CobraMarty
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I read a recent article about this, Valve Lift/Diameter Ratio. It said that for HP Street looks for about .25 and hard Core Perf. .28-.30 and pure race engines .35.
So what I can find on our Jeeps 4.0 with 1.6 rockers-
the Intake lift is .408" which is .255" cam lift on 1.91" valve
the Exhaust lift is .414" which is .259" cam lift on 1.5"valve
So stock Intake L/D ratio is .408/1.91= .2136 - I guess pretty poor
And the Exhaust L/D ratio is .414/1.5= .276 -seems pretty good
With 1.7 ratio rockers-
Intake L/D ratio is .434/1.91 = .227 better than stock
Exhaust L/D ratio is .440/1.5= .293 even better, but stock was good before
What does this all mean? ? Just something else to consider when comparing and building an engine.
For the 4.0 it looks like the stock intake valve size is fine, it just needs more lift. And the exhaust could need a bit bigger valve size. Everyone seems to run to big valve heads with emphasis on bigger intake valves. Just something to think about. I'm going to back test this on some known engines and engine builders.
So what I can find on our Jeeps 4.0 with 1.6 rockers-
the Intake lift is .408" which is .255" cam lift on 1.91" valve
the Exhaust lift is .414" which is .259" cam lift on 1.5"valve
So stock Intake L/D ratio is .408/1.91= .2136 - I guess pretty poor
And the Exhaust L/D ratio is .414/1.5= .276 -seems pretty good
With 1.7 ratio rockers-
Intake L/D ratio is .434/1.91 = .227 better than stock
Exhaust L/D ratio is .440/1.5= .293 even better, but stock was good before
What does this all mean? ? Just something else to consider when comparing and building an engine.
For the 4.0 it looks like the stock intake valve size is fine, it just needs more lift. And the exhaust could need a bit bigger valve size. Everyone seems to run to big valve heads with emphasis on bigger intake valves. Just something to think about. I'm going to back test this on some known engines and engine builders.