longer connecting rod

wiseman79

Top Fueler
Dec 18, 2004
2,565
0
0
Central Virginia
www.performancetech.net
Still need help reconciling my mental picture of how this should work. In my mind this works like a bike rider, the pedals are the crank, and your legs are the rods. (In my example the length of legs has no relavence, I'm only addressing the angle of the rods relative to the piston travel), a longer rod would leave it at an angle more inline with the travel of the piston. In my simple mind I think if I wanted to exert maximum force on the pedal I'd pump with my shins in line with the pedals travel, if my shins were at a severe angle to the direction of travel to the pedals path of rotation it would seem I would be wasting alot of energy trying to push the pedals in a direction they WERE NOT going to travel, along with putting alot of stress on my knees (pins). And if I were superman and push hard enough I'd be putting alot of stress on the pedal assemby (crank). I can't get this basic idea out of my head, I believe everyone's arguement that this idea is false as it would show up on a dyno, but can't think why it doesn't work. It just seems if I want to move something, I'd naturally want to push in its natual path and want my shins or forearm or left pinky finger or whatever in as close to a parallel angle to the direction of force as I could.
 
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Anonymous

Guest
This is the kind of discussion that will go on until the end of time. If you ask 10 different, knowledgable, people, you will get 10 different answers. All I can say is when you have professional engine builders such as David Reher saying that it doesn't matter, you kind of have to start to lean towards their way of thinking.

Here's a good article he wrote on the subject. http://www.rehermorrison.com/techTalk/10.htm
 

K-Star automotive

Amateur Racer
Feb 6, 2006
207
0
0
York, Pa
www.kstarautomotive.com
wiseman79 said:
Still need help reconciling my mental picture of how this should work. In my mind this works like a bike rider, the pedals are the crank, and your legs are the rods. (In my example the length of legs has no relavence, I'm only addressing the angle of the rods relative to the piston travel), a longer rod would leave it at an angle more inline with the travel of the piston. In my simple mind I think if I wanted to exert maximum force on the pedal I'd pump with my shins in line with the pedals travel, if my shins were at a severe angle to the direction of travel to the pedals path of rotation it would seem I would be wasting alot of energy trying to push the pedals in a direction they WERE NOT going to travel, along with putting alot of stress on my knees (pins). And if I were superman and push hard enough I'd be putting alot of stress on the pedal assemby (crank). I can't get this basic idea out of my head, I believe everyone's arguement that this idea is false as it would show up on a dyno, but can't think why it doesn't work. It just seems if I want to move something, I'd naturally want to push in its natual path and want my shins or forearm or left pinky finger or whatever in as close to a parallel angle to the direction of force as I could.


Did you make the paper model???? If you make the model up and pay attention to it you will get all your questions answered... Your thought process is correct, but what you are missing is the amount of change it makes... Again go to the isky chart and look at the piston location in respect to TDC and BDC with the different rod lenghts...It does make a difference....but how does that difference translate into real world HP????


Keith
 
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Anonymous

Guest
I read an article not long ago where they used 3 different rod lengths and same piston type with different pin locations to adjust for overall length. HP and torque were virtually the same. Pump gas (dwell at top) and piston strength seem to be more important. My .02 is as long as you can go and stay outta the ring lands.
 

Mistah

Frequent Racer
May 30, 2005
361
0
0
Maui, Hawaii
www.mistahrecords.com
OOOOKKKKK GUYS, I'M BACK!

Excellent input everyone! I can see this forum has definately established a place for itself on this board.

This subject certainly has been around for a long time, and before I chatted with that old German engineer I hadn't given it a blink of an eye. That 45 minute conversation over twenty years ago has certainly opened up my mind for more forward thinking on what's actually going on in the crankcase, and helped me "connect the dots". As a kid I was always interested in knowing why things worked the way they did. I remember at the age of eight, I took apart a clock to see what was making the little arms move around the dial. When I had it apart, it only had me asking more questions. While being punished for the clock incident, I was looking at a lamp and wondered what made it illuminate when the switch was turned on, and off again. I remembered in school where they taught us to respect a cartoon electric guy "Sparky", and thought if he were entering my lamp through the lamp cord, I'd try to trap him in there by cutting the lamp cord with a pliar. ZAP!!! blue sparks everywhere, then the lights went out. It blew a quarter inch hole in the pliers, which I still own today, thank you very much.

You have to ask yourself if a longer or shorter rod doesn't make any difference, then why has so much attention been directed at it by some of the biggest names in the business.......of all time. Sup was right, our resources won't allow the kind of testing that it would take like the big boys are able to do. Most of us don't even have the patience or tenacity to carry it out in the first place. But does this mean just because you can't see a ghost, it isn't there? Are we all athiests where we all don't believe in something or someone if we can't prove it? The results we are searching for are elusive because there are many different agendas and even more expectations. It's sort of like searching for extra terestials(?) and UFO's (THEY know the answer to this subject, I know because THE TRUTH.........IS OUT THERE MULNER) where people watch the skies at night searching for any signs of advanced life. Some just simply want to prove that they exist. Some may need to be entertained. Some may need to have a higher explaination to all of our worldly mystries, while others may try to capitalize on their technology and yet some may even exploit this for their own benefit. On the other hand there are those who have seen something and just need to pursue it to prove that they are not crazy. Like our corporate funded engineers, if our government does indeed know what's going on, do you think they would tell us?

