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Valve lift/ rocker arm ratio
I've been racking my brain and pestering other sites for info to no avail. Might as well bug you guys. Sorry, but it's winter. I am looking for the actual valve lift for 1200's and/or rockerarm ratio, and/or base circle diameter. Sales brochures and magazine articles said/say the 1200 had additional valve lift. They didn't say how much or how it's achieved. Cam data shows the 1200 probably had the least cam lift of the early four cylinder wings. Studying pics of rockerarms looks to me like the ratio was increased to get this lift, but for the life of me I can find no data to support or refute these claims.

Would anyone have or could they measure the actual valve lift, base circle, or rockerarm ratios for the 1200 vs 1000/1100??

For reference, because I know you'll ask, I have an 87 1200 block with 77 heads, cams and carbs. The pistons have been notched for the bigger valves. It runs great, but yeah, it's a hodgepodge. I am just looking for potential improvements still. I'm looking at using 84-85 cams for the additional overlap. Probably what I might gain from overlap, I will lose from lower valve lift because the 1200 cam had less lift and I am stuck using 1000 rockersrms due to geometry of the cam lobes and valves.

My bike has PowerArc ignition off the crank and a top mounted tank so it doesn't need the fuel pump, tach drive or cam driven ignition. As to the valve lift, it really doesn't matter in regard to what I'm attempting, but I have always wondered how a bike with about 100 ccs more, but almost 25% less valve curtain area could make 15% more hp an torque. I think the rockerarms had a higher ratio and therefore more lift than the cam bump indicates. I really doubt that big of a gain could be had by increased velocity through smaller intake tracts. A little I could buy, but not that much.

However, if the rockerarm ratio and lift are a lot more, perhaps trying to squeeze a 75-83 intake valve into a 1200 head might be a better approach. I stumbled on this site because of a discussion several years back about this subject. On the other hand, if the base circle is larger, it will be a better candidate to regrind for more lift as most regrinders take some of the base circle away, and though I may be wrong, I'm thinking the bigger the base circle the less bumpy the cam will be if you take material away. Most regrinders accomplish more lift by removing some from the base circle. Less bumpy should handle higher rpm better.

Thanks in advance for any replies.
#1 02-02-2017, 02:27 AM,

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