H Beam Vs I Beam Conrods

[Kranker]

Now ive pretty much settled on the bottom end of my RB26 build. CP pistons, Shotpeened nitrided and balanced std crank and Pauter rods. Only thing is Pauter rods are a bit pricey compared to some other rods, but you get what you pay for.

So what I want to know is what the general consensis is on conrods:

I beam or H beam. (Pauter rods are neither I or H beam, they are a cross or x shape, but im only concerned with I and H)

From what I know (and im still learning), I beam rods are lighter and stronger than H beams.

However ive read that when a H beam distorts or bends it does so much slower and in a more controlled way than an I beam.

So if your H beam rod goes, you have more time to turn your engine off and save it from destruction.

Dont know how true it is, there is a bit of mystery and magic when it comes to engine internals.

Would love to know what you all think.

H beam left, I beam right

[djr81]

Stop me if this gets too boring.

The four main issues are:

1. Strength in tension.

2. Strength/buckling resistance in compression.

3. Weight

4. Inertia (Different to 3)

#1. This is pretty easy - the more metal the conrod has in the cross section the stronger it will be.

#2. This is a function of both amount of metal in the cross section (ie how many mm's squared) & also the geometry of the thing eg H or I section. All else being equal I section is better - that is why they make beams in buildings in an I pattern.

#3. Obvious - lighter = better.

#4. Inertia - this is where the H beam picks up on the I beam. It has less inertia - remember that the rod goes around as well as up & down. Means that H beam rods will allow the engine to pick up revs slightly quicker.

Oh and as regards the rapidity with which they fail - dont worry about it. Once they go its going to get ugly quickly.

As to the Pauter rods - I have NFI why anyone would want to use that pattern for a conrod.

For me for a turbo motor I would go I section.

[Kranker]

Thanks djr81, great response.

Not boring at all, I love the physics of how engines work (im studying automotive engineering).

Lots of good info there.

From what ive read aswell, I beam is the way to go.

Cheers

[Kinks]

So if your H beam rod goes, you have more time to turn your engine off and save it from destruction.

I'm interested in the physics of it too, good wrap-up djr.

Pretty much any situation you get yourself into where you're bending a rod, is one where human perception of the problem and reflexes are absolutely hopeless. Anyway, a well built motor should not be anywhere near that situation.. ever!!

Go with the best performing rods and stop worrying about it is my advice

[Kranker]

Yeh i wasnt really worried about actually bending a rod,

Is meant as more of a discussion and throwing ideas around thread.

Not as a "which rod should i buy".

I like a good technical thread.

cheers for the replys.

[Kranker]

This is what a Pauter rod looks like anyway...

Its supposed to be some pretty good gear.

[rb26s13]

Very interesting about those pauter rods did a little search n found this

PAUTER RODS

Pauter Rods has years of hands-on experience working with rods of all shapes and materials. Through different types of racing-related abuse, and the resulting design successes (and failures), PAUTER has acquired a fairly comprehensive file on just what works - and what doesn't - on the subject of high performance connecting rods. From this body of knowledge they've selected and incorporated elements into what they think a great rod should be.

For starters, the simple beam design completely eliminates thin and non-uniform cross sections over the total length of the beam. This feature greatly improves resistance to crack-induced metal fatigue. In addition, the non-tapered profile of the beam helps to spread potentially harmful stress over a larger area, dispersing instead of concentrating these destructive loads. The design also efficiently places needed material in critical transitional areas, giving maximum support exactly where it is needed (such as directly under the wrist pin). The streamlined contour also provides subtle benefits in the form of windage reduction and breather/vacuum system function. The main beam rib continues around the wrist pin boss, perfectly integrating beam to boss, affording a small but important contribution to overall structural unity.

PAUTER RODS features:

• E4340 vacuum melt chrome moly forging, heat-treated to Rockwell C36

• All surfaces 100% CNC machined, and shot peened for stress relief

• Pauter 220,000 psi tensile strength MSP220 steel, J-formed, rolled thread racing rod bolts

• Aluminum-bronze wrist pin bushings

• EDM pressure-fed oiling to pin (available at extra cost.)

• Custom pin diameters and center-to-center rod lengths

• End-to-end balanced in sets.

[Bl0r]

Strength in tension is irrelevant for “H” or “I” rods. The weakest points in tension will be at the circular connections, orbits or whatever you want to call them, their cross sectional area combined will be less than that of the body of the rod. Either that, or the pins depending on their areas.

Buckling will occur in the middle of the rods, at the highest moment of inertia. Each of them by design has a weaker plane where they will buckle. The “I” rods will always buckle and gain in on its wider face (think about which way they’re used in buildings, they’re never used face up…). This is apposed to the H rods, which will tend to buckle towards the edges, or the outside of the rods. This direction is where most of the resultant shear forces and moments will occur in a connecting rod under normal conditions. With respect to this the “H” beam is less effective at holding normal loads common to an engine.

piston play or rattle will induce higher shear stresses in each beam depending on which way the piston deflects. The most common way for it to deflect is back and forth along its free axis; here the “I” rod would be better again because it’s in a stronger plane. However! The worst part about this would be the increase vibration and the effects of vibration will be more severe for the “I” beam because it will promote deflection along its weaker face.

Pistons can also twist under load. This will induce a torque and axial shearing and strain. Even though the highest points of rotation are on the outsides of this axis, you might assume the “I” beam will resist it better because it has more cross sectional area here. but because of its shape it will induce a high amount of strain before this comes into play.

