Twin cam A motor B motor question... : V-Twin Forum: Harley Davidson Forums

Mother · 11-20-2008, 06:17 PM

Is the 'B' motor at a disadvantage compared to the 'A' when it comes to making horsepower????

mungo · 11-20-2008, 06:21 PM

Disadvantage? Not by much. The output of a B motor is encumbered by the counter balance mechanism simply because it takes energy from the engine to put the counter balance mechanism in motion and keep it there.

I think the difference in output is maybe one horsepower and one foot pound of torque?

AZFXSTB · 11-20-2008, 11:44 PM

Quote:

Originally Posted by mungo

Disadvantage? Not by much. The output of a B motor is encumbered by the counter balance mechanism simply because it takes energy from the engine to put the counter balance mechanism in motion and keep it there.

I think the difference in output is maybe one horsepower and one foot pound of torque?

And everyone "says" you shouldn't spin a B motor past 6200 rpm

TheNowhereman · 11-21-2008, 02:00 AM

Having ten pounds of weight flying around in an engine to balance it just aint right.
Better to mechanically balance it the way your supposed to.
If I had to own a twinkie, it would be an A motor and I would throw some bucks down to re balance after I opened the exhaust, re-cam'd with Red Shift bump sticks, went to a gear drive, etc.
Oh yeah, I would never run a street V twin pump past 5500 rpm anyway; it doesn't make sense since your not making anything of importance in the way of HP or torque.
A full race motor meant for drag racing, sure but it wouldn't be useable for street operation nor nice to ride.

splitting_lanes · 11-21-2008, 02:26 PM

From what I've read, it's not possible to balance a v-twin that's separated by less than 65 degrees. Thus, our beloved 45 degree v-twin is and cannot be balanced, at least not completely.

GPO03FatBoy · 11-22-2008, 08:25 AM

All I know is that I've got a nicely balanced B motor (that I sripped the balancers out of), that will spin smoothly to 7,000 but is very streetable. I cruise back and forth to work on it in city traffic at 25-35mph, and it will run 11.5 in the quarter, in a fatboy. It's not a tech monster - just a 98 with a Timken conversion and a balanced/pinned crank. While you may need more loctite with a stripped/balanced B motor, it shouldn't be a bone shaker.

But as to whether someone should go with B or an "A", I guess it depends on what you have, what you are going to do with it, and what cam you are going to install (read - how high you want to spin it)...

skyhook · 11-23-2008, 11:44 PM

to me it's what bike you like best...a or b can be very quck...it's only money!

FLSTCI124" · 01-05-2009, 11:35 PM

Who did your re-balance once you stripped out your counter-balance system? I'm in the process of tearing down my 124" B nightmare build and am going to have Darkhorse do all the Crankwork.

Buddy Seat · 01-06-2009, 01:27 AM

Quote:

Originally Posted by TheNowhereman

Having ten pounds of weight flying around in an engine to balance it just aint right.
Better to mechanically balance it the way your supposed to.
If I had to own a twinkie, it would be an A motor and I would throw some bucks down to re balance after I opened the exhaust, re-cam'd with Red Shift bump sticks, went to a gear drive, etc.
Oh yeah, I would never run a street V twin pump past 5500 rpm anyway; it doesn't make sense since your not making anything of importance in the way of HP or torque.
A full race motor meant for drag racing, sure but it wouldn't be useable for street operation nor nice to ride.

'cept I never intend to own a twinkee...

EVOs...
& old Hdz 4 me