Rocker arms .... 1.4 or 1.6 ratio in my 1962 401 ?

Discussion in ''Da Nailhead' started by WPearson, Nov 11, 2015.

  1. WPearson

    WPearson Member

    I have noticed that while looking for a performance cam two different rocker ratios are being listed for the Nailhead a 1.4 and a 1.6 ratio. What rocker ratio is in a 1962 401 ? I under stand that the 1.6 will give more cam lobe lift and if my 401 has the 1.4 ratio can the 1.6 arms be a bolt in swap ? And where can the 1.6 arms be found ?

    Thanks

    Bill in Richmond, VA
     
  2. wkillgs

    wkillgs Gold Level Contributor

    The later aluminum rockers are about 1.6 ratio, maybe a little more.
    I have a set of the older cast iron adjustable rockers, they are about 1.5 ratio.
    I don't know where TA got their 1.4 and 1.6 numbers.
    If you want some hi ratio rockers, Tom's rollers have up to a 1.9 ratio! The TA roller rockers are only 1.6 ratio.
     
  3. TA Perf

    TA Perf Member

    Years ago when we were working on our roller rockers for Tom T. He had told me that he tested many NH rockers and they were a 1.4 ratio. It has been a long time for me but it seems that we also tested the stock rockers and came up with the same ratio Tom said. I think the next nail head we do I will retest them. Our roller rockers are listed and made at a 1.6 ratio mainly because most cam manufactures always spec out there cams with a 1.6 ratio. Our roller rocker are made a little over ratio meaning that when checked with a test spring you may find them at 1.64-1.65. When loaded they should be closer to the 1.6. They are sold complete with new billet rocker stands, ARP studs, 8620 heat treated shafts, Timken roller bearings, billet aluminum roller tip adjustable rockers bodies, and solid nylon tube rocker spacers. I have very surprised as to how many sets we have sold. More die hard Nail Head folks out there than I realized. Anyway that's where the 1.4/1.6 came from.
     
  4. wkillgs

    wkillgs Gold Level Contributor

    Thanks for the extra info Mike. Good to hear your Nailhead parts are selling well!

    I profiled a few cams with a degree wheel and dial indicator, measuring lobe lift at the lifter, and valve lift at the valve retainer.
    Stock '66 401 cam was 0.267" and 0.261" lift (intake/exhaust) at the lifter, and 0.448" and 0.425" at the valve.
    Ratio works out to 1.678 intake/1.628 exhaust with the stock '66 rockers at the MAXIMUM lift.

    I used a 'solid' lifter with stock pushrod and about 0.002" lash for my measurements. The 'solid' lifter was a hydraulic with a nut epoxied inside it and a stud holding the lifters' pushrod cup at the required height. Used a soft spring at the valve.
    Actual valve lift in a running engine will vary from the static measuring setup I used.

    Tom has told me the stock rockers will lose ratio as you add more lobe lift. I'll see if I have any ratio figures for a 0.500" lift cam.
    On nearly all(?) rocker designs, the rocker ratio will vary throughout it's lift range.
    I don't know offhand if there is an industry standard for determining rocker ratio.... whether it's at a specified lift, a max lift or a mid-lift range.
     
  5. gsgtx

    gsgtx Silver Level contributor

    gee Mike, how about a single 4 barrel aluminum intake for our nailheads:pray:
     
  6. telriv

    telriv Founders Club Member

    Rocker ratio at the factory level is measured at 1/2 the maximum lobe lift you can get into the engine. On a "Nail" max lobe lift that will fit in the engine, without boring cam journals, is .400". So ratio is figured out at .200". This in actuality works out to about 1.6 ratio, + or -. Anything over a .250" lobe lift & you start losing ratio unbelievably fast. Biggest factory cam had .441" lift. I believe this was for exhaust with a lobe lift of approx. .280". In actuality the lift AT THE VALVE was approx. .415". This now brings the ratio to 1.48. Added .030" on the cam lobe above .250" & only gained about .015" at the valve over the lobe lift of .250x1.6=.400" lobe lift.
    What started this whole thing is when we were doing some maintenance over the winter on a friend's car. We started measuring the valve lift, which was supposed to be .522" intake & .544" exhaust. Looked visually at the cam & it looked OK. Took measurements & in actuality had approx. .330" lobe lift on the intake & approx. .340" on exhaust x 1.6 = .522" & .544". Took actual measurements, MANY TIMES, with solid lifters & adjustable pushrods, with valve springs installed,& was amazed we ONLY HAD .476" intake & .490" exhaust. This works out to be a 1.44 ratio. To myself this is a LOSS of HP. This is where the 1.4 ratio came from.
    A cam you, Mike, made for this friend you said that you would get him AIR. This cam had a .400" lobe on both. .400"x1.6=.640". In actuality at the valve we had a smidge less than .530". This now works out to a ratio of 1.33.
    So, this is where the ratios come into play. Add .050" to the lobe lift & don't get even .050" lift AT THE VALVE.
     
  7. WPearson

    WPearson Member

    WOW Guys,
    Thanks for the responses.
    The camshafts I am looking at and wondering about the final valve lift are the TA-25, TA-30 and Schneider 270-80H because I would like to use stock compression ratio pistons with out cutting valve notches in the pistons. I hope then a stock replacement set of rocker arms will work.

    Walt,
    I see your from Bucks County, PA, the 1962 Buick Electra I am building came from Croydon in lower Bucks County.

    Bill in Richmond,VA
     
  8. gsgtx

    gsgtx Silver Level contributor

    did you look at the TA-20, in a big car might be better.
     
  9. bigcat

    bigcat Member

    I'm running a TA20 with stock rockers and dualquads in a 64 Riviera with a switch pitch. Runs great, lots of torque.
     
  10. gsgtx

    gsgtx Silver Level contributor

    how does it pull on the top.
     
  11. bigcat

    bigcat Member

    Pulls strong untill valves start to float at about 4800rpm in second gear. Shift to drive and keeps on going.
     
  12. telriv

    telriv Founders Club Member

    Needs new or better valve springs. My all stock '64 Riv. after rebuild & 270K ago would go to 5600RPM's WITHOUT valve float. Didn't take it that high. Shifted 1st.-2nd. at 5400 & 2nd.-3rd. at 5200. Now with MY rockers shift at 5000 & car is faster. A best of 13.902ET @ 98MPH.


    Tom T.
     

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