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Discussion Starter · #1 ·
Greatings all from the noob guy. Im getting ready for a build on my 06' Ultra. Ive read enough threads on here to make my head spin with information overload, which is great!

Im trying to see what the benifit is between going longer stroke or bigger bore. One of the big factors in my build is heat. In live in Texas where the humidity in the summer makes it hard to keep cool. So, should I go with bore or stroke or both or neither?

For reference:

06 Ultra TC88 (stock)
SE Stage I A/C
Rinehart True Duals
Stage I Map
 

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Greatings all from the noob guy. Im getting ready for a build on my 06' Ultra. Ive read enough threads on here to make my head spin with information overload, which is great!

Im trying to see what the benifit is between going longer stroke or bigger bore. One of the big factors in my build is heat. In live in Texas where the humidity in the summer makes it hard to keep cool. So, should I go with bore or stroke or both or neither?

For reference:

06 Ultra TC88 (stock)
SE Stage I A/C
Rinehart True Duals
Stage I Map
First off welcome to the forum.
Stroking an engine will produce more torque off the line and through out the rpm range than just installing larger pistons. The down side to the stroker is the piston acceleration speeds become higher with respective stroke and with this more engine wear.
Big bore with a short stroke is more of a higher rpm motor...ie, the power gain will be noticed more at higher rpm's than a stroked motor. Combine the stroker with a big bore is an awesome combination because bottom line you can't beat cubic inches for power.
I see your riding an Ultra....if you just install a big bore on this engine you will have 95'' build and this engine with the right combination of parts can yield you 100/105 which is awesome power for a heavy bike and I believe it will run much cooler in the hot Texas sun than a 113'' or bigger stroker. A 103'' build would't be a bad build either but now where do you draw the line.......lol
 

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HDMD88 summed up the below very well.

Under Square Engines

A piston engine is undersquare or longstroke if its cylinders have a smaller bore (width, diameter) than stroke (length of piston travel).

This can be a negative trait, since a longer stroke usually means greater friction, a weaker crankshaft (strengthen with weld, true & balance), and a smaller bore means smaller valves which restricts gaseous exchange; however, with the aid of modern technology, these are not the large problems that they used to be. An undersquare engine usually has a lower redline than an oversquare one, but it may generate more low-end torque. In addition, a longer stroke engine can have a higher compression ratio with the same octane fuel compared to a similar displacement engine with a much shorter stroke ratio. This also equals better fuel economy and somewhat better emissions. An undersquare engine does not overheat as easily as similar oversquare engine. Engines can be modified with a "stroker" crankshaft, which increases an engines stroke from stock, increasing torque. Increased stroke make the piston travel further up and down. Since the amount of time allowed for this movement is not increased, the piston speed increases with a Stroked Crank (piston must move a further distance in the same amount of time). This can sometimes cause pistons to wear more quickly.

Undersquare engines produce strong torque at low to mid range rpm's because of the "leverage" advantage of a longer stroke.

Large increases in stroke can decrease an engines ability to perform optimally at high rpm.

One disadvantage for some applications would be increased piston speed. Excessive piston speed can cause ring seal problems and lubrication problems, which decreases piston life. Piston speed will obviously increase with rpm and it will also increase with an increase in stroke. And then there's the loads on the crankshaft, pistons, the piston pins, connecting rods, and rod bearings that increase dramatically with increases in stroke (or piston speed). In general, a longer stroke leads to higher thermal efficiency through faster burning and lower overall chamber heat loss.

A longer stroke will have greater port velocity at a given RPM, more torque due to more leverage on the crank, will achieve it's greatest efficiency at a lower RPM, and have less peak potential than a shorter stroke motor. Smaller combustion chambers are also more efficient, with the flame front having a shorter distance to travel- this leads to being more detonation resistant, and having an advantage for emissions.

A longer stroke, however, increases piston speed per engine cycle, which causes greater side-loads on the cylinder walls and decreases maximum rpm's.

If you are a torque devotee, increase your stroke. If you are a horsepower (rpm) junkie, increase your bore. If you believe that too much power is just the right amount, you can increase both!

The added torque of a stroked engine makes it tons of fun to ride, and if that's what you want, more power to you.

Oversquare Engines

An engine is oversquare or shortstroke if its cylinders have a greater bore (width, diameter) than stroke (length of piston travel).

