Help me understand why bore/stroke ratio matters


Authorized Seller
Jul 15, 2007
Houston, TX
Preface: I started my education as an engineering major. I have had multiple physics, statics and materials classes. I am not afraid of a complex answer.

Not being an engineer, mechanic or tuner I don’t understand what under/square/over bore stroke ratio means to me as a performance car owner.

My Mk III Supra with a 7M has an undersquare cylinder, 83x91 as opposed to the oversquare JZ which is 86x71. Wikipedia says it has a 9.1:1 compression ratio. Since torque is force*distance, I get that a longer stroke engine could produce more torque, though a larger cylinder head could produce more force, offsetting the advantage of the longer crank arm. Longer stroke seems to me to be less capable of higher RPMs since the head has farther to travel. The increased stroke would seem to be a disadvantage to intake and exhaust, though this car has longer aftermarket cams and an upgraded turbo, so that seems to be less a hindrance than it would be in a stock NA or 7M-GTE engine.

I get the physics of what is going on. Can someone help me understand what all this translates into in actual vehicle operation, for example why is one good or bad versus the other?

Thank you.