Actually, the lift or profile/specification of the cam has nothing to do w/ the compression issue of the engine... Maybe you had this the other way around bro... The higher the lift, the lighter and easier it is to crank the engine, especially if it has big valves, trust me... That's why the compression ratio as well as the quench is being altered or piston is moved closer to the head... The reason why it's hard for the cam to complete a full cycle ATDC is because, mechanically, the Valve Spring became much stiffer and sometimes leads to coil bind if cam has a real high lift and has not been taken into consideration and this refers to mechanical issue not w/ compression... And the simplest answer regarding the disadvantage is a no brainer at all, the decompression assy is removed so the compression is high, as simple as that... Tnxtraxxas-modifier said:im reposting here what bro haen posted in some topics:
IF NOT REMOVED :
Advantage : easy to start whether using electric or kick start
the kick start wont 'bounce' back when u kick it
Disadvantage : because its working mechanism relies on engine rpm to throw it out of contact with the pin on the cam, sometimes when the rpm hits 1500-2000 its activated and makes ur engine lose compression, try this at gear 3 to gear 4 change, because the gear 4 ratio is soooo different, the rpm drops suddenly and makes this mechanism active and u get loss in performance.
IF REMOVED :
Advantage : no more compression loss of course
no 'sudden performance drop'
Disadvantage : depends on ur cam profile, it need a stronger force to kick start ur engine, if the cam lift is very high (higher compression), you might need stronger battery to start the engine using electric starter.
decompression assy is just a feature with its plus and minus side, so it wont hurt ur engine if you remove it or not remove it.
It's your choice, do u want max performance, or ease of start ?
technically, decomp assy should be activated only on rpm under 1500.. but u know.. sometimes something happen...
yes, thats why gear 4 dropped soooo much....