Downdraught angle vs seat angles?

Road-race engines and ancillaries - general discussion
4v6
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Location: Midlands UK (A)
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Re: Downdraught angle vs seat angles?

Post by 4v6 » Sat Feb 04, 2012 6:36 pm

Hi Tim.

Well I have indeed been doing some more testing over the past week or so only this time its been entirely based on the 45 degree valve seat angle suggested by Guy.
So far, its looking suspiciously like Guy may be right yet again, however Ive not yet tested a 70 bottom angle or changed the 30 degree top cut into the chamber, so the jury is still out on that one for now.
What I will say is that so far, the 30 top angle, 45 degree seat with a 60 then stock 70 or 75 as it is, is working better than the 45 seat with a 75 bottom cut that i put on myself.
I suspect though that when I do cut the 45 seat and go straight into the 70 lower angle that it will work better so Guy will most likely have been proven correct, not that I ever doubted his vast experience at all.
Oh by the way, the 45 degree seat does indeed show more promise but the 30 degree seat still works better at lower lifts, it does however run out of puff toward the mid lift point but I dont know if I can gain that back, maybe the 70 bottom cut will do it for me?
I will definitely try some epoxy and do some infilling at some point, I just need to get my skates on and probe the port to find out where any dead low flow areas might be.
That must wait for the time being though as the rest of the engine build is underway for my friend.
Tony Warren. GC #96.

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