Can we please put an end to the "long connecting rod" myth??

Highside

Highside

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Seriously people. I don't know how many times I need to explain this. In order to obtain the theoretical benefits of a long connecting rod, the rod would need to be a couple of feet long.

Pick up a scientific calculator with the trigonometry functions on it. Calculate piston movement for both a stock and a "long rod" engine.

Tell me, what is the difference in piston movement 10 deg ATDC?? do you really think this minescule change that you just spent several hundreds of dollars on actually makes a difference??

Or, you could go out and buy the book Reher & Morrison Championship Engine Assembly and have them tell you the same thing. Choice is yours.

I suppose you can lead a horse to water, but you can't make them drink. :shrug: :shrug: :shrug:
 
Highside said:
Seriously people. I don't know how many times I need to explain this. In order to obtain the theoretical benefits of a long connecting rod, the rod would need to be a couple of feet long.

Pick up a scientific calculator with the trigonometry functions on it. Calculate piston movement for both a stock and a "long rod" engine.

Tell me, what is the difference in piston movement 10 deg ATDC?? do you really think this minescule change that you just spent several hundreds of dollars on actually makes a difference??

Or, you could go out and buy the book Reher & Morrison Championship Engine Assembly and have them tell you the same thing. Choice is yours.

I suppose you can lead a horse to water, but you can't make them drink. :shrug: :shrug: :shrug:
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Highside,
To be blunt with you I really don't give a shitz what your opinions are or quotes from other authors cuz the fact is long rods do and will shift or alter the power band and in some cases with the right cam opening and closing events can yield some HP gains,your inexperience of actually building a long rod motor proves your true ignorance of the subject. I've been building long rod motors since the mid seventies and their are some benefits to be had even Mopar figured that out in the fifities and XS racers for decades have used long rods motors to cushion the power deliver to minimize tire breaking out in the turns but you already knew that to didn't you.
You might wanna take a trip over to "Speed Talk" where the real big boys hang out and their are a few who are real partial to long rod motors,you might even educate yourself some,image that:wtf:
 
highside, you are coming across more than just a little authoritarian here. jack and craig certainly have the runs on the board when it comes to making these things hop. you can disagree with them as much as you like, but most on this board and at the garage know that they can trust these guys, based on work that they have done. please post info on XS motors that you have built with some solid figures to back it up. if you want to just theorise, feel free. i think i can safely say that i speak for many on this board that, without providing real world experience, that you should leave the likes of jack and craig alone. your opinions are just opinions, argue the facts with facts all you like, but arguing fact with opinion just doesnt cut it. cheers

Posted via Mobile
 
Jack said:
Highside,
To be blunt with you I really don't give a shitz what your opinions are or quotes from other authors
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I'm not expressing an opinion here, I'm pointing to facts about the true effect of a longer rod. The difference is so small it's actually difficult to measure, at 10 deg ATDC, the difference is about .0005". Whoop tee doo!!!


cuz the fact is long rods do and will shift or alter the power band and in some cases with the right cam opening and closing events can yield some HP gains,
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Lets see the dyno sheets to prove it.

your inexperience of actually building a long rod motor proves your true ignorance of the subject. I've been building long rod motors since the mid seventies and their are some benefits to be had even Mopar figured that out in the fifities
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I do have a lot of experience building long rod engines. Motors I've built have set records in NHRA Top Fuel, Funny Car and Comp Eliminator. I finally realized what a waste of time, money and effort it was.

and XS racers for decades have used long rods motors to cushion the power deliver to minimize tire breaking out in the turns but you already knew that to didn't you.
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They have no way of actually proving it works.


You might wanna take a trip over to "Speed Talk" where the real big boys hang out
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:laughing:

No, the "real big boys" have been my co-workers and mentors. People like Austin Coil, Bill "Grumpy" Jenkins, and Alan Johnson. Well over 20 world championships between those 3.
 
mrriggs said:
Would you mind sharing the formula that YOU use for these calculations?
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It's no "formula" per se, just basic trig. As soon as the piston goes past TDC, two triangles are formed. Since the stroke and rod lenght are known, piston movement can be calculated. First you decide which degree you want to measure, lets say 10 deg. You take the stroke and divide by the cosine of 10 deg, this gives you the horizontal movemet of the crank and rod. You then divide that distance into the connecting rod length to see what degree it has moved to, then you use that degree to see how far down the piston has moved. When you compensate the difference in rod lenght, what you find is that at 10 deg, the difference between a stock rod and a long rod is less than .0005".
 
