Factory 107" vs factory 114"

[Thermodyne]

The difference is more than just the 7 cubic inches.  The longer stroke on the 114 gives it an advantage over the 107.  More torque down low where the motors live.

[ziggy24]

I'm going to go against the grain here. If I was looking to make an around town hot rodded bobber, I would go for the shorter stroked engine and bump it up to 124". It will wind up faster off the lights and your rings will love the slower piston speeds.

Piston is speed difference is negligible between the two. It's a whopping 1/8 of an inch difference.

107"  3.937 bore, 4.375 stroke

114"  4.016 bore, 4.500 stroke

107 @ 5000 rpm =3646 ft per min

114 @ 5000 rpm =3750 per min

[VernDiesel]

I hear you Ziggy. Not a deal breaker either way but still some pros & cons to each. Depends on bike and bike use priorities but as said not a deal breaker either way.  Using your example I see that the 4.5 stroke has the same piston speed at 6,800 as the 4.375 has at 7k. But even at the same piston speed the 4.5 would put more side load on the piston and ring seal. Ring seal and a higher average horsepower from shift point to recovery means more to me than the torque advantage of the 4 ci between the 143ci (4.500 bore to 4.500 stroke) than the 139ci that I hope to build. (4.500 bore to 4.375 stroke) To 99% of riders who's priority would be the below 5k rpm use the 4.5 stroke would be a little better.  I should add this is what I think I know.  Always learning is a good thing.

To me this is some of the kind of tech I like to see discussed or debated in this forum.  Sometimes it seems like little actual tech talk happens on this forum anymore despite its original intent.  Some outstanding engine builders here some sort of newbs and some in between with limited tech discussion between the groups or even between skilled builders for all to benefit from.  That said to my knowledge it remains the best harley tech on the net.

[kd]

I'm going to go against the grain here. If I was looking to make an around town hot rodded bobber, I would go for the shorter stroked engine and bump it up to 124". It will wind up faster off the lights and your rings will love the slower piston speeds.

Piston is speed difference is negligible between the two. It's a whopping 1/8 of an inch difference.

107"  3.937 bore, 4.375 stroke

114"  4.016 bore, 4.500 stroke

107 @ 5000 rpm =3646 ft per min

114 @ 5000 rpm =3750 per min

Throw a gearing change into the mix of options.  Lowering the gear ratio in effect mirrors the way the piston ft per second changes.  It's still a time / distance calc.  Just in a different way.  It never seems to get mentioned then.   

[joes124]

KD,

Your gearing comment is spot on.

[Killer]

Jeez, you guys never change. It's been a year or more since I visited and this is why came back. Many different opinions and it all boils down to... gas,check oil and ride.