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Selecting Connecting Rods for my L78 Build

For a stock replacement they're fine.

That's what I think, but this rod seems to be new...no reviews and I haven't noticed it before. So, assuming I have to go with pressed pins (due to my pistons) I'm down to the Scat Pro Stock I-Beam Rod, and the Scat Replacement I-Beam Rod. I did look at the Callies Compster I-Beam Rods w/ARP 2000 bolts, however it doesn't appear that they make them anymore (USA made in Ohio?...or at least machined there). As long as any of the pressed pin connecting rods I'm looking into are as good as the good ole GM dimple rods with 3/8" bolts that were stock back in 1967, I suppose I'm ok. I don't look to be at 500 HP or more with a stock L78 build so that should be fine. No reason to go with shot peening, polished, etc. more expensive race rods, or floating pin rods for this build. I'm estimating in the 460HP range with headers (just like my original L78 with the Mickey Thompson Super Scavenger Headers....sweet!).
 
I have two sets of rods on hand, both are resized OEM. One is a 7/16th Dimple rod full floater set and the other are a set of old Thumb Rods (press fit) with ARP bolts. I could personally go either way with a 600hp build and be comfortable. I see nothing wrong with the rods you listed. They are reasonably priced for sure.
I have 2 assembled engines, one a 565 with Callies Ultra Rods, a 500 incher with Howards Ultimate Duty Billet Rods and a 475 incher with Howards Ultimate Duty Billet Rods. The 565 uses a Callies Magnum crank, the 500 incher uses a COLA crank and the 475 uses a Scat lightweight billet crank. Point being I have no issue with using the Scat stuff because ii has a pretty decent history throughout racing. All three of my pieces use floating rod pins. Just my preference. My original 396 has press fit stuff and a cast crank which I'd not hesitate to reuse if the time ever comes in my remaining days.
 
Well, looking at both Jeg's & Summit, due to no feedback, and especially on Summit - they say the Scat Replacement Rods are not available until January 2022. It appears that this new design comes in either 3/8" through bolts or 7/16" through bolts. They are both press-fit design, and both are also shot-peened & polished. Honestly, I'm starting to lean toward waiting for this Replacement "Dimple-style" Rod from Scat. I would probably go with the 7/16" ARP bolts over the 3/8"s. I caught an error in the Summit description, but this is likely not that rare. Also, I'm thinking the Replacement Rods may be a bit better than the Scat Pro Stock at this point. Aren't "through bolts" better than "caps" or is it the other way around? I also like the shot-peened & polished rod treatment, and this is likely one reason the Replacement Rods are a bit more money. Thoughts?
 
Rod Bolts without nuts are preferred. 4340 is good strength metal but not all fasteners are created equal. ARP 2000 are good bolts. When in doubt, call Scat for information.
 
Rod Bolts without nuts are preferred. 4340 is good strength metal but not all fasteners are created equal. ARP 2000 are good bolts. When in doubt, call Scat for information.
I will call Scat to get more clarity. Thanks for your help on this! At least I’m narrowing down my options.
 
No need for 7/16" rods, 3/8" work perfect even at 7K, never seen a GM truck thumb rod ever fail. The ones out of a 454 are bullet proof we use them all the time without a failure.
 
No need for 7/16" rods, 3/8" work perfect even at 7K, never seen a GM truck thumb rod ever fail. The ones out of a 454 are bullet proof we use them all the time without a failure.
No need for 7/16" rods, 3/8" work perfect even at 7K, never seen a GM truck thumb rod ever fail. The ones out of a 454 are bullet proof we use them all the time without a failure.
Can you name a downside to a 7/16th rod bolt?
 
Can you name a downside to a 7/16th rod bolt?

I was told from some of the engine builders that the extra rod weight is not needed, same goes for pushrods the big cigar 7/16" not needed and holds extra weight in oil which can cause revability and stability problems at high RPM and my machinist is a Super Gas/ Comp racer. He knows what works. As a matter of fact I was going to use my 7/16" rods on the one 468 build and he was telling me "you don't need them so I used my 3/8" truck rods after he showed me they had more meat around the bolt and shoulder of the big end on the rods than the 7/16" rods.
 
