Stretching rods

[ajwans]

Let me see if I have this correct. If using an offset bushing to stretch the rods it will be necessary to use a thicker cylinder base gasket in order to maintain a negative 1mm deck height.

In order to maintain engine geometry w.r.t. the cams remaining central in relation to the timing chain housings one would need to deck the heads the same amount as the extra thickness of the cylinder base gasket.

The same compression bump could therefore be achieved by decking the heads and milling the chain housings at their gasket interface without stretching the rods.

So what is the recommendation for achieving additional compression? Engine is a 2.0S engine with the 67/68 style piston domes. Fuel here is good 98RON at the pump. No objections to looking into twin plugging if need-be.

andy

[KTL]

Andy,

It seems like you're trying to achieve two things. Those two things being, lengthen rods for better rod-stroke ratio and also bump compression?

You can "stretch" the rods just like you said- offset the wrist pin bushing and then fatten the cylinder base gasket to maintain your desired 1mm deck height. You can maintain the cam housing alignment independently of the compression ratio by fattening the gasket for the engine case-to-chain housing.

When you deck the heads to maintain cam housing alignment, you're risking running too little deck height. Yes it increases compression. But that's not a recommended method of increasing compression due to the potential for interference at the piston perimeter and combustion chamber perimeter. Typically compression is modified by using different pistons with redesigned piston crown shape and valve reliefs