A coworker has been a fountain of info lately, and showed me his copy of Dave Vizard's third book on Chevy engine building - specifically, 30 degree valve seats and how they produce more hp at low lifts with mild cams.
I nodded my head and answered yes to stuff like "you know how hydraulic lifters work, right?", so spare me - I was rodding a '66 Mustang in the '70's. I am familiar with some of those dohickeys inside an engine.
Point being, 30 degree valve seats, as opposed to 45 degree seats, or at least a 30 degree backcut, will produce more horsepower at low lifts. Google it, there are articles at the hot rod magazine sites. The net effect is to produce a 20% or so larger opening at low lift, which is seen twice on the cam. It doesn't help much at high lift or high revs, but 4.0's aren't either.
On the dyno, one user reported gains of 5-8 hp at lower revs, where we can use them. Of course the factories don't shape the valves that way - it costs money. Doesn't mean we can't.
Overall, with a 3 or 5 angle valve job - and including unshrouding work on the combustion chamber and block, the net gain is good. Money well spent rather than bandaid parts at high dollar costs. Stroker chambers could use unshrouding just to lower dynamic compression ratios and remove hot spots, but that's a different subject.
It's the details that make a NASCAR motor more on the track than the look-alike crate motor. I'll keep adding them as I find them.
Oh yeah, did you know there was a billet double roller adjustable chain set for the 4.0?
I nodded my head and answered yes to stuff like "you know how hydraulic lifters work, right?", so spare me - I was rodding a '66 Mustang in the '70's. I am familiar with some of those dohickeys inside an engine.
Point being, 30 degree valve seats, as opposed to 45 degree seats, or at least a 30 degree backcut, will produce more horsepower at low lifts. Google it, there are articles at the hot rod magazine sites. The net effect is to produce a 20% or so larger opening at low lift, which is seen twice on the cam. It doesn't help much at high lift or high revs, but 4.0's aren't either.
On the dyno, one user reported gains of 5-8 hp at lower revs, where we can use them. Of course the factories don't shape the valves that way - it costs money. Doesn't mean we can't.
Overall, with a 3 or 5 angle valve job - and including unshrouding work on the combustion chamber and block, the net gain is good. Money well spent rather than bandaid parts at high dollar costs. Stroker chambers could use unshrouding just to lower dynamic compression ratios and remove hot spots, but that's a different subject.
It's the details that make a NASCAR motor more on the track than the look-alike crate motor. I'll keep adding them as I find them.
Oh yeah, did you know there was a billet double roller adjustable chain set for the 4.0?
