H and I beam rods

[southy]

Hey just wanting to know the difference between H and I beam rods?and which one would be stronger?

[HARVZ-6]

i could only assume H beams would be

[southy]

yea, im guessing tht it would be the cross section of the rods, and yea i wouldnt have a clue what ones stronger.

[vyjess]

its no so much the i beam or h beam part of the rod that gives u trouble its the size and quality of the rod bolts and the strength of the area around them is the more inportant part! a standard i beam with good rod bolts and prepped properly will be alot stronger than a cheapo set of h beams!

[dons vs]

if you grabbed a rod and cut the little end section off and looked straight down the rod you will see a H or an I, that is where they get there names from one is shapped like a H and the other shapped like an I.
generally the I beams can be much lighter and are normally used in factory casting rods and some aftermarket gear although normally with aftermarket I beams they will take them to an A which is similiar to an I only with a much more stout bottom section.
The H beams are normally for high horse power engines and normally only an aftermarket forged or billet rod.
cost is much the same really though for retail anyway in fact some times the I beams are more expensive.

But its not just the shape of the rod you need to know, little end and big end weights are a big factor plus the over all weights and thickness of the rods.
material used and the fasterners used.
most off the shelf aftermarket rods will handle 500+hp so you dont really need to get to picky with them if your in the market for a set.
Just pick a set thats at a good price, a descent name and comes with some arp2000 bolts.
not to sure about commodores but a good set of h beam rods for jap 4 bangers are around 500-600 with arp bolts and a U buet set with arp625's or something can be around 1k
generally commo stuff is much cheaper but thats to give you an idea.

[southy]

thanks don im not lookin for any as of yet, but its jus been a question that i have wanted to ask just to clear things up. but cheers

[SilverVH]

dons vs: I agree mostly with what you say apart from 1 thing, that being rods handling a specified amount of HP.

Revs is what will kill a rod, not outright HP. You could safely make 500+ on a set of A9L's if revs are kept to a minimum, its when you start revving a motor hard when rods will stretch and break. H-beams are a stronger rod due to their design and will allow for higher revs whilst stretching and not suffer from breakage or un-roundness of the journal. I've seen I-beam rods last in 550hp motors and when pulled down, they are like new. Preparation is the key to having it last, balancing of the drivetrain is what is paramount to keeping an engine alive.

Hope this helps.

[dons vs]

your right revs do kill rods but out right hp can as well. All to do with the amount of force the rod can withstand, obviously with more hp your going to have a higher shock load on the charge which will put much more stress on the con rod.

[greenfoam]

dons vs: I agree mostly with what you say apart from 1 thing, that being rods handling a specified amount of HP.

Revs is what will kill a rod, not outright HP. You could safely make 500+ on a set of A9L's if revs are kept to a minimum, its when you start revving a motor hard when rods will stretch and break. H-beams are a stronger rod due to their design and will allow for higher revs whilst stretching and not suffer from breakage or un-roundness of the journal. I've seen I-beam rods last in 550hp motors and when pulled down, they are like new. Preparation is the key to having it last, balancing of the drivetrain is what is paramount to keeping an engine alive.

Hope this helps.

Also L34/A9L rods were used at Bathurst for many years at 7500-8000 rpm with 500 hp

[SilverVH]

Greenfoam, the state of the rods after a race wern't to healthy lol, engine failures wernt due to piston shattering either hehe.

The point I was getting across is there is no set HP limit on a set of rods They should be rated with revs in mind, even a perfectly balanced billet rod will still banana if you push it to hard, but no need to get into engineering lessons!

[dons vs]

its not just revs, boost and outright hp can kill them, poor oil pressure, detonation, there are heaps of reasons for rod failure.
Most of the rods we buy state a hp and rpm rating in there specs

[Reaper]

Greenfoam, the state of the rods after a race wern't to healthy lol, engine failures wernt due to piston shattering either hehe.

The point I was getting across is there is no set HP limit on a set of rods They should be rated with revs in mind, even a perfectly balanced billet rod will still banana if you push it to hard, but no need to get into engineering lessons!

Most of the engine failures in that era were not the fault of the rods. During the 70's root cause was due to a poor oiling system exacerbated by a stock sump and oil pickup particularly in the L34's. They did get around it somewhat by running an "oil cooler" which acted as a quasi dry sump however it took some time to iron out all of the glitches.

During the mid 80's there were a lot of failures due to the new "A9L" heads being poorly cast with flash being left in the coolant galleys causing hot spots, head gasket and other failures. This showed up at the HDT effort at SPA.

The later engines from the mid 80's onwards failed around the rear main where the blocks cracked. Check out the latest "Australian Muscle Car" magazine which documents these failures quite well.

Reaper

[SilverVH]

Where did I say rod failure was the main cause of engine failure? :S I said they wern't to healthy, if anything, the fact they held together should be a testament to their durability.

All I was saying is there should be no concrete HP rating on a set of rods. A 400HP engine revving to 8000rpm will damage a rod long before a 400hp engine revving to 5000rpm will. (Basing it on HP vs. Revs with no extenuating circumstances ie. oiling issues, tuning issues etc.)

Or am I by myself with this one.
Wasn't trying to start arguments guys lol

[Reaper]

Where did I say rod failure was the main cause of engine failure? :S I said they wern't to healthy, if anything, the fact they held together should be a testament to their durability.

The words you used eluded to rod failure being a major cause.

