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Reuse/Replace ARP 8740 Rod Bolts or Upgrade to Series 2000/L19?

9151 Views 4 Replies 4 Participants Last post by  rustbucket79
My block, etc are almost finished at the machine shop. My current rod bolts are ARP 8740's and have been used on two rebuilds, and I didn't measure their free length. On the last rebuild, the engine ran for six bracket-race seasons. Not having a stretch gauge, I have torqued them using the spec. given and using the ARP lubricant.

The rods are Eagle H-beams and I shift at 6K and trap a little under 7K. My power level is about 725 horse with the combo listed in the signature. The machinist mentions that the rods will need some work to accept an L-19 bolt.

I suspect I should at least replace the 8740's and measure the free-length before installation. Am I at a power level I should upgrade to a different bolt and have the rods reworked? The pistons are Diamonds and weigh 560 grams, give or take.

The 8740's have worked well over the long-term for me, but I would like to leave some room to grow the power level as well. Go with a proven combo, or upgrade - the cost difference between replacing the bolts and upgrading is probably minimal, but the extra machine work adds a little more cost to it.

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Oops - my last post didn't go through. The rods are Eagle H-beams. I spoke with a tech at ARP, who did a calulation involving the rod weight, piston weight, rod length, and rpms. He said they are looking for a load vs. dynamic force of 2 or so, and that mine worked out to 1.8, which is he had said was alright. I"m not sure what variable influences the result the most, but he said going to higher boost levels would not change the formulas result. (Rods 785g, pistons 560g, rod length 6.385, rpms of 7500 max)

The machinist said its $10 per rod to change from the 8740's to series 2000 or L-19's. I don't know what needs to be done to each rod to accept the stronger bolt, but this would be in addition to the new bolts which will add to $250 or so. Replacing the 8740's is $90

As I have had success with this combo over many seasons, I'm leaning toward just replacing the 8740's as I didn't measure their length in 2005, when I bought the Eagle rotating assembly. Don't know if I want to do sixteen machining operations to the rods, and I've already paid to have them rebushed and checked for straightness. Probably should have just bought the new rods as I"m already half the way to the cost of new ones, but now committed to the old rods. Also hate to "cheap out" on such an important part, though the ARP tech said I was alright on my load vs. dynamic force ratio.

Anything I'm overlooking - I've seen lots of blocks with sudden picture windows in them, at the track.
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