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Thread: Roller Rocker Question for Tom T.

  1. #1

    Roller Rocker Question for Tom T.

    Tom,

    What ratio did you wind up with on the NH roller rockers? I am using my Gessler heads on the 425. They are about .060" away from coil bind at .500" lift. I am using a KB Mark 2H that have .309" and .304" lifts at the cam and .494" and .486" lifts at the valve using a 1.6 ratio. I was never worried about coil bind with the stock rockers (as they fall off at lift), but I am afraid of going more then 1.6 with your rockers. I don’t think it is a good idea to go much beyond .500". The heads have aftermarket springs from Carmen, and have good seat and lift pressure for that cam. I would like to try the rockers out on this engine, but I guess I could wait until I assemble something with the Magnoti heads as they are good into the .600" lift range.
    Steve B.



    67 GS 525 Buick Stage IV
    66 GS Convertible
    65 GS HT
    63 Riv
    02 Subaru WRX Turbo
    03 Ford Cobra Convertible (Factory Supercharged)

  2. #2
    Steve, I have been telling everyone when they are building an engine to have plenty of V/P clearance for at least a .600" lift. This way for most, except the all out applications, there will be plenty of clearance along with figuring coil spring bind. The ratio starts out at 1.9 but because of the shaft rocker system loses ratio the higher the lobe lift goes over .250". In the case of your cam specs. your actual lifts at the valve are probably closer to .435"-.450" lift. Definately not the advertised of .486" & .494" lifts. With my Rocker Arms your lift will more than likely be in the range of around the .540" lift area. They will allow the engine to ingest more air & be better able to get rid of the exhaust. As an example, while checking for pushrod angles at higher RPM's, we brought Bob's engine up to 7100RPM's about 6 times. The amazing part was that with the stock rockers, when the HP peaked at 5700-5800 RPM's, the HP fell off sharply a few hundred RPM's after. With my Rockers the engine continued to make HP without falling off sharply all the way to 7100. It was almost a flat line. We peaked at just under 460HP with an average of just under 450HP between 5300-6300 RPM's & didn't fall below 400HP up to the 7100 mark when we decided we probably shouldn't go any higher. You will not be able to get a camshaft with a lobe lift high enough to give you the air flow the NailHead needs because of the lack of airflow in the heads. The Rocker Arms just help to increase the air flow which in turn makes HORSEPOWER!!!!! I would suggest you use a solid lifter & an adjustable pushrod to check your actual lift at the valve. You would then divide your actual lift with the actual lobe lift of the camshaft to come up with the true ratio for the cam you are using. IE, divide .486" by .304" & it will equal 1.6 or actually 1.59868. Or in theory if you end up with an actual lift at the valve of .540" with my Rocker Arms divided by the .304" of camshaft lobe lift you will end up with an actual ratio of 1.776. The higher the lobe lift of the cam the more ratio loss there is. You following me???

    I have to get up at 5:30 AM, so I will say good night for now. Give me a shout or e-mail.

    Tom T.

  3. #3
    Thanks Tom. That will do. I have a little wilder cam here that looks like it will be just right with my other heads. It has .315" and .320" lifts at the cam. That should translate into the .550"/.560" range with your rockers. I think the 4-speed will like this!

    Steve B.



    67 GS 525 Buick Stage IV
    66 GS Convertible
    65 GS HT
    63 Riv
    02 Subaru WRX Turbo
    03 Ford Cobra Convertible (Factory Supercharged)

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