Tensile and compression in Ti conrods.

[Boosted LS1]

I'm considering some forged (not billet)Ti conrods for a blown application. I was told that they tend to fail earlier under forced application usage as they aren't as strong as forged steel in tensile loadings. Personally I think this is inaccurate but I suppose it does depend on the mix going into the forging. I'd have thought a Ti rod was superior in many ways.

Also, a blown engine will make more tq so more rotation on the crank but that's compressive and I accept there will be more activity during the exhaust pulse but won't that to some extent be damped by the backpressure due to the bug tubbies I plan to use. I'm not planning on increasing rpm's over stock usage for these rods although reciprocating masses will be a tad heavier.

The Ti rods are used in a factory supercharger installation. Anybody got some engineering based comments to share? Thanks.

[Boosted LS1]

GavinPearson said:

It depends on the cross sectional area of the two parts you are comparing, material properties and at what point they will yield at.

Thanks. Hmmm, I have to do an apples to apples comparison as far as size and section is concerned. Any techie data won't be available to me but I can't see GM moving to forged Ti if it's inferior to forged steel especially in a s/c application. I won't be using an s/c though.

[Boosted LS1]

Evening chap, I knew you'd turn up sooner or later. I'm just wondering if ls9 rods would be better then a set of regular steelies in a 427. The Ti's look really nice in the web pics and I could polish them, surely they aren't going to be crap. Or I could go with that crude old tat, used everywhere, forged steel. Mind you, billet steel may be cheaper then forged tits

I'd like to know how turbo induction effects rods though, I suspect it's by not all that much if using sensible rpm's?

Boosted.

[Boosted LS1]

Thanks Dilbert, there's food for thought there. I am aware about the scratching issue.

Chris, I'm looking at Ls9 rods. They look quite chunky with strength where it's needed but it's impossible to say how much if anything they have in reserve

[Boosted LS1]

Vhris, I don't fancy the ls7 rod as it's got a wedged little end and a larger pin size then sbc. This narrows my custom piston options somewhat. I've also heard thet it's not an over engineered piece. The billet Ti rods I had a while back had a thick diameter little end which restricted piston bowl depth so it looks like I'll have to check out the 'steelies'. I'll start with Callies, they make nice rods and stuff

[Boosted LS1]

^ They aren't huge cost if you buy at the right time and the benefits are about weight and maybe wear in the bores. Downside is the unknown tensile factor. I'll check out those Howards though but the ls9 rods look equally capable.

Edited by Boosted LS1 on Thursday 17th January 23:49

[Boosted LS1]

Thanks Miffy, my thoughts were that so long as my peak rpm's stay the same then the rod stresses won't have changed unless I fit heavier reciprocating parts like forged pistons. So adding the turbo won't really effect peak stresses?

[Boosted LS1]

J17 said "Forged rods aren't as strong (like for like) as billet rods because the FORGING process folds and bends the metal, altering it's internal structure and creating high/low stress areas. If you're going for something reputable I wouldn't expect much difference in the real world though".

I thinke he made a typo, billet is where the metal is bent and folded etc which I would have though made for a denser stronger material.

Boosted.

[Boosted LS1]

Not sure what happens with the grain structure in a rod but the metal is just compressed into the finished shape so I'd have thought the grain was pretty random throughout the part. If it were a billet item the grain tends to run lengthways and be uniform which makes the part more stable. Not a very techie reply but I think you'll know what I mean.

[Boosted LS1]

Top postings, very interesting but there seems to be huge overlap with some of these processes. It's hard to know which is best so just buy from a good manufacturer? Apart from the factory forged Ti rods there are also the powdered metal rods. Another process which seems a bit similar to forgings.

Knighty said:

"all billet rods are machined from a rough rod-shaped forging, so they are the best of both worlds, machined and shot peened, with good grain flow.....they are NOT just machined form a square slab".

That seems like a huge short cut. Surely that can't be correct? Wouldn't that make a billet the same as a forging? I've seen the phrase near nett forgings referenced to TRW pistons which sound like what you're describing as opposed to a proper forged piston being made from a lump of solid?

[Boosted LS1]

Here's some interesting reading.

http://en.wikipedia.org/wiki/Forgings#Net-shape_an...

Rods appear to be 'impression die-drop hammer forged' which is why I assumed the metal in the rod was molten?

ETA, here's info about billet stuff. Look halfway down the page at how a billet crank is produced.

http://en.wikipedia.org/wiki/Crankshaft

Edited by Boosted LS1 on Saturday 26th January 20:19

[Boosted LS1]

I'm watching it, is he making a spanner

[Boosted LS1]

There must be a quicker way to make 8 con-rods then that, maybe make them in groups at a time?

[Boosted LS1]

Thank you guys.

These are what I'm probably going to buy but I can't make out the writing on the rod. Clearly a forged Ti rod.

[Boosted LS1]

^ Thanks. Chevrolet ls9 corvette, standard issue for a petrol engine with a supercharger. They won't cost F1 money

[Boosted LS1]

^ Thanks Knighty, the Ti ls7 rods are appx 480 gms iirc. My Ti billet rods from Crower were 500 gms but looked far stronger and were larger on the beams. The rods in the pic are certainly for the ls9 which should be in production at the end of the year? In my mind the ls7 rods would be suspect for big power hikes/rpm's as the wedged little end looks like an obvious weekness especially if you're hanging a forged piston on there instead of a eutectic lightweight. That said, they say the engine was routinely tested to 8k rpm's where it made no real power due to the camshaft.

The ls9 jobbies do look the business. It's a 6.3 s/c engine and I'd guess the raised piston dome may not just be about chamber burn but could also be there to allow clearance for the rod end. I've yet to see the underside of the piston.

[Boosted LS1]

^ Thanks. The piston has a similar wedge so will have some extra boss area whilst retaining a very short pin. Maybe the extra boss in the piston is to provide strength for tensile loads.