turbo charged 3.4 dohc....430 rwhp!

[Dave96z34]

Lol the pics of your car the link is unclickable.

[FerrariFan]

Lol. I know that's hilarious. try this link. Lol
what's even worse is that the website appears to be unattended and my repeated emails to change or edit the link have gone unanswered. LOL

https://picasaweb.google.com/103577966960525906703/AD355?authuser=0&feat=directlink

Lol. Here's a link to a Youtube video of a walkaround.

http://www.youtube.com/watch?v=H4ULcPq78v0

Thanks for letting my know about the broken link! LOL

[ForcedFirebird]

I remember this thread from years ago.

Over-engineering is fine, but to be honest the 660 has been proven to take boost and abuse just fine. I would be more comfortable with the early forged rods over the lat powder-forgings with snapped caps. I have never seen one break, but have seen them bent in BOTH directions on a Camaro that sucked up some water. Not sure if I still have the pics, but will look a little later.

In terms of bottom end, there are three things to be careful of. Boost, Detonation and RPM. Any of these can wreck a rod if it is extreme.

Not so sure on the boost part. Stock rods and short bursts of 21psi on Loner's car didn't bother the rods (9.1:1SCR 3400/3500), or the stock head gaskets for that matter.

[NateD4]

Some people run more than 25PSI and want to do it for extended lengths.

I sure wouldn't want my bottom end to come apart because I decided to run at high RPM for a few miles... Beside a Bonnevile run sounds fun!

Any rod can bend when the fluid in the cylinder goes from compressible to incompressible. If the rod doesn't bend... Something else will. Engines don't make good hydraulic pumps at high rpm.

The reason I worry about the bottom end is because of some research done on the Ecotec with PM rods.

Story here:

http://www.turbomagazine.com/features/turp_0203_gm_racing_ecotec_engine/viewall.html

"However, as the Ecotec pushed through 283 hp at 4400 rpm, all four connecting rods simultaneously failed catastrophically and smashed through the side of the block. Laboratory analysis subsequently revealed a mid-beam compression fracture on all four stock powder-metal rods. All other components checked out fine. GM Racing installed a package of components you'd certainly install if you were taking the trouble to open an engine to upgrade the connecting rods: Super-duty forged Crower X-beam rods-plus 10:1 JE forged pistons with thicker top ring lands and Hastings moly ring packs. The GM Racing team installed larger fuel injectors, and continued to lean on the engine. Power advanced quickly to 350 hp, at which point the engine ran out of breathing room on the exhaust side. The ratio of Reactants (exhaust) to Products (inlet charge) is very high on a nitrous motor. GM Racing found the stock Ecotec exhaust manifold became sufficiently restrictive above 350-hp that injudiciously adding more nitrous could actually make less horsepower-due to dramatically decreased efficiencies in scavenging exhaust gases from the combustion chamber clearance volume. "We finally made 370-375 hp on nitrous," says Bothwell, "but the engine was really pissed off." "

[TGP37]

Nate, tri-metal bearings. I suppose the word strong isn't the best word to use. Better, newer bearings since I planned on the turbo. Remember guys, this is my first build sometimes I say things goofy. I learn as I go.....keep on going.

[NateD4]

TGP37, no problem. I just like to be clear.

[ForcedFirebird]

Some people run more than 25PSI and want to do it for extended lengths.

I sure wouldn't want my bottom end to come apart because I decided to run at high RPM for a few miles... Beside a Bonnevile run sounds fun!

Any rod can bend when the fluid in the cylinder goes from compressible to incompressible. If the rod doesn't bend... Something else will. Engines don't make good hydraulic pumps at high rpm.

The reason I worry about the bottom end is because of some research done on the Ecotec with PM rods.

Story here:
http://www.turbomagazine.com/feature...e/viewall.html

The DOHC has true forged rods, man! I have seen them handle a lot of power. The car I just mentioned blew the 3speed trans all over the dyno at over 350whp half way through the tach with those same rods.

And no, not all rods bend, if the end cap can be sheared off, you don't think they will snap? Your quote even talks about it. Manufacturers cheeped out as of late, PM rods are easier to make. The Gen1 rods have been proven over 7500rpm.

