I use Kyosho oil when I want 4k.Its not the same but is easier than mixing X-ray oils to arrive at 4K.I was running running 7,5,1 & 5,5,1 Xray brand oil & am currently running 6,4,1 & 4,4,1 Kyosho brand oil to get the same-ish feel.Kyosho brand feels very similar,like 5k Xray might be 4.5k-ish kyosho or maybe even closer,almost imperceptible difference unless the track gets very loose thats when you feel the most difference.A 2.2 rear sway bar will make corner exit very easy just mash the throttle anywhere past the apex & it will keep the rear in line as long as you have a heavy front oil(5-7k). I ran my new front 2.2 sway bar last weekend & now that I have plenty of steering into the corner I am going back to 7,5,1 X-ray brand oil. The X-ray bottle costs twice as much but fits in my box much better due to the shape & it has lasted(stayed clean) very well in the past.Mugen 4k is not the same it feels like 3k X-ray. If you have time & oil to waste try the link & use one of those large syringes from a drug store.
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