Re: The famous '509 and rocker arm ratios
[Re: Jjs72D]
#1210031
04/05/12 05:16 AM
04/05/12 05:16 AM
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Joined: May 2008
Posts: 5,399 Aurora, Colorado
451Mopar
master
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master
Joined: May 2008
Posts: 5,399
Aurora, Colorado
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The higher ratio rocker will allow the engine a bit more airflow through the entire valve event, so the change would be simular to using a camshaft with a higher rate of lift. Shimming the rocker shafts is not a rocker arm "ratio" issue, but the combination of the rocker arm design, valve stem length, and valve seat height. To get a higher ratio, the pushrod cup is moved closer to the rocker arm pivot point. This moves the pushrod further in, and that can cause issues with the pushrod rubbing on the pushrod hole. The trade off of higher valve lift, is increased cam/lifter/pushrod load. The increased load could result in increased wear of the cam and lifter. Example, a 0.500" lift cam, using a 1.5:1 ratio rocker, with 300 PSI open spring pressure and 400 lbs/in rate (only 100 seat pressure), puts 300psi x 1.5 = 450 psi on the lifter and pushrod. Using a 1.6:1 rocker the valve lift is now 0.5333", and the open spring pressure is now 313.32 psi x 1.6 = 501.31 psi on the lifter and pushrod. Using a 1.7:1 rocker the valve lift is now 0.5667", and the open spring pressure is now 326.68 psi x 1.7 = 555.36 psi on the lifter and pushrod. Using an 2.0:1 rocker example, the same cam with 0.33" lobe lift now would open the valve 0.6667". the extra lift only adds an additional 66.68 psi at the valve spring, or 366.68 psi open spring pressure, but that is multiplied by the rocker ratio, so the cam lobe, lifter, and pushrod is now under 733.36 psi.
It is interesting that the higher ratio rocker arm may increase valve train stability. The higher load pressure should better control the inertia of the lifter and pushrod weight. An comparison example would be between two identical engines that have the same "Valve" motion. The same valve lift at acceleration. One engine would use a lower ratio rocker arm like 1.5:1 and a cam with aggressive high rate lobes. The other engine would use a high ratio rocker arm like 2:1, and cam with mild ramp rate and equally smaller lobe lift. In both engines the valve spring would have to control the same valve and retainer weight at the same acceleration rates for the valve opening and closing, but the lifter/pushrod on the low ratio engine are moving further and faster so it has higher inertia, and less spring load to control it. The higher ratio rocker arm lifter and pushrod are moving slower and a shorter distance (less inertia), and there is greater force acting to control that motion.
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Re: The famous '509 and rocker arm ratios
[Re: Jjs72D]
#1210034
04/05/12 03:23 PM
04/05/12 03:23 PM
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Joined: Apr 2005
Posts: 1,505 TN
SCATPACK 1
pro stock
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pro stock
Joined: Apr 2005
Posts: 1,505
TN
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Jeff Your buddy will get roughly 10% more effective duration and 10% more lift. Maybe the engine will like the extra cam opening or maybe it will not. Is the rest of the engine (heads,piston compression, valve springs, carburetion, torque converter, etc...) built to take advantage of the "bigger" cam. He may have to re-jet the carb a little richer. My bet is it will like the bigger cam. But if he has a torque converter and carburetor that will not let it RPM, then it would not benefit him any.
Old Geezer Racing
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Re: The famous '509 and rocker arm ratios
[Re: SCATPACK 1]
#1210035
04/05/12 04:00 PM
04/05/12 04:00 PM
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Anonymous
Unregistered
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Anonymous
Unregistered
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Most running Mopars with 1.5 ratio will run into pushrod rubbing when simply swapping rockers to 1.6 ratio. It is true that most every after market head needs grinding in the pushrod area for 1.6 ratio arms and most even need it for 1.5 and for sure when you run a 3/8ths pushrod. So...simply swapping rockers and hoping for an improvement usually results in trouble.
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Re: The famous '509 and rocker arm ratios
[Re: ]
#1210036
04/05/12 04:12 PM
04/05/12 04:12 PM
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Joined: Nov 2004
Posts: 3,544 Syracuse,NY
CompWedgeEngines
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master
Joined: Nov 2004
Posts: 3,544
Syracuse,NY
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RIP Monte Smith
Your work is a reflection of yourself, autograph it with quality.
WD for Diamond Pistons,Sidewinder cylinder heads, Wiseco, K1 rods and cranks,BAM lifters, Morel lifters, Molnar Technologies, Harland Sharp, Pro Gear, Cometic, King Engine Bearings and many others.
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Re: The famous '509 and rocker arm ratios
[Re: CompWedgeEngines]
#1210037
04/05/12 07:29 PM
04/05/12 07:29 PM
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Joined: Feb 2007
Posts: 5,080 organ
maximum entropy
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master
Joined: Feb 2007
Posts: 5,080
organ
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the 509 cam is famous for a reason. that combo would probably benefit from the added rocker ratio. the eddie heads increase in flow significantly between 500 and 600 lift. as mentioned, he will most likely need to clearance the push rod holes in the heads. duration will be increased only at partial lift points, and of course, lift will theoretically increase at the valve 6.6 percent. that is a great cam!
for what is the good life if not doing things thoughtfully?
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