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Discussion Starter #1
Just seeing what you guys think the best over-all value is in big bore kits, and what engine mods you might be doing.

So far im looking at Yuminashi light bore kit 150cc since i can use the original head. Most likely also looking at racing progressive double valve spring conversion set as well. And the light bore fuel injector.
Take the head to a local machine shop, and get some port polishing done. (maybe deck the head pending what compression that kit from Yuminashi is?)
Cam, anyone know of any? Havent seen any, but defiantly on the list.
Exhaust, and panel filter.
Some type of ECU box/controller

So what do you guys think? Any other inexpensive things to be done that could better performance for a decent value?
 

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Yuminashi has a cam and I have seen larger higher flowing injectors. From what I understand, with the larger injector the stock ECU map is fine up to 150cc. So far I think your listed combo sounds great. I am guessing a significant performance increase with like stock reliability and longevity. The only thing holding me back from similar mods is the exhaust. I really want a quiet exhaust.
 

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The only thing holding me back from similar mods is the exhaust. I really want a quiet exhaust.
Run a long muffler and a silencer.. Should be fairly quiet

Im going with a fuel controller and an exhaust first, maybe build a setup if these prices don't get more realistic for what I want.. pull the head, ill port it, have it shaved .010 or something minor, modify the throttle body or depending on its size upgrade to a 30mm and if I can take them apart I'll lighten the rocker assembly.. Nothing wild just something to pep up the engine
 

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Im going with a fuel controller and an exhaust first, maybe build a setup if these prices don't get more realistic for what I want.. pull the head, ill port it, have it shaved .010 or something minor, modify the throttle body or depending on its size upgrade to a 30mm and if I can take them apart I'll lighten the rocker assembly.. Nothing wild just something to pep up the engine
After reading more on what yuminashi says, I might be able to get away just letting the ecu compensate but man that would suck to get all that work done and the ecu can't do enough to make up for the port and tb work
 

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If you buy cheap parts your are going to have problems but there are millions of engines out there with big bore kits and lightened valve trains with no problems.
 

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idk. ive big bored a few of these size engines with 0 issues. z50 with 88 kit, z50 with 107. ct70 with 88 and race head. no issues
 

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These engines have a proven track record for reliability even with BBK fitted, unless your going over 150 I think the reliability will be fine.

BBK aren't that expensive if you re sleeve the standard cylinder.
 

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I'm not going that big to be fair as I want it to be pretty practical so, 150cc, fuel controller,big valve head, cam and a bigger throttle body.

Quite happy to line up against you but you'll have to travel over here, I'm scared of flying ;-)
 

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Okay ill bite lol first you think someone is "trying to prove you wrong"? Because they've actually done the opposite of what you're suggesting with no negative effect.. Doesn't sound like much trying, they proved you wrong

So a 150cc big bore, port work and cam is somehow 1500$ and you're engine will blow up but subtracting the bb and adding titanium valves, springs, rockers, balancing and blue print time and WPC is not only going to be cheaper but now live longer than a big bore? Interesting

Also as much as you seem to care about the longevity a bb with rob you of.. You fail to acknowledge that titanium fatigues very fast and WPC is only good for a short time in the real life of a daily used engine

You seem a bit defensive and are trying to basically tell the people who have built these same engines before that their bb won't live (when it seems they do).. Good luck with your "race engine" it sounds like you have a lot of years of bench racing under your belt
 

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I obviously have no idea what I'm talking about. I'll get a hold of you when I need some advice
Right because I posted out of nowhere telling people that their bb engines will blow up, then was set straight that they won't by people who have actually built them, then switched my argument to there being more ways to extract power without adding displacement fallowed by and apples to oranges bench race.. No wait, that was you

I have no problem discussing subjects but from your first post in here it seems you already have a set plan of race engine perfection, the same mindset that's keeping folks in the ruckus scene struggling to break 55 when the handful of heads I've ported and help set up are breaking into the 60s on stock cams and 49cc bottom ends.. We could sit and bench race all day because neither one of us has had our hands on a Grom, I have a solid idea I want to approach with mine and I'm sure you have the same with yours but don't post out of nowhere telling people their big bores will blow up when it's obvious you don't know what'll happen, if you want to start a "here's my replacement for displacement" thread then go for it but don't crap up a thread where people are discussing their ​ideal setups
 

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If you read carefully you will notice that I never told anyone that their engine will blow up. Also, I never crapped on anyone or their dream build. Seems to me that you are the only one that is angry, negative and likes to put people down. I really don't see what you're so upset about.
Beware of big bore kits! Changing the diameter of the piston just a small amount will drastically affect the pressure inside the cylinder by hundreds of pounds. This is why people commonly "blow up" their motors

I even read slow.. Maybe you didn't mean it the way you typed it, maybe I read it the wrong way

Either way it's pointless going back an forth, you posted something I disagreed with so I replied, that's all
 

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So I am thinking that what this forum probably needs is an Engine Builds Section. Where guys can post up what they have done to their engines and the results, whether it is a slower revving bored and stroked monster or a higher revving spinner. El Chorizo, are you listening?

Also, Strokd - I'd be really interested in hearing what you did to a 49cc Ruck to get it into the 60s. Not asking you to give away trade secrets, just in general terms what is required. I was looking at a Ruck but they are too slow. So I looked at a GY6 conversion but that looks like a LOT of work just in parts finding alone. So, what is the hot ticket with 49ccs?
 

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Regardless. A $300 big bore (150) cyl and piston is in no way 1/2 the price of the grom. I wish a grom was $600. I'd buy 10 of them. Not trying to "prove anybody wrong", but have you had big bore kits on these style of engines? Some engines do well with bores, some don't. Ruckus is one that does not. They blow head gaskets all the time. Kinda stinks. But because the ruckus does real well with head mods and not the bore, that does not mean all engines are terrible worth the bore so the only thing we can do is head work.

I personally want a 180 and the "race head" and am excited to pay $800 for it. Can't wait. 180cc and a good flowing head will be a ton of power, and with how strong this bottom end is, it will be completely reliable
 

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Also, Strokd - I'd be really interested in hearing what you did to a 49cc Ruck to get it into the 60s. Not asking you to give away trade secrets, just in general terms what is required. I was looking at a Ruck but they are too slow. So I looked at a GY6 conversion but that looks like a LOT of work just in parts finding alone. So, what is the hot ticket with 49ccs?
If you're over 180lbs a 49r is just too slow, you basically ride for the joy of riding, you can get decent mph but the way you'll have to set up the tranny it's going to have crap bottom end and get mid 50s, Going gy6 isn't a difficult swap but it can be pricey if you aren't the DIY type and the engines tend to have really stupid things go wrong with them so you have to enjoy working on them

As far as my "trade secrets" I spent time a lot of time reading other people's experiences, tips from people who port heads and a lot of trial and error but once I found out that honda built the head/cam combo to work at nearly 100% efficiency I decided not to necessarily open up the head but rather reshape the port around the valve stem and smooth them out, this is when we started seeing the best results, then we gave it an aggressive shave to bring the cr up to high 12s, with that and modifying the stock carb for better flow along with tall gearing for it to stretch its leg we were getting impressive results, so much that its become a joke of "Florida air" aiding in our speeds

My plan is to do the same with the Grom and incorporate things I've learn from rucks into these heads as well as tearing down the throttle body and modding it for smoother flow
 
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