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  #16 (permalink)  
Old 08-17-2010, 01:37 AM
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Look at KB/ICON Forged pistons, or Probe forged, they come in around $350 a set. Scat ProStock and Scat ProComp I-beam rods, in the $210 area.

I'm one of those guys that don't like Hypers in any performance engine, something goes wrong in the tune and they tend to explode. False economy if you ask me.

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  #17 (permalink)  
Old 08-17-2010, 09:25 AM
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Quote:
Originally Posted by cobalt327
The high dollar Howards PM rods use the fractured cap technique, I suppose broaching has done the job well enough that GM hasn't seen fit to expand into full-scale fractured rod technology yet, for whatever reason.
Broaching is a finish operation it doesn't have anything to do, as such, with separating rod shanks and caps where they are made in one piece. A one piece forging whether starting from billet or powdered metal will be separated by sawing or fracture, both with subsequent machine operations.

1) Sawing requires a finish operation after the cut on the sawed surfaces. First, a bore or a broach can be used to complete the hole shape. The bolt holes are drilled and reamed to size, the facing pads for the bolt head and nut are milled. The cap is sawed from the shank and their mating surface milled. There will also be an operation at this point in the case of using cap bolts where the shank would be tapped as well but the upper pad milling operation would not be necessary.

2) Fracture cap would first require that the bearing bore be finished in the part before separation of the cap from the shank. This would be done with a broach or a bore operation. The mating bolt holes are then drilled and reamed and the bolt head and nut interface pads machined. The rod is then put in a press and the cap fractured from the shank. This is a less costly operation than the using a saw to separate the cap as it has fewer operations which is why it was developed.

There are other operations in both cases to mill the thrust surfaces of the big end and relieve on one side for clearance to the crank pin end radius and certainly the piston pin end, a heat treat, possibly a shot peen, and balancing. The powder forging provides what's called a "near net part". At this point it reduces some machine operations and makes parts more common in weight which means less wasted material in balance pads and more material where the loads are running in the part. The ultimate goal would be to make a net part that doesn't need additional machining, ready to go like a plastic toy kind of thing.

The GM, PM production rods may or may not be fractured cap, GM used both processes on the late Gen I and Gen II engines. However, in either case people need to be sure the caps and shanks are id'ed to each other if they aren't already, same with main caps; as this column has seen plenty of bloggers that didn't do this and are now trying to figure out which part goes where and in which orientation.

Frankly, I'm not a fan of either PM or fracture cap technology. I use rods either forged from a billet or machined from stretcher plate depending on power output with the shank and cap separated by machine operations, not brute force. I've looked at Howard's PM, fracture cap rods but the pucker factor I get is too much for me to use them in anything beyond a hot street engine.

Bogie
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Old 08-17-2010, 09:32 AM
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Quote:
Originally Posted by oldbogie
Broaching is a finish operation it doesn't have anything to do, as such, with separating rod shanks and caps where they are made in one piece.
I do understand broaching isn't an op that cuts the cap off the forging- the point I am making is that there IS a finishing op, as opposed to no such op on a fractured rod, a la Ford, Howards, etc.

The research I've done (that I deemed to be within the realm of "trustworthy") indicates to me that the GM PM rods are forged w/an oval big end and are then cut and finished by broaching. Or if they are fractured they are then subjected to a broaching op to finish them.

If you have anything that contradicts this, I'm all eyes- finding GOOD info on the subject is difficult on the interweb... And the OM's aren't exactly yelling the details from the rooftop.

However, I have zero references or empirical evidence of fractured cap rods (w/the fractures left intact) having been used by GM on production Gen-1 or 2 or Vortec engines. What engines would they have been?

Are you sure you're not thinking about the Gen 3 engine? From an article on the Gen 3:

"The connecting rods are also powdered metal like the LT1’s but are “cracked,” meaning that the cap-to-rod interface is actually broken rather than machined. This creates a stronger cap position on the rod without the need for dowel pins."

Last edited by cobalt327; 08-17-2010 at 09:58 AM. Reason: Clarity.
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Old 08-17-2010, 10:20 AM
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BTW, the HR mag article linked above is linked solely to show where the quoted info came from- it is not (by me, anyway) considered to be any more reliable than ANY mag article.

Found a reference to 4.3L "Vortec" V6 in mid-2006 getting PM fractured cap rods (w/fracture intact)- http://www.fullthrottlev6.com/forums...rmation-needed

Engine Builders mag article on general info regarding PM and fractured cap tech-
http://www.enginebuildermag.com/Arti...ght_think.aspx

Everything else I've seen is all purely hearsay- some guys saying never were PM fractured caps used on anything before the LSx-series, then some saying that some LT1's had them, etc.- but none showing a photo or other empirical evidence of it. A real hodgepodge of mis-information, regrettably.
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Old 08-17-2010, 02:18 PM
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Quote:
Originally Posted by cobalt327
BTW, the HR mag article linked above is linked solely to show where the quoted info came from- it is not (by me, anyway) considered to be any more reliable than ANY mag article.

Found a reference to 4.3L "Vortec" V6 in mid-2006 getting PM fractured cap rods (w/fracture intact)- http://www.fullthrottlev6.com/forums...rmation-needed

Engine Builders mag article on general info regarding PM and fractured cap tech-
http://www.enginebuildermag.com/Arti...ght_think.aspx

Everything else I've seen is all purely hearsay- some guys saying never were PM fractured caps used on anything before the LSx-series, then some saying that some LT1's had them, etc.- but none showing a photo or other empirical evidence of it. A real hodgepodge of mis-information, regrettably.
I wasn't coming from what I read or what GM says, I'm coming from having opened several engine's up and saw what is obviously fractured cap rods. They look way different from the machined surface your used to seeing when the two parts are sawed apart and machined. The break of the fracture cap leaves a fine grain rough surface but it isn't like the surface left from fretting where the load is causing the cap and shank to walk thru the clamping force of the fastener. Next time I hit one I'll take some pictures, it's been on some, not all, Vortecs, LT1s and LT4s where I've seen them on Gen I and II engines. I haven't seen a Gen III without them, but I haven't worked on too many Gen IIIs either. One thing I've learned working on GM engine's is that you never know what's in there till you open them up, regardless of what the book says should be in there.

Bogie
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