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[fkjunkin]

Had a late night adult beverage influnced argument with a friend about bore vs stroke and displacement. In you guys opinion which engine would produce the most torque. A 88 to 113, a 96 to 113, or a cvo 110 to 113 all other things being equal? He claims displacement is the same so all measured output would be the same. I call BS  Have fun with this one.

[prodrag1320]

besides the 110 having better heads,they will be the same (and if your looking for just gobs of torque,the 110 heads may not be the best choice)

[GMR-PERFORMANCE]

Had a late night adult beverage influnced argument with a friend about bore vs stroke and displacement. In you guys opinion which engine would produce the most torque. A 88 to 113, a 96 to 113, or a cvo 110 to 113 all other things being equal? He claims displacement is the same so all measured output would be the same. I call BS  Have fun with this one.

With out picking a point for the tq I would say yes all would be in the same range.. 

113   4 x 4.25 ( we have built those )

113 4.375 X 4.060 yep been there

110 - 113  Yes as well


So being that we have built all of these and tuned them how does one say what is equal. As there where not all using the same head cam compression or even t/b however the final numbers ROM range as side are not too far off.


I went back through and looked as the build they could not be further apart..

SO here goes   88- 113  4 x 4.250             121  HP 125 tq    cnc stock 615 rr cam  Pipes are Bassani pro streets no baffle

                      96-113   4.375 X4.060        123 hp  128 tq   MVA heads tman 662-1 zilla

                      110-113                             123 hp   129tq   CVO heads our cam  58 t/b X pipe


Now this test is not great as it has softail , a dyna and bagger different types of t/b etc  but you asked so there you go HA HA The only real change you have is the 88-113 kit that is a big bore short stroke set up. That kit was a revolution kit to come up with that set up. With crap pipes never did see if you could drive the tq up early, as the big bore short stroke engines tend to favor RPM and HP

Do not know if this sis of any help but was fun looking through the old dyno sheets.
                       

[fkjunkin]

We were not counting any difference in head, cams, pipes etc just a dicussion about bore vs stroke and would there be any diiference in hp or torque in how you got to the final displacement. I would think that longer stroke would make more torque but am not sure. Just somthing to discuss besides what fits my bike.

[GMR-PERFORMANCE]

the 124 with a 585 would make more tq  HA HA   

The issue is that the engines being in the same CI size it really will come out to the same point. However the length of the arm will make a change in where the peak number falls into. As you find the limit of other items in the build. This was a huge topic when many went from 96 to the 107 with a bore only kit well the 4 X 4.125 was a popular kit and we saw power numbers all very close to one another on avg.

[HILLSIDECYCLE.COM]

All things equal, with the same swept volume no matter how you skin it, no real differences.
Scott

[Para Bellum]

longer stroke would make more torque but am not sure.

Torque is defined as turning force, and is measured in units of weight and distance, like foot-pounds.  Example: If you apply 10 pounds of weight at a distance of 1 foot away from the nut, you have a torque of 10 foot-pounds (10 x 1).  So a longer-handled wrench gives us more torque to turn a nut.

If *all* other components and factors were equal, the longer stroke would make more torque, since the stroke is the distance from the part that's turning.

As a rule of thumb, if you have two engines with equal displacement but different bore and stroke (say, 110 vs. 110), the longer stroke will make more torque, but the larger bore will make more HP.  The thing is, in real life, one engine might have better matched components than the other, so it is more efficient and performs better.  This is why all other components and factors have to be the same, and why comparing two or three engines with the same displacement (even with different bore and stroke) doesn't give a useful answer.

[dahsen]

Torque is defined as turning force, and is measured in units of weight and distance, like foot-pounds.  Example: If you apply 10 pounds of weight at a distance of 1 foot away from the nut, you have a torque of 10 foot-pounds (10 x 1).  So a longer-handled wrench gives us more torque to turn a nut.

If *all* other components and factors were equal, the longer stroke would make more torque, since the stroke is the distance from the part that's turning.

As a rule of thumb, if you have two engines with equal displacement but different bore and stroke (say, 110 vs. 110), the longer stroke will make more torque, but the larger bore will make more HP.  The thing is, in real life, one engine might have better matched components than the other, so it is more efficient and performs better.  This is why all other components and factors have to be the same, and why comparing two or three engines with the same displacement (even with different bore and stroke) doesn't give a useful answer.

Totally agree.

