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Xldevil
| | Posted on Monday, November 28, 2005 - 02:13 am: | 
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Something worth to read:
Let’s discuss the stock stroke and bore parameters of the Evolution Sportsterâ before we get into increasing their sizes. I’m ahead of myself already. What Does Cubic Inches Actually Mean?Cubic inches, (c.i.), in Standard measurement which are also referred to as cubic centimeters, (c.c.), in it’s metric equivalent are a calculation of the “swept volume” of the cylinders in an engine. This refers to the volume of the area a piston moves or sweeps over as it is directed up and down in the cylinder by the attached connecting rods and their position on the rotating flywheels. The width of the piston or cylinder diameter, (bore), also contributes greatly to the swept volume. This volume is multiplied by the number of cylinders, in this case 2, to obtain the cubic inches or cubic centimeters of the engine. Let's figure out the cubic inches of a 1200 XL.
The formula is: 1/4p x cylinder bore2 x stroke x number of cylinders
3.1416 inches = p This is a mathematical constant used to find the diameter of a circle
: 1/4(3.1416) x 3.4982 x 3.812 x 2
: .7854 x 12.236 x 3.812 x 2
: 73.27 cubic inches
Air = Horsepower
The cubic inch measurement gives us the volume or displacement available for the air and gas mixture to fill. If a bigger area becomes available through increasing the piston travel and/or the piston bore then the engine will become faster. It doesn’t get any simpler than more air equals more power. Stock Evo Engine Displacements The 883cc Evo Sportster debuted in 1986 and is still produced into 2002 while the short-lived 1100cc model exited after the 1986 and 1987 model years. The 1200 XL was first introduced in 1988 as the hot-rod production traditional Harley. It got very much faster with the introduction of the 1200S in 1996 through engine design changes, electrical and handling packages.However the main differences between the 3 versions are the bore piston size and the valves. 883 cc’s equals 53.9 cubic inches while 1100 cc’s equals 67.2 ci and 1200 cc’s is the same as 73.3 cubic inches. Stroke The stroke on all three is the same at 3.812 inches. This relates directly to the distance the piston travels from bottom dead center, (BDC), to top dead center, (TDC), referred to as "swept volume". The stroke is determined by where in the rotating flywheels the crank pin is positioned. Suppose, for argument’s sake, the crank pin that supports the connecting rod bottom end roller bearings and the connecting rods themselves which attach to the pistons via a wrist pin was positioned in the crank, (flywheels), center. In this scenario the piston would not move at all in the bore since the crank pin would rotate with the flywheels but not move from its centerline. The crank bearings would roll inside the connecting rod races but would offer no directional rotational change which would otherwise pull the connecting rod down and then push it up creating a swept volume. The further away from the center of the crank or alternatively the closer to the rim of the flywheels the crank pin is positioned the longer the stroke or how far up and down the cylinder bore the piston moves. The piston in the 883, 1100 and 1200 moves up their respective cylinder bores on the compression and exhaust strokes a total of 3.182 inches and then correspondingly moves down the same distance on the intake and power strokes. The four strokes compromise two revolutions of the engine or one complete cycle of bringing the air/gas into the combustion chambers, burning the mixture creating pressure driving the piston(s) down and then expelling the burnt gases. The longer the stroke the more power is created as a larger swept volume of air/ fuel mixture is produced. So, let's ask the obvious question.Why Didn't Harley Increase the Sportster Stroke? The short answer is that the Factory could have. However it would have involved more money. The Factory, (as any good capitalist), likes to keep its profit margins without increasing the cost of its product beyond what we can tolerate as consumers. The same blank flywheels could have been used but extra machining procedures would have to be implemented in order to bore different crank pin locations in them. Also, longer cylinders, smaller diameter flywheels or shorter pistons with different wrist pin locations would be required to ensure the ascending and descending pistons would not collide with valves and combustion chambers as well as the skirts hitting the rotating flywheels. The long answer that adds to the above is that reliability can become a very real concern when increasing stroke too much. Don't get me wrong. A great deal of horsepower, (swept volume), can be created by increasing the stroke because after all the old adage still applies….nothing beats cubic inches.Lets look at how far the piston must travel up and down the cylinder bore. Increase the stroke and the distance traveled also increases. The piston must travel disproportionately further with stroke increases in the same period of time. How is this accomplished? Obviously the piston must travel faster to accomplish the individual strokes. The formula for calculating piston speed measured in feet per minute is:
Piston Speed = (Stroke x 2 x rpm) ¸ 12
There are physical limits to piston speed. As these limits are approached reliability or longevity of the component parts is decreased. With a stock stroke of 3.812" at a rpm of 5500 rpm the piston speed is 3494 feet per minute. It is generally accepted to keep a street engine piston speed less than 4500 feet per minute or longevity becomes a real concern. Suppose we increase the stroke to 4.3125, (4 5/16" , at 5500 rpm. The piston speed is 3953 feet per minute. Now lets go to a 5" stroke, which produces a piston speed of 4583 feet per minute at 5500 rpm. We can now see that 4 5/16'' stroke would be safe while going to 5" would definitely create longevity concerns. The angularity of the connecting rods also becomes an issue. Since the stroker crank pin location is moved closer to the edge of the flywheels, the connecting rods must angle more from the perpendicular as they rotate. This is particularly onerous near the 3 o'clock and 9 o'clock positions where the connecting rod is positioned at 90 degrees to the center