turbo charged 3.4 dohc....430 rwhp!

[timg]

The key on almost every modern engine to making it last under boost is tuning. Without good tuning, you're sunk and your engine won't last long if you go over 5-7 psi. With good tuning, many factory engines can live long lives at 10-15 psi.

I'm very cautious about meth and E85. Both are awesome for boost, but both also introduce a lot of extra complexity, expense, and potential for failure. IMO, I would do everything I can to make a setup reliable on 91/93 octane. Water/meth injection has gotten more reliable, but doing it right is tricky and costly.

Tim

[ForcedFirebird]

So many failures are typically due to KR at high load, that is the most damaging on an engine and all your doing with forged internals is making the bottom end a bit more forgiving of a poor tune. As you guys have been saying if you get the tune right and get rid of the engine destroying KR then you can probably easily run 12-15 psi on a stock bottom end.

I run a 100 shot and have yet to blow up a piston; but everyone I tell that I'm running nitrous, and what shot they ask if I did forged internals and when I say no they all cringe...

15psi is not much for a modern engine. One of the locals here has a 99 m5 (s62 DOHC V8 ) with it's stock 11:1SCR and puts 1bar on it with a Vortech S/C and meth inter-cooling. Some of you guys remember Loner's car, that was 9:1 with FP HG's and stock 100+k mile bottom end. That was the most fun I ever had in a Corsica haha.

[3400-95-Modified]

So many failures are typically due to KR at high load, that is the most damaging on an engine and all your doing with forged internals is making the bottom end a bit more forgiving of a poor tune. As you guys have been saying if you get the tune right and get rid of the engine destroying KR then you can probably easily run 12-15 psi on a stock bottom end.

I run a 100 shot and have yet to blow up a piston; but everyone I tell I'm running nitrous and what shot, they ask if I did forged internals and when I say no they all cringe...

[TGP37]

I'm no expert but, my 3100 stock rods have held up to 8psi with occasional 12psi and a handful of 15psi runs.

I have heard and experienced, the tune means much more as a stock bottom can handle 15psi if tuned properly. But will self destruct at 8psi if not tuned well.

IMHO, what really matters is how the connecting rod is treated. I'm sure both types will fail under harsh enough conditions.

[ForcedFirebird]

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 don't have to be to know the limits of a motor I have been testing the limits on for several years, in which YOU obviously have NOT. You have no idea what you are talking about and posting quotes and info that is incorrect and it's getting old. If you aren't a rod designer, then you heed your own statement and resist arguing what you haven't experienced.

[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.

[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.

[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.

[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]

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.

[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.

[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?

[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.

[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]

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