Basically the “I” beams are superior at supporting normal (as in no deflection or vibration; linear, on-axis) engine conditions or loads and the “H” beams are better at coping with abnormal (vibration, twists ...et cetera ...) engine conditions or loads. That isn’t to say that H beams can support higher HP applications.

If you have a very good condition, decked, honed, rebuilt modified engine that runs smooth, I would go the “I” rods because, tuning permitted, they will be able to hold slightly higher amount of normal stress. But if you have major cam-age, stroker kit or a worn out older engine with more play in your parts like pistons and bearings Go with the “H” rods.

[Kranker]

Thanks for that Bl0r,

Good info there. Sounds like you know your stuff.

Again, I beams are reccomended.

Correct me if im wrong, but would building your engine "tighter" as in lower tolerances and gaps, reduce the rist of play and/or rattle? Therefore lowering your chance of causing damage?

rb26s13, the pauter rods are interesting arent they, i gotta do some more research.

Is anyone on here running them?

[Sydneykid]

The guys have pretty well covered it, I would add that I beam rods are better at taking impact than H beam. Any slight nick in an H beam rod and it's a throw away.

BTW, RB cranks are double nitrided standard, so shot simply bounces off, hence peening is a waste of time. As of course is nitriding them again. Check the straightness, lightly linish the bearing surfaces, balance it and move on.

cheers

[r33_racer]

dont pauter specialise in titanium rods? Isnt that their claim to fame? or is it ally rods?

[Bl0r]

Correct me if im wrong, but would building your engine "tighter" as in lower tolerances and gaps, reduce the rist of play and/or rattle? Therefore lowering your chance of causing damage?

lower tolerances are better with most things. but others. not so much. like pistons for example, drag cars have larger clearances between pistons and walls, this is to account for a difference in thermal expansion and pancaking of the piston through axial straining. (poissons ratio? ) thats why they can sound very rattley at idle and then they go PWHAAAAAORRRRRRR *screech* - NEEEEIIRRRRRRRRRRROOOWWWWWWWWWW, and then FKNBANG!@ (if its a holden). so if your clearances are too low its going to seize and if you have it too high your going to get blowby and an unhappy cylinder wall and piston skirting. as far as everything else goes, you want it smooth with no play, not exactly "tight".

as far as rattle goes, everyones heard it, especially when you push an old car in a low gear up a hill... its that eerr, rattling sound. even though i made mention of it in regards to conrods (disregarding the vibration caused) it damages your pistons and cylinder walls moreso than your conrods. its a normal thing (if you dont know how to change to a lower gear, or you drive an older automatic) and if you want to eliminate it by changing tolerances and inserting bigger cylinders, be prepared to seize your engine .

[djr81]

Buckling will occur in the middle of the rods, at the highest moment of inertia. Each of them by design has a weaker plane where they will buckle. The “I” rods will always buckle and gain in on its wider face (think about which way they’re used in buildings, they’re never used face up…). This is apposed to the H rods, which will tend to buckle towards the edges, or the outside of the rods. This direction is where most of the resultant shear forces and moments will occur in a connecting rod under normal conditions. With respect to this the “H” beam is less effective at holding normal loads common to an engine.

Not always....

[Kranker]

Pauter do make titanium rods, which are supposed to be dam good,

but they are much more expensive than their E4340 rods. Quite frankly out of my budget.

A set of 6 E4340's for your RB26 will cost $1176 USD, while a single titanium rod costs $1350 USD, thats $8100 for a set...ouch!!!

[2rismo]

Not always....

That'll buff right out!

[shanef]

That'll buff right out!

what about this one?

[Gav]

rb26s13, the pauter rods are interesting arent they, i gotta do some more research.

Is anyone on here running them?

I know of 5 RB engines in WA running Pauter rods (including mine). Many of these have been rebuilt after engine failures with the Pauter rods surviving just fine. Their manufacturing tolerences are extremely tight both in dimensions and weight also.

Can't say if they are better or worse than other designs, but I would probably use them again.

[2rismo]

what about this one?

"It is not the rod that bends...."

/matrix chick

[STATUS]

then you get some US race engine guru saying;-

"For years the battle has raged on as to which is better, an I-beam or an H-beam. In pure tension and compression, they are both equally capable, assuming equal cross-sectional area. But when you add the fact that some components of the combustion event attempt to screw the piston down the cylinder, the greater distance from the center-line of the pin to the edge of the beam gives the H-beam an advantage in resisting such twisting forces. We've seen both designs used successfully in a wide variety of extreme applications, so the jury is still out. Perhaps the biggest advantage of the H-beam design is that it gives the manufacturer more flexibility when sculpting the rod into the most effective form from a strength-to-mass standpoint"

Honestly i believe for our cars that ultimately the quality is more important than design, take for example TOMEI, TRUST (Carrillo) and various other companies all choose to use H-beam over I-beam because the service life is considered longer.

Tomei

http://www.tomei-p.co.jp/_2003web-catalogue/e060_conrod.html

GREDDY (offer H as premium and I as entry level)

http://www.trust-power.com/05engine/connecting_rod_i.html

HKS (premium rods)

http://www.hks-power.co.jp/products/engine...ting/index.html

Flip a coin and go for a reputable brand....

Budget - I-beam or A-beam (brand) or SCAT H-beams

Flush - H-beam (brand)

Rolling- exotic shizzle

[N I B]

Another vote for Pauter rods.Most top US Compact teams use them.Never had one or even seen a broken Pauter.