With 86mm pistons what kind of displacement would that be in a ls. Also should i get oversized valves if i do this. 12 to 1 comp ls block and itr head. I havent heard of any good things about the oversized valves except on muscle cars. would you recommend just porting the head then? and how much of a difference does port matching do? thanks

 

86mm bore should produce a 2068cc displacement

 

86mm, thats pretty damn big for an LS block. I didnt think you could do that unless you resleve the block and you would have to have the domes on the ITR head recut to fit the larger pistons or else you the domes will be to small if im not mistaken. I thought the B20z had different cylinder sleves than the other b-series engines that allowed them to have the large pistons in them. The b16a and b18c both have 81 mm bores dont they?

 

B20s use one-piece sleeves. 1.6 and 1.8L Bseries engines are all 81mm bore.

 

"Have the domes recut" that's a good one. It's called deshrouding the combustion chambers, just for reference's sake. And yes, you do have to widen the diameter of the chambers to match the cylinders if you widen the bore.

 

my block is already sleeved. The compression is at 10.5 but im gonna bump it to 12 to 1 so i figure i should bore the engine out some more while im at it.

 

If your gonna put 12:1 pistons in your engine why not just use longer rods and do some what of a stroker kit. Lenghten the stroke and you will get more displacement if im not mistaken. 86MM is a pretty big piston for a B18a engine. Im not sure what kind of displacement you would get from that, all depends of you use stock lenght rods or not with the pistons assuming your gonna upgrade to forged rods with pistons with that high of a CR and that big of a bore size.

 

Just put in B20 84mm pistons, probably be cheaper in the end.

 

Geez yall, it's not like an LS motor with 86mm pistons is going to have some crazy whacked-out bore/stroke. The K20 motors in the RSX and Civic Si have an 86mm bore and stroke.

The B18B is with 81mm x 89mm and B18C has a 87.2mm stroke. Heavier (i.e. wider) pistons put more stress on the reciprocating assembly, as does stroking the motor. If you have heavier pistons riding around at the top of your rods, it's generally not a good idea to make the stroke even longer. Pistons speeds are very high in the B-series motors because of their relatively long strokes and having a really big piston up there is only going to complicate matters.

 

Longer rods with 12:1 pistons could lead to some serious problems. Lengthening the rod will increase compression, but will not increase displacement. You either change the stroke (crank) or the bore (pistons), or both.:naughty: