H Beam Vs I Beam Conrods

[RB30-POWER]

Wouldn't metallurgy play a part as well, regardless of if its of H or I beam design if its made from chicken shit, it will be shit.

Shouldn't be much of a problem with reputable rod makers however...

[Kinks]

we're assuming "all other things being equal"

[Dejavu]

H-Beam: Offer the same strength at a weight advantage (ie lighter). The I-Beams are stronger in the case of a engine failure as they will smash through things that they hit

[Turbz_13]

after seeing those piccys im glad i threw in some H-beam eagle rods into my 26!!

[djr81]

H-Beam: Offer the same strength at a weight advantage (ie lighter). The I-Beams are stronger in the case of a engine failure as they will smash through things that they hit

Stonger - ok then how?

Stronger in tension?

Stronger in compression?

Stronger in bending perhaps & if so along which axis.

Stronger in torsion?

More resistant to fatigue?

The bottom line is that unless you can physically compare two rods (ie side by side), measure them up, weigh them etc etc there is no mechanism to make a sweeping statement about which is stronger or better. That is why you can commonly find both types.

Having said that I take the viewpoint that there are three things that will probably lead to the demise of my engine as far as the conrods are concerned:

Fatigue ie crack resistance.

An over rev ie wrong slot on the gearbox - this is about tensile strength & cross sectional area.

Failure in buckling about the same axis as the crank caused by bad tune or by getting too greedy with the boost.

For me the nominal advantage of an H beam rod ie lower rotational inertia is not of much interest in a short stroke turbo engine that only revs to 8000rpm.

So I would prefer an I section rod on first pass.

Lastly how is it that one of the conrods most important geometric properties -ie ITS LENGTH - never gets mentioned?

[Bl0r]

Stonger - ok then how?

Stronger in tension?

Stronger in compression?

Stronger in bending perhaps & if so along which axis.

Stronger in torsion?

More resistant to fatigue?

The bottom line is that unless you can physically compare two rods (ie side by side), measure them up, weigh them etc etc there is no mechanism to make a sweeping statement about which is stronger or better. That is why you can commonly find both types.

Having said that I take the viewpoint that there are three things that will probably lead to the demise of my engine as far as the conrods are concerned:

Fatigue ie crack resistance.

An over rev ie wrong slot on the gearbox - this is about tensile strength & cross sectional area.

Failure in buckling about the same axis as the crank caused by bad tune or by getting too greedy with the boost.

For me the nominal advantage of an H beam rod ie lower rotational inertia is not of much interest in a short stroke turbo engine that only revs to 8000rpm.

So I would prefer an I section rod on first pass.

Lastly how is it that one of the conrods most important geometric properties -ie ITS LENGTH - never gets mentioned?

how does a H beam have lower rotational inertia? just a bit confused about that.

over revving about tensile strength and cross sectional area? as far as i know that has everything to do with friction and heat --> seizing and pre-detonation. and also, everthing, more, plus, times, ten to the power of infinity to do with the spring rate on your valves. ie: too high revving the spring doesnt retract the valve fast enough and you have a collision and detonation.

length has not been mentioned because its not a factor in a comparision between H and I beams. they both are the same length.

even though theyre pretty much the same shit.....

ill run some numbers for the F**k of it

stay tuned.

Edited June 25, 2007 by Bl0r

[djr81]

how does a H beam have lower rotational inertia? just a bit confused about that.

Essnetially the same property that gives an I section better bending resistance (buckling resistance) about the crank axis gives it more rotational inertia.

over revving about tensile strength and cross sectional area? as far as i know that has everything to do with friction and heat --> seizing and pre-detonation. and also, everthing, more, plus, times, ten to the power of infinity to do with the spring rate on your valves. ie: too high revving the spring doesnt retract the valve fast enough and you have a collision and detonation.

Yes it is, but I did say as far as the conrods are concerned.

length has not been mentioned because its not a factor in a comparision between H and I beams. they both are the same length.

I understand this, but different length conrods can give markedly different results on the dyno. I just find it odd that no one bothers thinking about this one very important property.

even though theyre pretty much the same shit.....

ill run some numbers for the F**k of it

stay tuned.

Have fun.

Edited June 25, 2007 by djr81

[STATUS]

Essnetially the same property that gives an I section better bending resistance (buckling resistance) about the crank axis gives it more rotational inertia.

Yes it is, but I did say as far as the conrods are concerned.