[grc]

The most important thing about stroke versus bore is a little thing called piston speed.  For any given rpm, a longer stroke creates higher piston speeds, which tend to create higher wear.  Then we get into the subject of rod angularity, which affects the loading of the piston skirt to the cylinder wall (wear again).  And of course we also have the limitations of overall height of the engine to fit in the frame.  My point with this is to show that there is a lot more to the bore versus stroke determination than torque versus horsepower. 

Jerry

[Para Bellum]

The most important thing about stroke versus bore is a little thing called piston speed.  For any given rpm, a longer stroke creates higher piston speeds, which tend to create higher wear.  Then we get into the subject of rod angularity, which affects the loading of the piston skirt to the cylinder wall (wear again).  And of course we also have the limitations of overall height of the engine to fit in the frame.  My point with this is to show that there is a lot more to the bore versus stroke determination than torque versus horsepower. 

Jerry

Very true.

[TorqueInc]

  Piston and ring  technology has come a long way....a little faster that normal piston speed is not a big deal as long as you aren't bouncing it off the limiter wholesale.

  Since these twincams for the most part tend to operate in a pretty narrow rpm band and also tend to be underheaded id prefer a balance of both bore and stroke.

[HD Street Performance]

Bigger is better..
OK let me qualify that, up to a point.
Stroke and bore can be your friend if utilized properly. Using off the shelf parts and size combinations commercially available there are many constraints including and not to be forgotten, packaging in the chassis. Near the top end of the list is ring seal. Keeping the cylinder length stock when the stroke grows the piston required has a short skirt even with shorter rods. At BDC on the turn around ring stability is critical. When the gauge point is hung out in mid air and the skirts are short to begin with the rings struggle to find equilibrium. In essence the piston begins compression stroke with rings fluttering. The result is a loss of proper ring seal. This wears out rings fast. screws up bores, causes overheating, oil consumption, and last but not least a loss of ring sealing compression. These motors are never happy. Don't forget besides sealing and oil control the relationship of the rings to the piston and the motor are to transmit heat. While fluttering this is not happening either.
So as soon as the engine dimensions grow (larger bore can be the culprit too due to packaging) to the point ring seal is compromised by unstable cylinders and/or dimensions that force an unstable condition all bets are off. Cash in your chips and start over or better yet plan right to begin with.

[mike jesse]

Ring "flutter" as you call it can be reduced or eliminated by proper ring and piston design.
Tighten up the radial ring clearance and reduce the ring side clearance goes along way to help control this.
Long or shorter stroke doesn't matter.

Bigger is better..
OK let me qualify that, up to a point.
Stroke and bore can be your friend if utilized properly. Using off the shelf parts and size combinations commercially available there are many constraints including and not to be forgotten, packaging in the chassis. Near the top end of the list is ring seal. Keeping the cylinder length stock when the stroke grows the piston required has a short skirt even with shorter rods. At BDC on the turn around ring stability is critical. When the gauge point is hung out in mid air and the skirts are short to begin with the rings struggle to find equilibrium. In essence the piston begins compression stroke with rings fluttering. The result is a loss of proper ring seal. This wears out rings fast. screws up bores, causes overheating, oil consumption, and last but not least a loss of ring sealing compression. These motors are never happy. Don't forget besides sealing and oil control the relationship of the rings to the piston and the motor are to transmit heat. While fluttering this is not happening either.
So as soon as the engine dimensions grow (larger bore can be the culprit too due to packaging) to the point ring seal is compromised by unstable cylinders and/or dimensions that force an unstable condition all bets are off. Cash in your chips and start over or better yet plan right to begin with.

[HILLSIDECYCLE.COM]

I hate it when my rings flutter.........

[HD Street Performance]

Ring "flutter" as you call it can be reduced or eliminated by proper ring and piston design.
Tighten up the radial ring clearance and reduce the ring side clearance goes along way to help control this.
Long or shorter stroke doesn't matter.

OK so what HD piston from any manufacturer can provide a stable ring package when the gauge point is uncovered at BDC? I am not discounting what you said, those attributes are important too but won't correct lack of support at BDC on the skirts. The rings just can't be left carrying the whole bag. What I cited was told to me personally by Keith Jones from Total Seal piston ring company. Pistons I have inspected, the ring packages, on used motors present with the same results. If the piston can remain supported I agree the stroke is not consequential and as I stated bigger is better. But eventually packaging forces an unstable part combination.
The best I have seen to date with forged pistons were 117" MTC pistons, full face skirts, lathe ground not cam ground, Total Seal Rings. The back and side ring clearance were tight by design.