I have a question and need some opinions.

First the facts:
1966 F250 4speed
390 cu inch
427 factory cam
This is NOT a race truck. Its an everyday work horse.

I have always adjusted the valves to the factory 427 setting .025. Needles to say this is some what noisy in the cab when driving at high rpm

Questions: Does any one know what was the purpose of these settings? Was it just for race purpose?

Has anyone ever tried running a tighter setting for a street engine?

Need opinions: All and any

Thanks Jim

 

The clearance is to allow for expansion when things get warmed up. If the clearance was "0" then the valves would be held open a slight amount when the engine warms up and wouldn't seal.
The clearance is determined by the design of the cam's clearance ramps, hydraulic cams don't utilize the ramps thats why they tap so bad when just a little clearance exists when the lifter goes bad.
The clearance ramp is that area of the lobe that transitions from no lift to lift. It "gently" takes up the clearance and starts to open the valve.
Closing up the clearance is an old tuners trick, done all the time to fine tune the engine to a particular track or weather conditions.
Closing up the clearance increases both the lift and durration slightly so in a sense you are making the cam a little more "radical".
I would say closing the clearance up to maybe 0.015" to 0.017" would be okay depending on how close you're running your piston/valve clearance.
I would start at maybe 0.020".

Are you setting the valves hot or cold? and what kind of shape are your rocker arms in? If the valve contact area of the rocker arm is worn this will throw off your feeler gauge setting and there will be more clearance than indicated. Rocker arms can be refinished on a valve machine.

 

Mike,
Thanks for your input and info. The rockers tips are in excellent condition. I always adjust them hot. My thought was starting at .021. I don't think I would risk anything tighter. Heat isn't a concern either, it never runs over 180-190 unlike a race engine.

So I'll give it a try

Thank you
Jim

 

The early Ford performance engines with solids had a specification of .020 clearance so it would be okay to run that tight with no problem and it was used often by racers in fine tuning an engine to a specific track or condition.

 

Thanks for that additional info. I had never seen a .020 clearance specified anywhere. And I've been working on them since 1964. SO I should be good.

Jim