I was wondering seing as the 200b and series 1 bluebird have 8.5:1 compression and the series 2 which i have has 9:1, wether this is achieved by the pistons having more dish, or bigger combustion chamber volume? I have been thinking it must be the pistons but now im not sure and cant find any info anywere. Thanks

Or would it be possible to have a mm or so extra machined out of the dish, without afecting strength too much? Otherwise ill have to snoop around for some aftermarket pistons from some were!

Im heading out to u-pullit on the weekend, I can check the pistons out while im there. What about L18 pistons, they are the same bore, just the stroke is different I think.

The part number for all L20B cylinder heads is the same [200B & Bluebird, Series 1, 2, 3.] so the compression difference is in the piston.

alright thanks guys, i was just thinking since the l18 is same 85mm bore as l20b and they have the w53 closed chamber head YET still have 8.5:1 to compression that the pistons may have even more of a dish. That would be great if you could have a look at any headless motors out there for me, cheers sean!

well i have the truth now, there are u67 and v91 heads that i saw on the bluebirds, the l16 from stanza had a w53 and the 180bs with l18s had a87s. I got myself an l18 a87 closed chamber head in good condition, the only draw backs would be it appears to have a smaller combustion chamber volume and has smaller 32mm ports vs the v91 and u67 having 35mm ports. I am just hoping that with a better chamber design detonation will be easyier to control. I will measure both the v91 and a87 chamberer volumes and post here for reference. Also noticed that the l18 and 200b pistons appear to have identical dish volume which is substantially larger than the series 2 bluebird pistons which only have a tiny dish. I also got a set of deeper dished pistons from the 200b. I will also measure both piston dish volumes and post back, oh yea and series three bluebirds have the ####y ca20. So now im thinking that with the 200b pistons (same dish as l18) and l18 head ill have 8.5:1 compression and a good chamber design, still cant help wondering if i should have a mm machined from the dish to drop it further?

you will get lower comp using an l20b head, they have the bigger chamber

pretty much the same shape but the u67 an v91 have more cut out of the head

could just get the outside of the piston milled off, the part that isnt in the dsh.....then you will have low comp flat tops