I am currently trying to figure out my compression ratio whilst my engine is apart. i am using this calculator http://www.csgnetwork.com/compcalc.html

However it is asking for a head gasket compressed thickness which i can not find a spec for.

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If its yours, customize it !

Just measured 2-
.039" and .038".

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

yeah i always use .035" when calcing this stuff,,, it`s always more squashed than when it`s out of the car & also a little less vol in your calcs leaves you a little room for reality (on the safe side)

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

wow that was quick, cheers.

So ive down these measurement as best as i can.

Bore size: 73.5mm
Piston stroke length:81.28mm
Head gasket bore diameter:73.5
Compressed head gasket thickness:0.99mm
Combustion chamber volume:21cc
Piston dish volume -7cc
Piston deck clearence0.3mm

=11.3:1

Or my old head with combustion chamber of 23cc
=10.7:1

This is on my weekend driver tuned 1380.
Both heads are fairly standard (some might remember the drama from my purchase.)
My old head however does not have double valve springs and im unsure if its got hardened valve seats. Trying to work out what one to use. Currently saving for graham russell to modify me a head but for now i have to use one of these.

My new head also seems to have the valves deeper in the head than my old one. ill try get some pics.

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If its yours, customize it !

Old head:
23cc



New head:
21cc


Sorry about photos being rotated

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If its yours, customize it !

Interesting the old head has been bath tubbed, which in itself is a performance modification.

And the old head has life left in the seats and tapered valve guides.

Why not get GR to suss them (pm?)

Yeah i beleive it was done to lower compression.
Ill probably end up using the old one and possibly switch over the double valve springs onto it. Compression will be too hight otherwise. Maybe just go back to running valve saver just incase they arnt hardened seats.

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If its yours, customize it !