2.0 Long Rod X, A, or I beam rods

[kidtsi]

I wonder if those pictures came from this paper I was given a bit ago. There is a paper on rod design that a few people cite from time to time, that has some very bad science in it.

The connecting rod is a pinned connection, it should not have any bending moment on it. Bending moment comes from rod bearing friction, so if you have very much, you have other problems.

That plot of bending stresses and compressive stresses, doesn't really apply to us. For my setup, I figure I will have about 10 times the compressive stress at peak cylinder pressure, than tensile stress from the RPM. Besides that, that data looks sketchy at best.

As I said before, If you want any kind of decent life out of your motor, you will keep your maximum compressive stresses less than half of yield strength, and you will be golden.

In compressive stress, all that matters is cross sectional area of the beam. You can see it in the fea picture above, the peak stresses are in the beam where it meets the pin. By the way the rod in the fea picture is an I-Beam.

Oem's use I beams because they are produced more easily.

I stated long rods are over-rated because at the length differences we can accommodate, there is hardly any gain in mechanical efficiency, and little loss in piston acceleration. Don't belive me? Plot that shit. I have.

An H-Beam will have smoother stress flow into the pin bores (big and small) and an overall smoother stress flow, meaning it can withstand higher loads before failure.

For 1100hp you best be running a rugged ass piston pin. Ever wonder why diesel's have huge pins with thick walls? You'll have as much or more cylinder pressure than they do.

By the way, a stroker motor places less compressive stress on the rod for a given amount of torque. You will side load the piston more, and your mechanical efficiency goes down.

I just went through all this in January, with my rod choice. I have had eagle's and put them through way more than many others that have blown them apart lately. Then a guy who's opinion I take very seriously bent one. So I got nervous, and did a bunch of calculations, and consulted my colleges who, are some of the top minds in mechanical engineering, specifically machine design, FEA, and Non-Destructive Evaluation. My calculations were correct, and barring a material flaw, my eagle's were more than adequate for the level I was using them at. And would have been good for plenty more, if I kept the tune a bit more conservative.

I was set to buy Olivers, but I got a deal on Manley Turbo Tuffs. I will be running JE pistons with .210" wall 9310 pins.

FYI when your nearing MBT, a 1* advance can create 33% more cylinder pressure, while only making about 1-5% more torque. Keep that in mind when dialing it in.

Oh, Yes thanks for letting me know i posted the wrong picture there, i have to find the H beam on my filles.

To my understanding not only the peak stresses are in the beam where it meats the pin, but also in the big end parallel to the top.

Thank You for taking the time on posting all this, everything will be taken into consideration, hopefully someone else comes in to give more 4G63 engine related analysis, someone that builds over 100 a year not just 3 to 5 a year like me.

This thread has some amazing information in it. I wanted to quote this as most people don't really understand. This is even more important when tuning E85. Just because you aren't knocking does mean the motor won't pop. to both of you.

If you know anyone that can drop some knowledge, don't forget to let him know.

 

[spoonman]

I will say that I am a huge supporter of aluminum rods and love running them. But application dictates design and material.







Here is a simple observation that I noticed years ago. Both F1 and NASCAR engines employ (for the majority) H-Beam rods. There are no regulatory rules that limit these engines to this specific design. Maybe they know something.


But just an FYI there are plenty of A-Beam rods in F1 also.



At max compressive load, I-beam connecting rods have a higher buckling margin, than H-beam rods of a comparable cross section.



It has been my understanding that H-beam rods are better suited in applications that experience constant fatigue. Road Race, Salt Flat.
And this is due to its design which distributes the compressive load unto the crankshaft journal and bearings.



I-Beams on the other hand can handle very high compressive loads due to there cross sectional design.

I have never bent a rod from "making too much power", a tuning complication or fuel system failure. Yes. But it is more likely that the rod bolts will fail before you bend your rod in half.





As to which design is best? Hard to say. Even the best engineered rod can be manufactured poorly.

 

[bastarddsm]

Here is a simple observation that I noticed years ago. Both F1 and NASCAR engines employ (for the majority) H-Beam rods. There are no regulatory rules that limit these engines to this specific design. Maybe they know something.

It's because an H-Beam has better stress flow than an I beam, and thus they have a better fatigue life. It's pretty simple.

At max compressive load, I-beam connecting rods have a higher buckling margin, than H-beam rods of a comparable cross section.

