Posted By: Jjs72D
The famous '509 and rocker arm ratios - 04/05/12 05:23 AM
A friend of mine has a stroked 440 with 496 cubes, Edelbrock 84 cc heads and what he calls "The famous '509 cam." He has no computer so he asked me to post the question: What gains in performance do people see when switching from the 1.5 ratio to the 1.6 arms? I asked this question about my own 360 combo in another forum and told him that in my post, some guys said that shims may be required to get the geometry right. Is that also true with the big block engines? Maybe if you could tell me what ET gains you have seen, that would help too. Thanks, Jeff.
Posted By: 451Mopar
Re: The famous '509 and rocker arm ratios - 04/05/12 09:16 AM
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.
Posted By: Cab_Burge
Re: The famous '509 and rocker arm ratios - 04/05/12 05:26 PM
Posted By: Jjs72D
Re: The famous '509 and rocker arm ratios - 04/05/12 06:03 PM
Wow. You guys in this forum really know a lot! I feel like the guy that asked what time it is and you tell me the detailed history of the wristwatch!
Coil bind? Open seat pressure? I'm sure that these terms will make sense to me sooner or later. I am interested in learning. I thought that my question was pretty simple, but I guess it required a more detailed answer than I expected. Thanks
Jeff
Posted By: SCATPACK 1
Re: The famous '509 and rocker arm ratios - 04/05/12 07:23 PM
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.
Posted By: Anonymous
Re: The famous '509 and rocker arm ratios - 04/05/12 08:00 PM
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.
Posted By: CompWedgeEngines
Re: The famous '509 and rocker arm ratios - 04/05/12 08:12 PM
Posted By: maximum entropy
Re: The famous '509 and rocker arm ratios - 04/05/12 11:29 PM
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!
It also increases the valve spring pressures a little, not much usually is what I have found when setting up valve springs using both net lifts at the retainers. I try to set the valve springs up so I have between .060 and .090 room to coil bind on all 16 springs, I'm not real pushy on the seat pressures unless it is a flat tappet cam, even with them I shoot for 150 to 175 seat pressures as long as the open pressures don't exceed what my goals are for that cam, usually not above 375 lbs, maybe 425 on certain NASCAR style lobes 
My main message is to check everything in the valve traiin for proper clearnances and pressures, follow the cam and valves spring makers recommendations when in doubt 
