Head Skim

[wehey]

i have a spare head which needs a skim.
Whilst I'm getting it done I may as well have a decent amount taken off it to increase the compression on my 1.0L.
What would be a decent amount to have removed to achieve a good compression as a daily driver, and without the timing chain becoming too slack?

 

[frank]

2.5mm wehey with a half-link fitted the the lower chain http://www.micra.org.uk/threads/1-0l-pistons-and-rings.61075/#post-691623

 

[wehey]

What about without adding the half link? How much could I remove without effecting the chain tension.
I'm not sure if I want to start buggering around with the chain in light of my recent disaster lol

 

[frank]

2.5 mm is more suited to 1.3,s tbh anyway wehey and a bit high for 1.0,s, you could work it out tho (11:1 ideally)
stock combustion chamber is about 24cc iirc, + 4 or 5cc for the gasket eh

 

[wehey]

I appreciate the advice Frank but how the heck do I work it out lol
I have looked a some online calculators but am a bit stumped

 

[frank]

here,s an old thread wehey http://www.micra.org.uk/threads/1-0-pistons-in-the-1-3.30877/
you start with a volume of 250cc + 24cc (head) + 5cc (gasket) which is a total area of 279cc
then you squash that down to 29cc (the area of the combustion chamber + gasket)
which means its 9.5 times smaller
so you just work out the reduced chamber size for 11 times smaller

 

[frank]

i get it to 25cc combustion area (1.25mm skim ?)
250 cc + 25 cc divided by 11 = 25cc

 

[wehey]

You just beat me to it. I was going to suggest a 1mm skim giving a cr of 10.98

Saying that, it was a long time since I was at school and the above could be complete b*****s lol

 

[wehey]

Rather than starting another thread I may as well shoot a few more questions on here eh.

Cam timing: is there a proven and tested amount of advance/retard on either cam that will see any gains?

 

[frank]

Rather than starting another thread I may as well shoot a few more questions on here eh.

Cam timing: is there a proven and tested amount of advance/retard on either cam that will see any gains?

it depends how much slack you have in the chains really wehey, and moving the inlet cam will alter where the powerband starts and ends