That's basically true; steel doesn't have the finite life cycle like aluminum so long as the stresses are below the yield tensile strength. Here's the catch with that- how do you know that no part of the rod is being stressed into minute deformation? The first the thread or so of the bolt hole comes to mind. Yes I'm sure these were run through an FEA program to attempt to predict where the stresses are highest, but that pretty picture is only as good as the programmer.

I've always wondered how much torque a rod sees at RPM.

I'd venture to say that you can make a sufficiently stout 'H' beam lighter than the 'I' profile but the 'I' will always be stiffer overall. It's all about where you put the mass. Just a guess from some old statics knowledge.

Compression and power stroke help push things together.

Reason why HP1 keeps mentioning TDC at overlap is because there is little to no pressure (sometimes a slight vacuum) as the piston just rose and is now being yanked back down. Ie: Just after TDC the crank is trying to pull the rod cap away from the rod and piston. This is why we need killer bolts, not just good rods.

At BDC the forces are trying to push the piston and rod beam into the rod's cap.

Imagine if you will - throw a 1lb rock out straight as possible and yank it back while it;s still in the air, as slow as you can. Now, shoot that 1lb rock out of a cannon and as the rope just becaomes taught, yank it back as soon as you can. Your shoulder will seperate from your body.

Look at the following animated pic for a bit, and then imagine it spinning many times fast. You'll then see how the piston and rod are still wanting to go upward with much force, while the rod's cap and bolts are trying to pull it down.

https://d2t1xqejof9utc.cloudfront.ne...9a5/medium.gif

Here's a better animation, Starts at 500rpm and goes up to 7k rpm by the end.

https://www.youtube.com/watch?v=s5n-2gb8yfM&feature=player_embedded

There was a discussion about rod bolts about this time last year. Basically what was discovered was at the rpm level we are spinning these motors a stock fm rod bolt would suffice.

I'll throw this one out there. Who has had a stock gm Rod fail?

Great demo, I guess the part I'm missing is the rod should be many times stronger than the bolt securing it due to shear mass, new bolts is a no brainer. I also see that if your wallet is over full then just go with new and be done with it, but that's not where the whole discussion began :flag:

Well, we know how many stock 502 shortblocks with GM 7/16" 6.135 rod has been hammerd and all has been well. 800+hp even. Everyone remember, 4.00 stroke. When these are ever torn down, many people will rebuild with a stronger rod bolt, just because.

Now, with the 4.25" stroke motors how many stock rods where kept ? Probably not many, therefore we really won't know. Most step up to a 6.385 rod (or longer in some cases) and thus aftmkt rods and bolts.

Longer strokes = more piston speed.

You can't use a stock Rod with a 4.25 the piston will not clear the crank. Unless you can find an external balance 4.25 crank...

Back in the day I used to play around with Pontiacs. Back then nobody was putting Chevy rods on a Pontiac crank and there was no aftermarket parts for them. We would use stock Chrysler Rod bolt on the Pontiac rods 1200hp+ and spin them to the moon and never had any issues unless the tune-up was off and then parts we go flying...

Scat makes a cheap cast steel 4.25" crank that can take a 6.135 rod. Only a few I've seen use this. I wouldn't bother.

Ive seen a GM rod come apart at 6000rpm in a buddy of mines cat. It wasnt pretty.

The other thing i think that plays a role. Take 2 engines, both identical 900hp for example.

First engine goes in a boat that runs up and down the river all day, encountering the occasional pontoon wake. He runs hard, lots of wot time.

Engine 2, goes in a boat, that runs the ocean, great lakes, etc. Hes out there every weekend working the throttle like bob saccenti in and out of rough waters. His engine is rapidly decelerating, and accelerating quite often.

Which ones gonna be harder on rods, or more likely to break one ?

Start talking long stroke, long rod, heavy piston fire breathers beating it up offshore, you def dont want some ebay special rods in there

That's exactly why I bought my rods off amazon.

Are they "prime" rods ?

They sure are. Funny thing is my buddy is a Callie's dealer and he told me his price and I said they were cheaper on Amazon. He got pissed off and said there was no way they were cheaper. I went over his house after work he got Callie's on speaker phone they told him the price (I thought he was trying to make a couple bucks on me) he wasn't. We looked the rods up on Amazon same part number and everything. Ordered them 2day shipping and they drop shipped right from Callie's...

Thats a very good point as I fit profile #1 and generally boat on pretty smooth water,so I'm not thinking about the pounding they take in big water.

The 600 hp Volvo 540 used a crower 4.25 stroke crank and crower 6.135 rods I believe.

the point i am trying to make is it would cost no more out of pocket to buy a set of NEW eagle rods with arp2000 bolts than it will cost to rebuild the OLD eagle rods with new arp2000 bolts after the old rods are sold for 200 bucks.it,s common sence,at the end of the story the op will have spent the same amount of money.

What if I`m emotionally attached to my current rods?

in that case keep them (don't sell), and buy new rods for the engines! simple! best of both worlds!.

tkach;4382020]the point i am trying to make is it would cost no more out of pocket to buy a set of NEW eagle rods with arp2000 bolts than it will cost to rebuild the OLD eagle rods with new arp2000 bolts after the old rods are sold for 200 bucks.it,s common sence,at the end of the story the op will have spent the same amount of money.[/QUOTE]
Ok, I doubt its the same money, and I'm certainly no expert here, just adding to the dialog as this has been excellent discussion with no drama.

Paging thru some catalogs on these price related rods. Fwiw, heres what Im seeing. For 6.385 H Beam, with ARP2000 bolts except compstar, those have L19s.