An oversquare engine is generally more reliable, wears less, and can be run at a higher speed. In oversquare engines power does not suffer, but low-speed torque does to some degree, since torque is relative to crank throw (distance from the crank center to the crankpin)—the leverage, essentially. An oversquare engine cannot have as high a compression ratio as a similar engine with a much higher stroke ratio, and using the same octane fuel. This causes the oversquare engine to have poorer fuel economy, and somewhat poorer exhaust emissions. Engines can be modified by being "de-stroked", shortening the stroke to increase maximum rpms and top-end horsepower, at the expense of low-end torque.

Breathing is the important thing, then. Over square engines have an advantage here, in theory. In a big bore engine, the edges of the valve are less obstructed by the cylinder wall. This is called "unshrouded" and helps breathing. A big bore can fit larger valves and give them more breathing room, too.Engines used at sustained high rpm usually will be better with less stroke and more bore (oversquare).

A short crankshaft stroke reduces parasitic losses. Ring drag is the major source of internal friction. With a shorter stroke, the pistons don't travel as far with every revolution. The crankshaft assembly also rotates in a smaller arc, so the windage is reduced. In a wet-sump engine, a shorter stroke also cuts down on oil-pressure problems caused by windage and oil aeration.

Bigger bores with shorter strokes have the potential to turn higher RPM's, and larger/more valves will fit into bigger combustion chambers. Since the HP race involves turning ever higher RPM's to make more power, the oversquare motors have increased in popularity particularly when it comes to motorcycles.

Oversquare engines rev higher than undersquare engines and they can make impressive horsepower at top rpm.
 

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"Jane you ignorant slut!"
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A question; what is your budget?

A 95" can be done very reasonable imo. But what is reasonable for one may not be for another.

If you want to go to a 103", reasonable changes greatly. Considering the engine needs to be pulled out, the cases split, new crankshaft & all the other parts needed the price changes greatly.

Also, can you do the work yourself? This is a huge money saver in this kind of work.

Best of luck and let us know what you decide,

Chris
 

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HDMD88 summed up the below very well.

Under Square Engines

A piston engine is undersquare or longstroke if its cylinders have a smaller bore (width, diameter) than stroke (length of piston travel).

This can be a negative trait, since a longer stroke usually means greater friction, a weaker crankshaft (strengthen with weld, true & balance), and a smaller bore means smaller valves which restricts gaseous exchange; however, with the aid of modern technology, these are not the large problems that they used to be. An undersquare engine usually has a lower redline than an oversquare one, but it may generate more low-end torque. In addition, a longer stroke engine can have a higher compression ratio with the same octane fuel compared to a similar displacement engine with a much shorter stroke ratio. This also equals better fuel economy and somewhat better emissions. An undersquare engine does not overheat as easily as similar oversquare engine. Engines can be modified with a "stroker" crankshaft, which increases an engines stroke from stock, increasing torque. Increased stroke make the piston travel further up and down. Since the amount of time allowed for this movement is not increased, the piston speed increases with a Stroked Crank (piston must move a further distance in the same amount of time). This can sometimes cause pistons to wear more quickly.

Undersquare engines produce strong torque at low to mid range rpm's because of the "leverage" advantage of a longer stroke.

Large increases in stroke can decrease an engines ability to perform optimally at high rpm.

One disadvantage for some applications would be increased piston speed. Excessive piston speed can cause ring seal problems and lubrication problems, which decreases piston life. Piston speed will obviously increase with rpm and it will also increase with an increase in stroke. And then there's the loads on the crankshaft, pistons, the piston pins, connecting rods, and rod bearings that increase dramatically with increases in stroke (or piston speed). In general, a longer stroke leads to higher thermal efficiency through faster burning and lower overall chamber heat loss.

A longer stroke will have greater port velocity at a given RPM, more torque due to more leverage on the crank, will achieve it's greatest efficiency at a lower RPM, and have less peak potential than a shorter stroke motor. Smaller combustion chambers are also more efficient, with the flame front having a shorter distance to travel- this leads to being more detonation resistant, and having an advantage for emissions.

A longer stroke, however, increases piston speed per engine cycle, which causes greater side-loads on the cylinder walls and decreases maximum rpm's.

If you are a torque devotee, increase your stroke. If you are a horsepower (rpm) junkie, increase your bore. If you believe that too much power is just the right amount, you can increase both!

