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How Do I go Faster


Post by Detroitblue » Mon May 23, 2005 6:22 am

Now that I am closing in on my initial goals for my(Panhead) 1958 FL Duoglide, I got her running great, got lots of chrome, paint. Now I am starting to ponder about how to improve the performance.

Lets face it, She looks great but its an old bike. I can cruise about town with no worries but out there on the highway I am bringing up the rear and holding on for dear life at 70 mph. The vibration is crazy and I just struggle to keep up.

I realize I need 2nd bike, a road trip machine, something that I can push with confidance. However I would like to hear all the suggestion and options that you have for getting greater performance.

I am not limiting this by practicallity or finances.

For example: I have heard that Accurate makes some great panhead motors like a 93 and 120 cubic inch but I am not sure it will fit in my frame. I have heard talk about shaving the flywheel with a lathe. There are some carboration things I seen done to bikes.


going faster


Post by guest » Wed Jun 01, 2005 11:53 am

If you want to just get a little higher top end for crusing at highway speeds then you might want to just consider changing you gear ratio's.

I am no expert but if you think in terms of a 10 speed bicycle then you can see how this will help you

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Post by Cotten » Wed Jun 01, 2005 1:09 pm

As "Guest" mentioned, you can change the speed at which vibrations occur by swapping sprockets, but... if you've got horrendous vibes, something's wrong!

Inspect your motormounts first, especially the top one.
Then your drivetrain: are your chains stretched unevenly?

Most performance mods to a motor, such as increased compression, rad valve train, lightened flywheels/increased stroke, tend to increase vibration over that of a stock powerplant.
If your stock mill shakes badly all on its own, so bad that you cannot cruise at interstate highway speeds all day long, I would fear most that the flywheels are not true.

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Post by fourthgear » Fri Jun 03, 2005 2:07 pm

Just as cotton says if its not trued and ballanced ( there are different ways of ballancing nowadays) it will vibrate you hands off the grips . The older machines vibrate much more that the newer ones and should not be compared. I don't wish to tell you how fast I've had these old Pans , it scares me to think about what I did when young and dumb. Checking to see if somethings loose is where to start and check drive chains. My 56 had a loose cluch hub and I noticed it vibing and of coure did not check things out right away , untill the cluch hub spun the key and I still got it almost home to a friends garage .

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Post by Cotten » Fri Jun 03, 2005 3:08 pm

I underlined 'true' because ballancing is a fart in the dark on a stock motor.

There's plenty of "ballanced" motors that shake horribly, yet there are vast numbers of overhauled but not re-ballanced motors that cruise smoothly.

Most of what a rider feels are chassis resonances. If the motor alone is at fault, it won't be for long!

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Post by thsmith » Fri Jun 03, 2005 3:12 pm

Interesting discussion on vibration. I have had 2 Pans, 2 Shovels, EVO Softtail, Evo Rubber mount, TC Rubber mount and Softtail.

I never thought any of them vibrated badly, the most noticiable things I remember is the EVO Softtail at 85MPH your feet walked all over the footboards and the TC Softtail at 85MPH buzzes in the handle bars.

I will take vibration or Buzz.

Other than top end speeds I find really no differences except obviously the rubber mounts are smooth but I have no issue riding my EL hard for long periods of time, I consider hard 65 MPH with Sidecar attached but she does not complain and actually seems to like it.


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Post by Cotten » Sat Jun 04, 2005 1:15 am


Although your judgement of "likes it" might seem subjective to most of us, it has its foundation in hard reality.

Most all vintage bike rider's intuitive guesses as to RPM are nearly always higher than it really is.
And the true powerband of our v-twins is higher than we commonly use them, even with stock cams and compression.

I only proved this to myself in the mid '80's by traveling out of state on a '65 with loaded hack (pure torture to a motorcycle), following the bodacious new evos.
With the lowest factory sprockets (22 X 22), 80 mph produced an air-craft 'whine' that would scare most Sunday luggers out of their shorts.
But at that RPM, it could still run forever.

The machine is still running,..( as soon as she tells me),.. on the same rebuild, although it has been 'light duty' in my wife's hands.

