20 replies to this topic

[Apdiliars250]

that suggests that either the chambers have been taken out a bit already, or the pistons were a fair distance from the deck. ( or a mix of both)

 

Personally i don't like running pistons down  the bore for squish reason,s I always have the block skimmed to bring them up to about 5 thou down, leaving enough for a clean up skim if its ever needed. also Im not a fan of de comp plates for the same reason.

I have the engine apart now and yeah the pistons are far down from the deck I measured 1mm. I have not measured the chamber volume yet. 

[mini13]

that sounds fairly normal for something thats not been decked, IIRC factory deck height was usually 0.8-1mm ish although I think that can vary depending on the piston type used, also after market pistons are often slightly lower still ( presumably to allow decking even if the blocks been decked already) I seem to remember having 50thou taken off my last block to get pistons flush.

[Apdiliars250]

that sounds fairly normal for something thats not been decked, IIRC factory deck height was usually 0.8-1mm ish although I think that can vary depending on the piston type used, also after market pistons are often slightly lower still ( presumably to allow decking even if the blocks been decked already) I seem to remember having 50thou taken off my last block to get pistons flush.

that sounds fairly normal for something thats not been decked, IIRC factory deck height was usually 0.8-1mm ish although I think that can vary depending on the piston type used, also after market pistons are often slightly lower still ( presumably to allow decking even if the blocks been decked already) I seem to remember having 50thou taken off my last block to get pistons flush.

OK thanks. The block is all measured and good so pistons omega pistons have been ordered. Do you recommend 5 thou deck height with a 1380? A bit more would help with lowering the compression. 

[mini13]

general concensus for squish band distance for most applications (the distance between the outer band of the piston and the head face) is 30-40 thou, the BK450 gasket is quoted as 40thou, so you probably want to get the pistons as close to the deck as possible,  I  do 5 thou down to allow for a cleanup skim if needed during rebuilds.

on small bore blocks and even some smaller bore big bore engines ( 1293,1310 etc) motors have been built with the pistons sticking out a bit, up to around 15 thou, but this is betting specialist, and you have to be careful of rod stretch and the pistons kissing the head on high rpm race motors. on 1380's and 1400's the gasket can overhang the pistons, so do check that. on one motor I had to swap to a copper gasket as they have a slightly bigger bore, also cometic do a larger bore gasket, but they are £££ and you need a good ground surface finish for them.

 

i think I mentioned getting material taken out of the piston dish? this is a pretty simple proccess so can be done fairly cheaply, how many cc's do you need to find?

 

[mini13]

just reading back and theres no figures for the head you have? also do you have a target CR ratio?

[Apdiliars250]

just reading back and theres no figures for the head you have? also do you have a target CR ratio?

CR ratio I would say 9.5 would seem sensible. There's not really a target as such it not going to be a daily driver. Cylinder head originally I was going to use my stage 3 head from minisport. But I have bought a standard cylinder head to be modified for the turbo engine.