Anyone had their oil pan off their '99 or later L67 SC 3800 II?

[SubZero350]

I was wondering if GM was ever going to put forged rods in the 3800. The easy way to tell is to look at the rods from the side. If there is a thin (about 1/16" wide) parting or "casting" line that runs the entire length of the rod, it is cast. Typically the forged rod will have a harder to see thick parting line that is usually 1/8"- 3/16" wide that, too, runs the entire length of the rod. I would like to do a L36 - to - L67 buildup to accept a GN's turbocharger but would really like to stuff something a little stronger under the pistons. Please let me know...

 

[T-Keith]

I'm assuming your thinking of going with the L67s lower compression pistons and rods right? Have you looked into some aftermarket rods? Maybe rods from a different 3.8(turbo?) would fit, or maybe from an entirely different application? For instance I've heard that SBC rods will fit a 2.8. Other wise the L67s rods are pretty strong from what I've heard.

 

[SubZero350]

No other 3.8 rod will fit as far as I know. This is because the series II engines have a 1" shorter deck height. I would rather not use SC rods because they are still cast; regardless of how much power they are "supposed" to handle. I guess I might consider using them if I could find a good set for about $80. Silvolite offers aftermarket hyper pistons so no trouble there.

 

[Tom Mahi]

Uuummmmmmmm, what does the parting line on a powdered metal rod look like? GM is using these in some production motors and they're supposed to be pretty strong.

Aloha,

 

[SubZero350]

A powdered metal rod parting line looks very similar to a cast one but the actual finish of the rod is darker in color and more consistant. A cast rod typically will have a rougher surface than a comparable forged or PM rod. PM rods are stronger because of the intense pressure required to manufacture one. The main reason for forging or manufacturing any rod under pressure is to align the grain flow of the metal's molecules throught the structure. To put it simply, this helps reduce "stress risers" from within the rod as well on the surface. It should be noted that FORD and GM are using a new PM rod manufacturing technique that envolves breaking the big end in half instead of machining them apart. This is accomplished primarily by the dipping of the big end in liquid nitrogen or other very cold substance and then using a machine to "snap" the big end in two. While this is superior in assuring rod cap alignment, this also means that the rods cannot be resized; unless an oversize OD diameter bearing is manufactured like those available for the FORD PM rod. However, maximum machining will only allow for a +.015 bearing OD diameter with these rods as best as I can remember.

 

[383LT1]

I have a couple additions to make:

- Cracking the crank-end of the rod I believe allows for a perfect fit between the two pieces and perhaps better bearing life from desired clearances. It'snot as new as some may think, BMW has been doing this for over a decade.

- Powdered metal rods are strong because they supposedly don't have the micro-defects that can propagate into breakage. The hot forging process of the manufacture is just part of the story. And actually it's positive characteristics are mostly from where it all begins in the ingredients: carbonless iron powder that has been fortified with measured amounts of graphite, copper, and manganese sulfide. This powder is thoroughly mixed to gain a completely consistent mix of ingredients. It's the consistency which allows the minimum of internal micro-crack initiation sites that can lead to breakage.

- I don't know if the L67 rods are strong but the series II motor received a lighter piston and rod to reduce the work/energy to reciprocate the assembly. That in addition to other factors, is why the L67 motor can rev extremely freely (not too far off long-stroke touring motorcycle engines).

 

[SubZero350]

Thanks for the info check, but my primary concern is not RPM. I am going to be putting a GN's turbo onto a 3800 series II and don't want to end up with reciprocating parts in the oil pan. I only plan to run 6-7psi of boost initially, but would eventually like to hit about 15psi with forged pistons (when they become available).