If anything open up the heads for larger valves, not make the valves smaller

I believe we have a roller hydraulic cam. Different types of cams use different lifters, for different purposes. Hydraulic rollers are very smooth, and rev better and are more reliable..

Quick google resulted in this..

http://www.aperaceparts.com/tech/camterminology.html

Comp cams has more articles on different camshafts then basics.

In this particular case, Series 1 heads; due to the close distance between the intake and exhaust valve seats, you cannot open them up. The only way to do so would be to replace the seats and offset the valve guides; which adds to the cost.

Oh yeah, i remember checking them out and crying about that.

I don't want smaller valves? Oh..... I meant machine down the oversized valves to a little less oversized so they didn't hit eachother.

Thanks for answering what kind of cams/lifters we have, but I was asking why it mattered for valve springs. Summit asks what kind of cam when narrowing down spring choices.