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Discussion Starter #1 (Edited)
First of all, I'm not that good with engines... I plan to do this with the help of my friend who's a mechanic. Or maybe even take it to my buddie's mechanic shop. So I've been reading a few threads on the bbk's and was wondering which one fits my "needs". Well actually do they make a "plug and play" kit? Like where I wouldn't have to touch the bottom end? So basically

I don't want to touch the bottom end... do they make a bbk that works with the oem crank? I heard people swap those out... idk why.

Would I be able to run the OEM head? WTF is a "port and polish"? Would I need to touch the head?

I only have access to 91 gas... do the kits need higher octane fuel?

I see everyone says to get the 4V BBK... Ik there's two more valves, but what's the difference?

So what are my options here? Should I go 170, 186, etc. 4V or 2V? What brand? Lmk, thanks!
 

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There's a ton of different options you can do, all at varying price points and levels of difficulty. I would consider the following:
1) Do you have a certain power goal in mind?
2) Whats your budget? This will most likely determine which route you will go.
3) The OEM crank does not handle big bore kits well. I personally would only run a High Compression Piston or Takegawa 143 BBK on a stock crankshaft. Anything above that, and I would recommend that you get a forged crankshaft.
4) There is a lot of power to be gained from head work. You can use the OEM head, however it is restrictive, getting your head ported (bored out to certain specs to improve flow) and polished will unlock the potential of all your other mods.
5) 91 will work for higher compression bbks.
6) 4 valve heads have 2 more valves that 2 valve heads which translates to more flow which means more power.

Things you'll need for just about every big bore kit:
1) Fuel Controller with Wideband O2 Sensor
2) Injector
3) Intake
4) Exhaust
5) Cam
6) Clutch Plate
7) Clutch Springs
8) High Flow Oil Pump
9) Cam Chain Tensioner

If going larger than the 143, I would suggest the following:
10) Forged Crankshaft
11) 4th bearing support
12) Crankcase Ventilation
13) Manual Cam Chain Tensioner Adjuster
14) Upgraded Head Studs
15) 5 Speed Transmission

It gets expensive really fast. If you're not willing to drop a lot of money upfront, I would suggest starting with a Tuner w/Wideband O2, Exhaust, Intake, Cam. Those are all pretty much bolt on and can probably get you to 11 or 12 hp. If that doesn't satisfy you, get a HC Piston or 143 BBK. along with a cooling solution which should get you 14ish + horsepower. Maybe 16 with some solid head work.

Some people on here may agree with me, some may disagree. At the end of the day this is your bike, build it how you want, and most importantly have fun.

If you have any questions feel free to ask, I am sure all of us are willing to help get you sorted out.
 

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Since you're familiar with DHM, just get their drop in 186 kit. comes with most of the stuff you will need.
 

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Lots of old post on here, do a research. Reading, using your google search will make you smart or at lease look smart.

OEM engine are 2v some BBK kits are 4V

Do a google seach on how to hot rod a engine and you will find most of your answer.

main things to remember, timing, gearing, compression, cooling, crank case pressure, air/fuel flow into engine and combustion out.


Good Luck
 

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Discussion Starter #5
There's a ton of different options you can do, all at varying price points and levels of difficulty. I would consider the following:
1) Do you have a certain power goal in mind?
2) Whats your budget? This will most likely determine which route you will go.
3) The OEM crank does not handle big bore kits well. I personally would only run a High Compression Piston or Takegawa 143 BBK on a stock crankshaft. Anything above that, and I would recommend that you get a forged crankshaft.
4) There is a lot of power to be gained from head work. You can use the OEM head, however it is restrictive, getting your head ported (bored out to certain specs to improve flow) and polished will unlock the potential of all your other mods.
5) 91 will work for higher compression bbks.
6) 4 valve heads have 2 more valves that 2 valve heads which translates to more flow which means more power.

Things you'll need for just about every big bore kit:
1) Fuel Controller with Wideband O2 Sensor
2) Injector
3) Intake
4) Exhaust
5) Cam
6) Clutch Plate
7) Clutch Springs
8) High Flow Oil Pump
9) Cam Chain Tensioner

If going larger than the 143, I would suggest the following:
10) Forged Crankshaft
11) 4th bearing support
12) Crankcase Ventilation
13) Manual Cam Chain Tensioner Adjuster
14) Upgraded Head Studs
15) 5 Speed Transmission

It gets expensive really fast. If you're not willing to drop a lot of money upfront, I would suggest starting with a Tuner w/Wideband O2, Exhaust, Intake, Cam. Those are all pretty much bolt on and can probably get you to 11 or 12 hp. If that doesn't satisfy you, get a HC Piston or 143 BBK. along with a cooling solution which should get you 14ish + horsepower. Maybe 16 with some solid head work.

Some people on here may agree with me, some may disagree. At the end of the day this is your bike, build it how you want, and most importantly have fun.