It has been my understanding that H-beam rods are better suited in applications that experience constant fatigue. Road Race, Salt Flat.
And this is due to its design which distributes the compressive load unto the crankshaft journal and bearings.

I-Beams on the other hand can handle very high compressive loads due to there cross sectional design.

I have never bent a rod from "making too much power", a tuning complication or fuel system failure. Yes. But it is more likely that the rod bolts will fail before you bend your rod in half.

If your worrying about compressive loads, you are either going to replace them often, or you need beefier rods.

Life goes down the closer you get to yield strength, Profile doesn't matter until you yield the rod.

If you have 2 rods of the same cross sectional area, and you load it to yield for the H-Beam, the H-beam will bend on the first or second time it's loaded. The I beam will maintain shape, but fail (break in half) after ~100 cycles.

I'd rather have a rod that gently lets me know I'm asking too much of it, than fail abruptly.

 

[white92talontsi]

For your setup you need a lightweight rod.
One of if not the lightest I-beams would be a R&R steel rod.

The problem you have is at the RPM you turn and with staying in that RPM for a longer time a steel rod is going to reek havoc on bearings unless you have a Dry sump Oil setup.

For what you are doing I would either Run the R&R I beams or R&R aluminum's or BME Aluminum Rods.

You can throw all these Mathematical Equations in the Mix but real world testing tells more.

 

[bastarddsm]

For your setup you need a lightweight rod.
One of if not the lightest I-beams would be a R&R steel rod.

The problem you have is at the RPM you turn and with staying in that RPM for a longer time a steel rod is going to reek havoc on bearings unless you have a Dry sump Oil setup.

For what you are doing I would either Run the R&R I beams or R&R aluminum's or BME Aluminum Rods.

You can throw all these Mathematical Equations in the Mix but real world testing tells more.

That sounds like an oil system problem, not a connecting rod weight problem. Fix the problem, not treat the symptoms.

Lot's and lots of people run heavy steel rods at high RPM for long periods of time with more stroke than our motors, and have no problems.

 

[white92talontsi]

That sounds like an oil system problem, not a connecting rod weight problem. Fix the problem, not treat the symptoms.

Lot's and lots of people run heavy steel rods at high RPM for long periods of time with more stroke than our motors, and have no problems.

Yes and a 4G63 does not have the best oil system. With the bearing clearances required to keep a 1,000+hp 4G63 together the OEM oil pump will not keep up no matter what you do with it.

Even with a Dry Sump a heavy steel rod is not ideal.
The OEM oil pump at 9500RPM is the limit. People can argue all they want about it but the "facts" are out there and have been proven.

 

[Diamond Star Werks]

Since good info about high revving and the oil pump issue here.
http://www.dsmtuners.com/forums/showthread.php?t=458085

 

[Diamond Star Werks]

http://www.dsmtuners.com/forums/showthread.php?t=458085

 

[kidtsi]

My concern its not oil supply or to to high of an rpm for the stock Mitsubishi oil pump, all that is addressed since last year (Noticed i have been revving to 10,500 already) , as-well as an custom oil pump which i would not like to discuss here, maybe in another thread.

Lets not get off topic, maybe for someone else Aluminum rods will work better, not for my situation though, like i said i have Aluminum rod motor with Gorden Rods on them, which would be used for a different environment.

 

[kidtsi]

For your setup you need a lightweight rod.
One of if not the lightest I-beams would be a R&R steel rod.

The problem you have is at the RPM you turn and with staying in that RPM for a longer time a steel rod is going to reek havoc on bearings unless you have a Dry sump Oil setup.

For what you are doing I would either Run the R&R I beams or R&R aluminum's or BME Aluminum Rods.

You can throw all these Mathematical Equations in the Mix but real world testing tells more.

Are the R&R Billet I Beam lighter than 562g?

 

[white92talontsi]

Custom R&R 162mm I beam.

 

[bastarddsm]

That's pretty light. What's the cross sectional area of the beam on that?

 

[chaclark83]

I wish R&R's website had more info on it. Its a little lacking.

 

[white92talontsi]

I wish R&R's website had more info on it. Its a little lacking.

Call and talk to Mike, There is not many application specific things you can look up on there.

R&R can make any rod that you want. If you know all the dimensions they will make it. If you want one for your Briggs and Stratton they can make it.