CamKing wrote: ↑
Wed Nov 01, 2017 4:10 pm
David Vizard wrote: ↑
Wed Nov 01, 2017 11:16 am
The bottom line here Mike is not whether we should use a lift rule based on valve diameter,(although it seems like an easy way of doing it) but that we should pick a way to allow for a good working percentage so that whatever valve size is used no one will be penalized. In that respect we are both intent on achieving the same goal but are approaching this same target from significantly different directions.
My point is, if you go with a percentage of valve diameter for a max lift rule, you're penalizing the engine platforms with the smaller bores, twice. Say the CID limit was 427, the guy building a small block, that can't go over a 4.125" bore, is not going to be able to run as big of an intake valve, as the guy building a big block with a 4.300" bore. So, not only will he be handicapped by the smaller intake valve, you're now going to tell him, he can't run as much lift as the bigger bore engine.
All this would do, is give a huge advantage to the engine platforms that can fit a bigger bore and intake valve, and make the smaller bore engines non-competitive.
I get the point you are trying to make but why would any engine builder worth their salt build a non-competitive combo?
As you may expect I have thoughts along the lines of a 4.185 bore SBC for a big bore, short stroke setup yielding about 380 inches.
I have done some very strong power producing 23 degree Chevy heads with as much as 2.180 intake valves (1.56 ex) that flowed 334 @ 0.800 and 339 @ 1.000 with 225 cc ports The figure that I liked best of these heads was the 192 cfm @ 250 lift – that’s a 78.5% flow efficiency and that does not come easy. That is the sort of flow at that lift you would expect to see with a 2.3 inch diameter valve as per a BBC.
But let’s look at the lift I could go to with a 35 or a 38% lift limit. At 35% the lift limit would be 763 thou and 823 for the 38% deal. Should I build this SB I fully intend, rules permitting, to use 0.800 net valve lift in spite of the fact that the strong point of my heads was the terrific low/mid lift flow.
But let’s look at a compromise that should satisfy your argument and mine simultaneously. Let us say than any combination with an intake valve less than say 2.05 can have as much lift as the builder deems necessary. But for anything over 2.05 the lift limit is 38% of the intake.
So would that work for you Mr. Cam King sir???
And BTW agreeing isn’t going to let you off lunch!!!!