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Old 17th March 2009, 19:59   #1
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Default Increasing the cubic capacity of a bike engine - pros & cons?

Hi all,

I'm no newbie as far as driving and riding are concerned, but I am one when you're talking about the mechanics of bikes and cars - that aside, I've got a Honda Unicorn (bought in Feb '08), and for quite some time now, I've been feeling that the bike just doesn't have enough in the pickup, low-end pulling power, and top speed departments. I thought of doing the usual performance enhancing tweaks like adding a performance filter and getting a better exhaust, but then concluded the performance gain and comparitive FE reduction was not worth the expense.

I've been a member of this community for a while now, and I remember reading something about increasing the bore of the engine (i.e. adding more cubic capacity and replacing the piston) on one or more threads. I got owned on the road by a kid riding a Karizma today , and thought of this idea.

Is increasing the bore a good idea on a unicorn? According to what everyone says, the unicorn has the engine with the best build quality....

Has anyone here done it before? Does anyone know where I can get it done, and for how much? Are there any risks/hazards involved? (I hope not...)
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Old 17th March 2009, 20:45   #2
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As long as the engine has a liner and it is thick enough you should be able to increase the bore. Of course, you need to find a matching piston that is the correct height and mates up to your con-rod. Then you need to either upjet or get a bigger carb.

No guarentee that you will retain the smoothness of the original setup because the crankshaft balance is not correct anymore.

Couple of guys on the forum have done it on their Fieros and Zmas. Over to them.
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Old 17th March 2009, 21:04   #3
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Mr.Venugopal has a high level of expertise when it comes to oversizing, porting, polishing and has converted Fieros, Apaches & Unicorns into 200cc firebreathers. He is put up in Zen TVS, B'lore.
For info regarding process involved and costs you could get in touch with Joel(T-bhp id : fieroid) cos he's done 160cc as well as 200cc conversion of his Fiero.
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Old 17th March 2009, 21:35   #4
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welcome to the world of big-bores and upgrades. Been there, done that and still doing!
I've built the fastest unicorn(194.5cc) in the country. The bike clocked a true 128kmph in 400mtrs with our GPS strapped.
I own the fastest Fiero(194cc big bore) in the country @ 144.4kmph in 800mtrs
The fastest RTR(165cc, stock weight) in the country @ 136kmph in 800mtrs
I'm currently working on my drag Fiero(164.7cc) which has already won the Deccan Drag at Hyd and was the quickest 4-stroke of the day.
Hope you got an idea of what the story is like
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Old 18th March 2009, 06:50   #5
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Thanks for your replies, Mpower & dj_666!

Quote:
Originally Posted by fieroid View Post
I've built the fastest unicorn(194.5cc) in the country. The bike clocked a true 128kmph in 400mtrs with our GPS strapped.

....

Hope you got an idea of what the story is like
That's exactly what I'm looking for. I'm not exactly a bike enthusiast by TBHP standards, in the sense of taking an interest in the working or maintenance of the bike, like a lot of people on here do - but I absolutely love riding. I thought of going for a (second hand) RE Bullet initially (it's one of the few stock bikes available in India that suit my frame), but I quickly came to the conclusion it wouldn't suit either my riding style or my cross-the-bridge-when-I-come-to-it style of maintenance. Next I thought about going for a (first hand) Karizma but that's not going to happen any time soon, either.

fieroid, can you please spell out, step-by-step, exactly what I'll need to do to get this done? And if it's not too much trouble, could you please describe the actual specifics of the process in detail? (At the very least it should help or be of interest to others reading this thread) Everything that needs to be done, how long it would take, a ballpark figure of how much it would cost, and where I can do it or rather who can do it for me?

And.... dj_666, could you please let me know how I can get in touch with Mr. Venugopal?
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Old 18th March 2009, 16:29   #6
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Dude, first understand that these mods are not like a service job that anybody can do. The amount of work and efforts involved are far more than what u can imagine. There is a lot of planning and thinking involved.
FYI, I've been working on my Fiero since over 4 yrs now. There is no shortcut to success and performance dude.

@dj_666 - dude, venu does not work or is in no way invloved with Zen TVS. We both are enthusiasts and get our engines/bikes serviced at Zen and thats about it. venu has a different life, so do I.
All our engine works/mods are done by us and sometimes the engine is assembled at Zen, thats about it.
Its really surprising to know that a lot of people have the wrong idea about us.
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Old 18th March 2009, 18:17   #7
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Quote:
Originally Posted by fieroid View Post
Dude, first understand that these mods are not like a service job that anybody can do.
I do.

Quote:
Originally Posted by fieroid View Post
The amount of work and efforts involved are far more than what u can imagine.
That's a bit presumptuous considering the fact that you know very little about me, isn't it?

Quote:
Originally Posted by fieroid View Post
There is a lot of planning and thinking involved.
I know.

Quote:
Originally Posted by fieroid View Post
FYI, I've been working on my Fiero since over 4 yrs now. There is no shortcut to success and performance dude.
Ummm...what exactly are you trying to say here? That I should just give up because I said I'm not into understanding the working of a bike?

fieroid, you haven't replied to a single one of my questions, so I guess you don't want to. Sorry I bothered you. Thanks for deigning to reply.
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Old 19th March 2009, 00:57   #8
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ev1lsyk0 mate, understand something here,

fieroid has answered your question in a very subtle manner, unless you are ready to become the mechanic of your bike, understand and learn the way a bike behaves and works before and after big-bores, and unless you are ready to live with 'N' number of break downs/Trouble shooting, and the amount of TIME and MONEY one needs to spend learning, doing trial and error, R&D on the machine is almost equal to Infinity.

the question is if you have the Patience, Dedication, Money, Time and most importantly the Passion to keep you Driven, just stay with the stock bike, if you really want more performance, with out any of this then sell the Unicorn and buy a Karizma.

Edit:or a used comet should do just fine.

Last edited by rider60 : 19th March 2009 at 00:59.
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Old 19th March 2009, 16:04   #9
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Quote:
Originally Posted by rider60 View Post
ev1lsyk0 mate, understand something here,

fieroid has answered your question in a very subtle manner, unless you are ready to become the mechanic of your bike, understand and learn the way a bike behaves and works before and after big-bores, and unless you are ready to live with 'N' number of break downs/Trouble shooting, and the amount of TIME and MONEY one needs to spend learning, doing trial and error, R&D on the machine is almost equal to Infinity.

the question is if you have the Patience, Dedication, Money, Time and most importantly the Passion to keep you Driven, just stay with the stock bike, if you really want more performance, with out any of this then sell the Unicorn and buy a Karizma.

Edit:or a used comet should do just fine.
This is the point that most or rather all dont get.
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