of the crank. I realize this is difficult to grasp initially but the bottom line is that there is maximum sideloading of the piston against the cylinder wall, which of course increases wear exponentially with increased stroke. With all of this said and done companies like S&S produce flywheels for Sportsters up to 5 inch. A caveat that how the bike is ridden also has a huge effect on engine parts life. The Mean Manglers It is a Harley truism that some mean manglers can blow up a modest stroker in a few thousand miles while a knowledgeable, considerate rider can ride a radical stroker for 30,000 miles. Winding out the bike in all gears all the time is tough on an engine while short bursts of speed on a warm, broken-in engine in with clean oil is alright and not injurious. We at Heavy Duty regularly increase the stroke of Sportsters a 1/2" to 4 5/16" from the stock 3 13/16" with no adverse effects whatsoever. And guess what? Big inch large displacement, street Big Twins better not tangle with the smaller long stroke, big bore Sportys if the ownerships are on the line.Power to weight ratios enter the picture big time here. You might not remember your high school physics since we couldn't ever figure out what we would use all these useless formulae for as teenagers. But if you look at the formula for "work" it will become readily apparent that the energy required to move an object, in this case a motorcycle, is heavily dependant on how much it weighs. Lighter flywheels in the Sportster also allow the engine to rev faster and higher which really gets the bike motivated off the line relative to the more cumbersome Big Twin. Big Bore Increasing the bore diameter will also expand the swept volume.However there are NO parts longevity concerns, as piston speed is not affected one iota. Nor is there a connecting rod angularity problem since the crank pin location has not been moved. So, why doesn't everyone just increase the bore size to obtain whatever cubic inches are desired? The spigot holes into which the cylinders fit in the stock engine cases can only be made so big. First, lets see what Harley did in order to make different size displacement Sportsters and why. Harley Davidson like any good Capitalist company wants to keep its profit margins intact while also keeping consumer costs down in order to be competitive. If the Factory made 3 different size engines by fooling around with the stroke a lot more work and expense would be involved. Sure, they could use the same flywheel blanks and machine in 3 different crank pin locations but there is a lot more involved than that. If the piston moves up and down a cylinder further it will collide with the combustion chamber as well as the valves. Moving down the bore will cause the piston skirt to hit the flywheel rim. So how is this corrected? There are many ways. The flywheel diameter could be made smaller and the cylinder made taller. In this scenario, a new flywheel crank assembly, taller cylinders and frame modifications would be required which is way too expensive and cumbersome.Another way is to shorten the piston skirt for bottom clearance and relocating the wrist pin location to solve top dead center collisions. Parts longevity is affected here as the surface area of the piston contacting the cylinder wall is lessened. This is not a good idea for a production motorcycle where reliability is of paramount concern. Harley was using its noggin when it went to different bore sizes to increase the cubic inch displacement up from the 883 to the 1100 and the 1200. The engine case spigot holes were designed and manufactured to accommodate an 883 cylinder with a sleeve well over a half-inch thick approximating 19/32". Actually these figures should be halved since there are two sides to the cylinder at any given point. Coincidentally this thickness will also accommodate the 1100 and the 1200. This is remarkable when normal cylinders like the Evo Big Twin and the 1200 Sportster, for that matter, have a sleeve the is less than 3/32" thick when adding both sides. Yeah, I know that no modern engine would use a sleeve this thick as technically there are cooling concerns, extra weight and extra cost. But the cost savings factor easily overrides these relatively minor worries. The 1100cc Sportster has the same stroke as the 883 but the cylinder is bored out from the stock 883 bore of 3.000" to 3.350". Ditto with the 1200 except the barrel is bored out further to 3.498". An extra 317 cc's is obtained just by changing piston size with no loss of reliability whatsoever. Converting a stock 883 to a 1200 by boring out the cylinders is the cheapest bang for the buck horsepower on any Harley since day one in 1903. Big Bore Companies like S&S make 3 5/8", (3.625", big bore cylinders for stock engine casings which will take the cubes out to 78.7 ci, (1290cc). Unfortunately, in order to bore out the spigot holes to accommodate these bigger cylinders requires disassembling the motor down to the bare casings. Stroking at this time to increase the cubes further becomes viable since labor will not be duplicated. The spigot holes retain sufficient integrity to support these 3 5/8" cylinders but going any larger requires some old style hi-performance welding and machining techniques. The external meat surrounding the spigot holes have to be reinforced and made larger by welding on material if using cylinders bigger than the 3 5/8". Too much material and then the reinforcing begins to interfere with other engine functions such as lifter/pushrod guideblock location. Aftermarket engine cases are required for the really big bores. S&S manufactured Evo Sportster cases can afford a bore of up to 4.000 inches which increases displacement to 95.8 ci which translates into 1570 cc's. Combine these with a reliable stroke of 4 5/16" and we're broaching close to 110 cubes in a Sportster! Go radical with a 5" stroke with a 4" bore and we're off to 125 cubes. And on it goes. But lets not get carried away John as we are also into big money to do the above. Increased cubic inches are the most influential hi-performance modifications one can make. As always they are only part of the equation as support parts must also be changed such as cams, headwork, carburetion, ignition and exhausts. The "Team" of parts is necessary for the lung to breathe more air in and expel the equivalent out to produce the maximum ponies possible.
