Put another way, if a chain tensioner were to fail and we had a skip time, a collison could occur, correct? I ask this because I never really realized that the cam timing was such that the intake valve was not all the way out when at TDC. Of course now that I think about "overlap at TDC" and look at the amount of lift we are measuring on the valve, we are still a ways away from maximium excursion into the cyclinder.
7. No to belabor the point but #6 above was "discovered" in trying to figure out why the chain box was not aligned with the cam correctly. Started checking more things. Never thought to actually measure the Cylinder before that; but then..we said..what could it be. But when we took one off, sure enought we could see the machining marks and it measured 1.7mm short.
8. In summary then, the question is: do I make some spacers to bring the C's back to stock. Or do I use the modified chain boxes I have and go for even higher compression?
All input appreciated! Thanks.
-Allen-