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Author Topic: rocker arms  (Read 1194 times)

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rigidorbust

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  • no such thing as a straight road

    • CVO1: 2012 cvo road glide custom
rocker arms
« on: November 01, 2017, 04:26:19 AM »

i need new rocker arms and was thinking of going 1.72 arms instead of the 1.65. question?  what will the final lift be
in my t-man 625 cams, i have 650 springs, is it safe or should i stick to 1.65 ?
 :confused5:
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TIMINATOR

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Re: rocker arms
« Reply #1 on: November 03, 2017, 10:20:00 AM »

1.72 divided by 1.65 =  1.042. This multiplied by the existing cam lift gives the new lift. So: 1.042 X .625 = .6515. Whether this will work with your springs depends upon how good the person that set up your heads is. Most often we see spring problems: coil bind, retainer to stem seal clearance problems and such because the installer (usually someone in his garage,) just installed the new springs without checking/ measuring anything, and assumed that just because the springs were advertised for a certain lift that they would always work to that lift. Not so. Usually with any lift over .600 the valve guide needs to be shortened to allow for the desired lift and still have retainer to stem seal clearance. If the heads have had a valve job or two or a high lift cam is installed, the valve train geometry needs to be checked or corrected.
All of the above not withstanding, a gain of .027" is not going to be felt in "the seat of your pants," nor is it likely to be seen on a dyno. The other issue is that most heads, unless they are ported very well, will not flow hardly any more air or make any additional noticeable HP with only that amount of extra lift. IMHO the money would be better spent with porting, or more porting, or other upgrades to the throttle body or exhaust.   TIMINATOR
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HD Street Performance

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Re: rocker arms
« Reply #2 on: November 03, 2017, 11:20:06 AM »

Tim your premise is right.
.650 lift springs means nothing out of the context of the mating assembly. In other words they may coil bind or collars hit the seals/guides. Other considerations are valve to valve clearance at overlap TDC. The new higher lift can put the valves dangerously close on overlap.

Personally I would not install them if I was asked. If I was doing the heads and this was part of the plan from the beginning it would be easy and also easy to drop back to stock for tuning purposes if the result was not to your liking.

My opinion..
You're looking at the wrong way to tune. If the cam matches the build and the build does not meet your expectations after verifying the motor health I would be looking at tuning the exhaust and the EFI. Rocker arm changes when they help are only very small nuances.
« Last Edit: November 03, 2017, 11:41:41 AM by HD Street Performance »
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