What this all means is you have to ask why. Just being satisfied with so and so's answer isn't enough. If you're the type who goes out and copy's successful engine combinations or can afford to have an engine builder, that's cool too. But money can never be the answer to all of our combustion engine engineering issues unless you establish specifically what it is that you are trying to accomplish. Everyone wants more power. The smart ones want more power reliably and have it repeatable time and time again. This is why I am interested in the long rod theory. Those who refute this just for the sake of being right, don't belong on this forum. To say say there is absolutely no difference in the two is ridiculous (no offence intended) because a calculator does not lie. To make such a bold statement is moronic because it is 99.99999 % impossible to know this based on first hand information, and relying on second hand information is never 100% accurate. Everything is a comprimise. Money and time are comprimises. Meeting a specific need or requirement is also a comprimise.
To think otherwise would negate the need for many things that help keep things in check like rev limiters, 4 bolt mains, scatter shields, .......seatbelts, the NHRA rulebook, a fire department, and the military...........on, and on, and on. Comprimises are not all bad, especially where safety is concerned. It makes us work harder to overcome the challenges from them, and eventually establish new comprimises and perameters to deal with. It's called growth.
You have to establish a specific pay off, and all other side benefits will become a product of that effort. For me, the pay off is to get my high winding combination to live happily and reliably so I can consentrate on refining other areas of my program like the camshaft, heads, intake, and gear ratios, etc. . It's the platform that allows me to direct my attention elsewhere. Any other benefits are an added bonus, especially if they themselves are pursued and refined. My favorite is the longer dwell time, that allows me to cut back on my timing, I just don't think too much advance helps a racing engine. In my opinion if your motor seems to like it better, then you're probably using a rod with factory dimentions, and perhaps a poor choice for a camshaft.

Who do I have my suspicions on in drag history? Keith Black. Remember the Greer, Black Pruhomme FED?......with a win/loss record of 230 -7 in '63-'64 for starters. Then there's Bob Glidden's Plymouth Arrow....even more so than Jenkin's Vega because it was Jenkin's revolutionary tube chassis design that was the main advantage, where Glidden's advantage came primarily from the motor. AND........let's not forget Greg Anderson. Great guy( I assume) happy for him, but nobody is that good. Wake up guys, we are talking about NHRA Pro Stock where an azz hair separates the winners and whiners. He can smile all he wants to, but he's definately hiding something...........

My 02 - If you are following someone else's advice, then you can only hope to be as fast as him. If he still beats you, then he obviously isn't telling you EVERYTHING.

Hey I gotta go fire up my junk now, my wife just arrived with some Bosch 40 amp relays.............keep up the thread, I love to read your posts, this thread ROCKS!

ps - Annatomically speaking, does the arms of our down hill runner represent the heads of the motor? Let's go and hand-cuff somebody and see how fast they can run...............DOWN HILL to find out LOL!!!!

PSSSSS - Go watch Anthony Hopkins in "The World's Fastest Indian" and see if it does anything for you and your hot rodding spirit. If not you must be dead!!!! Coming dear....................

LMK!

Aloha,
Mistah
 
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Anonymous

Guest
Bigtime said:
My new answer on this topic is, : :roll:

My advice is, don't put a rod in it that will need a seat for the oil ring on the street.

Some general info: (short rod ratio 1.6, long rod ratio over 1.7)
A short rod pushes on the crank harder so therefore makes more torque
A short rod spends less time at TDC so it is less prone to detonation

Fri Aug 04, 2006 1:08 pm
 

Autometer

Dragway Regular
Oct 29, 2003
1,239
0
0
Houston/Texas
www.addisonracing.com
Cliffnotes anyone?

Well I plan on building a 406. I already have the 6.0 rods. I haven't decided on what crank yet. I did look around but haven't lately to decide on anything. The wristpin is in the oil rings, so there will be some oil consumption? How bad for a street car? It car won't just be for drag racing. Will see some road racing and wondered about oil consumption for about 30 min continuous hard driving?
 
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Anonymous

Guest
I have a 400 block that I plan on using soon. I considered using 6 inch rods until I did some math and found out how short the compression height would be. Any benefit that could be gained from running a longer rod, if there is any, seems like too much of a compromise if you have to run a special oil ring to clear the wrist pin.
 
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Anonymous

Guest
How long must a rod be to be a long rod? Hmm.. how dark must it be outside to be considered dark? I guess the only answer I can see is that a 'long' rod is one any longer than the factory-installed or used length for that combo, at least IMO. Some good discussion here. As to oil ring issues, there's always pin buttons to use...but not what I'd use myself in a street motor.
 

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