AMEN brother.
I read the same parpgraph in a soft back I have. "Modifying small-block chevy engines" by John Lingenfelter.
Talk about a wolf in sheeps clothing. Your slumming aint ya?[img]i/expressions/face-icon-small-smile.gif[/img]

 

<div class="FTQUOTE"><begin quote>Originally posted by: BigMc

Given the exact same engine, with a longer rod, the stroke is te same. But the centerline on the piston will need to move north, toward the piston rings, to acomadate the longer rod. This will improve the rod angle on the up stroke. This inturn reduces piston chatter, which will improve engine reliability.

The only way to fit a longer stroke into the "stock" motor is to change the center point of the big end of the rod. This will improve the stroke length, but the rpm's will be higher at any given point , compared to stock, due to the smaller circle the crank will rotate around its center.



J.R.

Step in when ever you see fit. After all, I could be wrong.</end quote></div>


Actually, that's pretty well said. Especially the part about the piston chatter. The longer the rod, the less the wrist pin actually has to rotate, therefore, the less chance for chatter. If the rod was infinitely long, you could actually weld the rod to the piston and not even need a wrist pin.

The only part I'm not sure I'm following is, "The only way to fit a longer stroke into the "stock" motor is to change the center point of the big end of the rod. This will improve the stroke length, but the rpm's will be higher at any given point , compared to stock, due to the smaller circle the crank will rotate around its center." I'm not sure how longer stroke and smaller circle relate is all.

I was planning some cad drawing tonight to illustrate the differences in rod lengths, but some friends came over and.... didn't get around to it. But, I will sometime this weekend.

 

The warrior bore n stroke is 83x64.5. So a quadsport has a 2.5mm longer stroke. Vince is and was correct.

What is particularly important is not necessarily the stroke, but the bore/stroke ratio. The zilla had 86x86 for a ratio of 1/1 or a "square". The latest quads seem to have a ratio of 1.4 to 1.6. The stock 230 is .99. The 260 kit makes it 1.04. The warrior has 1.29. The mojave has 1.28. The 250x has 1.29. So, the latest trend in engine design has been in favor of a large bore compared to the stroke. This is good for high rpm applications.

The next ratio to consider is the rod/stroke ratio. The YFZ450 is 1.65. The 250x is 2.13. The warrior is 1.74. The 230 is 1.66. With the longer rod it becomes 1.72. The longer the rod, the higher it can rev. I don't have enough data to decide what the latest trend has been, but I assume its a marriage between the longest rod possible while keeping engine size as small as possible.

 

<div class="FTQUOTE"><begin quote>Originally posted by: gforce34

I think this helped me understand.



One important factor in engine design is the rod/stroke ratio. Rod/stroke ratio is the ratio of the length of the connecting rod to the length of the crankshaft's stroke. An increase in the rod/stroke ratio (a longer rod, shorter stroke, or both,) results in a decrease in piston speed. However, again due to strength and size concerns, there is a limit to how long a rod can be in relation to the stroke. A longer rod (and consequently, higher rod/stroke ratio,) can potentially create more power, due to the fact that with a longer connecting rod, more force from the piston is delivered tangentially to the crankshafts rotation, delivering more torque. A shorter rod/stroke ratio creates higher piston speeds, but this can be beneficial depending on other engine characteristics. Increased piston speeds can create tumble or swirl within the cylinder and reduce detonation. Increased piston speeds can also draw fuel/air mix into the cylinder more quickly through a larger intake runner, promoting good cylinder filling.



Rod length and stroke length are independent variables. Rod length is expressed as Center-to-Center (c/c) length. An engine with a particular stroke can be fitted with rods of several c/c lengths by changing the piston pin location or block deck height. A rod that is longer in relation to stroke causes the piston to dwell a longer time at top dead center and causes the piston to move toward and away from TDC more slowly. Long rod engines with a particular stroke also build suction above the piston with less force, since the piston moves away from TDC more slowly. Consequently, long rod engines tend to produce a lower port air velocity, which also reduces low speed torque. Long rods place less thrust load on the cylinder walls, thus generate less parasitic drag and result in less frictional losses as engine revolutions rise. A "short rod" engine has the opposite characteristics. "The short rod exerts more force to the crank pin at any crank angle that counts i.e.--20° ATDC to 70° ATDC" (Jere Stahl). Short rod engines tend develop more torque at lower engine speeds with torque and horsepower falling off quickly as engine RPM rises to high levels. Long rod engines generally produce more power due to reduced engine drag, especially as engine RPM increases. Regardless of rod length for a given stroke, the average piston speed (usually expressed in Ft/sec or M/sec) remains the same. What changes as the rod length becomes shorter or longer in relation to the stroke, is the RATE of motion as the piston rises and falls in relation to the crankshaft. A long rod fitted to a given stroke generates less stress on the component parts due to the lower rate of acceleration away from and toward TDC. The average piston speed is the same; however, the peak piston speed is lower with long rods.</end quote></div>


Yep... some of what is said in that is why lots of guys like short rods. They like the large intake charge and say that offsets the friction. This may work well in v8's that dont rev that high to begin with, but in small, high revving engines like ours, I tend to think the longer rod is better. I'd rather make the power at the top and have the added benefit of greater longevity.

