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[dnlpnd]

Does anyone here know how to do the math to estimate the equivalent cam specs when changing from a 1.65:1 ratio rocker arm to a 1.725:1 ratio rocker arm?

see attached

Thank You,
dnlpnd

[grc]

Lift" / 1.65 X 1.725     OR    Lift" X 1.0454

.574" / 1.65 = .348" actual lobe lift;  .348" X 1.725 = .600"

        OR

.574" X 1.045 = .600"

Jerry

[dnlpnd]

So, assuming 1.625:1 rockers are stock and using the Jim's 1.745:1 rockers (because they are the most radical I could find) my cam specs would turn into the following:  see attached  Thanks for the Math lesson grc!

With that said, is there some reason unbeknownst to me why, if the goal was to get the cam lift up into the .615” range, a simple rocker arm change could potentially leave the cam chest untouched while doing a head and TB/intake upgrade?  I was considering either SE MVAs or R&R Stage V heads paired with a SE 58 mm throttle body with the intake opened up to 1.8”.

I realize the point of these 1.745:1 rocker arms is to achieve higher lifts when you’ve maxed out your high lift cam options, but thinking outside the box, why couldn’t this be a good thing for my situation too?

Thanks,
dnlpnd

[prodrag1320]

Make you check valve to valve & valve to piston @ TDC. we only use increased rocker ratio's when bigger cams are not avaliable on drag motors

[dnlpnd]

Make you check valve to valve & valve to piston @ TDC. we only use increased rocker ratio's when bigger cams are not avaliable on drag motors

 

[HD Street Performance]

There is no logical reason to do this
There are many .600 + lift grinds that fill the bill.

[prodrag1320]

100% agree`d

[Ridgerunr]

Several wise engine builders have said if "you feel it necessary to change rocker ratio, you got the wrong cam".

[grc]

I was hoping someone would mention the geometry change caused by the different ratio rockers, the affects that could have, and if it would be enough to cause a problem.

Jerry

[MCE]

Another thing to consider is; Do your heads flow any better at the new lift(s)?

[prodrag1320]

agree here too

[dnlpnd]

Thanks everyone for the feedback!  I did some asking around outside of CVOHarley.com too and the conclusion I am coming to is that if the varying the lift arm ratio gets you valve train properties you seek for your specific intake system, there is NO difference between changing the rocker arms or changing the cams.

I do understand the question of why would you do this, if cams are readily available for your application, but when you’ve already changed the cams, lifters, and pushrods it seems like a good choice to not disturb all of that again if a rocker arm change accomplishes the same thing during a new head installation.  Changing just the rockers arms, instead if the cams is not a money saver either, as higher ratioed rocker arms are about the same cost as cams.  All you really save are re-disturbing parts that have newly found their happy place, a little bit of labor cost, and the usual upgrade to roller rockers that tend to come with the higher ratioed arms.

My head builder, rrcycle.com, is going to let me know how to proceed…new cams or new rocker arms.  Bottom-line though, the engine does NOT care, cams or different ratioed rocker arms provided you get the correct valve lift and timing for your intake setup.

Thanks,
dnlpnd

[sadunbar]

Thanks everyone for the feedback!  I did some asking around outside of CVOHarley.com too and the conclusion I am coming to is that if the varying the lift arm ratio gets you valve train properties you seek for your specific intake system, there is NO difference between changing the rocker arms or changing the cams.

I do understand the question of why would you do this, if cams are readily available for your application, but when you’ve already changed the cams, lifters, and pushrods it seems like a good choice to not disturb all of that again if a rocker arm change accomplishes the same thing during a new head installation.  Changing just the rockers arms, instead if the cams is not a money saver either, as higher ratioed rocker arms are about the same cost as cams.  All you really save are re-disturbing parts that have newly found their happy place, a little bit of labor cost, and the usual upgrade to roller rockers that tend to come with the higher ratioed arms.

My head builder, rrcycle.com, is going to let me know how to proceed…new cams or new rocker arms.  Bottom-line though, the engine does NOT care, cams or different ratioed rocker arms provided you get the correct valve lift and timing for your intake setup.

Thanks,
dnlpnd

Installing alternate ratio rocker arms will also alter your valve train geometry.  You may want to quiz your builder to be certain there are no adverse effects...

[HD Street Performance]

the conclusion I am coming to is that if the varying the lift arm ratio gets you valve train properties you seek for your specific intake system, there is NO difference between changing the rocker arms or changing the cams.

This statement is not true
Changing ratios increases the lift rate, effectively adds a small amount of duration, and may cause an adverse effects for a lot of reasons. Think about what the added lift gets you on the exhaust side. .574 to .600+ lift. Where is the motor at in the point of the exhaust cycle near maximum lift? The blow down event has been over long before. Plus this cam is opening the exhaust VERY early already. So if there were any gains to be made on the intake side you then potentially give it back on the exhaust side. That said the exhaust is not ideal for a cam this short.

If you use either the R&R or the MVA heads, both which I am very familiar with, consider a new cam. The Feuling 574 is a poor choice lifted or not.

[dnlpnd]

If you use either the R&R or the MVA heads, both which I am very familiar with, consider a new cam. The Fueling 574 is a poor choice lifted or not.

So, if you could pick any chain driven cams out there, what cams would you recommend for the R&R Stage V heads with the 2.00 intake and 1.625" exhaust sitting atop the new SE 117 Kit w/SE 58 throttle body?

Thanks,

dnlpnd