Virt

Are the titanium rods the LS7 uses stronger than forged steel?

bernrex

Would have to be since Titanium isn't cheap.

Perhaps its also lighter ... although Ti is higher up on the Elemental Table in # ... which should make it heavier.

cbgpe

It could go either way but Ti alloys can be very strong and since the material is lighter it will allow higher RPM levels and quicker throttle response. Some racing organizations out lawed Ti rods BTW
Ti is more elastic and has a lower modulus of elasticity than steel ....much closer to Alluminium. It is tough to machine but if you can hold on to it (non magnetic) grinds really nice.

SWCDuke

If you compare suitable (for connecting rods) heat treated Ti and steel high strength, ductile alloys, both have similar maximum acceptable working stress (based on fatigue charactertistics), but since Ti is only about 57 percent as dense as steel and rod loading is due to inertia forces, a Ti rod engine will rev higher with comparable durability than the same engine with steel rods.

That's why very high revving engines have Ti rods unless cost or race rules dictate otherwise.

The NSX was the first production car with Ti rods, and Ferrari V8s followed suit beginning with either the 348 or 355. FI engines likely have TI rods (if not some other even more exotic materials). Champ car engines by the rules must use steel, and I believe the same applies to IRL engines.

After the demise of the Soviet Union, Ti prices dropped quite a bit as Russia has most of the world's proven Ti reserves, and they were interested in selling to generate foreign reserve currencies (like the dollar) to prop up their nearly worthless currency, so the price dropped and opened up a whole new world of Ti applications, and they're still scrapping Ti-hulled submarines.

Figure the Ti price drop was a "peace dividend" for car guys.

Duke

ghoffman

Compare any alloy with this free download:
http://www.hardbar.net/Documents/Mat...Properties.pdf

The most common Ti alloy is 6Al-4V, and the steel that is common for rods is usually 4130 or 4340. Since a large percentage of the rod stress is self induced due the mass in motion, the mass to strength ratio is very important.

LTC Z06

We had to sneak Ti from the USSR to build the SR-71s.

I've driven a Ruf 911 with Ti rods, I thought the engine was going to explode it revved so fast!!!

Tom Steele

http://www.key-to-metals.com/Article122.htm

and a bit more detail

http://www.azom.com/details.asp?ArticleID=1341

TripleBlack99

tom steele? does your middle name begin with an i? if so, what a great topic for you.

jvp

Actually, we didn't sneak it. We bought it from them outright. We just didn't tell them what we were going to use it for. :-)

jas

DJWorm

The OEM LS1/LS6 rods are Sintered Powder Metal rods which are then conventionally forged and then shot-peened. The rod bearing ends are then line scoured on the inside surface which creates a stress riser. They are then split fractured. Hence they are called "cracked" rods. This provides a precise location and locks the rod cap into place once assembled. The powder sintering method allows the rods to have a +/- 3 gram tolerence on the pin end and a +/- 4 gram tolerence on the journal end. These tight tolerences allows a good balance without balancing pads and reduces weight. The can handle upto 500 HP.
During the powdered metal process steel powder is poured into a mold and then compressed to form a "briquette". The briquette is then heated to just below the melting point which allows the steel molecules to bond.

Aftermarket rods are usually either normally forged (non powdered metal) or billet.

The LS7 Titanium rods are forged, machined and then heat treated. I haven't assertained yet if they are shot-peened. I have a hunch that they are not, as it is not necessary. They are as strong as or stronger than aftermarket steel forged rods. The balance is very close between rods. Titanium is @57% less dense than steel and saves 40% weight. The weight has been reported at either 460, 470 and 480 grams. As yet I have not weighed a set. to confirm. This would be about a 20% weight savings as the LS7 rods may be a touch beefier than the OEM rods saving about 100 grams a rod.

In contrast an Aluminum aftermarket rod would be 150 grams lighter than OEM but would have no where the strength even at twice the thickness.

The Titanium LS7 rods will allow the LS7 to rev higher and "spin up" faster. The Titanium rods will also be strong enough to support higher HP applications.

On a side note, if anyone is considering a build up for higher HP or for forced induction, and decide to go with stronger but heavier forged pistons they might also consider Titanium wrist pins to offset the heavier forged piston. Titanium wrist pins in the past have had problems with galling but a new coating has resolved this issue. These have been proven in NASCAR applications.

VV Last article has pic of coated vs. non-coated Titanium wrist pin VV

https://shop.sae.org/automag/material//04-2002/
http://casidiam.com/
http://www.casidiam.com/appn_3.htm

Thud

Being higher up on the table doesn't make it heavier necessarily... plutonium for example is less dense than aluminum.

Titanium is heaver (per unit volume) than aluminum, but it's also much stronger than aluminum, so you can make a part that is stronger than aluminum but uses less metal.

So Titanium gives you a lot of strength for its relatively low density.

LTC Z06

We were generally sneaky about it.

SWCDuke

WHAT???!!!

The specific gravity of Pu is 19.8. Al is 2.7. Ti is 4.5. Fe is 7.9.

Duke

bernrex

U are right about the AN. Its the density of the metal that matters. Steel is an alloy of iron + carbon + 'perhaps' other things too.

I wonder if the Titanium used is pure .. or also an alloy ?

LTC Z06

I believe most Ti used is an alloy.

SWCDuke

All structural metallic materials are alloys because alloys have better working properties than the pure base metal. "Steel" is an alloy of iron with a small amount of carbon and some other trace elements, some of which are contaminants. "Alloy steel" adds other alloying elements such as nickel and is called such to distinguish it from plain carbon steel that lacks other alloying elements other than carbon.

Densities will vary depending on the concentration and density of alloying elements, but the densities of the pure materials that are listed in most references provide a reasonable ballpark comparison of physical properties.

Duke

Thud

A few of the sites I found on google are a decimal point off it seems.... I thought it seemed a bit odd

http://www.simetric.co.uk/si_metals.htm

http://www.csgnetwork.com/specificgravmettable.html