Announcement

Collapse
No announcement yet.

Rocker Arm Ratios

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • #16

    Re: Rocker Arm Ratios

    ^^^ LOL. And what do you run 1.6s on... the dust bucket on stands?
    Nitrous, baby!!...

    Comment


    • #17

      Re: Rocker Arm Ratios

      I don't run 1.6 rockers for the added lift, I run them so I can run a smaller lobe on the cam..........
      So you want less contact area on the lobe so it will wear faster? That's interesting as the aftermarket seems to be going in the direction of larger cam bores so the core is larger and thus lobes are larger. Of course in the engine masters competition some builders are going larger than 2:1 rocker ratios and hoping they will last to the end of the competition.

      Comment


      • #18

        Re: Rocker Arm Ratios

        So you want less contact area on the lobe so it will wear faster? That's interesting as the aftermarket seems to be going in the direction of larger cam bores so the core is larger and thus lobes are larger. Of course in the engine masters competition some builders are going larger than 2:1 rocker ratios and hoping they will last to the end of the competition.

        Give me the biggest Core I can get my next may end up being a 60mm in a SBC with a .937 lifter.
        Last edited by JeffMcKC; July 5th, 2012, 12:21 PM.
        2007 SBN/A Drag Week Winner & First only SBN/A Car in the 9's Till 2012
        First to run in the .90s .80s and .70's in SBN/A
        2012 SSBN/A Drag Week Winner First in the 9.60's/ 9.67 @ 139 1.42 60'
        2013 SSBN/A Drag Week, Lets quit sand bagging, and let it rip!

        Comment


        • #19

          Re: Rocker Arm Ratios

          As others have said, if you run the numbers you'll get an increase in area under the lift curve, which has the effect of running a more aggressive lobe with the same rocker ratio. Also as already stated, if it goes faster you needed more cam for what you are doing with your particular combination. Changing one side at a time will provide more useful information.

          Last but not least an increase in rocker ratio has an equal effect on the pressure seen at the lobe/lifter intersection. If that is marginal the increase in pressure ration at the lobe can result in increased wear or ultimately failure if the oil film isn't up to the task.

          This is solid roller stuff, but it illustrates what can happen when the cam's heat treat and/or the oil supply etc. isn't up to the net effective pressure ratio acting on the lobe flank.

          Three of these are on the closing flank and a couple are the result of grinding a too wide lobe separation spec on a narrower heat treated core. As you'll have noted these are all solid roller profiles. With solids the damage would be worse.

          I'm not trying to scare you away form higher ratio rockers, these are all 1.8:1, but you need to be sure of what you are doing, what the component tolerances are, and what you are willing to deal with in terms of maintenance cycles.







          jammed roller lifter?

          1.6s are great when you're trying to decide between two similar cams; so you buy the lower one and then realize you should have gone one step larger...
          Doing it all wrong since 1966

          Comment


          • #20

            Re: Rocker Arm Ratios

            I don't run 1.6 rockers for the added lift, I run them so I can run a smaller lobe on the cam..........
            Thats a pretty stupid reason but from the rest of stuff you type about, its about on par with all of it.
            Im sorry I had to say it but geezee I would hate to ask about why its best to run a reverse flow water pump with aluminum heads and have to read your answer on that one!

            Comment


            • #21

              Re: Rocker Arm Ratios

              Thats a pretty stupid reason but from the rest of stuff you type about, its about on par with all of it.
              Im sorry I had to say it but geezee I would hate to ask about why its best to run a reverse flow water pump with aluminum heads and have to read your answer on that one!
              You do understand that a smaller lobe on the cam allows you to turn higher RPM's without needing massive spring pressure to keep the lifters on the lobe........

              Comment


              • #22

                Re: Rocker Arm Ratios

                You do understand that a smaller lobe on the cam allows you to turn higher RPM's without needing massive spring pressure to keep the lifters on the lobe........
                I think the running a bigger cam and 1.5s outweighs a smaller cam all the way around, its not worth it.
                Thats like running 5 inch exhaust pipes and compensating with 1.5 inch inlet mufflers.

                Comment


                • #23

                  Re: Rocker Arm Ratios

                  You do understand that a smaller lobe on the cam allows you to turn higher RPM's without needing massive spring pressure to keep the lifters on the lobe........
                  It's just not worth responding to anymore. The sad thing is someone might actually lend credence to what he says.

                  Comment


                  • #24

                    Re: Rocker Arm Ratios

                    It's just not worth responding to anymore. The sad thing is someone might actually lend credence to what he says.
                    Tell me then why do they run as much as a 2.1 rocker ratio in Nascar...... I mean if 1.5 will do, why bother with a higher ratio.........

                    Smaller lobes don't try to launch the lifter off the lobe like taller lobes do..........
                    Last edited by TC; July 5th, 2012, 04:57 PM.

