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Between 1.6 rocker arm ration and 1.72? Does this effect the camshaft I pick out. Have a chance to buy a set of 1.72 ratio and wanted to know how much difference there is between the two. Im running a 351 roller engine with 190R trick flow heads. Haven't picked out a camshaft yet. Thanks for the info Guys. Steve69
Last edited by Steve69 (7/19/2018 5:30 AM)
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Well Steve, the rocker ratio determines lift at the valve by multiplying the "cam lift". so...say you have a cam that has a lobe lift of say .300", and a 1.6 rocker ratio. By multiplying the cam lift by the rocker ratio you will get .480" lift at the valve. The 1.72 rocker will net .516" of lift at the valve. The higher ratio will also increase ramping speed and duration by a little bit.
I'd say talk to your cam supplier before changing the rockers from what the cam was designed to run with.
BB
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Pick a camshaft that allows you to run 1.6:1 rockers. Higher ratio rockers are a crutch for a cam that's too small. This is why Ford used the 1.7s on the Cobra engines in '93-'95, so they could avoid having to grind a Cobra specific camshaft, and still get a little more out of the cam to work with the GT40 cam and intake.
What they don't typically tell you is that higher ratio rockers increase valvetrain angularity and can affect the contact pattern of the roller on your valve tip. They can require different length pushrods, and place the valvetrain under more stress.
So if you're starting clean sheet you're better off just going with stock 1.6 ratio and a properly selected camshaft. Talk to the tech department of the cam company you are going to use (I prefer Crane because there is always someone on the phone with me in 5 minutes and they have been doing 5.0 and 5.8 roller cams for decades at this point; they were one of the first and biggest in the 5.0 market when those cars were new and hot). Give the tech as much information as possible (having head flow at various lifts is very helpful) and discuss your goals in terms of power, idle quality, if you want to be able to run power brakes, etc. Spec a 1.6 rocker ratio and go with what they recommend. I've never been disappointed going this route. They also have access to grinds that may not even be custom, but that won't show up on sites like Summit, etc. unless you actually have the manufacturer's PN to enter. Often they also have the cam on the shelf or can grind it and send it to you quickly whereas Summit, etc. doesn't, and is going to have to order it from them and time is lost in transit, paperwork, etc. I typically just buy from the cam company right on the phone. I figure the advice and help is worth the extra $15 I might spend on the cam.
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Thanks BB and TKO for the info on the rockers arms!
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