[NateD4]

Forging a rod doesn't make it good necessarily. The rods in the article had a compressive fracture not a shear failure. PM is probably a better material for rods than forgings. BUT, a lot depends on the geometry of the design. I'll be a PM OEM rod is stronger than a Forged OEM rod of the same geometry. There is a lot involved in the metallurgy.

However looking at my 3.9L rods (PM) they are very thing and very light. So I replaced them with a much better rod.

I think the 3.1L Turbo and the 3.4 DOHC were the only engines to have stock forged rods. And they are probably good for 550-600 HP with good bolts. I just wouldn't trust them at 8K RPM long.

[robertisaar]

I think the 3.1L Turbo and the 3.4 DOHC were the only engines to have stock forged rods.

all 3.1/3.4/3100/3400 rods have the same part numbers. 2.8?

[ForcedFirebird]

Forging a rod doesn't make it good necessarily. The rods in the article had a compressive fracture not a shear failure. PM is probably a better material for rods than forgings. BUT, a lot depends on the geometry of the design. I'll be a PM OEM rod is stronger than a Forged OEM rod of the same geometry. There is a lot involved in the metallurgy.

However looking at my 3.9L rods (PM) they are very thing and very light. So I replaced them with a much better rod.

I think the 3.1L Turbo and the 3.4 DOHC were the only engines to have stock forged rods. And they are probably good for 550-600 HP with good bolts. I just wouldn't trust them at 8K RPM long.

all 3.1/3.4/3100/3400 rods have the same part numbers. 2.8?

Again, Nate, you don't know what you are talking about. Reading stuff on the internet and DOING IT are two VERY different things my man. Robert is correct, the rods were identical from the 2.8 Gen1 until the Gen3 3400, they are forged and they are stronger than PM. Period the end. If PM rods were stronger, then BMW would be using them in the 350hp 3-liter engines, but they don't, they use the same design and material GM used to use and what's in the OP's car.

[NateD4]

Again, Nate, you don't know what you are talking about. Reading stuff on the internet and DOING IT are two VERY different things my man. Robert is correct, the rods were identical from the 2.8 Gen1 until the Gen3 3400, they are forged and they are stronger than PM. Period the end. If PM rods were stronger, then BMW would be using them in the 350hp 3-liter engines, but they don't, they use the same design and material GM used to use and what's in the OP's car.

I'm really not going to argue whether or not I know what I'm talking about. I don't read this stuff on the internet. I deal with this stuff like this for my day job.

Unless you are an engineer, metallurgist or connecting rod designer I don't think you are really qualified to argue connecting rod materials and manufacturing.

The rods may all be the same for the Gen I through Gen IV cars. I know the Turbo 3.1s had forged internals and have heard the 3.4s do as well. The other rods I'm not sure about because I've never had to mess with them and never really plan to.

The general understanding of forging I see on most forums is misleading at best. Just because it is forged doesn't make it a high strength, better part. I can forge 1010 steel and it will produce a lower quality part then say a good quality 5140 casting. While a 4340 forging will be better in certain planes than a 4340 casting. This is also true of powdered metals. Some are better than others. They are not all necissarily the same.

Also just because BMW uses something doesn't make it right or the best solution. It is simply a solution point in the design space of requirements put forth by the manufacturer (in that case BMW).

If you browse around enough for rod replacements you'll notice that few rods between brands are interchangeable (I looked at almost every option I could prior to buying my current set of rods). This is because each rod and engine brand has its own design and geoemtry (obvious right?). You really can't compare BMW rods to GM rods. The geometry of the design changes everything. It changes stresses, rigidty/stiffness, torsional strength, weights etc.. All you really can argue is material stress capability, stress-strain response and fatigue life. That is almost all that really matters in rod design anyway.

All the metalurgy put into them is to mitigate these properties to be useful for the intended goal of the part.

Each rod designer has different criteria and cost constraints that determine which processing and materials they pick.

Powdered metalurgy is actually a good choice for connecting rods. It is also technically a forged product (there is a difference between wrought forgings and the compression forging process used for PM parts though).

