1.7 16v Pistons into 1.7 8v? - Alfa Romeo Forum
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33, 156 JTD16v

1.7 16v Pistons into 1.7 8v?

Does anybody know if you can do a straight swap of 1.7 8v pistons for 1.7 16v pistons (using the original 8v heads)?

I know the dome on the top of the piston is much smaller on the 16v pistons and would therefore increase the compression ratio of the 8v if swapped. What I dont know is by how much as I dont know the dimension from the top of the piston at TDC to the block deck. I suspect that 16 v pistons are 'taller' than the 8v pistons and would protrude over the top of the block and give a riduculously high compression ratio (if they dont hit the valves). Can any experienced box er engine builder help me out here?



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sounds scarey, i could give you the nuber of a bloke down here who builds awasome engines, anything from ultra high compression to turbo,

His own sud is nuts with about 305bhp
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The 16v and the 8v had the same bore and stroke, so I don't think the new pistons will "stick out of the cylinder head".

The crown will certainly be different though as you have 2 big valves per pot, whereas the 16v has 4 little 'uns.

Apart from that, the smaller valves will have less lift in operation (allowing a higher crown on the 16v pistons).

If you fit 16v pistons with an 8v head you are going to wreck your valves (they'll be hit by the pistons) unless you remachine the pistons to match - to give you replicas of the 8v pistons!

If you want higher compression, I'd start at buying new rings, then go the head-skimming/lapping route.

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Really I must admit, if you're going to stuff around with the bottom end, do it properly and i would suggest to buy some forged pistons, and put it some good conrods or get your existing ones machined, heat treated and shot peined, and spare no expense on bearings, Putting stanfard pistons int an engine that it isn't really designed for can give some great results but they will only ever be short term,

If you turn the existing pistion over you also raise the compression, but engines only last about 5000ks but gee it goes well for those 5000ks

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