Gez

Hi Chaps,
Hope you have all had a nice Xmas! Well i have, the booze has started to wear off and before i get started on tommorows lot i wanted to ask what the difference between H section and I section con-rods! I see many people use Arrow rods in their re-builds but there are also many people using I sections! Are there many differences? Is one more stronger than the other?? Do they have different properties in the way the manage forces passed through them ??
Any input appreciated.

Regards

Gez

Katana

Um, in engineering classes, they're refer to the same thing. Now I'm getting confused. I must pay more attention to the lectures..

Gez

I wish i took note when i did a couple of automotive engineering modules at Uni. And i thought it would never come handy!

Gez

R19KET

According to the various rod manufacturers that "I've" spoken to, "I" section is stronger, and "H" section, lighter.

This is the general "rule of thumb", but vary in strength/weight, depending on manufacturer.

Whatever you decide to use, just make sure that it's been tried, and tested at the level of power you want to run.

Mark.

Katana

Now I'm confused. I thought they were the same thing. You might have just saved me from failing structures.

Pavlo

rotate an I section 90 degrees and you have an H section. Just a matter of which side the webs are on.

See here for some pictures by SMG. The Arrow rod is the one machined from a forging on the left, and it's an I section rod.

Katana, you'll have to pay more attention in classes than that...

Paul

Katana

I do, what i forgot to mention is that i'm hardly ever there.

joke.

Gez

Is there somewhere where i can check to what power/torque force etc various rods have been subjected too?

nom

Well, from my knowledge of this stuff (but it is the wrong sort of engineering ) I or H depends entirely on which direction the forces are coming from. H can be stiffer - and lighter - but at a reduced number of angles. I (or at least a 'rod type' I, which is more like a x if you ask me...) should be able to cope with less, but is less 'angle dependant' if you see what I mean?
My guess from this would be that as the 'angles' are purely compression/tension along the long axis (or are unless you're in trouble ), you want toughness to counter fatigue. Which would be the I (or x) section. Except the (possible) lightness of the H would reduce the forces to a point and so make the stresses lower, although that would be more dependant on the piston...

David_Wallis

paul...

erm..

read what steve said

David

Pavlo

okay david, you got me! I goofed! Dunno why I called the arrow an I section rod, I must hav been thinking of the std rod and looking at the arrow one, or something

Katana 1, Paul Nil

Sorry for the confusion!

Not enough sleep, (if you want less, get a baby!).

You can sit down and measure the section modulus (stiffness) if you like, i would estimate that the H section rods are less stiff in bending around the crank, and stiffer when trying to bend normal to the crank. But it really depends on the numbers.

A stiffer rod will be less prone to buckling, but if you compare the Arrow rod to the std rod, you can see the extra depth in the rod section. So much so I don't think bending would be an issue with these at all (and bending vs snapping is covered elsewhere .

I think the main thing is that some companies want to make parts that are different, and stand out, which the Arrow rods certainly do. But to my knowledge, I've never heard of any good quality (Arrow, Farndon, Lateral Performance, Carrillo etc) rods being the cause of failure on any high poweredscoob engines.

I'm sure Mark would tell you, if he was sly enough to give you a sales pitch for his rods, that the Lateral Perfomance rods are the same as those used on cars in Oz with over 500hp at the wheels, and that there have been no rod failures.

I think you'll find that correct design of the details, choice of material, heat treatment and surface finish/treatment are the most important things. You can have a bad implementation of either an I section or H section rod.

Paul