Aluminium connecting rods

[seang]

They are lighter than steel or iron, and more affordable than titanium. They are used in Top Fuel dragsters. However, I'm not sure of the service life of such a part as this. They might be somewhat less practical, and are more sensitive to temperature than steel or iron. Here are a few links,

http://www.bmeltd.com/rods.htm

http://rrconnectingrods.com/st....html

http://www.google.com/search?h...f&oq=

I noticed some Chromoly ones, too. They were more expensive than the ones made from Aluminium.

[ravera]

Way back in the day when alloy rods first hit the market the big problem with them was rod stretch. For drag racing, they're pretty much under fairly constant compression, while in street driving and road racing they not only have to push the car, but hold back is a major issue too, giving tension to the rods and thus you'd get the problem of rod stretch.

NOW the major issue is fatigue life. The thing with Ti rods is like steel they should have a relatively long (i think it may even be infinite, It's been a while since I've been big into metallurgy) fatigue life. That is, they can go through lots of tension and expansion cycles without the dilemma of cracks and fatigue. Aluminum has a very finite fatigue life and because of this don't hold up to non-full on drag applications very well. They're light and do great for drag racing, but seeing lots of miles and varying fatigue situations usually lead to rods not lasting to what steel or alloys of steel or even Ti rods do.

[RBbugBITme]

TF dragsters rebuild their engine after every race with new rods and pistons among other things.

ravera, I don't know where you get your info from but Ti fatigue strength (32 kpsi) is closer to the fatigue strength of Al (25 kpsi) than steel (50 kpsi). Your rod stretch argument is pretty ridiculous as well.

I've seen a few first hand accounts though where Al rods have lasted a long time on high horsepower DDs (4-500hp DSM for ex.) but not enough to feel comfortable to the point where I wouldn't want to inspect them from time to time which makes for a silly "daily driver".

[ravera]

Did I say fatigue strength? No I'm fully aware of the yeild (sheer and tension) of all three. I was talking about fatigue life. Aluminum has a fatigue life that is shorter than steel and Ti. This is why you can only make so many passes on alloy rods before inspection, and why airframes that are running aluminum spars on the main wing have to be inspected during the C and D checks to insure that the spar has not reached it's life expectancy.

And the idea's I've posted didn't come from me. They came from the BME site.

But I'm sure you know more than them...

http://www.bmeltd.com/rods.htm

[seang]

Aluminium aside, what about Chromoly? Here's a set for a Datsun L18/L20... http://www.zccjdm.com/catalog....RODS_

[RBbugBITme]

Granted I misread your post, your drag racing/daily driver comments make no sense. The highest stresses on a rod occur at TDC when there is no gas pressure acting on the piston. This occurs every cycle in a 4-stroke engine and the stress increases with RPM. So unless you don't shift until 7500+ RPMs between every stop light I think your point is baseless. In fact I'm not sure you even read your own source.... from the President of the company, "With the material we've got and they way we manufacture the connecting rods, they'll live a couple hundred thousand miles on the street because a street application is, for the most part, low load."

seang... 4000 series steels are probably the most common type of conrod on the market. I think all Eagle rods are 4340 for example.

[seang]

Is chromoly alot lighter than forged steel or iron? I know it's somewhat lighter, but just how much?

[RBbugBITme]

4340 is forged steel for this application. Just buy some Eagle's and be done with it.

[ravera]

Granted I misread your post, your drag racing/daily driver comments make no sense. The highest stresses on a rod occur at TDC when there is no gas pressure acting on the piston. This occurs every cycle in a 4-stroke engine and the stress increases with RPM. So unless you don't shift until 7500+ RPMs between every stop light I think your point is baseless. In fact I'm not sure you even read your own source.... from the President of the company, "With the material we've got and they way we manufacture the connecting rods, they'll live a couple hundred thousand miles on the street because a street application is, for the most part, low load."

ONCE AGAIN... You need to read carefully. If you notice, the first statement was talking about what the general misconception of the aluminum stretch that began in the early 70's due to lesser mfg processes that are in use now.

The second part of my post states that the reason alloy rods are not as common in street use NOW is due to the fatigue life of aluminum rods and the need to have them checked more often than Steel or Ti rods.

[RBbugBITme]

ONCE AGAIN... You need to read carefully. If you notice, the first statement was talking about what the general misconception of the aluminum stretch that began in the early 70's due to lesser mfg processes that are in use now.

The second part of my post states that the reason alloy rods are not as common in street use NOW is due to the fatigue life of aluminum rods and the need to have them checked more often than Steel or Ti rods.

Soooo you use a source to explain why aluminum got a bad rep in the early days all while not promoting their use on the street today which your source does state is perfectly fine to do because they claim to have handled the fatigue life problem.... Ok I got it now. Good use of your own source!

[RBbugBITme]

But I'm sure you know more than them...

http://www.bmeltd.com/rods.htm

I'll drop it and let future readers decide from here.