I don't particularly agree with your machinist. 7/16 rod bolts are stronger and 7/16 pushrods are less flexible than are 3/8 pushrods. You have to consider spring pressures on a high performance larger cammed engines. 325lbs on the seat is a bit of pressure. What we don't need in a high revving engine are wobbly parts and weaker rod bolts which are subjected to stress at higher rpm's. Sometimes a little weight is a necessary evil if it's providing more strength. Even the old L-88 427's used 7/16 bolts for a reason.
 
I don't particularly agree with your machinist. 7/16 rod bolts are stronger and 7/16 pushrods are less flexible than are 3/8 pushrods. You have to consider spring pressures on a high performance larger cammed engines. 325lbs on the seat is a bit of pressure. What we don't need in a high revving engine are wobbly parts and weaker rod bolts which are subjected to stress at higher rpm's. Sometimes a little weight is a necessary evil if it's providing more strength. Even the old L-88 427's used 7/16 bolts for a reason.

My NHRA A/Stocker guy said the same thing about the bigger pushrods you don't need them as it's the amount of oil in them that causes the problems. As for the 7/16" bolts yes they are stronger now but on a GM factory GM rod they is less area around the bolt than the smaller rod bolts. I have a set of Manley 7/16" rods for a SBC and the are super beefy around the the big end area. I also look at the some of the guys I knew years ago that raced little 238's punched out to 301's and ran 11/32" rods theses guys would spin them engine to 10K and never broke rods or bolts. I can still see why GM went to a bigger bolt in 1968 for the SBC. I also read in the Hi-perf Chevy book I had where GM said a 7'16" rod would last a lifetime at 7K but only 500 miles when spun up to 7500 RPM. I thought that was interesting back in the day.
 
I called Scat today, and I’m going with my first choice. The guy said that is a great rod for the money! I told him about the eBayer telling me to stay under 500 HP and the guy laughed...he sells that rod all the time and to some builds expecting 700 HP! I need to go with press-fit so I’m happy with my choice. Thanks for all the input! 👍
 
Ok, just a follow-up here: I have had my SCAT Rods for a month or so now, and while searching for a decent 6223 Crankshaft I stumbled upon these two connecting rod options on ebay:
1. Reconditioned Thumb Rods set:
  • These rods have been shot peen cleaned, inspected for defects, and remanufactured to factory standard big end specifications of 2.3247" - 2.3252" with 6.135" center to center length.
  • JAMSI Remanufactured Connecting Rods more closely match OEM rods in strength, dimensions, and weight than aftermarket rods.
  • NOTES: big end width .995", pin end diameter .987", forged rod with 3/8" bolts, torque to 50 FT/LB

2. GM 10198922 NOS BBC Press-Pin Dimpled Connecting Rod, Set Of 8) Pcs, (Will these work on my L78 build?)
LS-6, LS-7, GenV & VI 454/502, ARP 7/16" Rod Bolts, 6.135" Length, 4340 Steel, Excellent Condition!

I also found a couple more GM Dimple Rod sets on ebay, but they are more pricey, and not so sure they are matched & balanced ($500 to $650 range).
I'm happy with my Scat rods, but especially when it comes to that nice set of Thumb Rods, I'm wondering if I should just buy those as well, and leave it up to my engine builder?
Thoughts?


Thanks,

John
 
No reply’s? Oh well. Actually, as much as I’d like to install GM rods in my build I still think the Scat rods I bought are pretty solid and a good choice. One of the sellers above (Thumb rods) actually said he’d go with the Scat rods! Ha! The other seller said his rods were a perfect fit for my build, but the Scats are basically the same or similar design with the same forged steel and 7/16 bolts. So, I still think my choice is pretty good. Plus, Scat rods are machined at their plant in CA. I’m open to suggestions but I believe I’ll be safe with what I have.
 
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