yamaman said:
highside, you are coming across more than just a little authoritarian here. jack and craig certainly have the runs on the board when it comes to making these things hop. you can disagree with them as much as you like, but most on this board and at the garage know that they can trust these guys, based on work that they have done. please post info on XS motors that you have built with some solid figures to back it up. if you want to just theorise, feel free. i think i can safely say that i speak for many on this board that, without providing real world experience, that you should leave the likes of jack and craig alone. your opinions are just opinions, argue the facts with facts all you like, but arguing fact with opinion just doesnt cut it. cheers

Posted via Mobile
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Since when did trigonometry become "opinion"?? :wtf:

If you even bothered reading my OP, you would see that there's no opinion in it, just facts.
 
Highside said:
It's no "formula" per se, just basic trig. As soon as the piston goes past TDC, two triangles are formed. Since the stroke and rod lenght are known, piston movement can be calculated.
Click to expand...

I realize that this is simple for you but for the rest of us it's not that easy. Maybe you can help me out?

First you decide which degree you want to measure, lets say 10 deg. You take the stroke and divide by the cosine of 10 deg, this gives you the horizontal movemet of the crank and rod.
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74 (stroke) / 0.985 (cos10) = 75.14

Seems odd that the rod would move sideways further than the entire stroke.

You then divide that distance into the connecting rod length to see what degree it has moved to,
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130 (rod length) / 75.14 = 1.73

I would have guessed that the angle would be steeper since the rod moved sideways so far.

then you use that degree to see how far down the piston has moved.
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"Use" it how? That is one trig term I'm not familiar with.

When you compensate the difference in rod lenght, what you find is that at 10 deg, the difference between a stock rod and a long rod is less than .0005".
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I understand what you are trying to say but I'm having trouble seeing how you ended up at .0005". It's too bad that stuff like this can't be expressed with a formula.
 
sorry, i didnt realise you had another post that dictated your mantra. weather your right or wrong, i havnt a clue. its the way you go about saying that you have spoken and thats all there is to it that gets my goat. jacks and craigs opinions mean far more to me than yours do. not saying they cant be wrong, your going to come up with a little more fact and a lot less ego if you want to convince anyone about anything. cheers

Posted via Mobile
 
The most common statement I've always read or heard was that there is no replacement for displacement. Long rod or not I would like to see a way to make a stroked paired along with the 750 kit.
 
6772man said:
The most common statement I've always read or heard was that there is no replacement for displacement. Long rod or not I would like to see a way to make a stroked paired along with the 750 kit.
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The Aussies have been building stroked long rod motors for some time now. Yamamatim displacement is around 900 plus CCs using the 140MM euro rod. he sent me a photo of his Ross pistons and crank assembly:thumbsup:
 
yamaman said:
sorry, i didnt realise you had another post that dictated your mantra. weather your right or wrong, i havnt a clue. its the way you go about saying that you have spoken and thats all there is to it that gets my goat. jacks and craigs opinions mean far more to me than yours do. not saying they cant be wrong, your going to come up with a little more fact and a lot less ego if you want to convince anyone about anything. cheers

Posted via Mobile
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Just hit the "IGNORE BUTTON" has there are some who'll never shed their training diapers cuz of their one sided opinionated views
 
Highside-

I'm not quite sure why this bothers you so much that you would actually take the time to start a thread about it. Just doesn't seem to add up. What's the real issue here? Did someone with a long rod motor do something inappropriate to you in the past?

I'm not sure who made you the long rod police. Possibly the long rod sheriff? But I thought he was on vacation. If someone wants to build a long rod motor and experiment with these old Jap bikes, my advice is just let it be. People have built them in the past, and they seem to be very happy with them.

Maybe you should just focus on getting that John Deere tach to work and let these poor long rod people be...... Lol
 
Patches said:
Highside-

I'm not quite sure why this bothers you so much that you would actually take the time to start a thread about it. Just doesn't seem to add up. What's the real issue here? Did someone with a long rod motor do something inappropriate to you in the past?

I'm not sure who made you the long rod police. Possibly the long rod sheriff? But I thought he was on vacation. If someone wants to build a long rod motor and experiment with these old Jap bikes, my advice is just let it be. People have built them in the past, and they seem to be very happy with them.

