max lift on stock head without machining

[69 GTX]

When using 1.5 rocker gear what is the max lift you can get without coil bind on say 906's. A friend asked me and I didn't know off the top off my head.

 

[Cranky]

It depends on the deck height of the piston. You can run more lift with a piston that's .100 down in the hole vs one that's at 0 deck....of course. Valve reliefs is what you do for the pistons that are high up in the bore for example, a 6 pack piston.

 

[sam65]

I can't answer the coil bind,but I think the valve guide will be more concern on factory head.

 

[YY1]

I had to machine the guides in order to run the recommended spring for the 284/484 cam on my 70 383.

Looking back I'm not sure if it was because of lift, or simply the spring design...

 

[lewtot184]

coil bind depends on spring and installed height. stock springs won't take much (coil bind around 1.35") and retainer to seal clearance can start to get goofy at .480".

 

[67Satty]

I always thought that .510 was the magic number for the valve guide clearance and that's why they came up with the .509 cam way back when - so that people could do a cam swap on their motors without doing much to the heads. And that they made up for the small lift with big duration.

 

[69 GTX]

67 that's what I thought as I ran a 509 cam on stock heads but wasn't aware if more could be run or not. I'm aware of piston clearance, but just want to focus on the limits of the head.

 

[super-bee_ski]

That is why Cranky always says to "Dial in the Cam" to determine Valve Event...
I'm getting ready to do it on the GTXs 440....

 

[Budnicks]

with out getting overly **** retentive,
about "generally" max 0.525" gross valve lift to clear factory height valve guides tops, it's relatively safe before too many issues, but machining is cheap, better seals is a good idea too...
BUT that's depending on style/type of spring retainers, locks, seals & springs used etc.
allot of variables to deal with, allot of different mfgrs specs too, best is to always check


stock style retainers, locks & seals an old purple shaft 292*/0.509" cam will clear fine "USUALLY"

 

[lewtot184]

i just measured a '906 head with factory height valve guide boss, stock valves/retainer/locks/seal with one valve job done on them. allowing for the recommended .060" retainer to seal clearance, max safe lift at the valve would be .460" ,lock protruded below the retainer, .495" lift at the retainer stem. i have a set of '906's on one 440 that has installed heghts around 1.83" with stock valves and retainers. i remember back in the day putting a racer brown ssh44 (.514 lift, forerunner of the .509 cam) in a 383 with 906 heads and having to play with the guides to clear everything. don't take for granted all big block heads have a 1.88 installed height from the factory, most don't come close. anything around .480" lift at the valve and you'd better measure.

 

[69 GTX]

Thanks guys for the input.

 

[69 GTX]

Well I pulled apart my 452 motorhome heads last night to measure and looks like about .510-.520 is max lift before smashing the oil seals. Anyone know where I can pick up a cutter to machine these down a little. I'm assuming that is a arbor style cutter for the seals?

 

[lewtot184]

be sure to subtract .060" from those measurements for retainer to seal clearance.

 

[69 GTX]

I measured with seal in place and retainerand locks installed. Was the same int & exh

- - - Updated - - -

I could probably get more with stock seals. going to look into machining the guides down maybe .06

 

[dieseldazzle]

I'd put some retainer to valve seal clearance and installed height difference forgiveness in that equation at .030 total if I were you