Stock Rod Limitations?

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falston1

falston1

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At about what power level does it start to become necessary to use heavy duty forged I or H beam rods? I'm wondering how far I can push the stock bottom end in my 360 before I'll have to pull the engine to rebuild the bottom end. It's a fresh mild rebuild now that I'd like to build up a little more in the future.
 
what pistons are you using?

heavier the piston....more stress is on the rod....

in 30 yrs of drag racing I have only broken one rod...and it was a stock rod with a Heavy TRW domed piston..
 
Hard to answer without knowing more details. What kinda rod bolts? Old 100K plus miles? New stock replacements? ARPs? Were the rods resized? Stock pistons are a touch heavy. I think you'd snap a rod bolt in a mild engine before a rod. If you have them resized with good bolts, they can take 500 HP easily.
 
They are KB 107 pistons and I think they are stock replacement rod bolts. Nothing was done to the rods other than having the piston pins pressed in. I have another set of rods that I can rework this summer and change out whenever I get the chance if need be.
 
Your stock rod get's stressed out by high rpm. I'd limit that to about 6500.
 
In a 360 , I'd be more worried about the stock crank going south before the rods will.
If you had them out and replaced them with stock bolts , that was a mis step.
Buy the best bolts you can get and if you want to get really jazzy , grind the forging lines smooth and have them shot peened........these would stand up to a lot more power than a cast crank..........but after balancing and re-sizing , you are getting close to aftermarket rod prices.
And the cast cranks have stood up to some pretty fair power levels considering.
I'd get nervous much over 500 if you could get it in by 6,200 or so.
As stated , the heavy pistons are the real killer in these deals.
But a light slug and good balancing will let these suckers sing pretty good.
 
i ran for 3 seasons 3/8 mile oval track asphalt 390 4 bbl stock rod with wiesco every week end during the season practice, qualifying, heat race, 30 lap main event. never a failure. HP around 430. the part that most wont believe, i on a few occasions turned 8900 rpm during qualifying. during the race i would try to keep the engine around 8600 rpm. the work done to the rods as follows: sps rod bolts (old school) polished beams shot peened. factory rod can handle some major abuse try doing that with a chevy YOU CANT. i dont remember the weight of the pistons but this is a major factor to what the rod can handle. light pistons will help the live for sure. good rod bolt are a must and there cheep. if you have stock bolt with stock pistons weight wise i have push them to 6200 or so.with good bolt i have pushed the to 7000 all day long. the only reason to consider after market rods is price. after you get done with the machine shop cheep h beams are not much more. factory 340 360 and late 318 rods are bad boys all the way and i only have them in my engines. i think for drag racing these rods in good shape could handle well into the 600 hp range reliable. in pure stock shape i couldnt say for sure the bolt are important.
 
they will survive at 6500-6800 with a good rod bolt (arp,milodon) they r very strong ! i have a set that i had beamed and peened and survived nos for 4 years with 100 shot on a fairly hot 340 , around 375 at the crank without nos. the problem is you do u know how many miles r on them ? if u pulled them from a 300,000 mile motor that was driven hard i wouldn't be pushing them. but if it was an engine that was in a car that was pretty much takin care of, then you'll be fine at those rpm levels. cranks usually break because hp, rods usually break because rpm and weight of piston
 
Old schooled,crazy amount. Sides ground on a bevel,( NO BELT SANDERS!) Shotpennned twice(pay attention to the flow grain as working,it is fun!) Nasty. 340,working a single 250 hit.(AT 7800 RPM!)
 
oh yeah , the only reason i peened and beamed the rods was because at the time you couldn't buy a set of eagle rods or scat or whatever. there were the carillo's big money and the old direct connection hemi footprint rod. my brother had a set but never used them. they were huge , heavy and expensive. i might still have a picture of them, i'll have to look but they were beautiful rods. 7-1/6 bolts and good to 8500 rpm
 
p/schallenger said:
oh yeah , the only reason i peened and beamed the rods was because at the time you couldn't buy a set of eagle rods or scat or whatever. there were the carillo's big money and the old direct connection hemi footprint rod. my brother had a set but never used them. they were huge , heavy and expensive. i might still have a picture of them, i'll have to look but they were beautiful rods. 7-1/6 bolts and good to 8500 rpm
Click to expand...

yep i remember them rods and dreaming i would have some some day. big and heavy for sure super reliable at big rpm though. good old school us mopar guys have been blessed for years and didnt now it. and now with new tech we dont need those beast but wow at the time!!!
 
I agree, not costworthy now.But damn, those rods are in a 372 ,with W2s. They do run race gas,running a 350 hit(1shot!) . The rods survived,the wannabe driver didn't.By the way,mid nines at 140+.........
 