Maybe you should just focus on getting that John Deere tach to work and let these poor long rod people be...... Lol
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Because he likes sprewing his negative opinion about anything he can on this whole forum:banghead:
 
mrriggs said:
I understand what you are trying to say but I'm having trouble seeing how you ended up at .0005". It's too bad that stuff like this can't be expressed with a formula.
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Mr. Riggs,

Sorry for the garbaled explanation, but I'm a conceptual thinker, and formulas don't make much sense to me. I understand trig as a concept and not a formula. I'll try this again.

Since an answer in inches will make more sense to people, I'll take the xs650 stroke and round it in inches, it's just under 3" so I'll use 3" to make it easy.I'll then test 2 different stroke to rod ratios, 1.6-1 (4.8") and 1.9-1 (5.7") as an extreme example. The difference between the 2 rod lenghts is .900" which is beyond what you could reasonably stuff in most engines just to show how little change in piston movement that even a radical modification will make. I'll also round answers to .XXXX" and .XXX deg.

I'm calculating this for 10 deg ATDC where most of the supposed effects are claimed to take place, and also for 90 deg ATDC to show the full effect.

Let's start with the 4.8" rod. You take half the stroke and multiply by the sine of 10 deg, answer: .2605. That's how far the crank has moved horiz. Divide that by the con rod length, answer: .005427. Hit invert, then tang on your calculator and you get an answer of 3.106 deg, this is the angle of the con rod when the crank is @ 10 deg. Take the cosine of that angle, .9985 and multiply by the con rod length, answer: 4.7929. This number is now the baseline for piston height since everything else will be the same for both motors.

Now for the 5.7" rod motor. Since the crank is the same, the .2605 is the same crank horiz movement. Divide this by the 5.7 con rod to get .0457. Hit invert then tang on your calculator to get a rod angle of 2.617 deg. Get the cosine of that angle, .99895 and multiply by the con rod to get 5.6941. Since the wrist pin has moved up .9" into the piston, we need to subtract that from 5.6941 to get 4.7941.

Now you subtract the 2 wrist pin heights from eachother 4.7929 from 4.7941 and you get... .0012"

Zippity doo dahh!!!!!

Obviously, this difference is too small to have any effect on ignition or combustion.

Now for 90 deg. Obviously, we don't need to do trig to find the horiz offset which is known at 1.5". Divide this by the con rod length (4.8), take that answer and hit invert tang on the calculator to get an angle of 17.354 deg. Take the cosine of this, .95448 and multiply by the con rod to get a wrist pin height of 4.5815. Now for the 5.7" rod. divide 1.5 by 5.7, then hit invert tang to get the angle of 14.744 deg. Get the cosine of that angle, .9670 times tha con rod length to get 5.2123. Subtract .9 to get 4.6123.

Subtract the two heights from eachother to get... .031". Given the fact that this is 90 deg, where not much is going on anyways,This difference is too small to effect anything to do with cam timing.

So do Long rods still have any defenders or do I need to continue this??
 
Patches said:
Highside-

I'm not quite sure why this bothers you so much that you would actually take the time to start a thread about it. Just doesn't seem to add up. What's the real issue here? Did someone with a long rod motor do something inappropriate to you in the past?

I'm not sure who made you the long rod police. Possibly the long rod sheriff? But I thought he was on vacation. If someone wants to build a long rod motor and experiment with these old Jap bikes, my advice is just let it be. People have built them in the past, and they seem to be very happy with them.

Maybe you should just focus on getting that John Deere tach to work and let these poor long rod people be...... Lol
Click to expand...

:laughing:

My reason is that some people waste a lot of money on something that they think will increase the power of their engine and it really doesn't. If you're doing the work yourself, it's one thing, but to pay someone else can get expensive, and it's downright fraudulent if the people selling the work are making HP claims they can't back up.

... and my John Deere tach is teh coolest!!! I take it off the bike and cuddle with it at night. :bike:
 
Highside said:
Subtract the two heights from eachother to get... .031". Given the fact that this is 90 deg, where not much is going on anyways,This difference is too small to effect anything to do with cam timing.
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Why is that too small to make any difference? In the world of blue printing motors, thirty-one thousandths is like a mile. If you changed your valve lash by 0.031" or decked your block 0.031" there would certainly be a difference.

I'm not saying you are wrong, just that it needs further explaination. Most of us don't have your vast experience and knowledge so it's not as obvious to us.
 

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