Short rod dwells longer at the bottom and the long rod dwells longer at the top. Its a debate that will rage from now on. I think most of it has to do with what engine you have and what you want to do with it. There is always an optimal solution for every problem. Some cases its a short rod, some cases its a long rod. For my case, its the long rod.

 

<div class="FTQUOTE"><begin quote>Originally posted by: gforce34

I'm ignorant to engines, since this is my first teardown....but I thought the rod was directly related to the stroke....so the longer the rod the longer the stroke. I'm not sure if the crank plays a role in how big the stroke is.</end quote></div>

That may be my fault because I told you generally the rod gets longer with the stroke, but it doesn't have to. Usually when you buy a stroker kit though, it will come with longer rods to preserve the rod/stroke ratio. Or, similarly, you can buy longer rods w/o changing the stroke. Like I'm doing.

The crank is the only contributor to how big the stroke is. The rod has nothing to do with the stroke. Everybody has a rough time grasping this concept at first. Its not all that common sense.

Think of a bicycle, something we can all relate to in terms of power and how everything feels. The stroke is the length from the pedal to the center bearings. The rod length is the length of your leg. The piston is your knee going up n down. A bike with long cranks will have lots of low end torque, but its hard to rev that bike out. A bike with short cranks will be easy to rev, if you can get it up to speed because its so hard to pedal at first. You need strong legs to handle such a bike. Now, would it be easier to pedal a bike with long legs???? Or short ones???? The longer legged guy should be able to pedal faster than the short legged guy. The short legged guy should have more torque while pedaling slow. Pedaling slow doesn't win races though.

 

<div class="FTQUOTE"><begin quote>Originally posted by: BigMc

hey, i see were talking about rods. who has the longer stroke?..................

Mr Vince told me at one time that the 230 already had a longer srroke than the Warrior and that changing it could adversley affect the already low rev limit. Of course this was about 5 years ago now. Things do change when there is money involved ,..i.e the stroke comment above[img][/img]</end quote></div>

Does the 230 have a rev limiter? What I think he means is a long stroke will be mechanically slower due to having to move mass a greater distance (ie a large circle). The whole crank assembly becomes a "governor" and can only rev so high before it flies apart.... Or so much power is required to just rotate the crank that fast that the HP curve falls off at a lower RPM. In the world of small bores, RPMS is what we need to have any hope of keeping up with a big bore. We're not going to compete on torque, so we need to make up for it on HP. And that can only happen at high rpms. Therefore, a stroker kit would be shooting yourself in the foot.

 

J.R. your right. I was talking out my azz last night I guess. (to much southern coke i guess) If you move toward the cnter line of the crank, your not gaining a thing. Your hurten yourself.
But, if the big end center line moves away from center, say 2mm, you would gain a full 4mm in stroke. 2mm on botttom, 2 on the top. This of course gives you more CC.

Sorry. Ill try and put my brain in gear before runen my mouth next time. Booze and a keyboard, not a good mix.

 

J.R. I swear he told me that stroking the motor would affedt the revver adversley. But maybe Vince ment the total revs possible before it just, comes apart? Idunno. Thats why I like this place, no matter how much youve been around these things, you learn something new all the time.

P.G. Thanks for checking on that 250r case man. I guess i need to check out the bay again. Glad to hear your back in action.

keep-em-alive

 

I need to really pull my s^#t together and start schooling myself in the basic workings of motors and w/ that basic knowledge applying it to mods of an engine to understand just because one mods and engine isn't always in a beneficial way or it's effecting it in a way that one does not want to go and how it all relates to the other parts and workings.
You both helped tremendously helping me visualize the concept by breaking it down in lamens terms, much appreciated.[img]i/expressions/face-icon-small-smile.gif[/img]

One of the obvious and seems to be unanimous concept is a longer rod will increase longevity.

 

gforce, what is that finish on the swinger and axle carrier? I like. Ive been considering a tear down to repaint the frame and arms. I need someting that will cover the weld seams on the swingarm. That would work great I think.