308/328/348 ARP Rod Bolt Decoded

I recently ordered a set of ARP Rod bolts for my 1975 308 GT-4 Motor rebuild. I was shocked to find that a set of ARB Rod bolts cost over $400.00. The bolts I ordered were drop-shipped directly to my home address with the invoice pictured below. The internal ARP Stock number for the Bolts was AR 373-1, and the ARP Stock number for the Nuts was AMN 12-1 (See photo below).

When I could not find torque specs for these bolts on the ARP Web site, I called ARP to speak with one of their technicians. The ARP tech that answered the phone told me that all of their torque spec were on their web site, and I must have missed them. He then asked me what ARP Bolt Kit I had purchased. I told him that I did not buy an ARP Kit, that I bought them through a specialized dealer and that I only had the ARP part numbers from my invoice (AMN 12-1 and AR 373-1, see below). I could hear him banging around on a key board for a few moments and then he said, “Oh, you have a 2.0 Liter Alfa Romeo GTV. You must have bought ARP Bolt Kit 126-6101.” He then told me that the ARP Kit 126-6101 uses the ARP AR 373-1 Bolt, and AMN 12-1 Nut, further explaining that the AR 373-1 and AMN 12-1 number are the ARP internal stock numbers that make up ARP Rod Bolt kit 126-6101.

A few quick Google searches identified that ARP Rod Bolt Kit 126-6101 could be purchased from numerous sources for under $100.00. However, since the Alfa 2.0L GTV is a four-cylinder car, you would have to buy two of the kits for just under $200.00. Which is less than half of the $400.00 plus I spent buying the bolts from an F-Car specialty shop. My curiosity continued so I called back the specialty F-Car shop where I bought the bolts (for $400.00+) and inquired about the torque specs for my 1975 308 GT-4. They were very kind and provided all kinds of technical help so I thought I would try to get a little smarter for my $400.00, and asked if all F-Cars used the same rod bolt. After a lengthy discussion the technician assured me that all 308’s, 328’s, 348’s used the same Rod Bolt.

So the next thing I did was order APR Bolt Kit 126-6101 for Summit Racing for $96.00 (see photo below). When the bolts came to my house I compared them to the $400.00 bolts I had purchased from the F-Car specialty shop. Using a micrometer, I measured their dimensions in every way. My verdict, exactly the same size to the 100th of a millimeter as the bolts I bought from the specialty F-car shop for twice the price.

So I would be curious to see what my fellow F-Chatters think of all of this. It appears that there is not reason to spend a premium on “Custom” F-Car ARP Rod Bolts when they are available in other ARP kits for half the advertised F-Car cost.
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Sorry guys, I should have been a little more clear on this. This first photograph shows the Stock Ferrari rod bolts and nuts (from three views) on the left and the ARB rod bolts (from the same three angles) on the right. The stock bolts also have "castle" style nuts (notoriously weak) that were very common from this era.

Also, the three ARP bolts and nuts on the right side of the picture are a mix of the bolts I got from the specialized F-Car shop, and the bolts I got from ARP Bolt Kit 126-6101, that measure out the same in every dimension to a 100th of a millimeter.
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I've posted the data from this thread on the 308 parts cross-reference Sticky so I thought I would add a few extra observations about using the ARP bolts. The machinist reconditioning my rods noted the amount of distortion in the stock bolts. Many were so bent that it took a bit of effort to get the rod caps off and my motor only had 15,000 original miles on it. This will not occur with the ARP Bolts and will save you money down the road. Because my bolts were bent, there was quite a bit of off-set in my rod and cap marriage area. This is resulting in a good bit of rod reconditioning work. The increased diameter in the middle section of the bolt will go a long way to preventing movement in the rod and cap marriage area. Also, the ARP bolts from kit 126-6101 will not drop into your rods. This is by design. They are designed to be press fit. The clearance difference is very minor, less than a thousandth, and the ARP bolts will press fit into your stock rods with very little effort and remain snug without adding stress to the rod. Do not let the fact that the ARP bolts don't drop in place like the stock bolts deter you from using them.