I’m curious how many grams can be had by drastically cutting down the big end balancing pads on the cap screw rods. Anybody know a roundabout number?
Yes I have done a lot of work to 350 rods and it was not un-common to remove 25 grams while reducing stress risers. All the casting lines and rough spots should be removed. The major spots to save weight are the balance pads and the small end. I don’t have any pictures handy of some lightened rods but here are a set that were simply balanced for some Diamond pistons. You can see the parting line that should be smoothed out. The tip of the small end has extra material and also the big end balance pad.
Is that your mantle centerpiece Sean? Or are you just keeping that expensive Buick rod out of the kids reach?
Thanks Sean. With that much weight coming off from the polishing process, I'd guess that quite a bit of weight is stuck in the small end & big end balancing pad.
Here are nut & bolt, lightened, matched weighed, and polished. They are all within 1 gram at 618. Don't have stock unlightened rod here to weigh that is out of an engine. Have Sean weigh his mantle rod. They can be yours if you want them. Save you some dicking around....
The mantle rod is 670 grams. The nut and bolt rods are a bit weaker however if the engine is not making big power then the lighter weight may be more important than the extra strength. Nice light Hershe rods at 545 grams they are lighter and stronger than stock. Lastly here are the custom East end machine rods that are 686 grams and although they are a little heavy they are very beefy.
Thanks. I'll keep those in mind, Mart. Thanks again Sean. I've already done the side beam casting seams of my cap screw rod set, and they all weigh between 656g and 662g. My stock '71 piston/rod assemblies weigh between 1306g & 1315g. With my new pistons each weighing 715g, I'd need to lose about 65g a piece from the rods to have the assemblies "weigh the same" as the stock '71 assemblies. I'll have the rotating assembly balanced no matter what, but it sure would be great to not need any weight added to the ('71) crank. Seems like this number is being derived from comparing a cap screw rod to a nut & bolt rod, right? Wouldn't that be an apples-to-oranges scenario?
Maybe Sean has an untouched early nut/bolt rod to check weight differences, I think the capscrew style are heavier, hence the presumed extra strength. The nut/ bolt or capscrew fastener isn't where the added strength is from.
Top pic is my forged Auto Tec kitchen counter top piston with the Keurig in the backround. In the second pic we have the above piston now attached to the Molnar rod on the office desk
Yes I have stock early rods but they are connected to stock pistons so I can’t weigh them at the moment. I think you would be surprised how much little weight is removed even if it looks like lots is removed. The major amount of weight and strength that is added on the cap screw rods is at the big end location where the cam almost hits the rods. The early rods are super thin in that area and the later rods are much thicker. The wild card is luck. There is a guy running 600+ Hp on cap screw rods for 20 years under turbo boost. However then there was Darryl Roderer who had the cap screw rods explode on the dyno at 620 HP. Then there was a fellow running low 12s NA and shifting at 6500 for 7 years. Then one day the crank broke in half and ruined the whole engine. He ran aftermarket eagle rods and light Ross racing forged pistons but as luck would have it his crankshaft gave up. He was at about 450 HP. It isn’t always HP that kills parts it’s also luck of the draw.
It usually ISNT horse power that kills the rods, its RPM. Turbo 3.8's make tremendous torque and horsepower under 6000 rpm on stock cast capscrew rods.
I have 8 used, but nice cap screw rods with old style Kenne Bell 10 to 1 pistons wrapped in newspaper and in a box in the garage, I was entertaining the thought of those above the TV
I have an NOS Stage II piston & set of used & assembled Buick Stage II rods and pistons if that help any ?
