Dan, .021" lash shold give you an intake closing of 70ABDC.

.020" will be 72.5 ABDC

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico

I emailed Isky to see if they could provide an E4 ramp/lobe graph. Might be able to then calculate exact lash:degrees ABDC intake close. Guessing .020"-.021" will bring DCR to around 8:1.

6 VOLTS/POS. GRD. NW INDIANA

Dan, tightening the lash will lower the dynamic compression, looser will raise it. More lash, fewer degrees off the seat, earlier intake closing

Lash ramp designs vary considerably. Typically, we figure maximum safe lash to be where the valve side of rocker is moving @ .002" per degree of crankshaft rotation. Above that, tip wear on the rocker and valve stem will happen much sooner and it will get pretty LOUD. Most cam grinders will recommend something a little lower to keep things quiet. For the E4 with 1.54:1 rocker this occurs at .028" lash. At .016" lash the valve side of the rocker is only moving .0008" per crank degree.

You should be able to run the lash between .014 and .024" without damaging anything. I would try between .018 and .022" and see how it runs and if valve clatter is objectionable.

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico

John,

While some specifics still fuzzy (volumes of .150" cut Probe dome/out-of-the-hole portions & thicker Best gasket, E4 lobe profile, etc.), after rereading all the data and running various DCR program calculations, looks like even if rocker geometry/ratio is maximized I should be able to increase lash up to the point where noise is a concern, and still be just under the pump gas DCR limit.

Still a bit curious about variations in recommended lash by cam manufacturers. Aside from the relationship between advertised duration & running valve events, can only assume lash is calculated to minimize wear according to specific model ramp design?

6 VOLTS/POS. GRD. NW INDIANA

Frank,

Supposed to be 1.54:1.
Re: the Isky spec. sheet, they supply valve lift calculated at 1.5:1 using their lobe lift figures (@ .020" lifter rise) in amongst the recommended lash (.015"H/.017"C). Not surprising confusion often follows, as they don't provide any hints re: actual "valve event" specs.

6 VOLTS/POS. GRD. NW INDIANA

John,



Good guess. Inaccurate readings due to sloppy set-up. I went back and did it right (more solid support for the pushrod, much shorter indicator stand arm, etc.). Intake lobe right on the money (closes 58 degrees min. ABDC). Total lobe lift still 4-5 thousands shorter than advertised, but that's assuming my modestly priced dial indicator is accurate.



You would think the DCR program calculator should specify needed specs. are valve event. How many people likely bought the wrong cam or pistons after running that program, thinking the calculator data required was manufacturer lobe specs?!!

6 VOLTS/POS. GRD. NW INDIANA

Dan, when you use Isky's specs you are looking at the cam lobe only. In that case the tappet gets down to .020" off the base circle at 60 degrees ABDC. They call this intake closing but it is at the TAPPET.

The DCR programs use VALVE EVENTS with rocker arms and valve lash. This is what the running engine actually sees. In this case your intake closing is actually 83 degrees ABDC.

As far as .244" lobe lift, either your indicator was not properly zeroed or it was not firmly attached. I would not be surprised if the actual lobe lift was a few 1/1000's less than advertised .283". That's another gimmick that cam grinders do to make their life easier but costs us a small amount of lift.

Basically, when they grind a cam they leave a few 1/1000's clearance between the lobe master and the follower to make sure the base circle has no runout. But if the master has .283" lift and they leave .003" clearance your cam will have .280" lift.

http://ford-y-block.com 

20 miles east of San Diego, 20 miles north of Mexico

Dan, do you have the 1.54 rockers?  Although it wouldn't make THAT much difference, total should only be roughly 6%.

   (.283 x 94% = .266)

Frank/Rebop

Bristol, In ( by Elkhart) 

John,

Checked E4 specs. in my shortblock (#1 cyl.). Will repeat measurements to verify, but though finding precise crank degrees at .020" lifter rise difficult, it appears that specs. are very close to advertised. If anything, duration on both lobes measures 7 degrees short. Opening points are right on the nose (as expected with cam installed straight-up), but shorter closing would demonstrate a bit of built-in advance (unbalanced overlap). Disregarding heat expansion, it's hard to fathom how 51 degrees ABDC (.020" lifter rise) intake closing could end up being 84 degrees at .016" lash?

P.S. Total cam lift also comes up shorter than advertised (.244") Should be .283".

6 VOLTS/POS. GRD. NW INDIANA

Cerebral flatulence must be catching. If you stare at that circular cam spec. diagram long enough, it's like the pinwheel they use to hypnotize people. (was led astray since the "two revolutions" caption at the bottom in such ultra-small print).

6 VOLTS/POS. GRD. NW INDIANA