advice wanted for max power/stock cyl.

[2strokeman]

I have decided to pull my 87 down for a refresh. I have to split it to repair 4th gear anyway, [I hear it clicking/chipped tooth]. Im looking for power gains. I want to keep a stock cylinder, but I AM changing to a ported ATC. Other than that a CT mid pipe, and a shaved head are all I have. What is my next issue to be addressed? I am thinking reeds and/or a carb but I like this forum and would like some input. What is the advantages of a long rod? I can add a long rod for nearly nothing, I have a friend that does them. What you guys think?

If you really want to fly, talk to a few builders, pick the one you are most comfortable with and have that builder provide the complete package; porting, bench flow work, tapered bore carb, intake, reed cage & reeds, head design, pipe and case porting. I would seriously consider running 110 octane race fuel with 220-235PSI compression.

A great engine package is a Honda OEM cylinder at 69.00MM-69.50MM, with a +4MM Stroker Crank, Vforce3 Reed Cage & Reeds, 40.5MM Taper Bore Keihin, Modified Intake, PT Race pipe, TRX5 or TRX7 pipe (best to let the builder dictate the type of pipe based on your performance level and his overall engine build), Fully Ported & Cylinder Bench Flowed, 110 race Fuel with a matched head design for 225-235PSI…this little package is a killer set up!

Long rod, short rod, half a dozen of one or the other, short rods rev quicker, long rods produce a little more torque…more important is the build as a package or single unit. Let the builder build the complete system, backed up by his performance guarantee proven on the Dyno and seat of the pants experience.

Carlos.

[rustyATV]

Originally posted by 2strokeman
I want to keep a stock cylinder, but I AM changing to a ported ATC.

You're going to have limits with the ATC cylinder. I ran one with a lot of flow work in the transfer and running 210psi compression that cracked at the cylinder base stud.

The engine currently in my ATC250R seen in the avatar, is an 88 bottom end, with 89 upgrade clutch kit, with an 86 TRX cylinder bored to 69MM with a +4MM Honda OEM rebuilt crank, ported/flow benched to 190/129 running 112 race fuel at 235PSI on a PT High Rev Pipe, it has not been on a Dyno recently, however; when first built it put out 55-56HP…the rest of the engine is as described above.

It is noticeably slower than my 330R @ 68HP I had in the ATC a few months ago, however; still fast enough to smoke a lot of larger displacement engines…it is a real sleeper down to the Honda OEM head!

I use to run ATC250R 85-86 jugs in the 50HP-55HP range without issue; no cracked cylinders…guess I was fortunate.

Carlos.

[2strokeman]

I'll probably keep it around 190 psi, I ride it at least 10 hours a week. I have thought about a 310 kit, but how reliable are they? I know you have to sacrifice a little, but how much we talkin? Best brand? I'm not racing, except for the occasional drag for fun.

[rustyATV]

Originally posted by acecarlos
I use to run ATC250R 85-86 jugs in the 50HP-55HP range without issue; no cracked cylinders…guess I was fortunate.

Carlos.

Mine was ported so that you could stick your thumb through the transfers, so I think it was a little thin in that area. Plus, it was a woods motor in a TRX so was under load for long periods. I know the late cylinders have features added in that exact area for strength.

[2strokeman]

What about reeds? My buddy swears by V-force 3's, I mean my logical side say's they look like an awesome design, but I know this is not always the case. Cool head? CR ignition?

My intake transfers are aggressive, however; not as aggressive as yours…most of my cylinder work is in redirecting the transfers, boost and re-shaping the exhaust. The intake is also heavily modified and reshaped…30% of the porting time is consumed by bench flow matching all the ports.

As you know, MX engines are ported different; this one is a duner & part time hill racer…

Carlos.