ATC110 Headwork

[VintageHondaKid]

I'm building up a mini flat track atc 110 ... anyway, Ive got the motor apart putting a top end in it (56mm 10.5-1 compression piston) and I want to do some cylinder head mods to help it breathe. Putting a cam and valvesprings in it, and ill port the intake manifold as much as I can within reason. I spoke with the machine shop I use who said to just unshroud the valve stem area and smooth out the transitions near the valve seat. Who has experience with porting these heads? I plan on getting a 3 angle valve job, but has anyone ever put bigger valves in the head? If you have, what valves are they for, do they come off another bike? Obviously it will need a performance exhaust which I've already bought. Also thought about having it decked, any ideas? Also, the machine shop im using also does ceramic and antifriction coatings. Should I get the piston skirts done or just leave em alone?

[VintageHondaKid]

bump anyone?

[81Rmachine]

Id love to take care of it for ya but im limited on tooling that small. I work at a racing head shop as a porter/machinist and im looking into offering porting, decking, and multi angle valve jobs sometime in the near future as i enjoy working on these little heads, but I can give ya a few pointers if your willing? The 110 heads have a huge guide boss, there is plenty of aluminum to hold the iron guide in place, so i usually narrow that up quite a bit and then go ahead and make sure the aluminum is about level with the guide, shaping the guide into a tear drop is most ideal for airflow and is typically worth up to about a 5% gain on a sbc in the mid to upper lifts but im sure much more in this application as the guide takes up so much of the port. Also give the bowl some more volume this is the area just under the seat where the port turns make sure to transition the port roof into the bowl smoothly most of these hondas have a "closed bowl" where the valve guide almost looks like a shelf so i use a carbide along the sides of the guide to blend it into the roof. Be careful shaping the short side radius (the turn into the chamber along the port floor) the longer you spend here the faster you can screw it up so be quick and make a smooth radius from the floor to the seat. Two things you should avoid when porting is "gasket matching" and "polishing" if you really feel its worth a gain go ahead and polish the ex. all you want but never the intake. Ive tested before and after and its hardly worth 1 or 2 cfm on the flowbench. the intake port should be textured to induce eddy currents which prevent fuel from puddling causing reduced power and possibly backfiring. a carbide finish is ok but i wouldnt use a cartridge roll any finer than 60-80 grit on aluminum and keep grinder speed down as too much speed can make it too smooth. Also have your shop put a 30 degree back-cut on the valves this helps air flow past the valve and the seat and as long as the angle is no more than 15 degrees air doesnt know its there hence 45 valve angle to a 30 degree back cut. This mod takes a couple minutes to do and is definitely worth a noticeable gain in flow and power. let me know if you have any questions Ive ported my brothers '86 200x and i posted his flow results the first is a baseline before mod and the second is some mile bowl cleanup after the V.J. and then the entire port. As far as power its great. It gained a little bit off idle even but way more on top. It used to really fall on its face with no top end, problem solved.