Bonneville America Forums Forums Technical Forums Performance Mods Reworked top

A local company is offering a port job of the top including 1 mm larger intake valves and are promising a substancial improvement in the air flow - 100%. Anybody with an opinion or experiance on how this would effect a 790 America engine? Would it improve low end or whatever? I´m running with Thunderpipes. I have been thinking of big bore kit or modified cams but since there seams to be indications that the flow through the top is far less than possible I thought this would be the first thing to do.
Hasse

If you plan on doing a big bore and new cams, then the porting with oversized valves would be a good mod, but I don't think it'd be a good stand-alone mod at all. Also, what kind of airbox mods have you done? Freak?

All snorkels gone + Uni filter. Pulling +65Hp/65Nm at the dyno at the moment.

I think this would help quite a bit as the tops are pretty sloppy if you look inside them. Cleaning the flow is always a benefit, as is slightly larger valves. But wait till you see how much this will be! If you do it, you MUST replace the valve seals (not the guides themselves) as they are designed to be replaced if you remove the valves. Like most seals, once you take it off, you throw it away and replace it. I know the Triumph valves are in the neighborhood of $50 EACH and ther are 8 of them, seals are about $7 each too.
If you go with larger diameter valve stems, you will need to have the shop make new valve guides since they are not available as seperate parts, they are part of the entire head assembly.