1.5 vs 1.6 rockers

[Andrew]

Will someone please explain the benefits and drawbacks of using 1.6 rockers, as opposed to just buying a higher lift cam?

 

[Meep-Meep]

The rocker ratio from a mechanical perspective is directly opposite from what you would expect to make your life easier when lifting something. The purpose is to move the valve a greater distance with little movement on the push rod side, but that comes at a price in terms of forces involved. It's like if a see saw had a long and short side and you were lifting the kid from the short end. Kind of hurts my back just thinking about it. The benefit would be greater and faster valve lift for given lobe profile. I'd say good if your heads can tolerate those kind of valve events, but for a street car that you expect to run for many thousand miles, I think it's an exercise in materials testing of valve train components and oil film strength.

 

[Andrew]

Great explanation. I'll stay with 1.5's.

 

[lewtot184]

The rocker ratio from a mechanical perspective is directly opposite from what you would expect to make your life easier when lifting something. The purpose is to move the valve a greater distance with little movement on the push rod side, but that comes at a price in terms of forces involved. It's like if a see saw had a long and short side and you were lifting the kid from the short end. Kind of hurts my back just thinking about it. The benefit would be greater and faster valve lift for given lobe profile. I'd say good if your heads can tolerate those kind of valve events, but for a street car that you expect to run for many thousand miles, I think it's an exercise in materials testing of valve train components and oil film strength.

pretty good info. going from a "true" 1.5 to 1.6 may net 5-7hp. the valve will see around .030-.040" lift, depending on the lobe, and pick up about 6 degrees duration above .200 lobe lift. the power gains don't offset the cost if you already have an adjustable valve train with 1.5 rockers. down sides can be coil bind, retainer to guide and piston to valve clearance issues. something most people don't do with adjustable rockers is check their true ratio. every 1.5 that i have tested came out a true 1.6. the 1.6's i've tested are around 1.65, and the real myth is factory stamped rockers are 1.4 or less. the stamped steel rockers i've checked were 1.5. the issue lies with folks trying to measure rocker ratio and lift at the valve with a hydraulic tappet. that won't work.

 

[Meep-Meep]

pretty good info. going from a "true" 1.5 to 1.6 may net 5-7hp. the valve will see around .030-.040" lift, depending on the lobe, and pick up about 6 degrees duration above .200 lobe lift. the power gains don't offset the cost if you already have an adjustable valve train with 1.5 rockers. down sides can be coil bind, retainer to guide and piston to valve clearance issues. something most people don't do with adjustable rockers is check their true ratio. every 1.5 that i have tested came out a true 1.6. the 1.6's i've tested are around 1.65, and the real myth is factory stamped rockers are 1.4 or less. the stamped steel rockers i've checked were 1.5. the issue lies with folks trying to measure rocker ratio and lift at the valve with a hydraulic tappet. that won't work.

On my 440 I measured the valve lift at the retainer (straight shot with the indicator plunger) and came up with .462" on the .455" cam using a solid lifter and set at zero lash. This was with Crane adjustable rockers but I didn't go back to check it with the stamped steel ones. Doing the math that comes out to 1.52:1.

 

[lewtot184]

On my 440 I measured the valve lift at the retainer (straight shot with the indicator plunger) and came up with .462" on the .455" cam using a solid lifter and set at zero lash. This was with Crane adjustable rockers but I didn't go back to check it with the stamped steel ones. Doing the math that comes out to 1.52:1.

i have the same rockers on my 272-.455 cam and lift at the valve is .485. i've actually checked this with two different sets of crane iron rockers and the results are the same.

 

[Mick70RR]

I checked valve lift at the retainer using Crane 1.5 ductile iron rockers and it worked out they were 1.55. Also checked their 1.6 rockers and they were indeed 1.6.

 

[Meep-Meep]

i have the same rockers on my 272-.455 cam and lift at the valve is .485. i've actually checked this with two different sets of crane iron rockers and the results are the same.

Hmmm, maybe my Crane rockers are CARB (CA Air Resources Board) approved.

 

[lewtot184]

Hmmm, maybe my Crane rockers are CARB (CA Air Resources Board) approved.

i have a set of 1.5 crane gold roller rockers on another engine, same issue. i've done checking of harland sharp's and the same deal. the factory stamped steel i've checked were right on the money, not the mythical 1.4 or less.