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Sportster Motorcycle Motor - Top End Discuss Sportster Motorcycle Top End issues. Rockerboxes, Valves, Cylinders, Pistons, Rings, Lift Rods, etc...

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  #91  
Old 12th October 2010
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Zip Zip is offline
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It was interesting reading all the replies of mixed knowledge...

Under Carburetor Environment:

Dual Fire Ignition = Potato - Potato - Potato

Single Fire Ignition = Spud - Spud - Spud
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  #92  
Old 12th October 2010
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First let me say that I love threads such as this -

Those old british bikes, Triumphs, BSAs, Nortons, Matchless, Royal Enfield etc used what we used to call "virtical twins" (500, 650, 750 and 850 displacements). While each cylinder had its own crank throw, it was a 360 degree crank, that is both pistons hit top dead center at the same time although each was on a different part of the cycle, i.e. one pistion was on the intake stroke, the other would be on the power stroke. This smoothed things up somewhat, moreso than the V-Twin, but the british vertical twins could still give you a fair amount of vibration.

Someone had mentioned timing being something of a bear on the radial engines, you might wanna take a look at the Bugatti W-16 engine, you talk about some engineering, the guys at VW must have been on a high when they came up with the W configuration.
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  #93  
Old 12th October 2010
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The radial engine chopper made me wonder if anyone had ever built a sideways mounted wankel powered bike?

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  #94  
Old 10th November 2010
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quick note, both pistons on a triumph move together but fire opposite each other there is minimal vibration because the pistons are counter-balanced by the flywheel to about 80 percent. this does however give a slight rocking motion front to back . harleys are tits but trumpets are the whole body
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  #95  
Old 17th February 2011
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Default Trumpet v Hog

BOOG you have an iron butt or a unique trumpet. I rode triumph trophy and bonnys since '70, finally went hog in '96. My last Bonny was a '78, new ones have a different bottom end; but the old ones had no center bearing in the crank. So at high performance levels, the crank actually FLEXED and the vibration was ridiculous. Still, it was a great bike - best handling and most versatile I ever enjoyed.
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  #96  
Old 28th March 2011
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i love the way my 05 sounds, main reason i bought it. it makes a pretty good chick magnet too.
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  #97  
Old 29th March 2011
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Quote:
Originally Posted by chief View Post
yes the used materials are also inherent to the sound of an engine.
perhaps a real guitar freak will explain this..
Oh dear god.. you really want to get into this?!!!!

Maple (eastern, rock?) vs ash (asian, swamp?) vs mahogany (honduran, african?), rosewood (indian, brazilian, african)...


hahaha..
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  #98  
Old 4th December 2012
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This may or may not have any bearing on the potato potato sound...

I've had my ironhead for many years and over time have run different exhaust (always separate pipes, no crossover or 2 into 1), different carbs, mufflers, cams, magnetos and heads and have noticed, and wondered about, that the exhaust pulse from the front cylinder always seems stronger and steadier.

It's crossed my mind recently that when the rear cylinder fires and its piston starts its downward stroke it accelerates the flywheels and the front piston upwards over the last 45 degrees of its exhaust stroke; in other words some energy from the rear cylinder goes into "power assisting" the front cylinder's exhaust stroke.

On the other hand, when the rear cylinder begins its exhaust stroke, the front cylinder still has 45 degrees of its intake stroke to complete; no "power assist" available for the rear cylinder's exhaust.

After the first 45 degrees of the rear cylinder's exhaust stroke the front piston begins moving up on its compression stroke, and when the valves close the flywheel is putting energy into two kinds of pumping actions and must be slowing down. The fluctuation in crank speed would be more noticeable at idle, maybe helping exaggerate the uneven firing pattern.

I guess what I'm saying is the sound is more PUHtato PUHtato ("PUH" being the front cylinder exhaust event) and that emphasis adds to the sense of uneven cadence.

Whadya think, am I nuts or is this possible?
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  #99  
Old 23rd December 2015
Alexintenn Alexintenn is offline
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HP vs torque

A multi cylinder engine running at 12000 rpm making 40 ft/lb torgue

remember this is engine torque MEASURED at the REAR wheel

is making 12000 X 40 / 5252 = 91 HP

H-D twin engine running at 6000 making 80 Ft/lb Torque

6000 x 80 / 5252 = 91 HP

At the rpm where both engines are making max torque they are applying exactly the same rotational force to the rear wheel.

The amount of torque they make as they get to max rpm is a different story
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  #100  
Old 23rd December 2015
moparnut72 moparnut72 is offline
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Quote:
Originally Posted by ferris oxhide View Post
This may or may not have any bearing on the potato potato sound...

I've had my ironhead for many years and over time have run different exhaust (always separate pipes, no crossover or 2 into 1), different carbs, mufflers, cams, magnetos and heads and have noticed, and wondered about, that the exhaust pulse from the front cylinder always seems stronger and steadier.

It's crossed my mind recently that when the rear cylinder fires and its piston starts its downward stroke it accelerates the flywheels and the front piston upwards over the last 45 degrees of its exhaust stroke; in other words some energy from the rear cylinder goes into "power assisting" the front cylinder's exhaust stroke.

On the other hand, when the rear cylinder begins its exhaust stroke, the front cylinder still has 45 degrees of its intake stroke to complete; no "power assist" available for the rear cylinder's exhaust.

After the first 45 degrees of the rear cylinder's exhaust stroke the front piston begins moving up on its compression stroke, and when the valves close the flywheel is putting energy into two kinds of pumping actions and must be slowing down. The fluctuation in crank speed would be more noticeable at idle, maybe helping exaggerate the uneven firing pattern.

I guess what I'm saying is the sound is more PUHtato PUHtato ("PUH" being the front cylinder exhaust event) and that emphasis adds to the sense of uneven cadence.

Whadya think, am I nuts or is this possible?
I don't think so. I think you are right on the money. I don't remember when this whole scenario occurred but I remember there was a lot discussion about it. It was probably in the late 70's or early 80's that Honda Motors was spending millions to win the AMA Championship. They were doing fine on the road race tracks but were getting their butts handed to them on the flat tracks and other dirt events by the MoCo. Honda spent a lot of money developing a V Twin to beat Harley at it's own game. Their V was more technologically advanced than the HD with more power, rpm, etc yet they were still getting beaten by the Harleys. I think their V Twin was a 90* configuration.

It was explained by one technocrat that the Harley's unique firing events were responsible for success on the dirt. Two "closely" spaced power strokes followed by a longer interval of no power allowed the Harley engine to put a relatively long power interval to the rear wheel giving the bike a long smooth push followed by a period of no power. This allowed the wheel to give the bike a good push and then just as the wheel would start to spin too much starting to lose traction the no power period would time would kick in allowing the tire to regain traction in time for the next power stroke.

This is what I remember reading many years ago. It always made sense to me and seemed very plausible. I was not a HD fan as such at the time but I loved that Harley could win with their "antiquated" engine while Honda tried to buy the championship with cubic dollars. If I remember correctly Honda gave up trying to beat Harley on the dirt and went on to Grad Prix racing where they used their mega-bux to dominate that sport. They quit that too after dominating for a couple of years. I think they now build Gran Prix engines again but are down from the Mercedes and Ferrari.
kk
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