Finding Compression Ratio
 

Hi guys

I understand the compression ration formula for a 4-stroke engine would be

CR = (V1 + V2) / V2, where V1 is the cylinder volume at exhaust closing and V2 is the combustion chamber volume

would this forumla remain the same (with cylinder volume being appropriately replaced) with a 13B? If not, would you mind correcting me? Also, does anyone have the exact numbers for an FD? Thanks

Look in the Mazda FSM for specs...
It's a bit more involved to find true CR on a rotor.

FD's are all 9.0:1 stock.


-Ted

I believe finding the CR on a rotary engine is a moderately involved calculus problem. Plus you'd have to take into account the size & shape of the "divot" in the rotor (which isn't a particularly regular shape... it seems to vary somewhat between rotor sides).

-=Russ=-

Oh, and to actually answer your question, that formula should work (though it looks backwards to me... I thought it would just be (TDC volume) / (BDC volume) ), but finding the volumes is the pain.

-=Russ=-

Here you go: My compression ratio thread

same formula as with pistons:

CR=(Vd+Vtdc)/(Vtdc), =9.0 for FD, commonly expressed as 9.0:1

Vd=displaced volume of 1 face, .65L for 13B
Vtdc=minimum vol of combution chamber, at TDC.

You can use the above to calculate the stock Vtdc.

You can then calculate changes to stock CR, based on say an increase in pocket depth, if you know the volume of material removed.