Break-in rocker arms?

[ChargerST]

Instead of removing the inner springs when doing a new cam break-in it is possible to use rocker arms with a lower ratio. The Chevy crowd has some 1.3 ratio rockers for this. Are there any low ratio shaft rockers for BB mopars? Some claim that the stamped steel rockers are low ratio but I'm not sure if that's true or not (several numbers for actual ratio are floating around..from 1.35 to 1.48) and if it would actually work as break in rockers.
I guess modifying rocker arms for a lower ratio is not worth the effort though.

As for the why question: swapping rockers is much less hassle than removing inner springs and putting them back in after break in.

 

[toolmanmike]

That's a CHevy thing

 

[ChargerST]

Why? Physics is physics - regardless of engine brand

 

[toolmanmike]

Why? Physics is physics - regardless of engine brand

Nobody makes 1.3 ratio rockers for Mopar. It's all about spring pressure and not so much about ratio (lift). That's why you remove the inner and 3rd. spring.

 

[ChargerST]

Thanks! Cam sees more pressure as the spring rating suggests as it gets multiplied by the rocker ratio - it's all about the leverage. The ratio has an effect on lift, duration, and pressure.

 

[toolmanmike]

Thanks! Cam sees more pressure as the spring rating suggests as it gets multiplied by the rocker ratio - it's all about the leverage. The ratio has an effect on lift, duration, and pressure.

Ah no. At any given duration, the valve only stays open as long as the cam lobe will allow. The rocker ratio just gives more lift. It doesn't make the valve stay open longer (duration) it will open and close it faster because of the increase in total lift.

 

[Challenger340]

The 1.2 Rocker Ratio is a Chevrolet thing, I've thought about making some for a BB Mopar but that's as far as I went.

Higher Rocker Ratio Rocker Arms like 1.6 for example.... versus 1.5 stock RR
* increase the rate/speed at which the Valve opens
* increase the total lift the Valve opens, thereby increasing V/Spring peak pressure applied to the Cam lobe by the Lifter face on Flat Tappet Cams
and
* increase the duration @ 050 of the Valve(actually Flowing air by then) because the Valve reaches .050 lift sooner using the faster rate of opening.

Conversely,
using a 1.2 Ratio Rocker Arm for break in purposes reduces peak lift..... resulting in less V/Spring peak pressures being applied to the Cam Lobe by the Lifter face during break in.

 

[PRHeads]

It’s not only the loss of lift by the lower ratio, it’s that the lower ratio also lowers the spring force the cam sees, for the given lift.

Take two valves at .500 lift, both have 350lbs of force at that lift.
One gets to .500 lift via a 1.5 rocker, the other a 1.7 rocker.

The load on the cam thru the lifter for the 1.5 rocker is 525lbs.
With the 1.7 rocker that gets increased to 595lbs.

Basically, the pushrod side of the rocker sees the spring force x the rocker ratio.

 

[Hubbarocks]

yes removing the springs can be tedious but if you have a nice tool you can do the job in less then a 6 pack.

i made my own tool from scrap cuz im cheap, took me about 2 beers.

 

[ChargerST]

There is another option that might be a tad easier/faster than removing inner springs: just switching the regular valve locks for offset locks for break-in.

e.g.: spring is 400lbs/inch and seat pressure is 130lbs

Now if you use a +.050 lock the seat and open pressure will be reduced by a fixed amount of 20lbs (400 x .050) as the offset locks change the installed height.

 

[1967coronet]

Just pull the springs, you could have had one head done by now.