The added torque of a stroked engine makes it tons of fun to ride, and if that's what you want, more power to you.

Oversquare Engines

An engine is oversquare or shortstroke if its cylinders have a greater bore (width, diameter) than stroke (length of piston travel).

An oversquare engine is generally more reliable, wears less, and can be run at a higher speed. In oversquare engines power does not suffer, but low-speed torque does to some degree, since torque is relative to crank throw (distance from the crank center to the crankpin)—the leverage, essentially. An oversquare engine cannot have as high a compression ratio as a similar engine with a much higher stroke ratio, and using the same octane fuel. This causes the oversquare engine to have poorer fuel economy, and somewhat poorer exhaust emissions. Engines can be modified by being "de-stroked", shortening the stroke to increase maximum rpms and top-end horsepower, at the expense of low-end torque.

Breathing is the important thing, then. Over square engines have an advantage here, in theory. In a big bore engine, the edges of the valve are less obstructed by the cylinder wall. This is called "unshrouded" and helps breathing. A big bore can fit larger valves and give them more breathing room, too.Engines used at sustained high rpm usually will be better with less stroke and more bore (oversquare).

A short crankshaft stroke reduces parasitic losses. Ring drag is the major source of internal friction. With a shorter stroke, the pistons don't travel as far with every revolution. The crankshaft assembly also rotates in a smaller arc, so the windage is reduced. In a wet-sump engine, a shorter stroke also cuts down on oil-pressure problems caused by windage and oil aeration.

Bigger bores with shorter strokes have the potential to turn higher RPM's, and larger/more valves will fit into bigger combustion chambers. Since the HP race involves turning ever higher RPM's to make more power, the oversquare motors have increased in popularity particularly when it comes to motorcycles.

Oversquare engines rev higher than undersquare engines and they can make impressive horsepower at top rpm.
This is all correct. if you are speaking of a HD v-twin TC engine, you have a pretty good torque rate already.
Going up in piston diameter does not make the engine have less torque, it makes more torque, just not as much as a stroked engine.

I have been dreaming about putting together a 114, which is a 400 stroke (88) and 4.25 piston. This engine can have a good bottem end torque if you use the proper cam. It doesn't have to be pipey, it can have a broad powerband, just like the 88 or 95 or 98 does. It will also wind up faster from 3000rpm to 5000 rpm with great power.

If you decide to go to a stroked engine, lets look at a 4.675 stroke. if you use the same bore as a 98'' would be with a 4.00" stroke you have about the same displacement.

You would want to run a different cam to get the most out of this engine. You will get more torque at the bottom, and at wot, that piston is pounding the crank harder. If you have these engines in similar bikes, the stroker has more bottom end grunt, but will not wind up as fast and at a rollon contest the shorter stroke will take off. I don't know how much more the bottom end would be out of the hole, but I suspect that the shorter stroke would catch him very quickly and have a better 1/4 mi time. The shorter stroke will last longer and doesn't have to be run at high rpms.

The TC engine was designed as a torque engine even with the 4.00 stroke. If they used a 3.5 or a 3.00 stroke, that would be an engine that would have to be high compression and would have a much shorter powerband. It would also lack in displacement, because 4.25 is as wide as can be used on a stock case.

This would be true with this engine. The real thing is displacement. You can get more displacement with a stroker and large pistons. I think that 131 is th max combo with stock cases and stock height cylinders. You can only get 114" with a 4" stroke. The added displacement would make the stroker a faster engine.
 

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I now understand why the 117" has become so popular because the mixture between bore and stroke increase.
 

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Discussion Starter · #7 ·
I bow to your knowledge !!!

So, lets say I like to excel at low RPM's to get that harley thump, I would need to think about a stroker? How about the SE103 kit? I've read the SE255 cam is rather tame, so get the 103 kit and swap in a SE258? I want to keep the temps managable too. As I' ve read, the 103 kit should be around 9.6:1 CR? Im' not a fan of compression releases. I like to jump on and go.

Speaking of compression release anyone know if the ACR will work with the 06' ECM's? Or is that option a 07' and up?

A question; what is your budget?

A 95" can be done very reasonable imo. But what is reasonable for one may not be for another.

If you want to go to a 103", reasonable changes greatly. Considering the engine needs to be pulled out, the cases split, new crankshaft & all the other parts needed the price changes greatly.

