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Discussion Starter · #1 ·
The forum has gain alot good "Motor Men" , so i pose this question .
Advantages and disanvantages of either going big bore or stroker to get above 700cc for the xx.
I tried this once on another forum to do a 470cc on a TRX450r and never got a good answer.
I can't afford both.
Stroker is with stock spec piston and big bore is with stock crank.
Looking for power/torque differances or what would show up an a dyno chart.
I know this is guess work but it would help. :D
 

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A big bore unshrouds the valves for better flow. A stroker crank adds leverage to the crank centerline for torque.
 

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i generally see higher hp gains come from bore size, but having stroke is important as well the longer the power band the faster a bike is. Its generally a combo of both is what works best if you in a perdicament where $$ is the issue choose what needs replacing if both crank and cylinder are good i would say do big bore first then stroke later if crank needs replacing take care of that.
 

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Pretty much everyone on this site has rode a fairly wide range of bicycles I hope. Ever get on a bicycle that the pedals were fairly close together on the crank(a short crank like on a 12" bicycle). You can pedal it up to speed fairly quickly once it got going but you could only pedal it so fast. You get to a hill and it got really hard to pedal because the pedals were so close together you couldnt get any leverage on the crank. Now get on a bicycle that has a carnk with the pedals further away from each other. Its easy to get started and when you come up to a hill its easy to get leverage on the crank to push it over. Onve you got some speed up though the faster you got the more out of control it felt to really get it going fast. Think of your legs as connecting rods, the longer your legs(connecting rods) were the more controlled it seems at high speeds.
With that being said, for the engine to be as effecient as possible the longer the stroke the longer the connecting rod needs to be(for the most part).
 

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Discussion Starter · #8 ·
Cheers Bo , Now I understand better.
I guess my limiting factor will be the exhaust. I got tested with the Barkers with QC and screen at 96db. The UK limit is 94db.
So it would have to be something like a FMF Q4 or Leo Vince.
 

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Us Pontiac guys stand behind long rod motors ;-)
 

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Pretty much everyone on this site has rode a fairly wide range of bicycles I hope
Ya... if it doesn't have a motor or an ass I'm probably not interested in riding it :lol:
 

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a real good rule of thumb is big bore gives you top end hp, big stroke(longer) gives you bottom end torque.

doesn't always work that way tho. I did a 100 cc overbore on a 300 ex once that became a torque monster but wouldn't hit redline any longer because the head couldnt be opened up enough to flow that amount of air
 

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a real good rule of thumb is big bore gives you top end hp, big stroke(longer) gives you bottom end torque.

doesn't always work that way tho. I did a 100 cc overbore on a 300 ex once that became a torque monster but wouldn't hit redline any longer because the head couldnt be opened up enough to flow that amount of air
:tup:

the balance between bore and stroke needs to be kept close... adding a stroker would have helped pull longer on the head resulting in a longer power band, but Yes, if the head cant flow the cc size then their will be a KILL point...
 

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What's the kill point on the xx head before serious head work needs to be done. Just curious.
 

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well as soon as it gets to the part where i am going to put cam/pisto maybe bore/stroke,bo will be getting a head from me. i want about a 60 hors trail bike.
 
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