Valvetrain upgrade

[blos101]

I am going to get larger valves for my 12v head. What size are you guys running with larger valves on exhaust/intake? What brand? I have big schied cam, flycut aria pistons 11.1 comp. 13mm pump. Let me know thanks.

 

[Hamilton Cams]

With a .040" block some people are going to a 1.940" 11/32" stem valve on the intake and a 1.750" exhaust. I have had some slight cylinder wall scuffing from the intake valve on a .040" over engine using these valves. For this reason some people either clearance the cylinder wall or machine the valve down to 1.920" to unshroud the valve.

On stock bore engines I have run up to 1.885" intake without issues.

Good luck on your build.

 

[blos101]

Ok, my motor is .020 over so I guess I should just use the 1.885" intake size and 1.750" exhaust? Thanks for all your help, let me know if you just sell these that I could purchase from you? Brian

 

[Hamilton Cams]

Some people use small block bowtie stuff and I know some others that run some high end pieces from haisley.

 

[Mike Holmen]

Zach, how close does the larger valves come to the cylinder at 20thou over bore? How are you clearancing the cylinder for the larger valves? Thanks buddy.

 

[Hamilton Cams]

Depends on a few variables. If it is a new engine bolt the head on minus the valve spring before you install the pistons. Due to casting shift and differences from different factories, there will be a plus or minus factor, so clearances on a test engine might not apply to your engine. If it is a new engine just cheat smaller. I have run 1.890-1.900 on different engines with stock bores. I ran a 1.940" on a stock bore and it scraped the cylinder wall a bit. If you want to run something that big it should be a on a competititon only engine so that you can clearance the cylinder wall. Also it should be on marine or industrial pistons so that the top ring land is lower and is away from the clearanced cylinder wall.

If you want to be safe on a +.020" bore you are playing with an extra .010" per side. 1.900 will be a breeze. Any more than that I would pull it all down and check with a feeler gauge. Just remember, too close to the cylinder wall and you negate a lot of the benefits of the larger valve unless you clearance the block.


Zach

 

[Mike Holmen]

Thanks Zach, you have any pictures or suggestions on whats the best way to clearance the block. Just to make sure I'm doing it correctly.

Fresh motor, I haven't machined the block yet and I have 20thou over slugs. Going to set my piston to cylinder wall clear at 18thou. Might even go abit larger. I'm not running any engine coolant, in this engine.