Also, can you do the work yourself? This is a huge money saver in this kind of work.

Best of luck and let us know what you decide,

Chris
Chris,

Im looking at about 4 - 5 grand this includes the 6 speed cluster install.

Yes, Im doing the work myself. I love wrenching.

Again, thanks guys sharing you knowledge!
:clap:
 

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BB Kit

Twincamikers,

Before you buy an SE 103 kit I would suggest you may want to speak / interview with some of the site sponsors. There a few here who provide very sound advice and BB packages which will ultimately give much better performance and reliabilitiy for you money.

I know HDMD88 is who replied is one of them. Hillside, GMR and others all very reputable and know what they are talking about.

Do your homework.

Frank
 

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Discussion Starter · #9 ·
Twincamikers,

Before you buy an SE 103 kit I would suggest you may want to speak / interview with some of the site sponsors. There a few here who provide very sound advice and BB packages which will ultimately give much better performance and reliabilitiy for you money.

I know HDMD88 is who replied is one of them. Hillside, GMR and others all very reputable and know what they are talking about.

Do your homework.

Frank
Thanks Frank,
The BB would be an easy install as I wont have to pull and split the case. I think I would like the torque of a stroker though, especially at lower RPM's where I ride. It's gonna be a tough call for me. Im' still searching and reading threads here on cam's, headwork, kits, etc... There's so much.

By the way, nice ultra. Its the same as mine!
 

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BB 95 Ultra Classic

Thanks, Scott Palmer from Hillside cycles put together a 95 BB for mine. Should prove to be a nice ride, I'm excited. Went with the Hillside Stage III heads, Woods TW6-G Cams, Weisco Pistons 10.2-1 Comp.
It's in the shop now being put together will post the details when it's complete.

Frank
 

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Thanks Frank,
The BB would be an easy install as I wont have to pull and split the case. I think I would like the torque of a stroker though, especially at lower RPM's where I ride. It's gonna be a tough call for me. Im' still searching and reading threads here on cam's, headwork, kits, etc... There's so much.

By the way, nice ultra. Its the same as mine!
if you go with a 95 or 98 you can still get arm streching torque if set up correctly - see one of our sponsers.
 

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Twincamikers,

Before you buy an SE 103 kit I would suggest you may want to speak / interview with some of the site sponsors. There a few here who provide very sound advice and BB packages which will ultimately give much better performance and reliabilitiy for you money.
I know HDMD88 is who replied is one of them. Hillside, GMR and others all very reputable and know what they are talking about.
Do your homework.
Frank


Let's not forget the "King Of Cubes" HYPERFORMANCE when considering your build. :clap::clap::clap:
 

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twincam, do yourself a favor and ride a true 100/100 95 inch. you may find you want way more power------you may be like lots of folk and it may actually scare you!! lots of dufference between a moco kit and a 95 build by a good indy.

if you find 100/100 not enough, then concentrate on EXACTLY how much power and where. if you want big hit early, are you willing to give up the RH true duals?

http://s95.photobucket.com/albums/l...p/?action=view&current=dynarunsdownbagger.flv


video is 103 SE bagger vs 95 " dyna, bikes and riders = 60lb advantage to dyna.
bagger hooks and tqs off the line, dyna spins and runs bagger down on other end. this gives you an idea of tq/ hp, weight.

BTW, the bagger runs a 1.60 60 ft, and 7.42 1/8 mile!! its a mild build with woods 6 cams.
 

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Good post.

HDMD88 summed up the below very well.

Under Square Engines

A piston engine is undersquare or longstroke if its cylinders have a smaller bore (width, diameter) than stroke (length of piston travel).

This can be a negative trait, since a longer stroke usually means greater friction, a weaker crankshaft (strengthen with weld, true & balance), and a smaller bore means smaller valves which restricts gaseous exchange; however, with the aid of modern technology, these are not the large problems that they used to be. An undersquare engine usually has a lower redline than an oversquare one, but it may generate more low-end torque. In addition, a longer stroke engine can have a higher compression ratio with the same octane fuel compared to a similar displacement engine with a much shorter stroke ratio. This also equals better fuel economy and somewhat better emissions. An undersquare engine does not overheat as easily as similar oversquare engine. Engines can be modified with a "stroker" crankshaft, which increases an engines stroke from stock, increasing torque. Increased stroke make the piston travel further up and down. Since the amount of time allowed for this movement is not increased, the piston speed increases with a Stroked Crank (piston must move a further distance in the same amount of time). This can sometimes cause pistons to wear more quickly.

