Connecting rods
05-10-2011, 07:52 PM
#1
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Connecting rods guys, are stock connecting rods from a 5.7L vortec gen I good? i mean comparing them with an old 5.7L gen I. are they better than the old ones?
05-11-2011, 11:31 AM
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05-11-2011, 04:04 PM
#6
The Gen1 SBC rods will have to be machined to work on your LSx due to the difference in rod offset and piston design. Short answer: Save yourself the money and effort and buy the LSx specific rods 
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05-12-2011, 08:31 AM
#7
Your original wording makes it look like you wanted us to compare L31 rods against L31 rods.
L31 rods are Powdered Metal. This is stronger than older SBC rods, IF the cross-sectional area remains constant. Using L31 rods, it doesn't.
Back in the days of the LT1, ( '92-'97 ) Hypertech got best dragstrip results with a 6200 RPM upshift. So that's what they sold as standard in their programmers.
This worked fine at first, but then came the PM rods, and a few reports of them failing at 6200 rpm.
I bought a '95 Z28 convertible, and I used the Hypertech tune before I heard about the new rods failing. I was doing automotive machining at the time, but the new rods just weren't being brought into the shop.
My set of PM rods never failed, I drove that car into 2004.
If you want 7000 rpm, it's best to just buy a new set of 4340 rods. They're now the same cost as rebuilding early-'70s rods with new ARP Wave-Loc bolts.
If 6000 rpm is enough, then the PM rods will be okay in a 350. A 383 gives higher piston speeds, which pulls on the rods more, so stock PM rods should see less RPM in a 383. If you're doing a 383 that will see 6000 RPM, again go with new 4340 rods.
L31 rods are Powdered Metal. This is stronger than older SBC rods, IF the cross-sectional area remains constant. Using L31 rods, it doesn't.
Back in the days of the LT1, ( '92-'97 ) Hypertech got best dragstrip results with a 6200 RPM upshift. So that's what they sold as standard in their programmers.
This worked fine at first, but then came the PM rods, and a few reports of them failing at 6200 rpm.
I bought a '95 Z28 convertible, and I used the Hypertech tune before I heard about the new rods failing. I was doing automotive machining at the time, but the new rods just weren't being brought into the shop.
My set of PM rods never failed, I drove that car into 2004.
If you want 7000 rpm, it's best to just buy a new set of 4340 rods. They're now the same cost as rebuilding early-'70s rods with new ARP Wave-Loc bolts.
If 6000 rpm is enough, then the PM rods will be okay in a 350. A 383 gives higher piston speeds, which pulls on the rods more, so stock PM rods should see less RPM in a 383. If you're doing a 383 that will see 6000 RPM, again go with new 4340 rods.