Powdered metals have the ability to be alloyed in ways other metals can't be giving unique properties that are otherwise not possible with traditional cast and wrought alloys. They also allow for some very novel manufacturing techniques. Personally, though, I think a PM rod is pretty amazing as it is. A connecting rod sees a lot of loadings and the fact that a PM rod is competitive price and weight wise with a traditional forging is pretty cool. In fact I venture to say that PM rods are a higher quality part then a traditonal forging is. Mainly because the manufacturing process has better control over the end product.

Interestingly enough Porsche uses powedered metal rods and apparently crankshafts as well. GKN Sintered Metals has an interesting web site that shows many parts made from powdered metals. From oil pumps to gears. The strength of the powdered metal part really depends on a few factors: materials selected, processing operation used, cleanliness the materials and post processing of the metals as well as final inspection. If the company making the part can get all of those right they can produce a part equal to or perhaps better than a forged one.

There is a lot that goes into making a highly reliable part, the OEMs spend a lot of money to make them at a extremely low cost, while the aftermarket can make parts at several times the cost (ten or more times). Even within wrought forgings it is possible to introduce material flaws or use materials that do not perform satisfactorily. As an example there are several specs of 4340 available each of which has its own slightly different properties that make it suitable for certain applicatons and not others.


................

Once I disassemble my piston/rods I'll weight each rod to see just how consistant their weights are. I'm betting they are close then 5g to each other off the production line. I'll also try to weigh a set of 3400 LA1 rods for comparison.

Again just a few of my thoughts. Sorry about the lengthy post.

[Dave96z34]

I agree with you 100% Nate that's why I said changing the rods and other parts to expensive custom aftermarket parts may be stronger or it could have have a defect that makes its life unusually short. Bobby (dohcfiend) put huge money in to pistons and rods and then had problems with seating the rings. The machine shop had to pull it apart 2 times to fix it. My response to that iv never seen a rod or piston on a lq1 fail unlike the junk l67's. Bearings, bolts and a balance job may sound like im being cheap but if you cant break. Not worth the headache of potential other problems.

Whats funny about that is my brother works at a powdered metal plant in Maine making oil pumps and other parts. Iv seen the proses first hand I bet the are strong but shock kills them..

[NateD4]

It's all relative to what your goals are. In my case I'm pushing RPM and still want 100% reliability. I'll take upgraded internals.

Additionally the merits of switching from a 10 series steel to 4340 is a huge improvement in service life. And on turbo applications having a rod with a higher buckling capability means more boost and less chance of bending something with boost. Also in my case I may be taking an 80-100 gram weight penalty which adds to the stress (but still way cheaper then Titanium rods).

As far as not being able to seat rings with a set of custom pistons. That could be a different can of worms unrelated to rods.

In my experience rings that don't seat are one of a few things. Either the wrong break in oil (non detergent, non synthetic oil should be used). Or perhaps the deglaze/hone job was not done right. If the cross hatch is too light or too fine you'll have trouble seating the rings. If it is to course you'll never finish seating the rings until you've worn quite a bit away and loose end gap. It could also be the break in procedure. Interestingly most break in procedures that I've heard about recommend not keeping the engine at constant RPM until the rings are worn. I'm sure googling this will result in mixed opinions. However, like I mentioned, I've never had a problem with break in using this technique.

I haven't heard of many people having this problem. It could be a sew of things, perhaps even mismatched bore sizes or the piston manufacturer being overly conservative with piston clearances.

[SappySE107]

Unless you are an engineer, metallurgist or connecting rod designer I don't think you are really qualified to argue connecting rod materials and manufacturing.

I know the Turbo 3.1s had forged internals and have heard the 3.4s do as well.

Ok, which of those are you, engineer, metallurgist, connecting rod designer? Also, do you know the turbo 3.1s had forged internals from experience, or regurgitated misinformation you read somewhere? Only the rods were forged.

The OP has rods ordered so we don't need to keep discussing them in this thread.

[Dave96z34]

If I remember correct this is 5 years ago the machine shop determined the rings were cut wrong. Kinda why im an advocate of the stock lower end till it can be proven inadequate. My plains for the future include a Whipple 140ax with a 15psi goal so that will be the test to end all test.

Will also be the end all test of what a 284 getrag can do.