Undersquare engines produce strong torque at low to mid range rpm's because of the "leverage" advantage of a longer stroke.

Large increases in stroke can decrease an engines ability to perform optimally at high rpm.

One disadvantage for some applications would be increased piston speed. Excessive piston speed can cause ring seal problems and lubrication problems, which decreases piston life. Piston speed will obviously increase with rpm and it will also increase with an increase in stroke. And then there's the loads on the crankshaft, pistons, the piston pins, connecting rods, and rod bearings that increase dramatically with increases in stroke (or piston speed). In general, a longer stroke leads to higher thermal efficiency through faster burning and lower overall chamber heat loss.

A longer stroke will have greater port velocity at a given RPM, more torque due to more leverage on the crank, will achieve it's greatest efficiency at a lower RPM, and have less peak potential than a shorter stroke motor. Smaller combustion chambers are also more efficient, with the flame front having a shorter distance to travel- this leads to being more detonation resistant, and having an advantage for emissions.

A longer stroke, however, increases piston speed per engine cycle, which causes greater side-loads on the cylinder walls and decreases maximum rpm's.

If you are a torque devotee, increase your stroke. If you are a horsepower (rpm) junkie, increase your bore. If you believe that too much power is just the right amount, you can increase both!

The added torque of a stroked engine makes it tons of fun to ride, and if that's what you want, more power to you.

Oversquare Engines

An engine is oversquare or shortstroke if its cylinders have a greater bore (width, diameter) than stroke (length of piston travel).

An oversquare engine is generally more reliable, wears less, and can be run at a higher speed. In oversquare engines power does not suffer, but low-speed torque does to some degree, since torque is relative to crank throw (distance from the crank center to the crankpin)—the leverage, essentially. An oversquare engine cannot have as high a compression ratio as a similar engine with a much higher stroke ratio, and using the same octane fuel. This causes the oversquare engine to have poorer fuel economy, and somewhat poorer exhaust emissions. Engines can be modified by being "de-stroked", shortening the stroke to increase maximum rpms and top-end horsepower, at the expense of low-end torque.

Breathing is the important thing, then. Over square engines have an advantage here, in theory. In a big bore engine, the edges of the valve are less obstructed by the cylinder wall. This is called "unshrouded" and helps breathing. A big bore can fit larger valves and give them more breathing room, too.Engines used at sustained high rpm usually will be better with less stroke and more bore (oversquare).

A short crankshaft stroke reduces parasitic losses. Ring drag is the major source of internal friction. With a shorter stroke, the pistons don't travel as far with every revolution. The crankshaft assembly also rotates in a smaller arc, so the windage is reduced. In a wet-sump engine, a shorter stroke also cuts down on oil-pressure problems caused by windage and oil aeration.

Bigger bores with shorter strokes have the potential to turn higher RPM's, and larger/more valves will fit into bigger combustion chambers. Since the HP race involves turning ever higher RPM's to make more power, the oversquare motors have increased in popularity particularly when it comes to motorcycles.

Oversquare engines rev higher than undersquare engines and they can make impressive horsepower at top rpm.
First and foremost, I am no harley expert!!! I have however designed many an engine and build many a racing engine.

All of what you say and what doc says is in general terms correct. I would point out the increases in bore and/or stroke you are mentioning in a harley going from a 88 to a 95 (big bore) or to a 103 stroker are fairly minimal.

More cubic inches is more power. Period!

That said a good head clean up, slight bump in compression and a good 2-1 exhaust also results in some good dyno numbers.

As to dyno numbers on a touring bagger, how many people really run their engine above 5,000 rpms EVER and how many run their engine over 4,000 OFTEN? Reality check!

That said for the average bagger rider particularly the full dresser 2 up rider, good increases in torque in the 2000-3,500 range produce nice results.

Mike S at Latus motors has about 200 or more dyno charts showing every possible combination you could think of. Take a look and see.

He has shown some fantastic results with 103 bikes, with the 255 cam, very good heads, and a D and D exhaust. If you look as some of the dyno results you can see that the 255 cam pulls very very hard down low and starts to flatten out at 3500 and at 4500 it's about done. Not so bad for the average rider.

