The engine is a B18C1. The question is: If you increase discplacement by increasing the bore to say 84mm, does this alone increase compression????
AND if it does, WHY???

TIA,
Austin

 

yah , off course dude !
because CR was calculated by : displacement divide with the chamber volume then plus 1.
as ex.
if you got 1800 cc engine with 200 cc (each chamber was 50 cc) combustion chamber. The C.R was ( 1800/200 ) + 1 = 10 , then you got 10:1 CR.
now you increase the displacement to 2000 cc. (2000/200) + 1 = 11. now you got 11:1 CR

thats it

 

HEre have some fun.
http://www.bojangz.com/calculator/

 

hey thanks guys... I also found this site:
http://www.c-speedracing.com/howto/c.../compcalc.html

 

Well, this would be the way it works if you increase displacement by stroking, since stroking does not affect the total combustion chamber volume at TDC. But if you are increasing displacement by boring, this complicates things somewhat. The volume of the combustion chamber per say does not increase. But what does happen is that the total clearance volume (total volume at TDC) does somewhat due to the fact that you have increased diameter. Due to the fact that this increased volume is coming at the outer edge of the bore (where, unless you have chamber work done, the roof of the chamber is going to be the actual gasket surface of the head), compression will actually be increased somewhat. But not as much as from stroking.