One of my customers decided to cheap out and buy the IB spec H- beam rods in comparison to the I beam Crower billets as I advised him to. Unfortunately they did not ask me if there was any difference in the H beam vs the I beam. So I cannot compare the IB I-beam to the Crower I-beam, but I have been told the IB I and H's retain the same dimensions. If someone can prove to me that I have been mislead with information, please do so now. So with that said, here is some information to those of you who have considered running the rods. (I quoted a few sites so I don't have to spend all day typing out explanations here.)

What does the I and H mean?

The shape of the beam when viewed from the end

How are they manufactured? (quoted from an internet site)

"The billet rods are machined from a block of steel to the final configuration. There is considerable machine work and scrap left over when manufacturing in this manner, so the time involved sends the price pretty high.

The forged rods are frequently made from the same materials, but the actual process is far less labor and machine time intensive. The forging dies are engineered to produce a rod, which is very close to the finished rod size and
shape, so there is relatively little additional material removed.

Most folks are unaware that all metal has a grain flow just like a piece of wood. If you make something from wood, maintaining the integrity of the grain is mandatory if strength is a requirement. The same is true with metal components.

If you imagine that a block of billet has a grain flow from one end to the other and you "carve" a connecting rod from it, you now have a tremendous abundance of open ended grain, and that's not desirable for maximum strength. On the other hand, the forging process imparts a grain flow that is continuous from end to end and the machining process removes minimal material, so the grain is largely uninterrupted for the length of the rod. The preservation of the grain provides considerably more strength."

Which one is stronger? (hotrod.com)

"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 centerline 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."


Which design for which application?

Ok now that we have that out of the way... we will talk about which design beam is best for what application.

I beam - best for heavy load motors (ex. high boost pressures) since it handles compression strength better. Now when on a high pressured application (turbo, supercharger) the rod will want to fail/buckle, so to combat that you want to transfer the stress to the outside of the rod away from the axis that will inhibit the failure (the twising/bending moment of the rod since both end points are fixed and not allowed to move). When comparing the top of the rod that connects to the wrist pin, you will also see that the stress will be carried to the outside of the rod whereas with the IB the stress will be transferred to the center of the rod.

However for rod buckling which I imagine is the failure mode for high-high cylinder pressures (like in FI) the material should be concentrated away from the
buckling axis. Most likely bucking/bending would occur about an axis parallel to the crank since in the other direction the end conditions are "fixed" ( ie not allowed to rotate).

H beam - best for high rpm NA applications since the H beam rod is actually stronger in the unloading cycle (piston going down). When you think about it from a concentrated mass point of view, this is where this design is better. Basically your mass is concentrated in the center of the rod and that will result in a lower mass moment of inertia.

Now for the comparison of rods:



IB spec left Crower 4340 Billets right



IB spec left Crower 4340 Billets right





Now... measurement time.



IB spec: 3/8" ARP 2000 bolt
Crower 4340 Billets: 7/16" ARP 2000 bolt



Crower: 3.167"
IB Spec: 3.02"



Crower: 1.106"
IB Spec: .928"



Crower: .570
IB Spec: .549



Same spec.


Now, the IB spec I beam.



Definetely a better design for turbo than the H beam for FI, but still far from the quality of the crowers. The wrist pin location of the rod also tapers into the side like the H beam design unlike the straight design that the crower has. The taper will promote stress transfer but the flaw in my opinion is the actual oblong section that is removed from the front of the rod to give the I design. When compared to the crower, the IB rod does not taper into the I, instead it cuts quite drastically which will not provide the amount of same stress transfer to the outside of the rod that the crower will.

The proof is in the pudding. The IB's are scrawny in comparison and since the cross-sectional area of the two rods are not equal, you know which one will withstand the higher pressure thrown at it before failure is reached. As far as motors that are running the rods, I have not used any on the motors I have built, but I have been told by an EXTREMELY REPUTABLE SOURCE that they have seen a couple of rods fail on 300whp applications up to the low 400's.

I'm not a spokesman for either company, I just want to share this with you guys so when making a rod decision you know all of the pro's and con's. The only flaw with this comparison is the fact that I did not have the IB spec I beam to compare with, but from the reputable sources I have spoken with I have been told the dimensions are dead-on as well as their failure rates. If somebody has an actual I beam rod that they are willing to measure I would appreciate it to verify everything.

 

good post anthony, its interesting to see the differences in specs between the 2 rods, ive always liked crower, but have always wondered the difference between the regular crowers and the eccono crowers

 

sure is, I shoulda listened

 

damn! looks like you could strap a stick of dynomite to that crower rod and it would keep on tickin. back nick, BAD! If at all possible, i would get the crower rods if you have the funds necessary, and sell the others. you cant cheap out on motor parts, you are just askin for trouble.

 

dont worry im not using those toothpicks

im trying to get some crowers right nowd

 

didnt anthony say he had 1 set left in stock ? maybe he sold em. Well anyway, good luck with the build, and awesome info as always from precision

edit: maybe im thinkin he had pistons in stock instead. eahhh i forget.

 

I did have another set of Crower 4340's but they are gone now.

4-6 week order for the next set... unless I can pull some strings. I'll know first thing tomorrow morning.