Donny Petersen
Heavy Duty Cycles Toronto
www.heavydutycycles.com
Regards,Ralph |
Panic
| | Posted on Monday, November 28, 2005 - 11:00 am: |
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"nearly just as cheap to get the 1250 kit as it is to buy new pistons and bore stock cylinders"
About 4 times as much. |
Hobanbrothers
| | Posted on Monday, November 28, 2005 - 11:24 am: |
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I remember reading that a while ago, and it is funny how time changes somethings and some things never change.
1) Buell - different in every sense - still holds true as they took the unprofitable route according to Donny and changed the stroke between the 9 and the 12 - something Donny said HD would not do because of profits? I guess he did not think about a longer connecting rod to achieve this at what I would think is a fairly reasonable rate?
2) No replacement for displacement, very old saying and I think one that made S&S a lot of money. (Now I think it holds true to Revolution Performance with large bore cylinder capability)
3) Reliability - I truely believe that there is no comparing the reliability between a "stroker" motor and a "big bore" motor. I am willing to bet the "big bore" motor will outlive the other by 50% more miles.
We have been rebuilding cranks for over 25 years and have done both, but since Revolution has brought what they now have to market, a majority of the cranks that we do are stock stroke, large bore cranks, with the exception of SE 103" cranks. |
Panic
| | Posted on Monday, November 28, 2005 - 12:26 pm: |
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"This is particularly onerous near the 3 o'clock and 9 o'clock positions where the connecting rod is positioned at 90 degrees to the center of the crank."
This never happens. The rod is at its point of maximum angularity and maximum side-thrust vector at a different point in terms of engine rotation with changes in rod ratio (rod length between centers divided by stroke length), but this is never at 90 degrees (3 o'clock) and 270 degrees (9 o'clock).
A quick trip through Mr. Petersen's work was rather disappointing.
Example?
"So, what exactly are rocker arms and what function do they perform in an engine?
First of all, they are not used on overhead valve engines which Harleys are not"
Harleys are not overhead valve engines? Let's assume that's a typo.
Rockers aren't used in overhead CAM engines? Except for millions of Hondas, Toyotas, blah.
More complete crap:
"Now here is how each rocker arm pushes it’s corresponding valve open. The rocker arm tip rubs across the top of the valve stem as it is pushing the valve down to open it. This side rubbing pushes the valve against the guide which causes wear and resistance because of friction. Anything that can lessen this side thrust is a big bonus in terms of efficiency and horsepower that is not lost due to more internal work.
Of course if the valve was at 90 degrees straight up and down there would be no side thrust. This is why the hemi heads like the Pan, Shovel and Ironhead XL’s require roller rockers at lower cam lifts than the Evos. The angles of the valves are at a greater angle which produces a lot more friction than the Evos whose valves are at a more conservative angle."
I sincerely hope he simply copied this utter nonsense from somewhere, instead of just making it up himself. |
Panic
| | Posted on Monday, November 28, 2005 - 12:33 pm: |
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"I guess he did not think about a longer connecting rod to achieve this"
Leaving out H-D's notorious accounting department's control over engineering and product development, popular wisdom held that a rod ratio that large (2.33-1, even larger than the XR750) will have severe consequences in torque production, require major re-design of valve events, etc.
