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Discussion Starter #1
I tried doing a search and could not find what I was looking for. Not sure if I was searching the wrong thing...

I'm wondering if anyone has any insight/experience/etc. on a bored out throttle body versus a bigger throttle body (like the Koso one) versus even a bored out bigger throttle body.

The reason I'm asking is that I'm currently putting together a budget for my build and getting everything planned out. Depending on if there is a significant difference, this could effect when I swap/bore out the throttle body. If the larger throttle body is significantly better than a bored out throttle body, then I was going to grab that and the Chimera S intake for bigger throttle bodies and skip an intake for the stock. If the bored out stock throttle body is about the same as a bigger throttle body, then I'll just grab the MNNTBX intake. I really like that the MNNTBX Intake has a bracket to secure everything to the frame.

Not sure how the bored out throttle body vs the bigger throttle body would effect the torque at various RPMs either.
 

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Stock bored throttle body is still a stock throttle body,,, Taper bore is only going to increase incoming velocity does not make the throttle body itself bigger.

Your build is going to decide what throttle body is needed, if it does require bigger then yes Bore that sucker.

Are you building a low to mid range power set up or a top end speedster?

If your staying stock bore with stock valves... Stick with Stock throttle body bored or not.
 

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Discussion Starter #3
Stock bored throttle body is still a stock throttle body,,, Taper bore is only going to increase incoming velocity does not make the throttle body itself bigger.

Your build is going to decide what throttle body is needed, if it does require bigger then yes Bore that sucker it.

Are you building a low to mid range power set up or a top end speedster?

If your staying stock bore with stock valves... Stick with Stock throttle body bored or not.
Oh. That makes a big difference, I guess I should have researched that part out a bit more. I thought bored out throttle body was they were boring it out and putting a bigger butterfly plate in.

For my end goal... I was thinking of something with increased top speed and more mid-range power. I was looking at the bore kits and didn't want to go anything too over the top. My goal was the 164 maybe the 170 cc kits? Was considering hte 146 cc as well.

Would a larger throttle body be good for top end while sacrificing low end? I know the longer intakes will have better low end torque while shorter ones have better top end speed.
 

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I've got a ported NEO181 kit + 33 mm throttle (Honda StreetFire throttle, bored out). Mid-range is good, but it runs out of steam around 9,500-10,000 RPM. Probably wouldn't want to take the 181 over 11,500, anyhow. I sized a Keihin carb. to be 'correct' around 39 mm with a 181 cc single, so you could easily go 37 mm (Koso + GFZ mod) on the throttle if you really wanted to maximize the high-end.

The taper matters more when you're dealing with choked flow, though the geometry of the taper/funnel usually contributes less than 3% to the overall efficiency of the sonic nozzle you create. This is getting into fluid dynamics and probably more in-depth than most owners of a 9 hp bike are willing to look into.
 

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A stock bored out throttle body maxes out at 26mm. I think for stock bore setups it's fine. If you start going big bore, I would go with the readily available Koso 34mm and velocity port it. Yuminashi has what looks like a stock Keihin throttle body that's 28mm and looks to be velocity ported already. seems like a middle ground that has my interest.
 

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budget build

if you are staying stock bore 125cc, do yourself a favor and take the stock throttle body and inlet tube and plastic spacer and bore out the throttle body, polish the butterfly valve, open up the inlet tube and plastic and gasket to 26-27mm and also open up the stock head to 26-27mm to port match the intake to the new size inlet tube.

take the stock head and port the intake side and lap the intake valve and on the exhaust port of the head port/polish the side and also do a port match to the exhaust system you are using.

For cam get one of T-cam that most people are using.

The valve springs do yourself a favor and use a duel spring setup.

for F/I use a PC-150 and you will be good to go.

on the cam chain system, get the Koso cam chain sprocket setup/arm and GFZ manual cam chain tensioner unit that he makes.

ECU either flash your stock ECU or get Aracer, do not use a piggy back system such as PCV, etc or even the PC3 you are wasting your money.

modify your stock airbox and use a BMC washable filter.

stock cylinder/piston/crank should be ok.

add a oil cooler and also a CCV system to reduce internal crank case pressure and heat "CCV" via a oil catch can.

Good luck.
 

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Discussion Starter #7
yeah all that makes sense. My big thing was if I get say a Dingerbuilt intake, I don’t really want to have to sell it a year later because I’ve gone to a bigger throttle body.

Figured I’d get my plans ironed out. Do it once kind of thing.

At this point if I do stay with just a taper bored stock throttle body, I’m waffling between the short and mid dinger builts.
 

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Where can you get a throttle body bored out at?
 

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I would love to have a stock throttle body bored like the ones on Cameron Jones website. They look perfect. I guess they were CNC machined?
 
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