changing intake valve seat angle from 46º to 31º on intake worth a try??

markus

markus

Well-Known Member
#1
#1
I have seen in the past where its claimed that a 30/31º on the intake valve will allow a more little fuel and air to enter the combustion chamber for a power gain and supposedly no ill effects, anyone make the change on a Tecumseh? Currently thinking if giving it a go on an HS. I gave re cutting the angle to 30º on a standard 32644 intake valve a try with my refacers and got it done. That job would be better suited I am sure on a dedicated refacing/grinding machine as it fought a little with a Gizmatic and produced some chatter marks at first. So I did the main reshape cut then put it on my single blade recutter, smoothed it out, and then back on the Gizmatic and it was fine. I would imagine some that have converted to Briggs valves may have done this before?

I have not cut any seats yet in any blocks, Most likely do it to an HS50 that I have already bored .010 oversize and its just sitting around. If you have done it, or maybe seen it done on a small frame Tec with some feedback on how it turned out, I would be interested in hearing or reading about it as I would be curious on how your seats turned out (I do have a 15º cutter in my toolbox so I can make both upper and lower narrowing/adjusting cuts in this seat angle )

Before
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after
IMG_3906.JPG
 
Last edited:
Augiedoggie

Augiedoggie

Active Member
#2
#2
Common practice to run the 30° intake for better flow and keep seat face closer to edge on the intakes. This gives full valve diameter flow. You can cheat the intake rim margin a bit more than exhaust. Common to run seat width more narrow on intakes as well. Also good idea to relieve intake area on block near intake port. You can run seat higher on intakes without worry of burning valves but exhaust margin should center on seat face and run wider seat width.
 
markus

markus

Well-Known Member
#5
#5
Augiedoggie said:
You can run seat higher on intakes without worry of burning valves but exhaust margin should center on seat face and run wider seat width.
Click to expand...
check this one out, this is a shot I took checking fitment on a Motorsports H50 that a buddy dropped off for me to backdate the looks of so it match a 1969 Rupp. This engine had been assembled and run in only so say maybe an hour run time when he bought it. I spotted a couple of potential problems so Opened it up just to make sure it was overall alright and everything was torqued to spec etc., before I painted it. Glad I did, using a marker and my crank lapping tool to check fitment, the intake was taking a good set and looking good but the exhaust......not so much! Right at the top, and had a do a bit of re cutting to get it brought back down and centered better on the face.

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