I have a 96 c.i. engine with 6 speed and an Andrews 48H cam. I want much more torque in 1st and 2nd gears but I can't install a big bore kit because of the cam causing detonation. What would be the downside of changing to 30T front and 70T rear pulleys?

 

There is no downside IMHO! You will spruce up performance throughout your ride and increase engine speed by 32/30 in all gears. However you will have to dismantle the primary to install the new pulley and may have to fit a new shorter belt.

If you pay someone to do that check costs closely, then look into changing your cams for a more suitable set, plus that big bore kit! There is plenty of advice in the Engine section on how you can boost your bike's performance, by more than 32/30ths.

 

Not knowing the model year, can't comment on the 30/70 modification but as grbrown points out, dismantling the primary and removing the swingarm is a lot of work.

I am not sure why you thing installing a 103" kit will bring detonation with it?? A good tune should resolve any potential detonation issues. Having said that, while the heads are off, have the chambers measured to verify chamber volume. There are several ways to increase chamber volume by 2-3cc to lower compression if that is your concern. A .040" head gasket instead of a .030", valves can be dropped a bit in the seat and valve reliefs in pistons can be opened up. Much less work than the labor required to change pulleys and drive belt.

You can change cams; the 48 intake closes at 29; look at cams that close later. The SE204, TMans 555 Torkster, S&S 510 come to mind. The SE204, combined with a set of 1.7 ratio rockers has shown some great results in 103"ers.

I think I would be looking at options to improve motor performance first. JMHO

 

Thanks, grbrown and djl. I appreciate the important information.