Valve lift question

[Whisler]

The recent thread about mileage and cruising RPM got me musing about cam changes. Then I realized how involved that would be with the engine in place. Then I remembered seeing a recommendation of switching the rockers from 1.6 to 1.7 ratio, so I did a little investigating.

If my info is correct, my 351W cam (originally 2V) has 0.416 lift with 1.6 rockers. My calculations, if correct, show that moving to 1.7 rockers would increase the lift to 0.442. Would that increase in lift yield any noticeable power gain on my internally stock engine? I do have shorty headers with no cats and an Eddy AVS 600 cfm carb. but no internal mods.

Any comments welcome (even if they are "you are wasting your time")

[Gary Lewis]

The info on the 351W and then Specifications tab @ Documentation/Engines/Windsor shows the 1984 2V cam lift to be .260" for both intake and exhaust. And with the 1.6:1 rockers that would give .416", although the valve lift is actually shown as .415".

But the 4V, meaning the HO, is shown as having an intake valve lift of .448", which is pretty close to your .442". However, we aren't told if the duration is longer on the 4V cam, so we really can't draw any conclusions from this on the effect of higher lift with the same duration.

But, this article might help: http://www.superchevy.com/how-to/engines-drivetrain/sucp-0202-rocker-arm-ratio. (Yes, I know it is about Chevies. )

 

[Whisler]

The info on the 351W and then Specifications tab @ Documentation/Engines/Windsor shows the 1984 2V cam lift to be .260" for both intake and exhaust. And with the 1.6:1 rockers that would give .416", although the valve lift is actually shown as .415".

But the 4V, meaning the HO, is shown as having an intake valve lift of .448", which is pretty close to your .442". However, we aren't told if the duration is longer on the 4V cam, so we really can't draw any conclusions from this on the effect of higher lift with the same duration.

But, this article might help: http://www.superchevy.com/how-to/engines-drivetrain/sucp-0202-rocker-arm-ratio. (Yes, I know it is about Chevies. )

Thanks for the article, Gary. Very interesting, but I will probably need to re-read it a time or two, so as to fully digest it. One interesting point is that increasing the rocker ratio increased the duration of the cam. I had read that before but not with any numbers attached. "Veeeery interesting."

The rockers that I had seen recommended on FTE were roller tip rockers that supposedly needed no other changes, like push-rod length or valve springs. I will definitely do more investigating as this seems like an inexpensive way to increase performance without tearing into the engine.

It may have to get in line behind other truck projects because my next expenditures need to be on body work and paint.

[85lebaront2]

Thanks for the article, Gary. Very interesting, but I will probably need to re-read it a time or two, so as to fully digest it. One interesting point is that increasing the rocker ratio increased the duration of the cam. I had read that before but not with any numbers attached. "Veeeery interesting."

The rockers that I had seen recommended on FTE were roller tip rockers that supposedly needed no other changes, like push-rod length or valve springs. I will definitely do more investigating as this seems like an inexpensive way to increase performance without tearing into the engine.

It may have to get in line behind other truck projects because my next expenditures need to be on body work and paint.

The higher rocker ratio is an "old school" trick, putting Ford Windsor ball pivot 1.6 ratio rockers in place of the brand C 1.5 ones was a cheap upgrade, and since the Ford ones are cast steel rather than stamped steel they were more durable (saw a few Chevies back in the day with a push rod protruding from a valve cover).

The other item, a higher lift generally helps low end torque, one of the classics was the old "nail valve" Buicks which due to the head design had small valves, so Buick used a high lift cam. Those old engines had some torque, which they needed with the Dynaflush transmissions.