I understand this, but different length conrods can give markedly different results on the dyno. I just find it odd that no one bothers thinking about this one very important property.

Have fun.

yeah but you can get both i & h in different lengths so it is a moot point in a comparison. I do however agree that altered wrist pin location can have some interesting results, we used to do this alot in V8's especially clevo's and holden platics.

[djr81]

yeah but you can get both i & h in different lengths so it is a moot point in a comparison. I do however agree that altered wrist pin location can have some interesting results, we used to do this alot in V8's especially clevo's and holden platics.

So out of interest can you offer any insights with regard to RB rod lengths?

[STATUS]

So out of interest can you offer any insights with regard to RB rod lengths?

I honestley have never played with rod length in RB's.

Below is a PDF which explains the effect of rod length change, be awre it is for NA but the priciples are the same the application differs somewhat though.

RodLength.pdf

[donkey]

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.

hey sorry of the subject a bit, but god that batman thing is funney, the way he runs, excellent

[FineLine]

what about this one?

That one might need a full cut and polish

[bigmikespec]

Great thread, can see this getting a bit heated, so I will add my bit

I can see some people getting excited wanting to do some calcs on this. It is easy to apply basic stress theories to this stuff but for engine components it is very difficult to get an accurate answer. I mean, you can't even represent an engine cycle on paper without delving into some of the most complicated thermodynamics known to man!

Any answer you get will be very "approximate". Don't neglect temperature as being one of the most critical factors in the life of internal engine components. You have to factor in the growth of the component and changes in material properties due to high/low temperature changes. Each component has different metallugical compositions which would cause the materials properties to change at different temps... talk about a can of worms.

Anyway, good luck to who ever wants to have a crack.

Big Mike

[djr81]

The simple truth is that there are too many different considerations to get a definitive answer. There are any number of failure mechanisms, multiple areas of the conrod you need to focus on for strength considerations (eg little end, the rod proper, area adjacent to the crank, bolting etc etc), weight, materials,fit, finish, price & any number of other considerations. That is before you start factoring different engines, BMEP figures (or their peak equivalents), fuels, rev limits etc etc etc

Best advice is probably to find something you like & check it has been proven in similar applications.

[Roy]

Thread revival.... so who makes the lightest 26 rod that is decent enough, will have to handle around 350rwkws

It seems:

- Pauter are 530g

- Spool 548g

- Carrillo 474-507 depending on which rod

- Eagle 495g (I like)

- Argo ? RB30 rods are 643 so seem towards the heavier end of things

So the Eagles seem cheap, reliable and light? Anything i am missing?

[mr 32]

Thread revival.... so who makes the lightest 26 rod that is decent enough, will have to handle around 350rwkws

It seems:

- Pauter are 530g

- Spool 548g

- Carrillo 474-507 depending on which rod

- Eagle 495g (I like)

- Argo ? RB30 rods are 643 so seem towards the heavier end of things

So the Eagles seem cheap, reliable and light? Anything i am missing?

rb26 argos are 568 grams each and rated at 250hp per cylinder

[T-Rex]

Thread revival.... so who makes the lightest 26 rod that is decent enough, will have to handle around 350rwkws

It seems:

- Pauter are 530g

- Spool 548g

- Carrillo 474-507 depending on which rod

- Eagle 495g (I like)

- Argo ? RB30 rods are 643 so seem towards the heavier end of things

So the Eagles seem cheap, reliable and light? Anything i am missing?

Carrillo rods are a much better built rod than Eagle. I have had both side by side and after seeing the difference i would never buy an Eagle rod. I know there are a lot of high horsepower cars with Eagle, but in my opinion they are a second class rod compared to Carrillo. Also Carrillo have the option of CARR bolts which are stronger than the ARP2000 bolts that most rods come with, you will snap the rod before the bolts break!

[Roy]

BUT, 250hp x 6 is a lot i need more like 85hp per rod If they were not that much more expensive and lighter then ok...but no point going to a heavier rod which increases loads on crank and bearings if i dont need that sort of strength for my power goals ?!?!?!?!!?

[Ziller]

I beam or H beam?, I don't really know I'm not an engine builder, but I do know as a tradesman working in the building industry for many years, by sheer weight and design all the load bearing metal structure's that are built tend to use the H beam design, It;s been done that way for over 100 years, just my 2c

[bigmikespec]

Thought I would have my first go at thread digging/revival...

Anyone used Carillo A-beams? Or even used a set of H or I Carillo's with pressure feed oiling?

Care to comment?