Compression Ratio

[Rally-mad-harry]

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]

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

 

[Rally-mad-harry]

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]

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

 

[Skinner_87]

Frank fella what's the quench step?

 

[frank]

Frank fella what's the quench step?

these bits paul, i think the rising piston creates a vortex along the step/ledge near the valves that scavenges the chamber efficiently, and a cleaner burn

 

[Skinner_87]

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]

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

 

[Skinner_87]

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