Compression Ratio

Hello all you Micra men (and women)

Wondering if you could help please, I have a CGA3 1348 engine block fitted with forged pistons which are 72.145mm bore, which at TDC are flush with Deck height,

Bore Dia- 72.145mm
Head gasket compressed at 1.2 mm
Piston Stroke- 82.8mm
Head gasket bore Dia- 72.5mm
CC's within compression chamber- 23.5cc
Dome volume- 0

had approx. 22cc to start in the compession chamber, machined out either side the valves to now to get approx. 23.5cc, can I now machine the flat on the exhaust side to increase the CC to 24.5-25, or will this ruin the swirl and squish on the head gasket?

Looking on my figure 12.9:1 CR at the moment, Little High I'd say
 

frank

Club Member
i think the quench steps are the most important area to retain harry, opening the shrouding around the valves should,nt hurt eh,
and the inlet cam timing will have a marked effect on your C/R
 
I'm going to be running a set of 773's, and if I can increase the shrouding around the valves to increase my comp CC by another 1 to 1.5 hopefully I'll be OK, do you know how much these head gaskets can take Frank?
 

frank

Club Member
i would,nt worry too much about running 13:1 with those cams harry, i,ve run flat-top pistons (1.0 and corsa) with this 2mm skimmed/weldfilled head np :)

65410.jpg
 
Cheers Frank il have a look at mine when the head comes off as i think those have been machined on mine to make the compression chamber circular!

Sorry for the hijack Harry, nice engine build you have there :)
 

frank

Club Member
Cheers Frank il have a look at mine when the head comes off as i think those have been machined on mine to make the compression chamber circular!

Sorry for the hijack Harry, nice engine build you have there :)
i think i have made mine more det-prone but reducing the height of the steps (from the headskim) paul, yours may be even more det-prone if they have been removed eh
 
i think i have made mine more det-prone but reducing the height of the steps (from the headskim) paul, yours may be even more det-prone if they have been removed eh

Good job I never went for a turbo with this head, it was taken from a micra kit car so I guess it's purely for N/A power :)
 
Top