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10/23/2025
Location
Essex, ON, CA
Hey all,
I got a 2020 ktm 150sx. Full pro circuit system and jetting from the ktm 125-250 jetting thread here on vital mx. Running great. However, wondering if its worth getting an aftermarket head like rk tek, vhm, tsp or not and if it is which one is best. I dont really want to give up a lot of overrev, but some more peak power and wider powerband is nice. Secondly is sending the cylinder out to get Ported worth the performance to cost. I heard you can only manage a 5% gain with this. Finally, is changing the squish via base gaskets to 1.1 to 1.2 advised from stock? Heard mixed opinions as some say it takes away too much over rev for marginal gains.
They make so much power, I am not sure how much benefit you'll get without robbing Peter to pay Paul.
Dyno time migjt be the best value to fine tune.
What fuel are you running? You can try different heads or inserts. Might find something nice. I also have my squish on my 150 set at about 1.0 with base gaskets. Runs great and I don't think it lost much, if any, overrev.
I personally would not pay someone to port it unless I rode another bike with that porting to know exactly what I was getting and it was a no-brainer improvement. Pretty much every ported bike I've ridden had either a compromised or ruined powerband. Usually lost rideability or smoothness. And I've tried many from all the "industry experts". I think the stock porting on the Austrian bikes is pretty damn good and you're unlikely to get much benefit without compromise.
94 octane pump. How close was your factory squish to 1mm?
I put the 150 kit on my 125 so it never was a stock 150 specifically. However, all the 125/150 typically come with about .60 - .75mm total base gaskets when stock and I am running a single.40 or .50mm now. So, figure I am about.20 or .25 tighter than stock.
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Ah good to hear. So its stock probably 1.2 ish which is already good. Did you set the piston top to be level with the deck? Like deck height 0 and thats where you found the thickness of gasket to use? I heard thats usually the procedure people use.
Nope. I used the solder method to measure the squish and then used the correct base gasket to give me the squish I wanted.
Just to add into this, any time you mess with the head, porting, and base gasket thickness you will need to adjust the power valve. It won't take much, normally 1/8-1/4 turn to get it back to its sweet spot. You'll just have to try both directions in and out to see what works best for that setup.
I swapped my STIC Super X PWK onto a buddies 125SX and he came back saying it felt like a 150, but right off idle had no need for clutching. The design picks up a lot more fuel at low rpm signal and is in a cooler vapor state. The performance gain will pull harder than a $4k+ race build, as told to me by a race dad that A/B'd with his boys otherwise stock bike.
I just picked up a low hr 22 150SX….previous owner putted around chasing his kids….Drool coming out of silencer and powervalves were sticking….I went through it, did all the carb mods as per AJ & Digger”s thread. PC pipe & silencer……after riding it hard for 15 minutes the powervalves started working correctly…..WoW ! This thing barks! The only thing I will concentrate on is the gearing…thinking a 14/50-51 will work better for faster tracks…no way I would mess with head & cylinder…..
STIC pwk is the best mod there is
Check out https://www.youtube.com/@UpAllNight91/videos
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