Safe amount of valve lift

#1
I have an NR 285 cam in my gx200, larger 28.5mm inlet valve, 26lb springs. Will not be letting it rev over 7500 rpm(max). With this rev limit and these components, what would be a safe amount of lift, meaning how much ratio dare I put into the rockers with these springs.

Regards.
 

minidragbike

Supporting Speed Nut!
#3
If they are stock rocker that may break on you. Most run heavy duty rockers, and then your fine. You shouldn't have any valve to piston problems.

Letting the motor only rev to 7,500 RPM doesn't matter. The rockers are push the valves open to the max lift every revolution. RPM is just making it do that faster. And from 7,500-8,500 there is very little difference in the valve train speed.
 
#4
I suppose what i meant to say is, what is the most amount of lift I could go to, using the 285 cam and various ratio rockers, to avoid valve float at 7500 rpm, with 26 Ib springs? ie: 1:1 285"lift 1.12:1= 320"lift 1.2:1= 340"lift etc.

in short, what ratio rockers to give best lift, but avoid float.
Many Thanks.
 

minidragbike

Supporting Speed Nut!
#6
NR-Racing sells a valve lock the allows 0.065" more install height. That allows you to run .400" without coil bind with dual springs. Without those locks you will coil bind around .340" with the stock split locks and dual springs.

What we do is cut the spring pockets. This allows even more lift without binding. I have ran up to .440". But it took tons of work to get there.
 
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