Quote:
Originally Posted by micoulisninja
as I point out, it is unecessary or negative, performance-wise due to unecessary extra friction and stress to valvetrain to stiffen exhaust valve springs...
on the other hand corksil mentions that it is not the springs that have trouble handling the intake valves but the valves and the valve seats... when I took apart my last 250 engine which revved to 14350rpm I didn't notice major wear on seats but was more than the working hours would normally justify... valves were not n excellent shape, having their edges flatened out, but not to the point of losing compression but enough to have sunk a bit in the valve seat (which is very bad for intake flow especially low lifts and reduces CR by a tiny bit) So corksil has a strong point in general... however he has given us no data as to whether he had his valve seats resurfaced or angle jobbed because that definetely reduces 250's valve seat life as it also removes seat surface hardening...
And there is still valve float issue when revving past 14k... so in theory you need 1. harder valve seats 2. lighter valves (I chose the path of lightening the stock ones by 1gram each) 3. stiffer springs optionally
And in that order of importance...
To conclude and answer (eventually your question there are two options if you want stiffer springs...the first is expensive (IMO)
http://www.rdvalvespring.com/kawasaki.html
and have no reviews on it (yet)
and the second is cheap: you place a 1mm steel washer underneath the valve spring to preload it more...
now for some info I think few have and wish to share...
STOCK SPRING TENSION
@1mm 7kg
@7mm 30kg
@13mm 55kg
39mm total length, 26mm fully compressed
spring compression must by no means exceed 10mm when engine working
so if you are to use a 1mm washer under it camshaft max lift must not exceed 8,9mm (I have mine at 8,45mm...) considering that spring is already a bit compressed to be put in its place...
All of the values mentioned above apply only to the 250 and 300 engine |
After I installed the BRT CDI unit, I played with the limiter. As I was noob, my bike lost compression in 6 months of occasional abusive use. After twice valve lapping, the intake valve edge become too sharp and sunk into the seat. At this point I got my intake valves replaced plus cam chain (It rattled bad as well).
During those time I set down my redline limiter until I found safe redline around 13.5 K, and my bike still goes strong in this 3 months after rebuilt. Even that I dont overrev my bike too long, just to provide me some more time/ RPM to shift up before the CDI kills the spark.
TBH, I am courious and envy how the older ninja is set up 14K redline from factory. Did the older ninjas come with stronger cam drives? Has anyone ever thought to put older ninja valves into EX250J / EX 300?