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Another Cam question - calculating total lift

Moderator: Mod Squad

sp_alloy_head
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Another Cam question - calculating total lift

Post #1 by sp_alloy_head » Tue Jan 03, 2012 8:59 pm

I'm trying to figure out what the exact lift is for
my solid lifter cam.

1.) .480 total lift / 1.5 rocker ratio = 0.320 Lobe lift
2.) 0.320 lobe lift - .014 valve lash = .306 inch
3.) .306 in. lift * 1.5 rocker ratio = .459 net total lift

So the total net lift is .459", right?

Cam Specifications:
Intake Duration (gross): 274
Exhaust Duration (gross): 274
Intake Duration (.050”): 228
Exhaust Duration (.050”): 228
Intake Valve Lift*:===== .480"
Exhaust Valve Lift*:==== .480"
Lobe Separation:======= 110
Intake Valve Lash:===== .014"
Exhaust Valve Lash:==== .014"

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bubba22349
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Re: Another Cam question - calculating total lift

Post #2 by bubba22349 » Tue Jan 03, 2012 9:11 pm

No I would think it still would be .480 total lift, the .014 valve lash is for clearance only it shouldn't reduce the lift. Though you would need to set it up on some V blocks and measure it with a dial indicator to know it’s exact lobe lift. The other thing that can vary are the rocker arm ratio's again you would need to plot total lift with a dial indicator at valve with the cam and rockers assembled in your engine.
A bad day Drag Racing is still better than a good day at work!

I am still hunting for a project car to build but with my current low budget it's not looking so good. My Ex- Fleet of Sixes these are all long gone! :bang: 1954 Customline 223 3 speed with O/D, 1963 Fairlane project drag car with BB6, 1977 Maverick 250 with C4, 1994 F-150 a 300 with 5 speed.

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wsa111
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Re: Another Cam question - calculating total lift

Post #3 by wsa111 » Tue Jan 03, 2012 10:17 pm

.480"-.014" = .466 net lift.
Your duration @ .050" is closer to 218 degrees cause you have to figure the valve lash into the real duration. Bill
67 mustang,C-4, with mod. 80 hd, custom 500 cfm carb with annular boosters, hooker headers, dual exh.-X pipe, flowmaster mufflers, DSII dist. MSD-6al & MSD-Blaster 8252 Coil. Engine 205" .030" over with offset ground crank & 1.65 roller rockers. 9.5 comp., Isky 262 cam.
2003 Ford Lightning daily driver. Recurving Distributors. billythedistributorman@live.com
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sp_alloy_head
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Re: Another Cam question - calculating total lift

Post #4 by sp_alloy_head » Wed Jan 04, 2012 2:38 am

Okay, thank you for this information. I'm looking for a cam to remedy my too-high-CR and I'm hoping this will help bleed off some pressure.

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Re: Another Cam question - calculating total lift

Post #5 by Does10s » Wed Jan 04, 2012 8:50 am

Valve lash has nothing to do with valve lift. When the cam lobe it at the top of it's rotation, there isn't any lash! Everything associated with that valve is tight. So there's absolutely no way that valve lash can effect total lift.

Lash does change the duration for sure! The more lash, the less duration. The cam has to rotate just that mush more to take up the slack. This goes for both the upslope and downslope of the cam lobe.

Later,
Will
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wsa111
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Re: Another Cam question - calculating total lift

Post #6 by wsa111 » Wed Jan 04, 2012 11:11 am

The gross lift is the measurment from the bottom of the base circle to the top of the lobe, minus the diameter of the base circle. Then multiply that figure by the rocker ratio & thats your gross lift.
The net lift you subtract the lash from the gross lift. Bill
67 mustang,C-4, with mod. 80 hd, custom 500 cfm carb with annular boosters, hooker headers, dual exh.-X pipe, flowmaster mufflers, DSII dist. MSD-6al & MSD-Blaster 8252 Coil. Engine 205" .030" over with offset ground crank & 1.65 roller rockers. 9.5 comp., Isky 262 cam.
2003 Ford Lightning daily driver. Recurving Distributors. billythedistributorman@live.com
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sp_alloy_head
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Re: Another Cam question - calculating total lift

Post #7 by sp_alloy_head » Wed Jan 04, 2012 11:48 am

Does10s wrote: The cam has to rotate just that mush more to take up the slack. This goes for both the upslope and downslope of the cam lobe.

I can picture this in my head, it makes total sense.

@Bill(WSA111), I'll add that to my notes, I was overthinking the whole lash / lift aspect.

Thank you to Bubba, Does10s and WSA111.

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