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BBC "Thumb"rods

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#3 ·
Are they really stronger is what always entered my mind.
If you use good rod bolts and prep the rods the same are you gaining any needed strength?

Have you ever broke or ruined any sbc or bbc rod that was the rods fault.

I never have.
I have shifted my stock sbc rods with stock bolts past 7500 rpm many times in 350" for hundreds of thousands of miles.

455 olds shift points were 6700 rpm, never hurt rods or anything
BBC 7000+ rpm never any issues.

Never ran more than 12.0 compression so maybe if you get into the really high compression and high rpm area 8500+.

Really curious if anyone has had a rod fail.
Hydraulic from stuck injector or flooded carb or water into the cylinder or bad tune does not count.
Wrong piston to head clearance does not count either.
 
#4 ·
The 1986 RV 454 I had did have Thumb (you can put your thumb on the side of the rod in a thumb shaped groove) rods, pretty sure they were used in HD applications, trucks, RV's I've only broke 383 mopar rods,,Twice
 
#5 ·
In my experience, thumb rods were found in truck motors, 366/427 tall deck engines. I had several sets at one time and ran a set in a 427 with a set of heavy as hell Speed Pro 12:1 closed chamber pistons and a solid flat tappet cam. That motor saw plenty of 7K blast in my younger reckless days. Never hurt a rod, but nowadays, you can buy a set of chinesium rods cheaper than what it would cost to refurb a set of stockers with new bolts and bushed ends.
 
#8 ·
A little eye opener on big block Chevy rods. The pictures below are from my 454 that I grenaded 5 years ago when the head of an intake valve broke and wiped out the motor. Forged rods don’t break, they bend.The forged Mahle piston was turned into gravel. If something is going to fail on a connecting rod, it will be the rod bolt. My 2 cents.
Image

Image

Image
 
#10 ·
Hit a forged rod hard enough and it'll break. One or two rods in my 572 mopar got pretty broken up. Engine wasn't mine when it grenaded, but it did a pretty good job. Hit somewhere around 10 grand, maybe a bit more. Rev limiter wasn't set.
 
#11 ·
v8440 said:
Hit a forged rod hard enough and it'll break. One or two rods in my 572 mopar got pretty broken up. Engine wasn't mine when it grenaded, but it did a pretty good job. Hit somewhere around 10 grand, maybe a bit more. Rev limiter wasn't set.
Click to expand...
Mine was nowhere near 10 grand when it let go. I was cruising in 5th gear at 2200 RPM. I can't imagine the carnage at full throttle.
 
#14 ·
AS I sit here and ponder the question, I do believe the 1970 / 71 454 LS6 engines came with the "Thumb" forged rods, and I have seen mine when I replaced the Oil pump for a better unit, but I can't remember if I even paid any real attention at the time, but I will say this, my wife has hit 8,000 rpms several times doing the Powder Puff BS back in the day.
 
#15 ·
Every light duty truck Mark IV 454 and marine Mark Iv 454 I have taken apart had the "thumb" rods. The Gen V & VI engines did not have "thumb" rods. My understanding is that they were used in applications where higher RPM's were sustained like Marine or Towing running 3,000-3,500 all day long. I will use them if I have them, but as others have said with the cost of aftermarket rods, why?
 
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