rockers

[cwhubb]

Does the accuracy of the ratio of rockers really make that much of a difference or is it splitting hairs? example: stock 1.5 rockers which are closer to 1.48 vs a true 1.5, can you actually seat of the pants feel a difference or is it race et dynamic?
Thanks

 

[snakeoil24]

When your buzzing an engine above 7000 rpms it does? It affects the Geometry how the rocker strikes the tip of the valve and behavior of Spring harmonics. In a street car running a hydraulic cam no much. The factory rockers especially stamped units where off at least that much.

 

[Budnicks]

IMHFO if they were all 1.48:1 ratio it would be one thing, but they usually & rarely are/aren't... it doesn't make that big of a difference on a completely stock engine, but if you want all your potential HP/TQ it does... but you start adding more compression, bigger bore, bigger better lighter valves, more lift on the camshaft, especially with longer durations & then add roller rockers & roller camshaft & stroker crank, it makes a world of a difference, every HP counts, it's worth a few extra HP, you only talking about 0.02% of rocker ratio vs gross camshaft valve lift, if they were all the same... It's like blueprinting an engine you can pick up maybe 10% just having everything in perfect spec.'s... 1.50:1 ratio rockers with a 0.450" gross "valve" lift camshaft advertise lobe size rated at 0.300"... same 0.300" lobe camshaft x 1.48:1 ratio is a 0.444" gross "valve" lift, you loosing 0.006" {6 thousands of an inch} & probably 5+ cfm of air flow, so yes it effects HP maybe not seat of the pants feel at a completely stock level, more mods done, then the more it will be notice/felt or more it will hamper the performance... my $0.02 cents

 

[cwhubb]

Gotcha, I'm really trying to decide if going to rollers is worth the big bucks, so far I haven't found anybody that makes ratio accurate non roller rockers, I'm not going to run anything more than a 557 lift cam or 10:5:1 cr anyways

 

[Sweet5ltr]

IMO, if you're looking to waste nearly a grand on a high end roller setup then go ahead. Yes, you will see a horsepower decrease on the engine dyno with a rocker setup that is a hundredth or so off the advertised ratio. You may also see a dramatic power loss by running exhaust manifolds and 2.5" exhaust tubing, air cleaners that can't even pull 50% of the carbs rated CFM due to low surface area, power gulping Dana 60's behind factory RB's, and the list goes on and on but you will hardly see anyone complaining on those items listed. Buy yourself the most heavy duty rocker system available that has the best durability for a street application, and we all know that the Ductile Iron rockers by Isky or Crane have worked for decades. Roller setups are fairly new, and IMO, too fragile for daily use (in Mopars!) and just aren't a worthwhile expense. Some, with unlimited bank accounts may differ. How anyone could justify $500-600+ more dollars for a roller setup than a used set of ductile iron rockers that are indestructible is beyond me. Don't even get me started on that trash that Indy and 440 source try to pull off as quality, budget minded roller rockers... Harland Sharp is the only way to go in a good, quality RB rocker setup if you decide to go that route. Now if you are running a .700 solid roller, then of course buy the best rocker available, but for a camshaft that will hardly have much over .500 lift after lash; don't worry about it and just have fun!

 

[Meep-Meep]

X2 ^^^

 

[747mopar]

My Comp Magnum rockers that I have seam to be really nice pieces, I was going to use the Inskies but found these new for cheap. If you go roller "do not buy cheap ones" the ratio is usually off and causes poor tip to valve contact. I'd do as they said, solids, Harland Sharps or in my case Comps. The one thing I like better about Comps is that they're bushed instead of bearings on the shaft meaning more meat, more oil control and with the shafts being fed oil I don't think a bearing is much of a benefit on Mopars.

 

[IQ52]

In my eyes, the advantage in changing to another rocker arm would be the adjustability factor. At one time we were running the stock rockers on a hydraulic flat tappet and were getting valve float at 5400 rpm. We did nothing but go to adjustable rockers, set the preload to zero and the engine would wind to 6200 rpm.

If you are changing rockers from the stock stamped steel, go to a 1.6 ratio and get the advantage of the extra lift and adjustability.

 

[cwhubb]

I definitely am going to need adjustables, I'm switching to the mp 557 lift solid cam, adv duration is 296 and I think it's 252 @ .50 @ sweet5ltr... I agree and I'm going to have fun with it, I may have found a set of crane ductiles just have to see if it pans out. @ IQ52 I am kicking around the 1.6 idea, the thing that makes me think twice is wear and tear, and the adv duration would jump to the 300 range

 

[IQ52]

Unless you are doing some serious racing, I have found that it is best to design the camshaft around the 1.5 rocker arm. The reason being, when you go 1.6 and a 3/8 pushrod, some cylinder heads have a pushrod to intake port wall interference and you must grind the outside of the port wall to keep the pushrod from rubbing.

 

[cwhubb]

aah ok, is that what push rod pinch is?

 

[IQ52]

aah ok, is that what push rod pinch is?

The pushrod pinch is the area inside the port that is pinched off by the way the port is cast to allow the pushrod to pass by the outside of the port wall.

 

[Herr_Poopschitz]

Unless you are doing some serious racing, I have found that it is best to design the camshaft around the 1.5 rocker arm. The reason being, when you go 1.6 and a 3/8 pushrod, some cylinder heads have a pushrod to intake port wall interference and you must grind the outside of the port wall to keep the pushrod from rubbing.

Not sure about pushrod to head interference, but from my understanding, it's normal practice (wise) to use the highest ratio rockers available for any given combination that allows geometry to be acceptable throughout the valve lift. This allows milder cam lobes to be used as well as less movement of the pushrod...which means more valvetrain stability and effectively the use of a lighter valve spring to control the movement of the valvetrain as a whole, as compared to an equiv setup using 1.5's.

GenIII Hemi's if I'm not mistaken use something like a 1.6, and LS's use 1.7 from the factory. I know aftermarket LS's have 1.85's offered...food for thought...