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Fastest Monkey in the USA!!!

19K views 51 replies 10 participants last post by  mumdb1 
#1 ·
The Grom guys have a top speed guru. Who is going to be the guy with the fastest Monkey? I think there’s a guy with a 170cc on here. My top speed on flat ground, no wind, no tuck, full face helmet, 225 lb ride is 60.5mph gps verified. Stock 125cc, 16t and 32t. Stock sprockets was 52 mph top speed. I drafted a semi at 69.5 with new sprockets, it felt stable. I have the yuminashi 1 to 1 fourth gear to install, but I think the 181 NEO will be able to power the stock 1 to .92 fourth gear. It felt real good drafting the semi, almost like third. I can only hope our troll buys a Monkey. One of our Grom heavy hitters bought one.

And we need Monkey stunters.
 
#3 ·
Thanks CiscoSanJose. I was looking back at your posts. I like your build style, fast but streetable. I saw a post from 2014 where you were determining how to install an O2 sensor. Thanks for laying the groundwork. I don’t necessarily want the fastest Monkey, I just want to keep up with cars. My Yamaha xt225 had 20hp, it did everything I need in the highway. So, I want a 24 hp Monkey. I’m going with a 181 Neo, port the 2v head, the injector that comes with the Neo kit and full Aracer RC1 setup.

So, which throttle body?

Any other fast Monkeys???
 
#4 ·
a 170cc won't get you much in top speed even with changed gearing. The 170 kit will give you a lot of bottom end power, but top end is pretty much the same. I had a 170cc kit with a yoshimuira cam. Top speed was unchanged for the most part. It was just easier to fight a headwind.

I'm 250lbs. 125cc stock piston, Fueling, Yoshimuira cam, and full yoshi gets me right at 60mph verified GPS sitting bolt upright with no drafting or wind. top speed typically increases as it gets hotter outside with these bikes. So I'll revisit in the summer months.
 
#5 ·
For reference, I'm 165lb and my basically stock Yellow without ABS with the full Yoshimura system, 14t front sprocket hit 61.7 mph in a tuck the other day, verified using the iOS Speedomter App at 5,053ft of altitude. My speedo showed 67mph.
 
#10 ·
Yep, and honestly I'm not going for top speed here. Our elevation where we live is a little over 5,000ft and I'm planning on riding my Monkey up to over 12,000ft so I need all the torque I can get up those mountain roads. The 14t has definitely helped out in acceleration and responsivness throughout the gears.
 
#11 ·
Awesome info, thanks. I am at sea level in the Florida Keys. I plan to install a Neo 181 soon. Then fourth should have the power to push the 16 32. Should I keep the stock 1 to .92 fourth gear or go with 1 to 1? If the 181 can push it, the .92 should offer more top end. I drafted a semi and stock fourth was amazing, easy 69mph gps verified. It felt very responsive like third. So I think .92 might work with more displacement. There is no replacement for displacement!! I want the fastest Monkey in the USA.
 
#12 ·
Just FYI, I've tried 17/32 and 16/32 on my NEO 181 and I finally settled on 15/32. 15/32 would get me to 84 or 86 mph dependent on the direction I was traveling. 16/32 or 17/32 was slower as the bike didn't have enough ass to push the tall gearing in 4th gear.
 
#13 ·
I was waiting for you to chime in. I am following a few of you Grom speedsters and our one Grom guy that bought a Monkey. There’s only one guy missing. I’ve talked to him on the phone. Who could it be? Oh, and I pulled our troll out on my first thread. He went all in.

Anyway, thanks a million for the sprocket info. What do you think the yuminashi 1 to 1 fourth would do to the equation? It might let the 181 spool up.

I am laying out an eighth of a mile drag strip.
 
#14 ·
It may help by closing the gap between 3 and 4th. I'm sure if I had a 5-speed the 16t would've been fine. The problem is the gap between 3 and 4 are so damn big you lose the rpm needed to keep pulling when shifting into 4th. 15t gave me enough pull to get out of the bottom of the gap and into the upper rpms to start pulling again.
 