If you have any questions feel free to ask, I am sure all of us are willing to help get you sorted out.
1.) I just want something that can hit 70 haha...
2.) About $500
3.) So I wouldn't be able to run a 170cc 4V with the stock crank? Or even a 2V? (wouldn't see how that would affect it)
4.) Who works on the grom's head?
5.) I told you, I know nothing. How can you tell which one has a higher compression piston?
6.) What would you say is better for me?

I already have a flashed ECU, new sprockets (14/37), bassani pipe (coming soon), I did the clutch plates with the stiffer springs, I put an MNNTHBX MTake (air intake)... and I think that's about it.

Now thinking about it, I think ima just go with a cam and a reflash through DHM... But I heard the cam makes you lose that "quickness" (groms were never quick). It just has a pull... well that's what I heard at least.
 

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Discussion Starter #6
Since you're familiar with DHM, just get their drop in 186 kit. comes with most of the stuff you will need.
Would I still need to change the crank? I don't want to split the cases bc of the big bore kit. Like I don't even want to touch the bottom end.
 

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Discussion Starter #7
Lots of old post on here, do a research. Reading, using your google search will make you smart or at lease look smart.

OEM engine are 2v some BBK kits are 4V

Do a google seach on how to hot rod a engine and you will find most of your answer.

main things to remember, timing, gearing, compression, cooling, crank case pressure, air/fuel flow into engine and combustion out.


Good Luck
Yeah I was going to put an oil cooler... now thinking about it I think ima just throw in a cam and call it a day!
 

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1.) I just want something that can hit 70 haha...
2.) About $500
3.) So I wouldn't be able to run a 170cc 4V with the stock crank? Or even a 2V? (wouldn't see how that would affect it)
4.) Who works on the grom's head?
5.) I told you, I know nothing. How can you tell which one has a higher compression piston?
6.) What would you say is better for me?

I already have a flashed ECU, new sprockets (14/37), bassani pipe (coming soon), I did the clutch plates with the stiffer springs, I put an MNNTHBX MTake (air intake)... and I think that's about it.

Now thinking about it, I think ima just go with a cam and a reflash through DHM... But I heard the cam makes you lose that "quickness" (groms were never quick). It just has a pull... well that's what I heard at least.
1) 70 is an easy goal to get to for relatively cheap.
3) You can run whatever you want with a stock crank. It is small and made from cast and thus will not last long. I personally wouldnt go over a 143 on a stock crank, others may disagree.
4) Many companies port heads, or you can just pick up a finbro head.
5) Based on specs of the piston, Jug, Head set up.
6) With a $500 budget, do this kit: Honda Grom Stage 3 | DHM Piston, ECU Reflash, and TB Camshaft it will include flash, high comp piston, tb cam, and make sure you buy it with a new cylinder, don't reuse your old one. This will run you $389.00 plus tax and shipping if applicable. This will net you the largest gain keeping below budget and should get you over 70 mph on 14/34 gearing, don't use the 37, it will will take too much off your top speed. You may even consider going back to 15/34 gearing with this kit.

Brian at Ren Motorwerks also has a great set up that I've heard has gotten to about 16hp. RMW SUPER 125 – Ren Motowerks, but you will need a tuner with wideband o2 abilities and this will exceed your budget.

Do the DHM Stage 3 kit it will almost double your bikes power and for the price, it's definitely worth it.
 

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Discussion Starter #9
1) 70 is an easy goal to get to for relatively cheap.
3) You can run whatever you want with a stock crank. It is small and made from cast and thus will not last long. I personally wouldnt go over a 143 on a stock crank, others may disagree.
4) Many companies port heads, or you can just pick up a finbro head.
5) Based on specs of the piston, Jug, Head set up.
6) With a $500 budget, do this kit: Honda Grom Stage 3 | DHM Piston, ECU Reflash, and TB Camshaft it will include flash, high comp piston, tb cam, and make sure you buy it with a new cylinder, don't reuse your old one. This will run you $389.00 plus tax and shipping if applicable. This will net you the largest gain keeping below budget and should get you over 70 mph on 14/34 gearing, don't use the 37, it will will take too much off your top speed. You may even consider going back to 15/34 gearing with this kit.

Brian at Ren Motorwerks also has a great set up that I've heard has gotten to about 16hp. RMW SUPER 125 – Ren Motowerks, but you will need a tuner with wideband o2 abilities and this will exceed your budget.

Do the DHM Stage 3 kit it will almost double your bikes power and for the price, it's definitely worth it.
so is that considered a big bore kit or is it still at 125cc? Also can the stock crank handle it?
Would I need to work on the head or is it good to go?
Why would I need a new cylinder? Just wondering haha
WOW! $340 since I am already a customer!
Also I have an OG Grom so ima have to contact David and see what he can do to make it work with my 2014. I'm sure he can make something happen
 

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so is that considered a big bore kit or is it still at 125cc? Also can the stock crank handle it?
Would I need to work on the head or is it good to go?
Why would I need a new cylinder? Just wondering haha
WOW! $340 since I am already a customer!
Also I have an OG Grom so ima have to contact David and see what he can do to make it work with my 2014. I'm sure he can make something happen
It is the same diameter as the stock piston, but you can see from the pictures that the piston is taller which fills more space in the cylinder, creating more compression. I believe that setup is 12.2:1 or 12:4:1 compression (don''t quote me on that) compared to the stock piston which is 9.5:1.

