Connecting rod design?

[Machineman]

What are people thoughts on con rod styles i have been working on modeling rod for my 3.0 tdi build and have been informed that h beams are inferior apposed to a i beam design i have modeled both styles and weight seems to be similar although depending on cross section

 

[Machineman]

 

[Machineman]

 

[Machineman]

 

[Fix_Until_Broke]

I believe the H beams are much stronger than stock and easiest to manufacture, however the I beam is ideal from a strength to weight ratio and most efficient use of the material due to the moment of inertia.

TDIMiester had a great explanation on this a few years ago - if I find it, I'll post a link

 

[mrchill]

I usually use H beams. I find them lighter than I beams....and more than strong enough.

 

[[486]]

H-beam's easier to hack outta a generic rod blank
just gotta use a horizontal mill cutter to get the sides hollowed out, instead of a small cutter in a vertical to profile the windows in the big end

I beam is preferred for reasons that elude me, but it takes either a lot of time with smaller cutters, or dedicated forging dies to make the blank for only the one rod length

 

[Digital Corpus]

This flame war has numbers in it and a whole bunch of reasoning before it devolved:
http://forums.tdiclub.com/showthread.php?t=427563

I think I know what post FUB is talking about, but I can't find it either.

 

[Fix_Until_Broke]

Thanks for the link - Post 42 is the one I was thinking of, however the whole thread is worth a read for context

http://forums.tdiclub.com/showpost.php?p=4663440&postcount=42

 

[Machineman]

Well this topic has me stumped I'm starting to wonder if it's worth it I have the 4340 material to make the rods already but I am wondering if I will never achieve the breaking point of stock ones I have ran 75 lb of boost on bhw rods without any failure and the 3 liter TDI rods are even more robust they have 30mm pins and a larger cross section in the beam they already been confirmed to 500 awhp with bobbys car I just don't want to be the one that pushes them to 650 Hp and they break

 

[andy2]

I'd say it depends on how much torque that you put through the engine.If you plan on running a big or large single then the factory rods might be ok.

If running compounds then mabye consider a rod upgrade.

My old ALH based engine years ago broke 3 out of 4 H-beam rods.
I now use aftermarket I-beam rods with a 3/8" rod bolt.

The funny part was that I had the BEW rods in my old ALH and decided to upgrade to the H-beam rods as I was worried about the BEW rods failing.

It might be possible that the PD rod would take all the power/rpm I could make with only mabye upgrading the rod bolts,who knows ?

 

[adamss24]

If you intend to drag the engine then by all means- upgrade the rods, if you are thinking to drive the car sensibly and let it warm properly then stock rods will last... I have been in bobby's car and it sounded fine on a full throttle and he was driving it properly! Them 3.0 tdis are strong engines!

 

[Machineman]

I'd say it depends on how much torque that you put through the engine.If you plan on running a big or large single then the factory rods might be ok.

If running compounds then mabye consider a rod upgrade.

My old ALH based engine years ago broke 3 out of 4 H-beam rods.
I now use aftermarket I-beam rods with a 3/8" rod bolt.

The funny part was that I had the BEW rods in my old ALH and decided to upgrade to the H-beam rods as I was worried about the BEW rods failing.

It might be possible that the PD rod would take all the power/rpm I could make with only mabye upgrading the rod bolts,who knows ?

You broke a set of rostens right ? So you're running I beams ?? Are those the cuttingham ones

 

[andy2]

Yeah,Cunningham I-beam.They are a heavy rod in comparison to the H beam but that doesn't seem to matter at all.

 

[[486]]

Still on the smaller journals to fit the larger bolts, I assume?

ETA: on stock rod failures, every ALH with supposedly "weak" rods I take apart already has #2 and 3 bent from getting slugged with oil
No rod has any strength if it's already bent.

ETA2: take this post as a vote for stock rods, possibly with better bolts

 

[Machineman]

I already have upgraded arp2000 bolts for the stock rods

 

[Macradiators.com]

Arent rods available yet for the 3.0 engine ? I see you are custom making them.

 

[Machineman]

Yeah,Cunningham I-beam.They are a heavy rod in comparison to the H beam but that doesn't seem to matter at all.

I think im gonna go for a i beam design

 

[Machineman]

Arent rods available yet for the 3.0 engine ? I see you are custom making them.

Nothing available that i know of that is why im considering the effort/risk of making them

 

[Machineman]

Yeah,Cunningham I-beam.They are a heavy rod in comparison to the H beam but that doesn't seem to matter at all.

Were your rods from Cunningham forged machined or billet machined ? I know they do either or

 

[Pat Dolan]

The whole purpose of a rod is to remain in column to carry compressive load, and from the lateral reciprocating forces, and I beam has cap strips to give greater bending strength for same given mass.

 

[brnsgrbr]

Thanks for the link - Post 42 is the one I was thinking of, however the whole thread is worth a read for context

http://forums.tdiclub.com/showpost.php?p=4663440&postcount=42

Thanks for the link!


Sent from my iPad using Tapatalk

 

[diffas]

Where did you get bolts from?

I already have upgraded arp2000 bolts for the stock rods

 

[Machineman]

Where did you get bolts from?

They're the same ones used in the older two liter tfsi m8x50

 

[Machineman]

If you are interested in them I might sell them cuz I might upgrade to M9 they have never even been torqued

 

[andy2]

Were your rods from Cunningham forged machined or billet machined ? I know they do either or

They were forged machined.I don't think it matters too much if it is I beam or H beam as long as there is enough extra mass to the rod.

 

[diffas]

Actually I might. I ordered 2.7biturbo bolts but they are bit beefier. I think they are m9 even etka says m8.5. Wanna change? Haha. To me they are useless anyways.

If you are interested in them I might sell them cuz I might upgrade to M9 they have never even been torqued

 

[TDIMeister]

I have never, ever seen separated rod caps and pistons through the head due due to failed big-end bolts in a TDI. More like a subtle but noticeable squiggly bend along the length of the main rod column to something more dramatic like Andy's pic above but in any case, the bolts have not been the weak spot.

Edit: @Machineman, since you've already modeled both I- and H-beam rods in SolidWorks, you can easily query the software to report the moments of inertia Ix and iy of both designs. It would be very illuminating if you would post the results. And if your SolidWorks has the FEA module, you could do a quick and dirty stress analysis at different rod inclinations. I can give you some representative cylinder pressure vs. crank angle data for that analysis if you like.

 

[diffas]

Oe bolts most likely holds just fine but rather safe than sorry. High reving engines with heavy pistons are most likely cause of rod caps to seperate.

 

[Machineman]

Actually I might. I ordered 2.7biturbo bolts but they are bit beefier. I think they are m9 even etka says m8.5. Wanna change? Haha. To me they are useless anyways.

Are they arp2000?