#15 ·
Very interesting, firsthand experience. I looked at the 5 speed. The final ratio is .92, same as stock. You are spot on, the only thing I saw was closer ratios bringing the rpm up to the .92. So...what should I do? Get the 5 speed? Use the yuminashi 1 to 1? The 1 to 1 might give me enough. I just want to terrorize Key West!!
 
#19 ·
the 1:1 is the Kitaco 5-speed, you will need to also order their speed sensor. If you do the Takegawa 5-speed you can keep your current sensor.
 
#27 ·
DIY drag strip day. Did 2 runs in opposing directions, hard launch, full tuck, never hit fourth, a tenth of a second difference in the runs. 16f 32r, no other go fast mods. Streetable top speed is my goal, that’s 60mph so far. Stock sprockets was 52 mph. I know she’s not set up for dragging, but it’s fun. Very fun.
 

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#28 ·
I'd be curious to see those same runs with the stock sprockets, 16x32 is very very long, even with a BBK.

And if you want speed I'd look at the Koso 4 valve setup. The Neo and Takegawa 4 valve BBK are very nice, both have their advantages but out of the box the Koso is just faster.
 
#29 ·
Thank you for the info, yep, I set up the sprockets for top speed n decided to drag. I just want some baseline. I am going to get half mile and mile times n speeds. That’s where I should see my improvements after the 181. I like the neo because I don’t want to have to adjust valves. Originally, I wanted a 4v, of course. Keep the posts coming!!! I appreciate all the advice.
 
#33 ·
Dribbly, you made a few very intelligent posts on some of my other threads. Do not drop back into your troll mode. This is a motorsport thread, we want to go fast. Since the dawn of time speed has been valued. Effort equals results. Any duck can make silly internet posts. Show up at Barber and introduce yourself in person.
 
#37 ·
This was today, I'm 162lb and my daughter was riding in front of me with her feet on the air box covers, she's probably 58lb. 14t sprocket, cheap Ohlins knock off's in the rear, Yoshimura Race RS3, stock intake/tires, etc. and we're above 5,000ft elevation as seen. The monkey has 281 miles on it.

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#38 ·
This was today, I'm 162lb and my daughter was riding in front of me with her feet on the air box covers, she's probably 58lb. 14t sprocket, cheap Ohlins knock off's in the rear, Yoshimura Race RS3, stock intake/tires, etc. and we're above 5,000ft elevation as seen. The monkey has 281 miles on it.

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Awesome data, thank you!! Dropping a tooth on the front sprocket seems to be good at 5000’. I plan on going back to stock 15t and see if it helps me. I am at 16f 32r, apparently it may be a little extreme. Thanks again. Monkey on!!! Send pics!!
 

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#39 · (Edited)
The Neo is great, but you should go for a 4 valve head if you want serious speed. In my opinion, it will probably be more reliable since your working with smaller valves which don't bash the valve seats as hard or float as easy. The cam doesn't have to be as aggressive either because you're getting more airflow thru the extra valves.
 
#40 ·
I agree on the 4 valve (Koso that is), why go with the Neo to then have it ported and add more go fast parts when you can get that kind of power right out of the box with the Koso kit? And much more if you port it.
Plus at 24hp with the Neo you'll need all the supporting mods anyway so price wise it really won't make much of a difference.
 
#41 ·
Incredible info!! Thanks. I have to reconsider my love affair with the neo. It just seems simple and well engineered. I think I have read posts from guys that do not ride their 4v Groms as much because of the valve adjustment requirements. Also, I am pretty sure the Hardracing guys talk about the high performance vs maintenance trade offs with a 4v head. I just want to ride hard n fast.
 

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#45 ·
Just so you're aware, I haven't changed my signature or posted in my build yet, but I no longer have the NEO on my bike. As much as I did love it, I needed something more. Currently tuning a Koso 4v with all the trick stuff done to it, sitting on top of a Drowsports 181 piston and cylinder.

Again, I was tossed between 2v or 4v from the start but ended up settling on the 2v because I only intended on the Grom being a commuter. Well the bike has evolved into so much more and the 2v was no longer doing what I wanted it to do. Food for thought :encouragement:
 
#52 ·
Hit 65.9MPH on a slight downhill yesterday with the Kenda Big Blocks on if anyone was wondering how they affect speed. If I didn't have a head wind I may have gotten another mph or two.
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