Heymow - Lawnmower Racing Forum
Engine Help => Other Engines => Topic started by: trbinrat on November 20, 2012, 09:49:50 pm
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As I put my plan together for my Kawasaki flathead. I keep coming up with more questions and most of them revolve around flow. The Kawi already has a decent size intake valve (1.5") but would it benefit from a larger one. What dictates the size of the valve besides the space available.
I know velocity is very important in filling the cylinder but can't that be dictated by the size and shape of the intake tract and cam overlap and lift. Volumetric efficiency and HP are the ultimate goal but can you go to big with the valve?
Thanks
Mark
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I have always been told to use the biggest valve possible until you start to lose velocity.
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How far are you going with mods? It all works as a package, cam, carb, bore & stroke, compression, and timing. If you are running a limited class you may want to leave stock valves in it and work on the ports [not to big]. Flatheads are all about flow and bigger does't mean better. You can really kill performance with to big. To big and it won't run good until you get up there in rpm's and with a limited build you won't get enough to benifit bigger valves.
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No limited build here going all out. I've been reading lots and lots of ford flathead stuff and have learned a lot and have two good machine shops that can do anything I need. (With in my budget LOL)
I all so found this site http://www.hipermath.com/math_center/index Looks like I'm going to have to sharpen my math skills some.
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YUP! You are goimg to sharpen your math skills!! LOL
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A lot of people get caught up in the "big-small" thing. What it boils down to, is quality of flow. A smooth, clean flowing port is what you are after. Turbulence causes a port to act smaller. Think in terms of gentile changes in directions. A toboggan run is what you're after in a flathead. Think in terms of inertia, what would happen if you dropped a marble down the intake ( OK, a marble small enough to fit through the valve lift). The valve lift is a part of your intake track as well! The least amount of turbulence. How does the mixture pass through the valve and transition into the cylinder? Barney Navarro had it together back in the 40's. Check out Ron Main's Flatfire. If a bigger valve can do this, cool, don't toss anything out without looking at the entire picture, twice!
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Yes I do agree it's the whole package. I've been reading lots and lots on the subject of port flow the last few weeks and have learned a lot. Now its time to put a flow bench together and do some more learning.