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Can anyone tell me if Chevrolet 1960's/70's Special High Performance small block engines used better quality rod bolts than your average auto/truck engines?
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Re: SHP Rod bolts
Frank-----
All small blocks of a given year used the same rod bolts EXCEPT for 400 cid engines. This included the lowest horsepower all the way up to the highest.
1955 through 1967 used 11/32" bolts; 1968-97 used 3/8" bolts.In Appreciation of John Hinckley -
Re: SHP Rod bolts
Hi Joe, Best of the New Year to you!
What is the difference with the 400 rod bolts? Size or quality of material?Comment
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Re: SHP Rod bolts
Frank-----
As far as I know, it was length only and 2 different lengths were used for 400 engines. 1970-71 400s with 4 barrel carb used bolts that were 2-1/2" long. All other 400s used bolts which were 1-23/32" long. All other 68+ small blocks used bolts that were 1-59/64" long.In Appreciation of John HinckleyComment
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Re: SHP Rod bolts
Frank,
Think about the loading condition for the rod bolts...
In the most severe piston/rod loading conditions, (compression and combustion) the rod is bearing the brunt as it is in "compression". The rod cap and bolts are along for the ride.
The only real "load" the bolts ever see occurs when the piston is on the down stroke pulling in a new charge of fuel/air. This is negligable because the intake valve is open.
The outfits advertising "super duty" rod bolts are selling hype...
tcComment
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'70-'71 400 W/FBC was a .030 over 396 *NM*
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You might be suprised
If one of the engineer types here calculates the force required to accelerate the rod and piston from a dead stop to however many FPS, 6000 times a minute, you will find it is a considerable load.Comment
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Re: '70-'71 400 W/FBC was a .030 over 396
Mike-----
The 400 with 4 barrell that I was refering to is the small block 400. The big block that you're refering to was known as the 402.In Appreciation of John HinckleyComment
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Re: SHP Rod bolts
The greatest load on the rod is on the exhaust stroke. On the power stroke, cylinder pressure acts in the opposite direction of the inertia load, and at high revs the inertia load far outweighs cylinder pressure load. The load on the rod bolt is the sum of clamping force plus the inertia load of the piston and rod trying to pull away from the cap.
At BDC the bolt only sees clamping force load because the inertia load is in the opposite direction. It's this cyclic loading that can limit the life of the rod bolts due to fatigue phenomenon.
DukeComment
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Joe, I realize you are the master of the parts
book. However, in my '70's period parts books they differentiate between the two "400" cu in. engines as 400 W/2bc and 400 W/4bc even though like you say, one of them was a 402 BB. Chevrolet parts books of that era did not refer to these engines as "402". At least none that I have seen. They separated the engines by referring to the carburetor mounted on the intake. Small block having a 2 bbl and big block having a 4 bbl. I believe Chevrolet Promo litierature referred to the 402 engine as the Turbo Thrust 400. To confuse matters more, the engine ID nomenclature on the front fender of at least some models continued with the 396 badge.
I don't believe a four barrel was factory installed on a small block 400 in '70-'71. Two barrel only and rated at 265 horsepower. Later in the 400 small block cycle they were available with a four barrel on truck engines.
If I am confused, please advise.Comment
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Re: SHP Rod bolts
I'm with you Duke, I think we only differ in our definitions as to where the line is drawn between exhaust and intake stroke. (I probably over simplify this in my feeble brain) The peak tensile load on the bolts would in fact be at the roll over point from the top of the exhaust stroke over to the start of the intake stroke.
Because we know objects in motion want to stay that way, the rod and piston would want to fly into the head at this point. We have the mass of the piston and rod pulling the hardest on the bolts here plus the clamping load constant.
Clamping loads are a constant at any point on the crank revolution.
All I really wanted to convey was the rod bolt loading conditions between a 250hp and a 375hp would fall well inside the margin for yield strength of the bolts.
As you have posted before, the rod casting itself is more prone to failing due to fatigue than the bolts.
Thats why they are the same in the small block applications listed by Joe L.
tcComment
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Re: Joe, I realize you are the master of the parts
Mike-----
You are correct; the 1970-71 "400 cid engines with 4 barrel carbs" were big blocks and not small blocks. However, GM parts references do make reference to 402 cid engines. For 1970 and 1971, the big block engine was referred to as "400 with 4 barrel carburetor". For 1972, it was referred to as "402". That's what created the confusion on my part. There was a slight difference between the 400 cid big block and the 402 cid big block.
The 1970-71 400 cid small block had a bore and stroke of 4.125" X 3.76". The 70-71 400 cid big block had identical bore and stroke dimensions. The 1972-only 402 cid big block had bore and stroke dimensions of 4.126" X 3.76".
Of course, neither the 400 cid small block, 400 cid big block, or 402 cid big block were ever originally used for any Corvette.In Appreciation of John HinckleyComment
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