[Tom Vaught]

Oliver has these rod lengths for a reason.


Oliver Rod Lengths
6.135" (stock) (1)
6.385” (+.250) (4)
6.535” (+.400) (4)
6.635” (+.500) (3)
6.660” (+.525) (1)
6.700” (+.565) (4)
6.735” (+.600) (1)
6.800” (+.665) (4)
7.000” (+.865) (2)
7.100” (+.965) (2)

So you have lots of choices for Pin Compression Heights on pistons and different block heights.

Smokey Yunick was a big advocate for building engines with longer rod lengths for durability.

Tom V.

The RA V rods were 7.080" center to center. The 7.100 rod would work great in a V engine vs the old stuff and have better
materials and machining coming from Oliver.

[hurryinhoosier62]

Originally Posted by Tom Vaught

Palbykins NA 473 cid engine used a 2.10" SB Chevy Rod Journal on his cast iron 455 crank. Custom Rods and Pistons. Believe the Pistons were Ross.

So you can go smaller than a 2.20 rod bearing.

Tom V.

Which begs to ask the question as to WHY this isn’t used more in all out Pontiac competition engines? It makes sense if your are attempting to vastly lower the connecting rod bearing speeds.

[hurryinhoosier62]

Originally Posted by Tom Vaught

Oliver has these rod lengths for a reason.


Oliver Rod Lengths
6.135" (stock) (1)
6.385” (+.250) (4)
6.535” (+.400) (4)
6.635” (+.500) (3)
6.660” (+.525) (1)
6.700” (+.565) (4)
6.735” (+.600) (1)
6.800” (+.665) (4)
7.000” (+.865) (2)
7.100” (+.965) (2)

So you have lots of choices for Pin Compression Heights on pistons and different block heights.

Smokey Yunick was a big advocate for building engines with longer rod lengths for durability.

Tom V.

The RA V rods were 7.080" center to center. The 7.100 rod would work great in a V engine vs the old stuff and have better
materials and machining coming from Oliver.

Tom S. and I had a long discussion on the 7.080”, RAV Trans Am engines verses the 6.625/RAIV Trans Am engines. We came to the conclusion that you COULD have a connecting rod so long that it hampers the engine’s ability to accelerate efficiently. What blew my mind the first time I ever saw one were the 7.2” NASCAR Hemis. Those rods look like they belong in a diesel! I know when my friend and mentor, Bud Brown, was still building USAC Silver Crown engines they were normally short stroke, long( well for a SBC Chevy) rod combinations with incredibly light pistons, pins and ring packages. They were routinely run as high as 9,000 rpm.

[grandam1979]

Originally Posted by Stan Weiss

There should have been no problem running the same rod with either the 4.21" or 4.25" stroke. The 4.21" needed a 1.47" compression height piston the 4.25" needed a 1.45" compression height piston.

Stan

So I looked in the shop for a stock 455 piston but I don’t have one I was hoping to mic it. So my option is they didn’t want to thin the area below the oil rings even .020 for service reasons. Also as I said before the more common they keep things the lower the cost for the company. It could have been a piston machining issue without being involved it’s hard to say for sure. I do service work in automotive plants and the more they can do in one cell “cassette” the better they like it. a lot of what we do if your off by .020 it might as well be 2” because bad things are going to happen.

[Dragncar]

I learned about the Pontiac long rod thing from Dan Whitmore. He used 7.125 rods with .927 pins in 400s and 6.875 rods on 4" stroke builds( I traded those rods from Dan to Tom for a Scat crank)
He told me in the 400s the engine got 200RPM more "pull" out of them. He had a 3900lb TA doing 10.80 with one of his long rod 400s. So it worked for what he was doing. Again, this was with iron heads. Dans health went down not too long after the aluminum heads came out.
Longs rods do hurt your low end. He said you can keep stuffing longer rods in a engine until your 60' suffer if you wanted to.
He also used the sbc 400 as a example of poor rod stroke ratio wearing out the middle of the cylinder bores. He said most of them had severe wear with high mileage. They have the same rod/stroke ratio of a 455 Pontiac so I am sure he put longer rods in those also.
They way he explained to longer rods helping out a 455 was it slowed the piston down at TDC and BDC. Since you could only get so much air though Pontiac heads at the time they ran out of breath early. Pontiac 455s with iron heads and sbc 400 with iron heads ran out of breath about the same RPM. The 455s piston speed is so great it starts pulling away from the "push" of the flame front at a relatively low RPM. Can only get so much air in the hole.
I have proved this drag racing my own 455 with stock length rods and iron heads. It always ETs best when I shift very quickly. See, at first I wanted to rev my engine and went against what Dan said. Then one day I red lit, pissed off and just hit 2nd and 3rd as quick as I could and ran it out. Ran its best ever ET. Dan was right.
From then on I am in 3rd gear before 100 feet. If I am slow on a shift the engine is at a much higher RPM crossing the line, but I am slower.
So, long rods were a crutch and only needed with max effort iron head builds. No one does that anymore.
Just use the rod that fits and concentrate on your engine breathing well.

https://www.youtube.com/watch?v=zn6mwFoI_Ms

So he jammed a longer rod in there to help out a tad.

[Tom Vaught]

Still have those 6.875 rods, Dragncar, at some point on a short stroke 366 (3.375" stroke) crankshaft project.
Should work well vs the NEW Old Stock 7.080" Carrillo RA-V Rods that I will probably never use.

Any 303 or 366 Engine builders out there?

Tom V.