Big day today, both cylinder heads have returned from the machine shop.. I say "both" as I ended up reconditioning both the 9.5:1 and 7:1 CR heads. Why? You ask when I am only going to use the 7:1 in the new engine.. Well slightly annoyingly I took the 9.5:1 in to be refurbished before realising that I really wanted a 7:1 head. Before I could contact the shop the head was reconditioned.. So will have to put it down to experience and now I have a nice rebuilt 9.5:1 head with new valves, seats and guides in case I go back to injection. The good side of this is that I can show both heads next to each other.
Interestingly there immediately seems to be some differences between the two heads. Try playing spot the difference:-) there are at least 7. See below for answers.
Did you find them all?
RED: The large elgonated opening on one side of the head is missing in the 7:1 head.
YELLOW: Two of the holes between combustion chambers seems to be filled in the 7:1 head.
Blue: Four of the holes on the opposite edge of the block to the pushrods are missing in the 9.5:1 head... So why are there differences and is it a bad thing? My guess is that in the cases where they are missing in the 7:1 head it is probably the result of less being machined of the head meaning that the passages weren't broken through. But this doesn't explain why some holes are missing in 9.5:1 head.. Interestingly the yellow holes seem to be blocked by some material different to the cast iron of the head.. So what to do? (Answers on a postcard)?
I had a look at the cylinder block as well to see if the holes matched. Matching holes seem to be present for all so in effect neither head has all the holes found in the cylinder block. I also took the chance to measure the depth of combustion chambers to show how this changes with CR.
As you can see the combustion chamber in the 7:1 head is 4 mm deeper than the 9.5:1 head.
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