KartFab
Active member
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.
Small Block vs Big Block Speed Difference? What is Better?
- Thread starter SquidBonez
- Start date
I have a 390 i've been deliberating putting on my manco. Do I need more revs out of it, or just 'stage 1' air filter, carb jet, and exhaust upgrade? Currently getting about 25-30 out of a 212 stage 1 with CVT.
KartFab
Active member
You should get a billet rod, advance timing by 4 degrees, and get an NR racing 280 cam, torque grind.
My power land 420cc Dragbike went 60mph at 300’. It was limited with the stock flywheel not enough timing.
it only had a NR racing 306 cam , 34mm eBay koso carb , exhaust , and the 40 series plated kit from gopowersports. And a flywheel timing key. And a long rod (piston top lip shaved off by hand to clear !)
it only had a NR racing 306 cam , 34mm eBay koso carb , exhaust , and the 40 series plated kit from gopowersports. And a flywheel timing key. And a long rod (piston top lip shaved off by hand to clear !)
SquidBonez
Active member
Did you have problems shredding belts? If I was going to build a big block it would probably just be Stage 1 with billet flywheel/rod, thin head gasket and a timing advance. Maaaaybe a cam but I'd probably be fine with the stock cam (not sure how much RPM the stock cam is good for though...any idea @KartFab?)
KartFab
Active member
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.
so eliminate the governor in that case since i'm cracking it open for a rod and cam?
SquidBonez
Active member
In that case I might go with a stock lift cam (since I'm already opening up the engine anyway). NR Racing makes one called the 250 Twister. Sort of like a MOD2 but for a big block. 5,500 - 6,000 RPM would be all I would need since if I ran a big block I'd probably run 22" ATV tires. 6:1 maybe 6.2:1 gear ratio. That would be killer.
SquidBonez
Active member
Definitely ditch the governor if you're going through the trouble of putting a rod in it. Also get a billet flywheel if you're running anything other than a GX390. The genuine Honda flywheels are supposedly built pretty good, but the clone ones are a bit weaker.
Sweet. it's for sure a 390. Shoot. Now I'm tempted to put this on my coleman ct200.
No. I never made it that far cause it kept melting the internals on the 44c magnum driver. But the belt never had issues.
I was always build my stuff for heads up drag racing stuff. Might have a little effect on it also. Not a lot of actual off-road areas for karts in my area.
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SquidBonez
Active member
Would you say the regular 40 series driver is better than the 44c driver then? Or did you only ever run that 44c? I'd probably pick up a Comet 40 kit from OMB Warehouse rather than GoPowerSports. They're cheaper there (probably because the backplate they use is a lot less sturdy). $220 vs $370.
Kartorbust
Well-known member
The 44 magnum with the magnum driven gives a high ratio of 1.24:1, with the 40 driven you get a 1:1 ratio. Low range with the 44 is 2.83:1 and 2.43:1 respectively.