: With the tax refund coming, it's time to order
: a bigger and better cam for the
: "Screamin' Six" engine. The 268
: Purple Shaft is not enough, and is barely
: noticeable in everyday driving with what MP
: claims is 228 degrees at 50.
: Engine Specs - 1973 225 bored 30 over, deck cut
: 60 under blueprint to 10.62", Fel-Pro
: head gasket, almost uncut cylinder head, 57
: cc chambers. 1.78"/1.50" valves,
: Offenhauser intake, Holley 450 mechanical
: secondary, Clifford street rod headers, 9.04
: actual measured compression, 190-195 psi
: cranking pressure, Sterling 244NP flat top
: pistons .105" down in the bore at TDC.
: I don't expect much problem with valve to
: piston clearance.
:
: This engine is going into my '74 Duster, which
: will be a mostly race and only some street
: car. It'll be lightened to somewhere under
: the 3000 pound mark with me in it, and I'll
: start with a 3.55 axle ratio. Wide ratio
: 904, which will eventually get a 3000 stall
: converter.
: The cam I've selected is the UltraDyne NF-57,
: .904" lifter extreme solid grind. 282 @
: 20, 255 @ 50, and .582" gross lift on a
: 1.5 rocker, then subtract 0.016" for
: lash, plus whatever the rocker ratio
: actually is. If they are 1.45, that'll get
: me .547" net lift. The guy at UltraDyne
: said I'll need #3939 dual springs for it,
: and I'm ok with that, but I didn't know what
: to say for lobe seperation. 106? 108? 110? I
: need some technical opinions on this one.
: I'm thinking either 106 or 108 myself. My
: old 268 Purple Shaft is 106.

: Just a W.A.G. would be 108 to 110 lobe
: seperation.
: FYI, This cam is a big "jump" from
: the 268 / .460 cam you have now.
: Did UltraDyne give you a projected power band /
: RPM range on this NF-57
: "bumpstick"?
:
: Be forwarned that SL6 cams running over .500
: lift need some extra installation attention
: to make work. The 1.7 installed height of
: the stock valve springs (valve length) is
: the key limitation when going over .500
: lift. Do you know your current valve length
: / spring installed height?
:
: I would advise that you pull-off the valve
: cover and do some measurements before you
: order this cam.
: Do you have a dial indicator?
:
: Pull the valve cover and all the spark plugs.
: Set-up the dial indicator on the v.s.
: retainer while the valve is full open. (
: spring fully compressed )
:
: Now use the adjuster and "crank down"
: another .125 while watching for coil bind
: and / or retainer interferance to the top of
: the guide.
: (If the adjuster screw does not have enough
: thread showing, back-off and insert a thick
: lash cap or suitable shim to get more
: adjustment)
:
: OK, no coil bind, no retainer to guide
: "bottoming". Now carefully,
: *slowly* rotate the engine by hand, over to
: TDC Exhaust stroke. (overlap event)
: "Feel" for valve to piston
: interferance. If you make it past overlap,
: screw-in another .06 of lift (adjustment)
: and test again. If you make it by a second
: time, there should be enough valve to piston
: clearance.
:
: Realize that these tests are just to get a
: basic idea on clearance available, if things
: seem close or "not quite right"
: don't chance it, pull the head off, measure
: and set the clearances.
:
: One last thing, if you do not have a dial
: indicator, you can still do this test if you
: define how much lift change you get per
: revolution of the adjuster screw. To find
: this value, have the valve closed, adjust
: out all the lash, back-off the adjusting
: screw exactly one full turn, then measure
: the gap created with a feeler gauge. You
: will have to do some math to convert lift
: movement into adjuster screw thread turns.
:
: Keep asking questions,
: DD