1.5/ 1.6/ 1.7 ratio rockers

[JGC403]

When is there an advantage to going with a different ratio rocker arm? If you want a certain amount of lift why not just get a camshaft with that amount of lift when paired with the factory 1.5 ratio rocker arm? Why go to a 1.6 ratio or 1.7 ratio rocker?

 

[12many]

When is there an advantage to going with a different ratio rocker arm? If you want a certain amount of lift why not just get a camshaft with that amount of lift when paired with the factory 1.5 ratio rocker arm? Why go to a 1.6 ratio or 1.7 ratio rocker?

One answer is that it's easy to swap a set of rockers and get a little extra lift before lunch, pulling a cam could take all weekend. Assuming we're talking a running engine vs a new build. Obviously

 

[273]

One reason I could think of is it you could get more lift without adding more duration.

 

[Killer6]

Easy, because you get a larger lift curve, and more flow without having to increase the duration in order to do so. There is a limit, even with our gifted .904" lifter dia. Mopars,
to how much lift you can achieve for a given duration flat tappet cam. More lift and a bigger curve = more torque and HP in the same operating RPM range.

 

[JGC403]

Easy, because you get a larger lift curve, and more flow without having to increase the duration in order to do so. There is a limit, even with our gifted .904" lifter dia. Mopars,
to how much lift you can achieve for a given duration flat tappet cam. More lift and a bigger curve = more torque and HP in the same operating RPM range.

So is there a down side to using higher ratio rockers? Why bother with the stock ratio then, everyone should put the highest ratio rockers in they can as long as their is enough piston to valve clearance and when your rebuilding an engine that shouldn't be a problem.

 

[yellow rose]

So is there a down side to using higher ratio rockers? Why bother with the stock ratio then, everyone should put the highest ratio rockers in they can as long as their is enough piston to valve clearance and when your rebuilding an engine that shouldn't be a problem.

Yes, there is a downside. The higher the ratio, the greater the load on the cam at the same spring load.

You can only make the rocker arm so long from the centerline of the shaft to the tip, and you can only make the pushrod so close to the shaft. If you she a 1.5 ratio rocker, the length of the rocker from the center of the shaft to the tip must be 1.5 times longer than the distance from the centerline of the shaft to the pushrod/adjuster. If you make the rocker a 1.6 rocker, you can make the rocker longer from the shaft to the tip, but it can be difficult to make the geometry correct. Or, you move the pushrod closer to the shaft. You only have so much material to work with.

The benefit to using a 1.6 rocker over a 1.5 (as an example) is you keep the seat to seat duration very close but you increase the lift and the area under the curve (rate of lift) without making the lobe more aggressive.

 

[273]

So is there a down side to using higher ratio rockers? Why bother with the stock ratio then, everyone should put the highest ratio rockers in they can as long as their is enough piston to valve clearance and when your rebuilding an engine that shouldn't be a problem.

Depending on the heads most you don't need crazy lifts. Also needs more spring pressure and can make the ramps to fast to control are the few I can think of.

 

[Killer6]

So is there a down side to using higher ratio rockers? Why bother with the stock ratio then, everyone should put the highest ratio rockers in they can as long as their is enough piston to valve clearance and when your rebuilding an engine that shouldn't be a problem.

It depends on the profile of camshaft You're starting with. If the cam is mildly aggressive, say a Comp Cam 280 Magnum, it would be a nice bump in that cams effectiveness
w/o too much worry about having to run super-stiff pushrods & high spring loads. If it's an extreme velocity design based on pushing how much You can get away with on the
lifter dia. you're running, You have to be prepared to pay the freight for that, and Your build would have to warrant that. If it's a roller cam, well, you will be upgrading the
majority of those things anyway unless it's a mild street roller.....in which case there wouldn't be a need for the increased rocker ratio........................