CamKing wrote: ↑
Fri Oct 27, 2017 11:54 am
David Vizard wrote: ↑
Fri Oct 27, 2017 11:19 am
CamKing wrote: ↑
Thu Oct 26, 2017 11:58 am
Huge problem with that.
If that was the rule, I would put the largest intake valve I could fit in the bore(way over what it needs), and just do the valve job, and seat work to make it act like the proper size valve. Now I've got an engine with the effective valve size that's proper for the engine, running the allowed valve lift of the much larger valve.
You'd be handicapping engines with smaller bores, and heads with smaller valves. For a given CID and RPM, the smaller valve will need more lift, not less, to make the power of the larger valved engine.
I think you may have over thunk this!!
It is almost impossible to get a valve/port that will work above .35D. Think about this - it does not matter what size valve you choose it still won't work above .35 D. If that does not produce the results it is not because that valve is restricted on lift. It's because the rest of the head and block specs are out of whack!!
(no more rum and coke for you!!!)
I think you're hitting the sauce a little early today.
Here's an example.
Chevy Bow Tie 034, Ported by Meaux Racing
223cc Intake runner
According to you, with that 2.085" valve, it's almost impossible to get the port to work above .730" lift.
As you can see, you're only .170" off.
It's not uncommon to see a 1.94" valve flow past .800" lift, a 2.15" valve go past .900", or a 2.18" flow to 1.000"
Restricting lift to a % of valve diameter is a horrible rule, that will do nothing but give a large advantage to the guys that can fit the largest intake valves in their bores.
My apologies for not being as precise with my original valve size values as I could/should have been.
However my little slip there did reveal one thing – namely that you're very concerned about how this engine competition goes and I am well pleased with that.
But back to this lift deal. Whether we look at it your way or mine, the final results, which is all that matters, means we are closer on this than you might think.
Here’s the deal. The more precise numbers (as I spell out in my classes) are:-
of vertical/parallel valve heads reach 98%
of their max flow at lifts no more than 38%
of the valve diameter.
If they do not closely approach this then the ports, from an all out power prospective, have room for improvement.
Let’s use the figures from Larry’s Dart heads as you did.
At 38% D lift the valve will be 0.792 off the seat where its flow is 318 cfm. Peak flow was recorded as 322 so at 38%D lift the flow has reached 318/322 = 98.7% so, based on Larry’s head, which BTW is somewhat above the norm, what I teach in class actually proves very precise.
But (there always is one) I did say set the limit at .35 or 35% of the valve diameter so let’s look at how much off I was on that as I think that was the real issue that got you going here (hence the first line apology).
At 35% D the flow would be 310 cfm so we have 310/322 which comes out at 96.3% of max flow. So with your example we would, at 35% D, be able to access 96.3% of the flow even with a port as good at hanging in there as Larry’s.
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.
And by the way, apologies aside
, it is still your turn to buy lunch!!!!
PS Mervyn is bringing over a $250 a bottle premium rum – saving it for
Xmas - are you in on a test run!!! (should be able to grind some really way out cams after!!)