how close can you run inline valve---to each other?

[bill jones]

-I am installing a set of valves that are too large into a set of 302 Edelbrock heads and in 3 cylinders the valves can touch each other if I mildy force the valves towards each other at max lift.
-I have machined .010" off the margin on those 3 and they just barely clear.
-Has anybody ran valves this close and if you did was there anything about this idea that you'd care to share?

[Bos's5.0]

Hey, are those performer heads? Is there anything in those ports that made you think, "wow, that is poorly designed"?

[bill jones]

-yes and yes, and that's why I'm trying to do some thing different than normal.
-These heads are going on a 408W with a turbo and intentions to run about 8# of boost on a daily basis.
-The daily driver car ran 12 ohs with the 302 and a belt driven blower here in SLC Utah and never ran over 6000rpm, so we are looking for another full second--maybe even a little more than that---with the bigger engine.
-But we can't do it with 1.91" intake valves and those little bitty shorty headers and puny exhaust ports.

[Greenlight]

I've run the valve to valve clearance as tight as 0.030" measured with the valves on the seat.

During overlap the valve aren't at max. lift, they're likely to be at ~0.175" or so.

Depending on valve guide clearance I think 0.035" measured on the seat is O.K.

Perform the same check with the valves at the actual lift seen during overlap and see if they touch with little force applied.

[maxracesoftware]

I am installing a set of valves that are too large into a set of 302 Edelbrock heads and in 3 cylinders the valves can touch each other if I mildy force the valves towards each other at max lift.
-I have machined .010" off the margin on those 3 and they just barely clear.
-Has anybody ran valves this close and if you did was there anything about this idea that you'd care to share?

i like to have between .020" to .025"
but have setup Heads with tight valve-to-guide clearances
to .015" between valves and not hit each other

at other times ...have seen valves lightly hit each when clearances were
between .010 to .015., it depends on guide clearances, valvetrain geometry, stem diameter/flex, valve temperatures

i'd recommend atleast .015" min

[bill jones]

-Larry---what happened to the valves and or guides on those valves that actually were lightly touching?

[maxracesoftware]

-Larry---what happened to the valves and or guides on those valves that actually were lightly touching?

since it was strictly a DragRacing Engine ..nothing happened to the valve guides as far as wear...but both valves had little dents/raised margin edges...i just turned down the exh valve OD another .010" and the Intake OD another .005"

for long term Street engine i'd run .020+ between them
for DragRacing atleast .015"

i've seen bad valvetrain geometry along with .310" stem valve
flex enough to need atleast .025" clearance or slightly more
at hi rpms. The tighter the LCA and the more actual OverLap Period effective Lift you have on both those valves, the greater the possibilty of them hitting each other if tighter than .020"

[bill jones]

-the cam we are using is a mild hydraulic roller 227x 234 at .050" with a 112 and right at .550" lift so the overlap should be around .115" at split overlap.