All I was saying is there should be no concrete HP rating on a set of rods. A 400HP engine revving to 8000rpm will damage a rod long before a 400hp engine revving to 5000rpm will. (Basing it on HP vs. Revs with no extenuating circumstances ie. oiling issues, tuning issues etc.)

Why not? Surely it would be an ideal indicator for the application. I think it is fair to require that the other systems on the motor are functioning correctly. It is a bit much for a manufacturer to accept liability if his component was an innocent casualty of war.

Reaper

[dons vs]

Where did I say rod failure was the main cause of engine failure? :S I said they wern't to healthy, if anything, the fact they held together should be a testament to their durability.

All I was saying is there should be no concrete HP rating on a set of rods. A 400HP engine revving to 8000rpm will damage a rod long before a 400hp engine revving to 5000rpm will. (Basing it on HP vs. Revs with no extenuating circumstances ie. oiling issues, tuning issues etc.)

Or am I by myself with this one.
Wasn't trying to start arguments guys lol

Ok in your same argument then with a different scenario.

2 engines both have same rods in them
both revving to 8k
ones making 200hp stocko
the other is a supercharged engine making 500hp

which ones going to shit its self first?

Of course rods have a hp and rpm rating, its not all about revs, outright cylinder pressure and hp will effect the life of a rod no doubt about it.
40psi into a squared chamber running alot of advance timing will bend a rod no worries even if its only doing 4-5k if it pre dets.

[SilverVH]

Your bringing external influences into the equation. Outright HP has nothing to do with those external influences. Timing, pre-detonation, lean AFR of course will factor into rod longitivity (or lack of) regardless if it is a 300hp streeter or a 1000hp screamer.

I'm not saying that manufacturers don't brand rods by hp rating (simply because its easier to rate and simplier to compare) yes they do. Do I agree with this form of measurement to rate rods? No. There is to many varying factors in every combination, that you can't just say, these rods are rated to 500hp. Sure it may be an "ideal indicator" to base stength on, but it is simply false. HP does not affect torsion strength, casting quality, material grading of a rod, shock rating, yield strength, stretch, it has absolutely nothing to do with it but yes cylinder pressure can play a part. How fast a motor is revolving is the relevant and contributing factor.

When is cylinder pressure at its highest?
What factors contribute to cylinder pressure?
How does cylinder pressure relate to the peak HP of an engine?

[pumba]

Your bringing external influences into the equation. Outright HP has nothing to do with those external influences. Timing, pre-detonation, lean AFR of course will factor into rod longitivity (or lack of) regardless if it is a 300hp streeter or a 1000hp screamer.

I'm not saying that manufacturers don't brand rods by hp rating (simply because its easier to rate and simplier to compare) yes they do. Do I agree with this form of measurement to rate rods? No. There is to many varying factors in every combination, that you can't just say, these rods are rated to 500hp. Sure it may be an "ideal indicator" to base stength on, but it is simply false. HP does not affect torsion strength, casting quality, material grading of a rod, shock rating, yield strength, stretch, it has absolutely nothing to do with it but yes cylinder pressure can play a part. How fast a motor is revolving is the relevant and contributing factor.

When is cylinder pressure at its highest?
What factors contribute to cylinder pressure?
How does cylinder pressure relate to the peak HP of an engine?

how will my Procomp H-beam rods go when i am revving my motor to 7500rpm? they told me it will be fine at those revs. I am hoping to make at least 600hp

[vt1538]

how will my Procomp H-beam rods go when i am revving my motor to 7500rpm? they told me it will be fine at those revs. I am hoping to make at least 600hp

Good luck.

[vyjess]

they will end up in ya sump!

[pumba]

^^^ I was hoping they would give me a new glory hole in the side of my block... It would be handy to be able to see inside the running motor

Just for your info, im not actually building up a Procomp motor... I just know how much 'SilverVH' likes Procomp gear

[Tsunamix]

Let me settle it for you -

There are technically only 2 ways to break/bend a rod. Application of excessive acceleration (Brute force) and Work hardening (brittle shatter due to to strecth).

Fact one. Material governs stretch and stretch recovery. Choose your materials well. Bear in mind that EVERY material has a limit on how much stretch it can handle, and how often it can handle it. The amount of stretch is generated by piston head acceleration. This comes from a mixture of cubic capacity of the combustion chamber, compression ratio, fuel being burnt and the length of stroke. The higher any one of these numbers is, the higher the acceleration (and deceleration) forces are.

Fact 2. Revs themselves do NOT kill a rod. Run at 6.5 to 1 compression ratio at rev to 20,000 rpm and your accelerative forces aren't as high. However - run at High revs, Hi compression ratio and long stroke and your rods better be the best in existence.

Fact 3. The weakest point in any conrod is the smallest point of contact. This can be the rod bolts, or possibly the small end journal. In these instances - bigger is better - but you CAN go too big and have no material holding the bolt/journal in place. So pick the very best quality.

There is a long stroke ducati motorcycle engine that has an oval piston, that runs at 13:1 compression ratio with a turbocharger, and revs to 20,000 rpm all day. It has 2 conrods per piston. Maybe thats the best explanation righ there.

[vt1538]

Fact 2. Revs themselves do NOT kill a rod. Run at 6.5 to 1 compression ratio at rev to 20,000 rpm and your accelerative forces aren't as high. However - run at High revs, Hi compression ratio and long stroke and your rods better be the best in existence.

Compression ratio has nothing to do with piston speed & accellerative forces.