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You can get most realistic numbers from the off the shelf engine descriptions from NR racing

.039-.041”

Yerf dog runs a 7” driven. Run the sprocket on the outside of the jackshaft and relocate axle sprocket.

Compression on a compression release engine means nothing. look up summit racing compression ratio calculator.

Easy, set your valve lash to .002-.003” with feeler gauges.

If I remove governor, then I’m putting a cam in it. Stage 1 adds like 10-25% more hp, and a cam adds a crap ton more.

You should get a billet rod, advance timing by 4 degrees, and get an NR racing 280 cam, torque grind.

The gx390 Mano I have was stock stage 1 believe it or not. I upgraded a few things on it like 280 cam and connecting rod, but other than that it was stock. It actually was a very mild build.

Mild modified big block was floating the valves at 65 mph in under 300 ft, where higher stage small blocks were barely able to hit 55 mph in the 1/8th mile. This was at a drag race a few months ago.

this is about right but yours will make less because the carb is more restrictive than the stock appearing 24mm http://www.nrracing.com/product-p/eng-rac-420-pack2.htm

Hmm so what you really mean to say is the following? Q: Why are you replacing the clutch? A: Because I keep burning through clutches. Q: Why do you keep burning through clutches? A: Because my gear ratio is either 4.1:1 or 5.0:1 Q: Why is your gear ratio like this? A: Because it was modified...

Claims Some people say you can take a 5-6.5 stock engine and then bolt on a stage 1 kit and you get 10-12 hp. I am not one of those people because I have tested stages 1-4 on my dyno. Real Numbers On a briggs flathead, you see about a 0.5 hp with a "stage 1" mod. On ~200 cc small block OHV...

Remove the jackshaft. Place the driven on a vise, but don’t crank it down all the way, then use a metal punch (awl) in the center of the jackshaft and beat it out. Do not hit the jackshaft with a hammer or you will mushroom it out. ---------- Post added at 07:21 PM ---------- Previous post was...

I wouldn't let it idle above 13.2:1 FYI. Try blipping the throttle to 1/8" open. you will get a better response if you are idling at 12.5-13.2 MAX AFR. I wouldnt be too worried about the low 11s on gas, but you will get optimal hp around 12.2-12.5 AFR. Main jet is the only thing you need...

dont forget spark plug to piston clearance too. You can check that with a little bit of math and a striaght edge over the mating surface of the head with the head off. I had a head milled .030 and the spark plug was protruding into the piston if turned too far one way or the other. just FYI.

that blows man, did you ever use roundup? If so, you could be entitled compensation. :cheers2:

the 780's shred belts on v-twin high output engines. the 40 series wont pull the cogs off of the belts they have. This is 2nd hand info from someone who has ran the 780s a bit. the 780 is a bit too expensive for me actually. I plan on running a 40 series on an 18 and a 20 hp v-twin stock...

there is a high (final?) drive ratio and low drive ratio(starting). depending on the series of torque converter, as well as the driven unit diameter, you will get varying high/low ratios. There is a balancing act here with gearing, weights, and the actual load that the torque converter has...

stock gx 390 has a dished piston approximately 6-8 cc's of volume added to combustion chamber vs flat top (guess) piston sits approximately 0.005" to .010" in the hole at TDC head gasket is 0.050" combustion chamber volume is approximately 41cc's all else the same, you can mill about .050-.080"...

also most go karts use standard bearings. The two most common bearing sizes are 5/8"id x 1 3/8" od for driven units of torque converters, jackshafts, and front wheel bearings. Rear axle bearings are almost always 1" ID bearings. There are exceptions to all of this as well. Beyond this, if...