So what I'm getting is that I can rework the stock rods (as long as they aren't abused) and not really have to worry about them until I hit about 7000 rpm without too much problem? I'm working at a machine shop for a summer job, so hopefully I can do this minus the labor costs. It seems that the rods may not be as much of a problem area as I thought, then. I guess I'll rephrase my question; What are the areas that need the most attention at abot the 550 hp/6800 rpm range?

And yeah, I got all the parts when I was 15 so I wanted to see what mistakes I made and what I did right with it. (I'm 19 now)
 
You do know more than you telling us.You really to ask your machinist what he is comfrtable doingthat is 15 to 20 man hours to prep those.That is a high end workjob now.The trick is the compression, head size, camshaft.
 
I think you'll be just fine with the stock rod considering your using the KB 107. Good advise on grinding the parting lines in the forging and shot peening! I always have been a fan of the stock rod. It's never a problem,just upgrade the bolt's. ARP has several different products;I'd spend the most money I could on this part.
 
yeah when my bro was planning on using those rods he also had a vintage set of 1976 2.08 w2's. i run them on my 416 stroker and they work awesome. there was an article in a mag i think it was like 1978 and the guy had a 73 dart sport that ran like 10.50's on gas. it was what my brother was going to build until he went 440. anyways about the stock rods and it's kind of cool because your young and i was young when i had my rods done . they work really well and if u can have the work done cheap , go for it. one thing i'll recomend if you go that route is to use a stretch guage instead of just tourqing them when u put the engine together. sounds like you know your stuff and just like stated earlier keep learning the trade. it will save you thousands
 
One thing I've heard time and time again from machinist's is that it's not worth rebuilding the stock rod,because the new ones are so cheap.Weird. I'd think the machinist would want the work? And I cant really see thier point either,as a new rod is somewhat of an unknown compared to a proven piece like the stock mopar rod.I see thier point when it comes to chevie,as g.m is junk anyways.
 
With new ones, you got Chinese metalurgy to worry about. Some of um are good, some of um ain't. That's the problem. It's a gamble. I've always preferred the stock rods in anything but the most extreme applications. A good stock reconditioned Chrysler rod will take a lot of abuse.
 
Ys the stock rod was all guys had until the aftermarket FINALLY stepped up but guess what; Chevie guys must have started the rumour about stock rods needing replaced,as a chev most DEFINITELY needs a beter rod. The mopar came with the better rod from the factory,as well as the better crank,block and heads,lol!!!
 
falston1 said:
At about what power level does it start to become necessary to use heavy duty forged I or H beam rods? I'm wondering how far I can push the stock bottom end in my 360 before I'll have to pull the engine to rebuild the bottom end. It's a fresh mild rebuild now that I'd like to build up a little more in the future.
Click to expand...

if you figure out the cost of resizing and new rod bolts...then compare that to the cost of a set of scat I beams at 300 bucks....how much difference is there/

one thing that is not being discussed is weight...a stock 340/360 rod weights around 730 grams...a scat I beam will come in at 600 grams...

130 x 8 is 1020 grams...over 2 1/4 lbs of weight you will not be spinning...

and given the age of the rods....you don't know the complete history of the stock rods...how much abuse or overheating they have seen....how many times have they been resized..

i guess you never really expressed you intentions with the engine...daily driver...stay with the stock rods...going racing..i would spend a few extra bucks for the scat rods..

and the new rod gives you room to grow with.....

just looking at it from a difference point of view...
 
Its anywhere form 9-12 bucks a rod to clean, mag,press bolts, resize, bolts are about 45-50 bucks.
So 145 bucks 'old rods' compared to 300 bucks 'new rods'

We like to use 40 yr old blocks, lots of heat cycling there. Rolls Royce sets blocks out in a field for yrs before using them in production. will a rod grow more as it is new compared to one thats old, already cycled and proven to be good?
Just ponderings.

Its my opinion that sometimes people just like buying/replacing parts, even when it's unnecessary.

I do agree that the scat i beams are quality rod, but why not just go h beam for another hundred bucks and have even more room to grow? lol ...how about a race block too and some w9's....oh wait, whats he building again? jk
 
Looking for a street legal drag car (10 second 1/4) as an end result. Also a college student whose parents are splitting so moneys pretty tight right now. I'm trying to work with what I have at hand right now. I basically am looking for advice on how to save money and still have a rotating assembly that'll put up with 600 hp and 7000 rpm. This is my daily driver at the moment, but I just got a better milage car so I'm getting more serious with the Duster.
 
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