What difference would I expect going from a 2 degree advance to a 4 degree advance? Would it dramatically reduce top end going to 4?

 

advance moves the valve opening/closing events toward the exhaust side of top dead center. this tends to give lower peaks for torque/HP. More directly, the 2 deg would shift when the intake valve would close, the most important factor in peak position relative to RPM. this would also affect dynamic compression.

2 deg, according to the knowledge that I have seen on the boards, lowers these peaks around 100 rpm.

not a dramatic change, probably inperceptible.

 

its not wirth pulling everything apart to change it but if you are installing a new cam depending on the size of it, its something to think about

 

I have a small cam on a 115 LSA. They ground in 5* of advance to pull the curve down and the cam peaks at about 5,900 RPM whereas normally a 115 LSA would have a higher peak RPM.

 

That says it pretty well

 

Ok, so it wouldn't necessarily make much difference to go from a plus 2 advance to plus 4. Thanks.

 

If you want to bring the band down a bit that could mean 100>200 rpm lower.
Like the difference between shifting at 6700 or 6500, trq will peak a bit sooner too cam will not carry as far after peak