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Discussion Starter #1
Alright I got a bbc
468
Patriot headed motor.
13.1 comp
Aluminum Manley rods
Got the motor on trade brand new still wrapped up. I want to use it for a street strip car when I say street I mean maybe a 10 mile cruise tops.
And at the track run high 8s on 1 kit.
Let me hear pros and cons and how long till it comes apart due to rod failure lol.
 

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50Sick
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I drive mine on the street and put alot of miles on aluminum rods. I use GRP only so I cannot speak for other manufacturers.
 

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Heat is your enemy !!!!!!! Always use and MONITER an oil temp gauge . I have built with alot of success many aluminum rod engines that were street driven . OIL temp will kill this type of engine quickly . Keep the oil temp under 210 , preferably under 190 and you will be okay . Also dont be a cold revver guy , always operate the engine within a certain temp range . hense put a rod in the freezer , then in a vise and smack it and it breaks - and then put a rod in the oven and then in a vise and smack it and it bends - Once again temperature is EXTREMELY IMPORTANT , Bobby
 

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Aluminum has a fatigue life that is determined from the stress applied. The graph of this is called the S-N curve, Stress vs Number of cycles to failure.

The S-N graph has Stress on the vertical axis and the Number of times the material is stressed on the horizontal axis. For a connecting rod, the failure mode (outside of detonation) is tension--the weight of the piston going over TDC creates a tension stress in the rod. The shape of the curve looks like:



The Number of cycles to failure is logarithmic, meaning each mark is exponentially greater than the last, usually by a factor of 10. i.e. 1000, 10,000, 100,000, 1,000,000 cycles to failure.

Looking at the graph, a large stress = very few cycles to failure. So, you change Al rods in a race motor at certain intervals because high RPM = high stress.

But at lower stress the Number of cycles to failure is much, much greater. So, you can putt around in a street car with aluminum rods for a LONG time.

However, aluminum does not have a fatigue limit. The curve continues down and to the right. That means that no matter how small the stress, it WILL eventually fail. Even if you only put 1 lb of load on it, there is a finite number of times it will cycle before it breaks.

Steel, on the other hand, has a fatigue limit. The S-N curve goes horizontal at a certain stress. If the rod is stressed below this limit, it will never fail under fatigue. That's why steel rods live forever in passenger cars--they were designed to operate below the fatigue limit.

That's the engineering geek answer, anyhow! :p
 

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Oh, and to tie into what Bobby said about temperature, S-N curves are temperature dependent, with a shift in direction and a change slope.
 

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50Sick
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I don't know much about heat versus cycle life but I do monitor my oil temp. The oil temp is generally always thirty degrees warmer than water temp. And the usually means anywhere from 210-230. The last rods have about 4500 miles on them with no visible or measurable problem. That's not to say the next time out they could fail. I'm sure mrsmisery is knowledgable with aluminum rods this is based on what I have experienced with the rods I use.
 

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I have always run steal but have heard of guys doing it with aluminum just watching temps and preheating the oil before firing
 

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I would not run it on the street. In fact, it is the wrong combo for you.
Put in on a pallet and ship it to me. I will dispose of it properly.

PM me for address.

Thank you




LOL
 

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time to go racing yet ?
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hey if a chainsaw can have an aluminum rod so can a street car .


i would think if its a streeable combination it would be ok ...... guy i knew had a bbc with aluminum rods and he didnt know it {bought motor assembled and was never told} but he must have had 1000 runs on the thing before he freshend it up ... he nearly shit a brick when he seen the rods ................ btw they where ok ....
 

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I run GRP's in my pontiac. Was always told not to run 20/50 Brad Penn and to let oil reach 150 deg. before putting a load on the rod's. I am on my 3 yrs. and street drive alot w/ 13.5-1 comp.
 

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More engineering geek stuff - many aluminum alloys age harden within our lifetimes (they get harder and less ductile just sitting on a shelf or in an engine). I made the mistake of using a set of rods that had been sitting for many years. I never turned that engine very high, but this was the result:
 
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