Which Cam For S16 With A 88mm Stroke Crank

[mos 1]

hi,

 

pretty much as in the description really.

the thinking behind this is that if xuj10 cams are designed for use with a crank of 86mm stroke would these cams be in the incorrect position for opening valves etc when used with an 88mm crank, hence should i be using xuj9 cams instead when employing the 88mm crank.

or is this statement a load of rubbish (i do strongly suspect it is) and all that will happen using a longer stroke crank is the pistons and conrods will travel further up and down the bore in a given time but the pistons and valves will still be in the same position at the same time as when using a 86mm crank, so the xuj10 cams are the correct option?

 

i have been pondering this one a lot in my head today and i cant decide what is the right answer?

if i had to guess i would say xuj10 cams are the right option as all the longer crank will do is cause the piston to travel faster and cover the extra distance i.e 2x88mm (up and down the bore) in the same time it would normally cover 2x86mm. but i am not 100% on this and i am certainly not an experienced engine builder so can someone set me straight.

i will ask matt at qep when i phone him for an update on my engine but i though someone here may be able to help me.

 

 

thanks

 

mark

[petert 586]

The XU9J4 grinds are identical to the XU10J4, so if you're using standard cams it doesn't matter. As the piston will now be level with the deck at TDC, you need to be carefull with bigger cams. If you're choosing a grind with more than 0.100" inlet lift at TDC, you'll need to verify valve to piston clearance. The std. cams run 0.032" at TDC. If you're sensible, you'll use a std. exhaust cam, so you won't need to worry about it. The valves are actually 0.010" closer at 6 deg. ATDC on the inlet. So take that into account.