what is a "supercart"?

[jeeperjoel]

my idea of a "supercart" must be able to pop wheelies, and hit 70 mph on flat ground, my current vancart build has a lightly modded gx 390, 40 series comet converter, 10 pinion, 45 chainring, 18" tires, i tached the engine at 7100 rpm wound out, my math says it would be going 84 mph at redline, or max rpm, of course it won't do that, probably would hit 75 (we'll know for sure this weekend), but wheelies aren't happening, now if i go to a 54 tooth chainring it drops the max speed to 70 mph, but the lower gear ratio will let it get closer to max rpm, so on flat ground it might go 65, a little under goal, but could that lower ratio let it wheelie? seems like it's close, but that's without van body.... what do i need to do? have the head milled? that'd be the next step for engine, it's advanced 8 degrees, aftermarket air filter, "custom" exhaust (that's about to get re-done larger) hd valve springs, re-jetted carb no govenor, has billet rod, awaiting billet flywheel... another idea is to wind driven 1 notch tighter to keep the rpm up higher, but will this put me above the max torque output rpm in low speed driving situations? or all the time? i don't think putting lighter weights in the clutch will help, it'd be the same difference as winding the driven, except there'd be less force on the belt.... any advice? ideas?

 

[karte_m0lim]

Reduce weight to get better weight/power ratio
Reduce drag...
With same engine top speed would not be changed but you be there faster...

 

[jeeperjoel]

not sure of where to drop weight, anything i'd cut out would be structural, or not running the van body... the billet flywheel im saving for will help, trying to maximize torque vs. top speed in gear ratio, and clutch engagement vs. powerband of engine...

 

[BirdFanatic]

http://www.diygokarts.com/vb/showthread.php?t=16518

 

[jeeperjoel]

there is however the bottom line of "is my engine making enough power to both pop wheelies, and achieve 70 mph on flat ground if clutch timing, and gear ratio are optimized?"

 

[landuse]

This might be one of those situations where you are just going to have to go with a ratio and see what happens. You can always change again if you don't like it

 

[Half-breeder]

there is however the bottom line of "is my engine making enough power to both pop wheelies, and achieve 70 mph on flat ground if clutch timing, and gear ratio are optimized?"

IMO to get the torque to do wheelies... AND... do 70mph... youre gonna need gears!... as in manual transmission.

 

[KartFab]

Wheelies are more about center of gravity. This is a stock gx390 with 6:1 ratio on 18" tires. Engine is back behind axle, riders are light. Front of kart is light. Won't do wheelies with me on it, only my light kids.

https://youtu.be/54aJQ3_MGx4

 

[jeeperjoel]

nice! so the cart in the video is doing about what i'd like at low speed, but says it tops out at 33 mph? does it still have a govenor?

 

[Joe-405]

My barstool wheelies as soon as you touch the throttle and it's only a bsp 212cc engine. Refer to my build thread for ideas and pics. So the large engine is definitely not your issue for sure.

This is my version of a super kart !, and I want one

Superkart is a form of motor racing based around a racing vehicle sized like a kart but with several characteristics more strongly associated with open-wheel racing cars.

The most obvious difference between a Superkart and any other form of kart is that they have full aerodynamic bodykits and can race on car circuits over 1,500 metres in length. The power unit, most often, but not exclusively two stroke 250 cc engines, can be specially designed kart engines or production motorcycle engines with either five or six-speed sequential gearboxes. Owing to their high top speed and superb cornering ability, a Superkart's aerodynamic bodywork includes a front fairing, larger sidepods, and a rear wing. They use either 5-or-6-inch-diameter (130 or 150 mm) tires and wheels and most often race on full size auto-racing circuits.

250 cc Superkarts often[quantify] set faster lap times than much more expensive and technically advanced racing machines.[1][2] Some British and Australian classes also include 125 cc gearbox karts.

Superkarts race on "long circuits"[3] (e.g. Silverstone, Laguna Seca, Magny-Cours). In the UK they also race on "short circuits"[4] (e.g. Kimbolton), "short circuits" are under 1,500 metres in length.[5]

Superkarts are raced worldwide. There is a multi-event CIK-FIA European Superkart Championship (for 250 cc karts only),[6] and there has in the past been a World Championship, which was last run in 1995.[7]

 

[Russell ATV]

Three things; power, gearing, and load.

Power - it takes a set mount of power to overcome air, inertia, and drive train and wheel drag. In cars, they say you need 250 WHP (wheel Horsepower) to get 150 MPH, 500 WHP to pass 200MPH, and 1000WHP to get to 250MPH. Karts are fairly poor at air drag, so hard to find any that can top 60 MPH without having at least 20 WHP. Some racing karts can do it, and more, but they are low, and have some aerodynamic help.

Gearing - Notice I do not say gears, as your CVT can give you a 3:1 all the way to a .8:1 total ratio. This is about the same as any gear based transmission when it comes to Karting. The key is to match the drag/power limits with the RPM limits. Some of my friends would drop in low rear end gears in their muscle cars for better acceleration, but they would also give up top end speed. Probably a good idea in a car with drum brakes. If you care more about acceleration that doing 60MPH, gear it lower.

Load - load is the sum of weight, bearing friction, drive inefficiencies, aero drag and wheel alignment and pressure (rolling resistance). As you improve any or all of these, so will you increase your acceleration and maximum velocity for the same power. Increase the power while maintaining the load, you will get better performance as well.

Finally, wheelies are a bad thing. It might look good to see a drag racer pulling a wheelie, but they lose the race when they do. Traction and acceleration is what you want. At the edge of grip is where you want to be, besides, you need those front tires to steer and sometimes brake.

Russ