Tweet
Anyone have any 230 intake/exhaust valves out for quick measurements? Ran across an interesting mention of a guy using Chevy 350 valves as a replacement in the 230- this could lead to some very beneficial flow increase possibilities if it checks out. The Chevy valves are readily available with a very flat underside- which might be good for 30% increase in intake flow- you'd definitely notice that!
-
-
Here are the three contenders I've acquired for the Sideways Flow Sweepstakes- Pic #1 shows the stock intake valve at left, a Manley Street-Flo exhaust valve for 350 Chevy (PN #10721-1), and a British RimFlo for a MG.
The Manley was selected on the basis of a rumor that Chevy 350 exhaust valves could be used in place of the stocker, and the RimFlo because it was specially designed on the flowbench for high sideways flow- at $41 each, it better flow well! Manley will make a custom valve for around $25- which is not a bad price if you can really up intake flow in the most restrictive part of the head. The stock valve stem is 4.845"x.3402" (slightly under 11/32"), the Manley is 4.911"x 11/32" (~1/16" longer), and the RimFlo is 4.360"x11/32" (too short). Note that the RimFlo has the most undercut head and smallest stem dia (.015" less than the Manley) - it would outflow the best racing valves of its day (late 80's) by 15-17%, and outdo the production valve by ~ 30%. Pic #2 shows the top of the valve heads, from left, RimFlo, Manley, Stocker. The bowl in the RimFlo is 1/16" deep, and helps prevent reverse flow- most intake valves flow better in reverse! Head dia is 1.536" on the RimFlo, 1.500" on the Manley, and 1.531" on the Stocker. Pic #3 shows valve land & seats- from left, Stock, Manley, and Rimflo. The RimFlo has a much wider land than the other two, and a 1/16" seat. This also was part of the anti-reversion design. Now to find out if backcutting a stocker will flow as well as a RimFlo, or whether Manley will make some flathead RimFlo's for a reasonable price.... -
Is the major bottle neck for the 230 the intake and exhaust valves, and seats? The port shape, or the head design? I thought someone mentioned that the head design was too flat, and that was the cause for large restrictions..Comment
-
The entire intake/exhaust path is a flow disaster, you have to work on the worst first. The most restrictive part of any engine is the valve area, but you have to be very careful not to go oversize, or you'll fall off a cliff. Since the flathead has such a large sideways bias on valve flow, I thought this might be a good place to look for intake gain. These engines pull high vacuum- people trying to adapt HEI's have found that the vacuum advance springs are too weak to prevent an overly quick advance. They also respond well to better carbs- which tells me there's a lot of intake restriction. The Siamese intake port doesn't help much either, but we just have to try and make the best of it. I've heard that backcutting the flathead Harley intake 30 deg yielded a 30% flow gain, and resulted(along with other work) in a bike that would idle along at 15 mph in high gear and then accelerate up to 60 without bucking like a Texas bronco. That's why I think sidedraft carburetion and intake valve mods might help the midrange 2000-3000 rpm area, where the PW 230 starts laying down.Comment
-
humm..
guess I will keep working on building an intake manifold.. and see where that leads..
sounds like you will have quite a flat head once you get yours all set up. Keep at it.Comment
Comment