Slant Six Forum :: What lobe seperation should I get for this cam?

: 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

Author:	Tim_K [ Wed Feb 06, 2002 10:04 am ]
Post subject:	What lobe seperation should I get for this cam?
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.

Author:	Doc. [ Thu Feb 07, 2002 4:29 pm ]
Post subject:	Re: Big SL6 Cam Issues PIC
Quote: : 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

Author:	Tim_K [ Thu Feb 07, 2002 8:40 pm ]
Post subject:	Re: Big SL6 Cam Issues
Quote: : 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 Thanks, Doug. I spoke to the machinst who did the original work on my /6 block and head. He builds a lot of circle track and drag racing engines, and he thought it would work pretty good, although it would definitely not be an everyday driver camshaft. That's ok with me. I can get the needed springs from Ultradyne, so that's not a problem with my ~1.68" installed height. The machinist will have to recut the seats to allow dual springs on my intake valves. The longer Shivvy exhaust valves already have a shim that makes them flat for the spring seat, so I may not have to cut them. The valve lock/retainer to guide clearance will be checked and cut if needed, which I expect it will. I'll also take the opportunity to get some flow numbers on the head and maybe revise the porting somewhat. Valve adjuster screws have a 42 pitch, which means 0.024" of movement per turn. He seems to think a 106 lobe seperation would work best for my application. I'm not too concerned about valve to piston clearance problems, but I will be checking it. Currently, the piston is .105" down at TDC, then I have the 0.039" gasket, plus however far above the heads' surface the edge of the valve is. These pistons have a pretty thick top, so I'll just Dremel some SMALL notches if needed.

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