The real mystery is how such a powerful highway machine was developed when most roads were rutted gravel. This single quality is what propelled the whole 'Muricun motorcycle phenomenon to a worldwide affection. (Please ignore all modern hype!; I refer only to vintage enthusiasts.)

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Power, speed and vibration


Post by FlatHeadSix » Sat Jun 04, 2005 2:49 pm

Panheads provide plenty of all 3: Power, speed and (of course) vibration. They're all "built in", came from the factory that way, so get used to it. I guess that's why the Motor Company spent so much time and money on re-engineering, rubber mounts and balanced twincam 88's.

Cotten put something into words that I've always wondered myself; who needed that much power back when we didn't have good roads to use it?
My dad said the same thing when I bought my first panhead and retired the 45 flatty to the back of the garage in the mid sixties; you don't need a motorcycle with that much power or top end. He said only the cops needed it, not me. In fact, my first FL was a Milwaukee cop bike that I bought at the police auction.

Anyway, what I really got on here to say is that years ago I read something in an old rider's manual or shop dope or somewhere that when you ride at sustained high speed (whatever that is) that you should routinely snap the throttle shut to pull a little extra oil into the top end. I started to that and found that it really does make a difference, especially in the valve train noise. So now, when I'm cruising at constant highway speed, I snap the throttle full shut every once in a while to oil things up and quiet down all the valve clatter. can't hurt.

I'm still running the 1st generation hydraulic push rods that came with the bike in '49, maybe some day I'll upgrade to the newer retro fit or switch to solids but I firmly believe in the old adage that if it ain't broke don't fix it.

put some velcro on the bottom of your boots so your feet don't skate off the floorboards Tracy, and enjoy the ride!

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Snapping the throttle shut


Post by Cotten » Sat Jun 04, 2005 11:39 pm

The topic of snapping the throttle shut has come up recently on the FHP forum.

The oiling aspect was apparently linked to the case baffles and female-forward rod arrangement, eliminated by '40 or so.

The tradition carried on with the Knuckhead literature that instructs to do so in order to drain the spring cups.

By the time Pans came along, both of these concerns were engineered out of the motor.

If it eliminates some valvetrain noise on your Pan, it would seem most likely that your pancovers are filling up. This is not an unusual problem for '63-'65s (and anything with a chubble pump), but noise isn't usually a symptom. Usually it's pancover leakage and oil down the exhaust guides.

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Post by fourthgear » Mon Jun 06, 2005 4:55 pm

Sorry Cotton , I am one that was shown that ballancing any motor is good for it and its performance , not to mention felt harmonics ( vibration ) I'll admit I was a hard sell ,but the ballancers won me out with a couple of motors. They showed me and told me the benifits of doing it properly to any motor ,car ,truck , motorcycle , boat , stock motor , racing motor ect. Just showing me the weight diff. of stock pistons kinda freaked me out .Any thing I can do to a motor when it is completely torn down for rebuild will beifit it in the long run. Just my 2 cents and I'm a believer. I fart in the dark every chance I get . No one knows who delt it .

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Balancing beliefs


Post by Cotten » Tue Jun 07, 2005 2:52 am

To All!

My contention is that vibration problems are most often not balancing problems.
If your re-built motor is suddenly smoother, hadn't it better be?!?!
Just how much of it would have come out in the wash anyway, and how much was actually worth paying for?

Modern ballancing techniques applied to a vintage motor are snake oil.
Been there done that on a Stewart-Warner more times than I ever wanted to.

Unless a motor is being constructed from scattered parts or rad performance modifications , it is just profit margin for the builder. Or a subcontractor. And then add the delivery service both ways. (and don't forget the"insurance" cut). All for a few tenths of a mythical percentage factor point. If they even do it right. Who's to know?
As long as it was trued properly, it will be smooth!

In a stock frame that is.

Modern mystery #1: Why do so many different modern builders spec so many different factors for the same motor design, and why are they nearly always different than what the Factory spec'd? Can they all be right? Can they all be wrong?

Modern mystery #2: How come so many "balanced" motors still shake like an air-hammer?
Aw, they all do that. (Especially after a dyno run for a break-in!)

Modern mystery #3: How come un-balanced motors can be so damm sweet ( Of course that's timeless, and not just a modern occurrence.)
Marvel Mystery Oil?

