How much stronger are forged rods?

[Bored?]

I've been doing some math on various engine configurations, including calculating peak piston acceleration. This gives me some idea of how stressed pistons and rods will be as revs, rod length and stroke are changed.

What I'd like to know is how much additional tensile strength a forged steel rod would have when compared to a standard one. This would be useful in approximating how much the redline could be increased.

I realise that this is going to vary from rod to rod, so I'm just looking for ballpark figures to get a conservative approximation.

I'd also be curious about titanium rods...

[1jzracing]

all standard rods are drop forged!

what you might be looking for is hi tensile billet machined rods like carillos etc

you will need to find the cross sectional area and look up the properties of the material used, then run it through some basic tensile calculations

i would guess steel like 4340 or something would be used

[Bored?]

This URL is somewhat useful in clarifying existing rod materials and manufacturing processes:

http://www.hotrod.com/techarticles/c...nnecting_rods/

[oldcorollas]

a well made rod is better than a stock rod

basically, rods fail from overloading of defects... reduce defects = reduced failure.

but, increasing RPM = increasing the square of the load...

as far as calculating redline, that partly depends on the lifetime you expect. every loading cycle above a certain load reduces the rods life, but how much and the details will be almost impossible to know, without extensive empirical testing. (ie, other peoples broken engines, but even then, that is a very big ballpark)

so anyway, it is not so much the total tensile strength that is the number to look at, but the fatigue strength, and the reduction in size of defects etc...

[Mooro]

I presume if it is a fairly common material you could potentially find an engineering fatigue curve (S-N) for it which would be based on empirical testing. THe based on engine speed, weights etc you could calculate the tensile loads on the rods and from the S-N curve determine the expected number of cycles before failure. Not the most accurate approach but would potentially give you a sound engineering solution. The difficulty comes in that the engine doesn't operate at constant revs so the tensile loads are continually varying and therefore have a varying effect on the tensile fatigue life of the rod so you would need to make some assumptions/simplifications.

Also as mentioned it will be highly dependant on the quality of the forging and number/size of defects etc as these act as crack propagation points and will reduce the fatigue life.

[30psi 4agte]

This is slightly of subject but.... Most rods fail due to the bolts themselves breaking.

Thought you may just want to keep that in mind .

[oldeskewltoy]

This is slightly of subject but.... Most rods fail due to the bolts themselves breaking.
Thought you may just want to keep that in mind .

absolutely

[The Witzl]

I'll also add that Titanium rods are anus-bleedingly expensive.
Like US$400-500 EACH ROD.

[rob20v]

It depends on what you are going to do as to how much money you want to spend. I know with the clubman racing a few years back they used Corolla engines with falcon studs on the bottom end which was the weakest point on the standard bottom end. I built a low cost 4K engine with these mods and never had a problem.

[Billzilla]

I'll also add that Titanium rods are anus-bleedingly expensive.
Like US$400-500 EACH ROD.

You're joking ....
Try closer to US$1,000 each mate. If you shop around they can be had for less though.
I ordered a set from a company in Aus over a year ago, and am still waiting for them.
FAR from impressed about that.

[The Witzl]

Billy.... you may very well be right.... im just going by what i remember when we were looking at getting our 18R-G rods done by Crower. They had a price like that on their website IIRC.

The custom 4340 billet rods were about US$180ea from crower.... so custom rods aint cheap by any means

[celicapain]

you know its expensive when your anus bleeds

[Bored?]

From Crower's website:

http://www.crower.com/cat/rods.shtml

"4340 steel billet rods run $167 per rod. Billet titanium rods run $459 per rod."

Personally I don't think that's too bad, especially if you're only building a 4cyl - only $1168 more than a set of steel rods.

[Billzilla]

Sorry - I see the price of off-the-shelf titaniun rods is much less than the customs ones I'm getting done.
I quizzed Cunningham Rods in the US and they wanted US$1,000 each for them.
Ouch!

[JustenGT8]

Anyone care to comment on the strength of sintered rods.....the 1UZ is the only engine i can recall using them