Naraku High Performance Gear Upgrade

You are absolutely correct. However I can tell you they made a big improvement over stock. I dont know how and I dont know why but its true. My head is hurting right now trying to figure this out.

I did make one typo, the stock gears are 52/15 on this particular scooter.

Stock Gears 52/15 = 3.46
Naraku 52/14 = 3.71

My thinking is the lower ratio keeps the engine in the powerband letting you get to your top speed quicker. However that would increase your rpm's at WOT.

I guess Im baffled by the top speed gain reported by my customer.

Nice write up and Pics Jeremy. So 55-57mph is pretty impressive in my opinion. I can't see getting much more out of a 4-stroke and it still be streetable.

Im no gear guru so Ill let Kliff do the talking for me on this one.

From a PM Kliff sent me.

Gear ratios, 101

definitions:

HIGH ratio, means HIGH speed, usually with a slower acceleration

LOW ratio, means a LOWER top speed, with a substantially quicker acceleration

Examples, just examples, because I haven't been in the 50cc box yet, and don't even know the stock set up, so the following are examples.

Suppose the stock gears are a 15/45 combination.
That is a 3.0:1 ratio. It's not high, it's not low, UNTIL we compare it to alternatives.

Now we come up with a 15/30 combination. That is a 2.0:1
In comparison to our stock ratio, this is a HIGH ratio. IF the engine has the power to pull it, in the upper RPM ranges, top speed would be drastically increased. On a 50cc, probably worthless. I've already seen a 180cc burned up, literally, melted piston, due to the load this gear put on the engine. It was only pulling 5K at 63mph, but did not have enough torque to continue, and the owner kept the throttle pinned....meltdeown, in 10 miles.

Now 16/40... 2.5:1, still higher than OEM, still a big engine gear, I wouldn't look at this ratio with anything but a 180cc or better.

Now 16/46...2.87 higher, but faster, gonna need a few mods...
72cc engines, with some variator work, maybe 2K clutch springs.
Possible 60mph with the right 72-85cc, at around 8K...but heat is gonna be a factor, this won't be a hi way cruiser.

BUT, put a 16/46 behind a 59mm or any other 157 engine, 115mm variator, 1500 rpm pills.... 65mph cruise w/12-13" tires at UNDER 7K.... don't worry too much about heat until you push beyond 7700rpm in a steady run... I'd add an oil cooler fer sure.

All of those have been Higher ratios, though the numbers look smaller than the OEM, they all look for higher top speed.

But without spitting gear numbers out, suppose you came up with a 3.20:1 gear set..... acceleration to kick ass with, but with a rev limited engine, a noticeably slower scoot. For gears like this, the CDI will need to be de-restricted, and the engine built for high RPM. All this, and a very much shorter engine life. GREAT for racing, but measure engine life in hours, not miles, and 2 digits, or less in the hour column, should be sufficient.

For the engines we are building, MOST customers will be happiest with ratios in the 2.75:1 > 3.0:1(stock) on the 157 engines. and just as an assumption, cause my experience is still limited with the 50's, but I'd say no more than 5% deviation going to LOWER gears(acceleration), and no more than 10% deviation for a HIGHER gearset....with a BUILT engine for either.
But especially on a 10% higher set. The engine will need the power to pull the gear, and even then, will NOT be a highway cruiser, NO extended top end passes. Run it up, 10-15 seconds, piss off you buddies, and back it down to cruise at their speed.

When it starts spitting molten aluminum at the guys behind, from the tail pipe....it the beginning of a real bad day.....LOL

Cool gear ratio calculator
www.precisiongear.com/pgtechratio.htm

From my understanding these gears offer better top end because they keep your engine in its powerband at higher rpms.

Stock gears = 52/15 3.46 ratio (better for daily drivers)
Naraku gears = 52/14 3.71 ratio (better for the track)

These are definitly track gears. More torque less over top speed from what I understand about gear ratios. However say your racing on a 1/8 mile track or road racing. Faster off the line and top speed only matters after about a 1/2 mile on one of these anyways. Whats 2 or 3 mph faster when it takes over 2640 feet to get there.

Yea fastenal is a little high on their products.

DEFINITELY! a lower gear will always help on hills.

Quick shipping, THANKS Jeremy... but you should also mention a new gasket comes with the kit. Other than lube, it's ready to go!

Yup, got the gears, and decals, I appreciate both. Now I have a delima....how to finish up the week tomorrow.... go ahead and install the gear on the 72cc unit, or do some more fabrication on the NOX system?

I think tomorrow I'll work on the No2/Gasoline blending nozzle for the NOX system along with the auxilliary float bowl for that unit....

Hey Moto do they make a performance gear set for the 150's?? I was just thinking if they did and add this to my prodigy variator then going up these hills I might jusr run over somebody with my old Bali! LOL JRR

Alright!!! May just have to look this over, do you have a link to such sets and some advice or recomendations Moto? After looking over this thread I see no difficulties in making this modification kind of like years ago when I was a kid and helped the uncle change out rear ends on the old mud track cars they ran on Saturday night! Funny the things we used to do like weld up the things and make positive track out of it. Had to always have plenty of axles around when ya snapped one! LOL JRR

I dont think hes installed them yet. However all my customers that have absolutely love them.

Enviro- are they reporting top speed gains, or just better acceleration?

If you can verify it, I will get one really soon! ; )