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I have a ZZ4 Crate motor in my 67. I am going to purchase the LT4 hot cam and they sell the cam along with 1.6 ratio rockers. Does anyone have a feel for how much the rockers ratio increase helps? If I go down the rocker road I have to change out the valve covers too(not enough clearance)..
 

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rj
I believe that you will need to replace the valve springs if you are using the HOT cam and 1.6's in those heads. The roller rockers will fit under the stock stamped steel rocker covers that come with the engine on the fast burn heads but I don't know if the ZZ4 heads are the same. If you had the fast burn heads you would not have to change springs.
Try a search in the archives here for zz4 valve springs and hot cam. http://www.sallee-chevrolet.com/Discus/board.html

Jim
 

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When I spoke to comp cams, the info I got was that there is a .030 lift difference between 1.5's and 1.6's. add that to your cam lift and you'll know your total lift and the height your springs will have to allow for.
 

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If you want to know the difference between 1.6 and 1.6 ratio rockers on a "specific" cam it depends on each cam, you cannot say .030 difference accross the board though it does get you pretty close in the .450 - .510 range, the higher the lift on the cam the further off you get if you just assume .030.

Here is what you need to do to figure it out. Take your cam card, get the lift number (lets say .480 for this example) take .480/1.5 = .320 you then take .320 (which is the lift at the lobe of the cam) and multiply it by your new rocker ratio, in this case 1.6 (.320 X 1.6 = .512)
 
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