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Big bore means better milage.

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I've just installed a Lukes Racing 434/5 BB kit to my 05 SM conversion and was very happily suprised that I picked up another 5 mpg.

I'm running 15/39 gearing, FCR, hotcams and yosh exhaust.

Having put 500 miles on since the big bore it seams I'm now getting 95 miles on a tank before reserve happens. This is up from a consistant 85 that I was getting before. An unexpected benefit.

If anyone is interested I got super fast service from Luke for a total cost of not much more than $400.

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Did you do more mods at the time? If not, how much difference did just the BB make?

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I already had the pipe,FCR and cams.

I'd estimate the BB gave me as much again as the previous mods.

Part of doing the big bore is that you use a smaller main jet, a 155 n my case.

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Someone care to explain this??? :thumbsup:

The bike makes more power but he is not using all of it right now. An engine will run more effeciently at 60% max than one at 80% max if producing the same amount of power.

In other words, he's not having to twist his wrist as much right now as he was before.

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the BB makes more power in the bottom end which lets him lug a bigger gear (lower ratio) at a lower RPM...... less RPM = more gas mileage since each additional intake stroke requires another charge of fuel... as he stated a BB also pulls on the carb jets harder which allows you to run a smaller main jet... this gives you a better fuel/air mix due to the harder pull and faster air velocities in the intake... It all adds up to extra woohoo! :thumbsup: Andrew

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Thats going to be my angle " honey I need a BB kit in order to get better fuel economy" :thumbsup:

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More MPG is fine but what I would really like to know is... how are wheelies with the 434 and the 15X39??? :thumbsup:

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WOW! This is exactly what I am getting ready to do to mine (see the "jump ship?" thread). Already have the RS3/FCR/3x3. Happy for the most part with the power, but not with interstate rpm. How much did the 39t reduce rpms around 70mph? I was actually looking at doing the 38t but knew the motor as is would lose quite a bit of punch, hence the need for big bore and cams. Basically I'd like it to pull as hard as it does now but without the extra revs on the interstate. Would you say your current setup is what I'm after? Will it still do roll-on wheelies in 2nd & 3rd (no clutching it)?

Thanx!!!

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...... How much did the 39t reduce rpms around 70mph? I was actually looking at doing the 38t but knew the motor as is would lose quite a bit of punch, hence the need for big bore and cams.... (no clutching it)?

Thanx!!!

38/41 = .927 or about 7% less rpm

both examples would need an equal % HP increase for previous performance

39/41 = .951 or about 5% less rpm

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For those asking about wheelie power and grunt.....I went from 15/41 and non o ring chain to 15/39 and x ring chain and lost alot of umph.

This prompted me to go for the BB. I got the power back and then some...70 to 90mph passing power especially, cruising at 75 to 80 is effortless.

I'm no wheelie fiend but I do have to keep my weight more forward to stop the front from lifting.

My rough estimate is that the BB gets as much performance gain as the FCR, cams and pipe. However you'd only get the full gain if you already have the FCR and pipe.

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.

I'm no wheelie fiend but I do have to keep my weight more forward to stop the front from lifting.

And in what gears would that be? I'd guess most likely 1st and 2nd, but what about 3rd with your 15X39? Does it want to lift in 3rd with power only?

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Ahhh...this is really sweet! Sounds like I'm headed in the right direction with my mods! Might have to do it before the end of the season instead of having it be a winter project as planned...

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My rough estimate is that the BB gets as much performance gain as the FCR, cams and pipe. However you'd only get the full gain if you already have the FCR and pipe.

What compression ratio where you running previously (stock S?) , and what are you running with the BB kit? I think they offer two, the highest one seems a bit unpractical (~13.5) Also, what octane fuel does it like?

It makes sense to me, it's a bit of work, but sure seems like the best performance mod for 400. anyone could do.

"There is no substitute for cubic inches"

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It's been a long time since I had a stock S but I think it has a 11 point something cr.

The JE piston I have in the BB kit is a 12 point something cr and runs fine on super gas.

If you had to run on regular just put a stock S gasket under the jug and you get the lower cr.

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