rocker ratio guidelines?

[Ghoste]

Is there a rule of thumb some of you use when deciding on a rocker ratio?

[firefighter3931]

Depends on the combo. A 1.6 rocker will speed up the valve action, which can be helpful with slower rate of lift grinds. There is an obvious increase in lift which helps assuming the heads flow well at the higher lift that the new rockers will be opening the valves to.

Personally, i prefer a 1.5 rocker with the correct cam sized accordingly for the build. A fast rate cam and 1.6 rockers are a bad mix for the street, inmo. The valve action is too violent and beats up the valvetrain. The faster the valve action, the more spring pressure you need to keep the valvetrain stable at higher rpms. Higher spring pressures increase the possibility of wiping a cam lobe.....so it becomes a viscious circle.

I'd consider running a 1.6 rocker on a slower grind like the MP or Comp Magnum series cams to bump up the total lift. The Comp extreme energy high lift (xehl) and Hughes fast rate stuff are cams i would stay away from with a 1.6 rocker if this was going to be street driven. Idling at low engine speeds is hard on components in these types of applications.

Ron

[Ghoste]

So a case like mine with a MP .484 cam, it would seem on the surface that I'd benefit from 1.6 but with my stock heads I wouldn't see the full benefit and thus making the expense hardly worth it?

[firefighter3931]

If you template ported the heads it would be worth it for sure. It depends where peak flow stalls on you current heads as well. The other thing to remember is stock rocker arms are not a true 1.5:1 ratio....they're more like 1.4:1 so your .484 lift cam is more like .451 lift. With a true 1.6 rocker you would be seeing .516 lift at the valve. So there is a .065 increase in valve lift and the valve is being opened slightly sooner with the increased valve speed generated by the bigger rocker arm. You would effectively be increasing the area under the curve.

How much this affects power is combination specific but even on a motor like yours there will be a power increase. Open up the bowls a bit and increase flow and the increase in power becomes larger.

Ron

[Ghoste]

Okay thanks.  In all honesty, it was another one of my "what if" questions.  Were I to go to the trouble of pulling the heads to port them and add the expense of different rockers, I'd likely step up to aluminum heads and roller rockers.  Of course adding that means I may as well get a better cam and well, you know how that goes.
Out of curiosity, are the MP heavy duty 1.5's a true 1.5?

[CFMopar]

What push rods do I need with the roller rockers?

[firefighter3931]

Okay thanks.   In all honesty, it was another one of my "what if" questions.   Were I to go to the trouble of pulling the heads to port them and add the expense of different rockers, I'd likely step up to aluminum heads and roller rockers.   Of course adding that means I may as well get a better cam and well, you know how that goes.
Out of curiosity, are the MP heavy duty 1.5's a true 1.5?

Not another "what if" question   I kinda figured you were fishing   I understand your dilemma with the engine mods but you could see some appreciable gains with minor expenditure. Remember you're working with a 383, not a 440 so you don't need 440 type flow #'s to show an improvement in power, especially in a street type application. Basicly a well "bowl ported" iron head should be plenty for what you're looking to do.

Stepping up to e-heads usually means a compression ratio adjustment and cam swap. Often just bolting on the heads won't show as big an improvement as you'd like. It's all about the combo and matching everything well....and you know that.

The crane ductile iron 1.6:1 rockers would work well in this kind of application, inmo. With some home porting and a good valvejob it would be an "economical" way to go without going too far into the motor. Sounds like a good winter project to me.....

The MP HD stamped non-adjustable rocker arms have the same issues as the stockers. The truth is that they're all over the place in terms of ratio and can vary anywhere from 1.4 to 1.45 on the sets i've seen. There is usually some variation within the same set....some low some high, so valve lift becomes inconsistent from cylinder to cylinder.   Put a dial indicator on a couple of your retainers and take some measurements and you'll see what i mean.

Ron

[firefighter3931]

What push rods do I need with the roller rockers?

Ball/cup pushrods are needed with any adjustable rocker arms.

Ron