If some of you do not see the pattern forming, please remember that "beliefs are only someone else's strong suspicions" (Ridnick Wysdom).
It didn't take computers for the original designers of v-twins to figure out how forgiving they are, nor bells, whistles, or even strobelights and a print-out.
V-twins are blessed with the ability to run long and hard over a wide range of factors. 43% for a VL; up to 60+ for modern OHV stuff; 65% for a Chief; and 85% for a Sport Scout. I still have a hard time with that one myself.
Technically, a v-twin cannot be out of balance. It can only be poorly balanced for a particular application.

And that has more to do with the chassis than the motor itself!
If you have a rad chassis, and your balancemeister does not inspect its design before he factor's your crank, he has disrespected you both.

(I no longer accept new motorwork accounts, so this is for everyone's entertainment only.)


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Post by FlatHeadSix » Tue Jun 07, 2005 2:05 pm

Right on the money Cotten!
Like I said in the earlier post, there is some vibration inherent in the design. When you have 2 pistons flying up and down in a 4-stroke engine that only fire every other time they make the trip, and then you make them fire unevenly and rely on a big heavy flywheel to carry them through the rest of the revolution (boom-boom coast, boom-boom coast) its gonna shake a little. Like Cotten says, all that spinning stuff has to be true, if you have any runout, side to side or up and down, it'll throw you off the bike.

no different than lacing up a spoked wheel, the factory specs for runout are pretty tight. You can balance a wheel all you want but if the thing isn't true in both directions it'll shake you off the bike when you get it up to speed. It won't matter how tight you crank the steering damper or how good that mono shock on the spring fork is. True it first, balance is just icing on the cake.

Cotten, what were those percentages you just posted? 43% of what?

Look at the 45's, Harley built that engine basically unchanged in design from about 1932 until the last Servi in '73 and I don't think they ever balanced a single one of them.

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Post by Cotten » Tue Jun 07, 2005 2:53 pm

By factor, I mean the percentage of the real reciprocating weight to which the countermass is made to equal, or balanced to.

There is a general multi-dialogue at where I still find useful info. The "Theory" discussions were very revealing, as I had never considered the critical chassis aspect. (Or why the top half of the female rod cannot be made equal to the male!)

HD production, and Indians as well, were probably always balanced by batches, where all of a similar lot of flywheel forgings would be drilled to an prescribed number of holes of a given depth. Nearly always at about six o'clock on the inside rim. "Flyer" holes elsewhere would indicate a more sophisticated approach was used. All the 45" wheels I still have laying around look like swiss cheese. Damn hotrodders.

The bottom line is that a v-twin is very very forgiving!

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Still gather all the information


Post by Detroitblue » Wed Jun 08, 2005 5:24 am

Thanks for all of the insite. I have just now read your replies. It had been such a long time before getting even a nibble that I had givin up on this topic. But I have been doing some reading and poking around the local shops for Ideas.

1. Yes that phenomon of the feet skating across the floor boards at about seventy mph is what I was refererring too. I see I am not the only one. I will check the mounts and everything else I can find.

2. I also plan to look into the sprocket resizing Idea. That seems like a cost effective way to get up to a 100 mph. Yeah! if I could cruise at about 85 or 90 then that would do the trick I think. Then I could hit the road with the Big dogs. I guess I would only like to reach 100 mph now and then.

3.My Old Man told me that he had a stroker kit and short pistions on the bike before I had it rebuilt. He tells me that the bike ran much faster then. But truth is it didn't run worth a cuss as far as I could tell without smoking like crazy and frequent repairs. Didn't want to start up ethier. However I still have got the stroker kit and it might come in handy. I was wondering how much of a boost that might give me?

4. And finally I was just wondering what should I expect to run with my bike? Most of you guys have one just as old as mine or older so is there anybody out there raising any hell on these things anymore? And if the answer is yes then what kind of set up do you have?

I saw one guy with a set up that was wound so tight he couldn't get it to crank over. But they tell me that once he got it going it would blow by even some ot the imports. What he was running was Dual plugs, high compression pistions, super carb, 5 speed in a 4 speed case and a lot more.

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Post by panhead » Fri Jun 10, 2005 3:56 pm

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