wsa111":2h0ylpt5 said:
Just to say a cam has 224 degrees means nothing as far as valve spring requirements.
It all depends on the cams rate of lift & of course total lift of the cam.
Yes there are variations and also the weight of the components
after the pivot point of the rocker arm count a lot to spring requirements. That's also why we sixbangers can use the VS-733 for example, with bigger duration cams than those guys using it in a 289/302 environment as we typically have lighter valves, locks and retainers. And less lift than what a SBF cam would in many cases have with comparable duration.
wsa111":2h0ylpt5 said:
Any decent performance camshaft will need at least 110# seat & possibly 280# open pressure.
Check with your cam grinders recommendation for the spring needed for the camshaft you choose.
Just going to a 1.6 rocker ratio will help a mild camshaft.
Depends on what is considered decent. I think a CSC 274/110 is a decent cam in our motors, and that lives with 80lbs on seat. At least my engine does as it runs fine to the rpm the cam specs give for its powerband without floating.
I'd follow the cam grinders recommendation too, in most cases. What I have noticed though, that usually the recommendations are a little on the dangerous side (which is strange, to my thinking) as they recommend springs that feel 'mild' for the application. Especially true with Comp Cams, and some others. Or maybe they recommend the spring for a little uncommon application, like 8mm valve stems, titanium retainers, and/or around 1.300" OD springs with smaller retainers etc. Also the springs may fade very soon so that should be taken into account too. I've seen 140lbs on seat vanish into 110lbs during a 25min break-in period plus a few dyno pulls. Bill is absolutely right that you should be on the safe side and add a little extra on the springs. Fortunately our sixes are not at all so prone to big disaster if the valves float, as there seem to be plenty of room between the valve and piston even with tight deck heights, as the cast iron heads have the valves deep into the chambers. Take a performance SBF head like the AFR, and you have valve's edge
below (intake) or very close (exhaust) to the deck surface. Enter valve float - bang - your exhaust valves meet with pistons.
After changing rocker ratios I'd also consider spring changes. Higher ratios boost the cam without affecting its basic timing. In any case I see a major problem is flow at low lifts of the cam which is typical for a small bore engine. Add bigger valves and it doesn't help much. Backcut intakes - huge improvement. Plus more gains with chamber work and unshrouding, which is free of charge if self-made and doesn't require valve spring considerations...
Sorry off topics a little, you can throw things at me at the meeting in AL next week. Moderators feel free to delete if necessary.
