Higher ratio rocker arms

[vettedog72]

I am in hopes some one will enlighten me and possible others about the rocker arm ratio when the ratio is increased from stock.

I am wondering about the change of the rocker arm length. I guess the valve side of the rocker shaft remains the same length as stock (so it will line up on the valve stem). So the push rod side must be shorten? If that side is shorten will there be any material effect of the change of the angle of the push rod at the lifter?

The 1.5 to 1 bolt on roller rocker kit sure seems to be a way of adding a few horses to the tractor but I have never seen a direct comparison.

 

[poolboy]

I have 1.55 to 1 roller rockers over a stock cam and it does make the engine more spunky. Addiing a higher ratio rocker to a high lift cam and whoever does it better really know what they are doing.
Here's a link that you might find helpful.
https://www.pontiacstreetperformance.com/psp/RockerArms.html

 

[Brosky]

I've seen some guys have issues with these when using them with a higher lift (than stock) cam. I guess I'm old school too. The cam should do the lifting and the valve train geometry should remain the same, unless you are into all out racing and then you run at risk all the time.

 

[TR6BILL]

You are wasting your money adding roller rockers to a stock cam. The minute increase in horsepower is not worth the money. Just install loud mufflers and you will think you have more power. Or an aluminum flywheel.

 

[MDCanaday]

I have to disagree with Bill,the net effect of the 1.55 rollers is of value even with a stock cam.It will have the benefit of installing a better cam,without having to do major engine work.In addition the life of the valve guides is improved.As long as your lifters are in good enough shape to take a few more pounds of loading I say do it!
MD(mad dog)

 

[poolboy]

I disagree with that, too, Bill. I know first hand the difference it makes.
Whether it's worth the added expense..I guess that would have to be a personal opinion, though.

 

[Brosky]

Bill, I think that I will respectfully agree to disagree with you on this one.

 

[SkinnedKnuckles]

It's more a question of bang for buck. High lift roller rockers will make the engine breath better and reduce friction on the valve train. It's a very modest improvement on a stock engine, though. Less than increasing compression to 9:1 with a stock cam. And yes - I added rollers before a rebuild & new cam. If you're looking to increase performance get a new cam.

 

[poolboy]

Copied from the link I provided
"More Power? This is the really big question and the answer varies with different applications. As we know, an engine runs best within a given rpm range with an ideal cam - correct lift, duration, and lobe placement. If we have that ideal and perfect cam installed, higher ratio rockers will not help performance. In most cases, we don't have the ideal cam, and additional lift and/or additional duration might help performance. As it is quite easy to install rockers, providing all safety points mentioned above are met, direct testing can be conducted with any engine. I maintain and have proven to my satisfaction that higher ratio rockers can provide the same benefits as more exotic cams but without the excessive costs. The secret to any engine's performance is to obtain maximum area under the valve open curve with the minimum overlap and mildest valve train action, again assuming the open time occurs at the optimum time. High ratio rockers accomplish that due to their complex effect on the valve train dynamics. If we would compare two cams of equal duration and lobe positions, but one with more lift on the lobe and 1.5 ratio rockers, and the second with less lobe lift but higher ratio rockers to equal the lift of the first, the milder lift cam with higher lift rockers will always provide more performance (again providing the cam is not to large to begin with)."

 

[SkinnedKnuckles]

All that does it make the engine "breathe" better. Doesn't change duration like a cam.

 

[poolboy]

Right, but adding to that, again, from the link:
"By making the rocker some greater ratio, such as the standard 1.5, the lift of the lobe is multiplied by 1.5, the opening and closing rates are much faster, and the area under the overall "curve" is much greater. This becomes very obvious by reviewing the graph."
You might have to go back and open the link to see the graph.
".. The secret to any engine's performance is to obtain maximum area under the valve open curve with the minimum overlap..."

 

[JFS]

Word of caution: Measure the compression limit of your valve springs before simply changing to a higher ratio rocker set up on an engine with a higher than stock cam lift. Measure the point of valve bind and make sure your total lift does not approach that point. You may need to replace the springs with a set that won't bind at your total lift. Don't ask how I know.

 

[SkinnedKnuckles]

Yep, JFS. Good point to remember.

 

[poolboy]

Why I went back with a stock cam...

 

[Brosky]

WOW!!!

When I pulled my original cam, it had three lifters that looked like the two in the bottom left of the picture and I thought they were bad.

And I do agree with the coil bind situation described above, which is why I said what I said in my post.

 

[poolboy]

Nothing like a little miscalculation or misinformation to mess up an engine.
I have to add that it ran great for 20k miles and in fact had just completed the 1700 mile round trip to the TRials 2 weeks proir to the rocker arm break. Got an updated assembly and noticed an unusual engine noise. So the day before I decided to tear it down, I made several runs up over 90mph in an effort to break something so I could get to the bottom of the noise that had recently developed.
Still running fine, but noisy, that's what I found the next day.

 

[SkinnedKnuckles]

Ouch! What was the culprit? Springs? Oiling?

 

[poolboy]

No, the combination that JFS talked about.

 

[SkinnedKnuckles]

Spring bind? You find broken springs?

 

[poolboy]

The head was in perfect condition, albeit too much spring for the combination of a shaved head, high lift cam, and rocker ratio.
Like I said it was the combination of those mods.
Less spring. thicker head, milder cam, stock rockers, any one of those would probably have prevented the damage.