However what caught my attention was the same basic build BUT with Baisley (his favorite) heads the 255 can hangs in with big torque to about 4500 rather than the 3500 so the head design for some reason allows the 255cams to "carry on" for 1,000 rpms longer.

Worth thinking about!
 

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twincam, do yourself a favor and ride a true 100/100 95 inch. you may find you want way more power------you may be like lots of folk and it may actually scare you!! lots of dufference between a moco kit and a 95 build by a good indy.

if you find 100/100 not enough, then concentrate on EXACTLY how much power and where. if you want big hit early, are you willing to give up the RH true duals?

http://s95.photobucket.com/albums/l...p/?action=view&current=dynarunsdownbagger.flv


video is 103 SE bagger vs 95 " dyna, bikes and riders = 60lb advantage to dyna.
bagger hooks and tqs off the line, dyna spins and runs bagger down on other end. this gives you an idea of tq/ hp, weight.

BTW, the bagger runs a 1.60 60 ft, and 7.42 1/8 mile!! its a mild build with woods 6 cams.


Was this one of your builds?
 

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Discussion Starter · #17 ·
twincam, do yourself a favor and ride a true 100/100 95 inch. you may find you want way more power------you may be like lots of folk and it may actually scare you!! lots of dufference between a moco kit and a 95 build by a good indy.

if you find 100/100 not enough, then concentrate on EXACTLY how much power and where. if you want big hit early, are you willing to give up the RH true duals?

http://s95.photobucket.com/albums/l...p/?action=view&current=dynarunsdownbagger.flv


video is 103 SE bagger vs 95 " dyna, bikes and riders = 60lb advantage to dyna.
bagger hooks and tqs off the line, dyna spins and runs bagger down on other end. this gives you an idea of tq/ hp, weight.

BTW, the bagger runs a 1.60 60 ft, and 7.42 1/8 mile!! its a mild build with woods 6 cams.
I rode a 105/110 bagger this year in CO. through some of the passes. I loved it!! You could feel the back end torque up nicely when you roll on the gas. It was very rideable too, the power was in the lower-mid RPM's. Only thing I wasnt crazy about was having to set the compression releases every time to start it. Maybe electric ones wouldnt be bad. I also wonder how hot it would run down here in Texas with the heat.

Thanks to all for your input!

Im thinking on starting with the SE103 kit. Then working the heads some more and changing cams. 255 or 257, Im not sure. I really want to keep the RH true duals as I love the stereo sound. Ive got the SERT and I'll start with a Dyna map for a 103. Then work from there. I'd be OK around 100/100 if I can keep it cool and just push the button to start it. Im not looking to race, just to be able to throttle past the big rigs in the wind.

Oh yea, cant forget to put the 6 speed cluster in while I got it apart. I better tie a string on my clutch lever so I dont forget. :chopper:
 

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"Going up in piston diameter does not make the engine have less torque, it makes more torque, just not as much as a stroked engine."

Actually, a shorter stoke motor is capable of more tq. It may not have as a favorable RS ratio to stave off low end ping if the chamber ain't done right or the CR is way high but done right a longer stoke can make more HP and more peak TQ with the higher rod to stoke ratio. Longstroke motors and short stroke motors have exactly the same TDC/ BDC dwell times if the R/S ratio is the same. If both have the same VE, displacement and generate the same cylinder pressures, the short stroke motor will win out due to less piston friction.


Bruce
 

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Build

As already mentioned in this thread, a 95" powerplant, could be all you want/need. Touring builds typically will be 100-105 hp and 110-115 ft/lbs.
Set-up correctly, they will spank engines of much larger size(torque set where you can use it) that come though the back door of most dealers.
We have heard(clients alerting us) of our 95", easily getting around the 110" bikes, and getting better fuel economy while doing it. Again, clients reporting 48-52 mpg. We have always been aware of the increased fuel economy in our engines, but I make mention of it more, now, as the price of gas continues to increase.
 

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<<...but done right a longer stoke can make more HP and more peak TQ with the higher rod to stoke ratio.>>

Bruce,

Unless you have some new break through I think you mean the "shorter stroke" (read bigger bore) can make more peak TQ due to it's longer rod to stroke ratio.

Correct?
 
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