Molnar 729 grams

Eagle 785 grams

K1 technologies 740 grams

Manley 810 grams

Engine pro 809 grams

Lunati 790 grams

Callies Compstar 816 grams

A visual difference I noticed, out of all of them, is the Callies Compstar rod, has a reinforced area on the cap. Design wise, they all about look the same. The Molnars and K1's, look to maybe have a slightly narrower beam. Thats just looking at various photos though.

Buck, Your average cost to rebuild a set of used rods, is around 150 bucks these days, give or take. . New ARP2000 bolts, are around 150 bucks as well. That's 300 dollars you're spending, to recondition, and upgrade your old rods, Eagles in Dan's case.

A brand new set of Eagles, are 500 bucks, WITH ARP 2000 bolts. Now, this new rod will also have to be checked out for roundness, , pin fitted, etc.

Dan could sell his old rods, on ebay, or whereever, and probably get 150-200 bucks easy. So, its a no brainer to me, to simply buy brand new rods, that havent been fatigued, etc. He does not know the history of them, how old they truly are, etc. If he was going to reuse them in a 500hp deal, maybe it be worth saving a couple bucks keeping them, but in a 900hp blower engine, ehhh,...its one thing to even use that rod in this application according to some, let alone saving a case of bud light worth of money, to rebuild the old stuff. I mean, I think he's fine either way, but sometimes, when its only a few bucks, going new is nice sometimes.

Just to give you an idea what is involved in reconditioning rods, look here

http://www.enginebuildermag.com/2007...nnecting-rods/

he could get 2-300 for old rods all day long.... I have sold a few used sets they always pull that just helps even more!!

Good read, and as previously mentioned not arguing just asking as many people's budgets get tight during rebuilds, as costs can spiral out of control in a hurry.

Personally I never rebuild rods. As a old crank grinder i'm extremely picky when it come to re-sizing. i've yet to see a perfectly square machine / hone job. As for changing rod bolts, as we know caps will shift requiring re-sizing and balancing. Pressed pin style get to go through the heater again. I've used H-beam Eagle with good success. Never been an import fan though. I like to spend time on the complete rotating assemble. if it spins, it goes on the balancer after the crank and harmonic balancer are done first.

Wait, it's winter. We are talking rod bolts without drama so far? Is this OSO or too early yet? AB

my guess is the threat of getting banned is real,i am liking the tranquility.

in that case take a picture of them before you list them on ebay!

Longer stroke = more piston acceleration and then only if the rod stays the same. If you keep the rod ratio the same then the piston acceleration will remain the same. This is why you go to a longer rod with more stroke.
4" with 6.135 rod = 1.53 ratio
4.25" with 6.135 rod = 1.44
4.25 with 6.385 = 1.50
We build a lot of 532" (4.6 bore x 4.0 stroke) combinations with a 6.535 rod and that seems to be a really nice combination. Puts the rod ratio @ 1.63 and these engines always seem to make great power with exceptional tq curves.

The K1's and Molnars do have narrower beams but the webbing is thicker. I'm pretty sure Tom Molnar owns K1.

You could ask all the different rod manufacturers that question and all their engineers, and at the end of the day you'll not get a definitive answer. Stronger how? In compression and column strength? In bending? In twisting? Tensile strength? Resistance to fatigue? Both designs have their strengths and weaknesses. Is it a high HP build, or is rpm a main consideration?

This is a pretty easy to read and easy to follow write up on rods, designs and applications:
http://www.enginebuildermag.com/2008...-many-choices/

scott,the longer the stroke the faster the piston travels per revalution period.the piston has more distance to travel so it has to go faster,this is why it is harder on the rod on the exhaust stroke.it is my understanding that rod angel is not as important as it was once thought to be.

Mike, you're right but I'm talking about piston acceleration, not mean piston speed. Piston acceleration is where the main difference lies with different rod lengths/ratios.

Either owns it , or started K1, or something like that.

Off topic a bit, but just wanted to say thanks for participating on the forum here. I know you took a bunch of criticism and what not, but didnt lose your cool and kept it technical based on the other threads. Also, thanks for proving your not just here to sell parts or push anything, per your convo with my buddy who contacted you about some parts he wanted prices on.

Was hoping to make it to PRI this year and swing past the booth, but my work schedule isnt going to cooperate.

correct me if i am wrong but i always thought the rod angel plays a part in the dwell time at tdc&bdc.

He started K1 and left after 5 years. K1 rods are not the same quality as they once were. Big business got ahold of the company that's why he left...

Standard!

You ever use the molnar rods ?

Nope. Think I may order a set of 7.100's before the day is over. If Dan is on the fence with his Rod selection he really should call Tom. I think it might finalize his decision.

all though i have never used a k1 or the molnar rod i have installed a lot of eagle rods with arp2000 bolts,and some with 8740 bolts on lower power standard stroke stuff.imo if dan chooses to go with rods in that price range the eagle with arp2000 is as good of a choice as any.i check the big end of every rod that i am going to install for size&roundness and the eagle,s have always checked out good.

I have a schitload of connecting rod ads on OSO now. I guess the search engines and ad tracking devices are pretty freakin strong on this site.

Absolutely. The shorter the rod for a given stroke, the more rod angle. Short rod angles can accelerate the piston quickly which will put more demand on the induction and give a little better "quick" cylinder filling, but at the cost of higher side loading of the piston and more friction in the cylinder. Good for drag racing and short acceleration distances. Not so good for endurance or long, higher rpm runs.

Thanks Thunder...I appreciate the kind words very much.

I wonder if that had any influence on the old 427T tall deck truck engines design concept. Using a short stroke , long rod combination. I know they had the 4 piston ring deal, but wonder if they knew those engines were going to need to last in heavy duty commercial trucks, with short gears, and not wear things out