A cylinder typically comes with honed/textured walls, this allows the piston/ rings to essentially mate surfaces while breaking in. You either typically hone an old cylinder when installing a new piston, or in our case where cylinders are cheap, just replace them. Doing this with proper break in procedures will result in maximum performance. Don't forget to gap & clock your new rings on the piston during installation.

The stock crank shaft will be fine.
 

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Discussion Starter #11
It is the same diameter as the stock piston, but you can see from the pictures that the piston is taller which fills more space in the cylinder, creating more compression. I believe that setup is 12.2:1 or 12:4:1 compression (don''t quote me on that) compared to the stock piston which is 9.5:1.

A cylinder typically comes with honed/textured walls, this allows the piston/ rings to essentially mate surfaces while breaking in. You either typically hone an old cylinder when installing a new piston, or in our case where cylinders are cheap, just replace them. Doing this with proper break in procedures will result in maximum performance. Don't forget to gap & clock your new rings on the piston during installation.

The stock crank shaft will be fine.
yeah this seems like a wayyy better option... I'm going to look into it! Thanks!
 

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been running a kitaco 164cc "light" big bore kit for 4000 mi on a stock crank for a few years, never an issue, and it gets beat on. Biggest thing to make power above the 7k rpm mark was a bigger valved head (27/23 monkeyfather head) so it could breath (paired with a mild kitaco type 2 cam as well) all ran by a finbro ecu. Got a big ole oil cooler on her n never had a problem. But this is a setup of the past.

If i had to do it over again. Hmm. a Kitaco 164cc neo full kit is enticing. But really, id probably go with a high comp stock bore piston, freer flowing head, mild kitaco type 2 style cam, reflashed stock ecu and call it a day. MAYBE a Kitaco side cover, but honestly the extra rotating mass of the oil spinner is a nice thing to have down low. (I have considered going back to a full one vs the turned down one i have)
 

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.... But really, id probably go with a high comp stock bore piston, freer flowing head, mild kitaco type 2 style cam, reflashed stock ecu and call it a day. MAYBE a Kitaco side cover, but honestly the extra rotating mass of the oil spinner is a nice thing to have down low. (I have considered going back to a full one vs the turned down one i have)
This is exactly what I'm trying to get info on. Any idea what this setup would do torque wise? Also with the freer flowing head would you stick with the stock valve size or get larger valves?
 

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This is exactly what I'm trying to get info on. Any idea what this setup would do torque wise? Also with the freer flowing head would you stick with the stock valve size or get larger valves?
From what I've seen and read, you get the most gains in the head porting vs doing oversize valves. Yes the oversize valves will help flow more, but good porting is where the real gains are. Stock bore high compression doesn't make much more peak TQ vs a standard stock bore piston, it just makes the TQ a bit sooner and will hold it for longer before dropping off. So you really need the revs to make the HP.
 

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This is exactly what I'm trying to get info on. Any idea what this setup would do torque wise? Also with the freer flowing head would you stick with the stock valve size or get larger valves?
Watch out for aftermarket cams... especially the tb. You will lose low rpm torque in order to gain high rpm horsepower. If you scream around wide open throttle at redline all the time, then you'll want a cam. But if you don't, you won't and will need to do other mods in order to try to compensate.


Performance addiction can be an expensive rabbit hole to go down when trying to make a Grom into something else that it isn't. Once you do, there is no such thing as "enough". You will always end up wanting more.

If you want a faster bike, it's better to simply buy a faster bike. ;)
 

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Things you'll need for just about every big bore kit:
1) Fuel Controller with Wideband O2 Sensor
2) Injector
3) Intake
4) Exhaust
5) Cam
6) Clutch Plate
7) Clutch Springs
8) High Flow Oil Pump
9) Cam Chain Tensioner

If going larger than the 143, I would suggest the following:
10) Forged Crankshaft
11) 4th bearing support
12) Crankcase Ventilation
13) Manual Cam Chain Tensioner Adjuster
14) Upgraded Head Studs
15) 5 Speed Transmission
I would say that 3, 6, 8, and 9 are 'wants' rather than 'needs'. 2 and 5 are often included in the BBK, anyhow. If you go larger than 143, the 181 NEO kit is a quick, easy, reliable solution.

10/11/12 are good ideas (and the NEO kit includes the crank). 13/14 are unnecessary. The 5-speed has nothing to do with the BBK... but it should be standard from the factory.

You will probably want an oil cooler by the time Summer arrives.
 
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