                    Comment


                    • #25

                      Re: Rocker Arm Ratios

                      First, to answer the question originally asked at the beginning of this thread. "If" you have enough piston to valve &/or retainer to valve guide clearance yes, run more rocker ratio. Be aware that you can also have rocker arm to retainer clearance issues too and may even need different length push rods to get the geometry correct. Sometimes you can have guide plate interferance too. However, many street performance engines respond well to extra rocker ratio.
                      BUT, to give you an example of what you're getting it's a simple math issue, so make sure if it's worth the trouble.

                      Example of what you can "gain" by changing rocker ratios. With a camshaft lobe lift of .350 (which is a common small block lobe) you do the following: .350 x 1.5 = .525" of valve lift (theoretical) Now do the same with the other rocker ratio. .350 x 1.6 = .560" lift. So your net increase is .035" lift. Not a whole lot but it does show up in power sometimes.

                      Now, as for you TC, I try to back you up from time to time or just stay out of it all together but this time you're wrong. I'm not going to spend tons of time trying to type it all out but just know on this one you're wrong. If you really need to understand why call me. It's much easier than spending all the time typing it out.
                      Last edited by Dynoroom; July 5th, 2012, 05:29 PM.
                      There are very few people in this world who's opinion I value, you are not one of them.

                      300 in 1999

                      Comment


                      • #26

                        Re: Rocker Arm Ratios

                        Damn, now you got me thinking about 1.65 rocker arms on my Buick. Been thinking about upgrading the cam, but putting actual math and numbers to it, the 1.65 (from stock 1.55) might be just what I want. I need to upgrade the rockers if I want to upgrade the cam, so perhaps I'd just be happy upgrading the rockers. Thanks Mike!
                        Escaped on a technicality.

                        Comment


                        • #27

                          Re: Rocker Arm Ratios

                          Now, as for you TC, I try to back you up from time to time or just stay out of it all together but this time you're wrong. I'm not going to spend tons of time trying to type it all out but just know on this one you're wrong. If you really need to understand why call me. It's much easier than spending all the time typing it out.
                          Well, I was wrong, and I'm man enough to admit it....... It just seemed like good theory, guess I have a bit more to learn on that subject..... Thanks for Correcting me MIke.......

                          Comment


                          • #28

                            Re: Rocker Arm Ratios

                            ... It just seemed like good theory, guess I have a bit more to learn on that subject..... Thanks for Correcting me MIke.
                            LOL. That's always the issue with you. Your posts are based on "your theorries"... not experience.
                            Nitrous, baby!!...

                            Comment


                            • #29

                              Re: Rocker Arm Ratios

                              If you have given valve events optimized for whatever you want to optimize for
                              and
                              At teh "small, torque cam end of the spectrum
                              If the he cam is ground with maximum acceleration for the size lifter you have and your longevity parameters
                              then a "bigger" cam may not be the answer- you would move your rpm range, loose low end torque, etc
                              whereas you could get more area under the curve by going to a higher ratio rocker
                              Another poster above is correct in that you do pick up a few degrees at .050

                              At the BIG cam end of the spectrum
                              You are limited by the size lobe that will fin into the block, among other things

                              If you have flowed your heads you can get a better answer
                              IMHO higher ratio on the intakes helps more than on the exhaust except on those motors with (relative to their intakes) bad exhaust ports

                              Do not just consider the maximum lift
                              The higher ratio gets the lift into higher flow areas of the head faster even if you go above any further increases in head flow.
                              In that case you could get a cam that "rolls over" the nose to limit lift (and make it easier on the springs)

                              For the short duration (towing) stock gears and converter) motor consider 30 degree intake valve seats
                              pick a cam lift
                              at the lower cam lifts the distance from the seat to the valve (curtain, window) is greater at 30 degrees than at 45 degrees
                              flow may be better at high lift with 45 degree valve angle but that may not make up for the better flow at all the lower lifts with 30 degrees

                              Comment


                              • #30

                                Re: Rocker Arm Ratios

                                So Walt, did someone clue you into the Pit Stop story in the new format HRM to see what we internet dipsh*ts would write so that could be included in the next column on the "The Internet Lies"?

                                Don't answer, but there is a nice little story in the Pit Stop section regarding upgrading form 1.5 to 1.6:1 rockers on an SBC. It also touches on the benefits of rollerizing the rockers in the first place.

                                It also introduces a new-to-me Lift/diameter ratio or LD as a way of assessing intake at the valve lift in proportion to intake valve diameter which works on all engine sizes. Simply divide intake lift at the valve by intake valve diameter, in their example .447/1.94=23%. Fun stuff they go on to say that hi-po street should shoot for 25%, full race 35%.
                                Drag Week 2006 & 2012 - Winner Street Race Big Block Naturally Aspirated - R/U 2007 Broke DW '05 and Drag Weekend '15 Coincidence?

                                Comment

                                Working...
                                X