Seems to work pretty well! |
Oldog
| | Posted on Monday, November 28, 2005 - 01:12 pm: |
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skipping the economics here for a second, The X1 redlines @ 6800 Rpm with a race kit 7000, @ 7k the piston speed is 4447.333, so the piston speed limits the revs not the valve train. Increasing the stroke makes this "worse"
If Air = HP then getting efficent fill of the cylinder is paramount because you can have paint buckets for pistons if the engine can't breath it's all useless expensive metal.
This seems to follow all of the common hot rodding stuff that I have Ever read.
help the breathing, Inlet & exhaust, then cams with or with out head work, then displacement increases seem to make sense to me.
The more power that you make the more exotic the engine becomes (in a given size range) and in some cases the shorter its life span.
(Message edited by oldog on November 28, 2005)
Edited to correct common misconception on race module rev limit... Buell race modules maintain the same 6,800 rpm rev limit as the OEM module. 
(Message edited by blake on November 28, 2005)
(Message edited by blake on November 28, 2005) |
Blake
| | Posted on Monday, November 28, 2005 - 01:18 pm: |
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Yikes! That is some seriously wrong stuff. Thanks for pointing that out Jeffrey. |
Panic
| | Posted on Monday, November 28, 2005 - 01:57 pm: |
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Actually, the rocker can operate equally well at a 90, or even 180 degree angle - if (and only if) the rocker "levers" (individual arms - the pushrod end and valve ends) are "cranked" or rotated to align with the stem or pushrod axis at 50% lift (or your choice for geo). The XR750 motor had the ends individually aligned to the gear before shipment. This is also why the knuckle motors which used an individually aligned rocker for each valve (all 4 are different) worked better than the pan/shovel motors where H-D saved money by using 2 pairs of identical rocker arms which averaged out the alignment.
I have a feeling that serious XL type race motors have hand-set rocker angles for those .800" lifts. |
Panic
| | Posted on Monday, November 28, 2005 - 02:08 pm: |
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BTW: any Buell engine with much more lift than stock needs to have its rocker geometry re-set. This is frequently as simple as measuring the stem heights to be sure they're within limits, then subtracting old from new left, divide the result in 1/2.
Add this to your stem height with a lash cap (or longer valve, if replacing).
For example: old lift .440", new lift .520".
Math says +.040" (.520 - .440 = .080, /2 = .040), but caps aren't available that thin (weak?), generally start with .050" thick. In this case the error from .010 too tall (cap - .040 = .010) is much less important than being .040 too short (as if no corrections made).
This not only makes more power but reduces guide thrust and holds adjustment longer.
Cases where the lift diff is much more than cap thickness need a more complex remedy - e-mail me if you have one. |
Blake
| | Posted on Sunday, December 04, 2005 - 11:41 pm: |
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"90" is a HUGE set of barrels. I stuck to 88", thinking I could maintain 15 hour a day-coast to coast reliability."
Revolution Performance provides a lifetime warranty on their 90" barrels. Heck they warranty the entire 90" kit for life...
quote:Kits come complete with Revolution cylinders, forged pistons, wrist pins, circlips, and gaskets as well as a lifetime warranty.
Wow! That's and impressive warranty! |
Ryker77
| | Posted on Monday, December 05, 2005 - 10:13 am: |
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I'd guess that warranty is only valid if they install the kit? |
Tramp
| | Posted on Monday, December 05, 2005 - 10:18 am: |
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can't understand why anyone would want to stroke one of these engines.
i've done many big bores for customers, wouldn't think of stroking a sportster-based mill. |
Blake
| | Posted on Monday, December 05, 2005 - 02:51 pm: |
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Ryker,
I believe that warranty applies regardless. If it didn't, they would sure need to clarify that on their site and they don't. |
Fullpower
| | Posted on Monday, December 05, 2005 - 03:06 pm: |
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tramp: the simple reason that one would stroke a sportster is TORQUE. sheer bring-tears-to-your-eyes third gear wheelspin scare the crap out of you TORQUE.
there is something about cracking the 2-1/16 inch throttle plate, feeding methanol to a 4-5/16 stroke 12 to one compression 89 inch sportster that one does not soon forget. it is like being shot out of a cannon.then you shift, and you get launched again. |
Blake
| | Posted on Monday, December 05, 2005 - 05:49 pm: |
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Sounds like fun for sure. But I've ridden a couple 88" stock stroke Buells that produced much the same effect on pump gas. Absolutely no way to go full throttle short of 3rd gear without the front tire smacking you in the face. |
Tramp
| | Posted on Monday, December 05, 2005 - 05:51 pm: |
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errrrrrrr...I more than understand what stroking does, 'fullpower',
really, i do. i've stroked many big twins.
I just cannot make a reason for it on one of these nicely balanced little engines. |
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