Hi I have a set of new 426 Hemi pistons I got with a block I bought several years ago. They are stamped 28068790 on top. Is that a Mopar part, or can anyone ID them? Thanks, Joel

Might help. Take the 0 off the end. e-bay

The TRW forging piston that 99.9% of the guys used back from the mid 60’s until the early 70’s , replaced by the same forging with pent roof domes.

I have three sets of new race pistons, a couple sets of new rods and used rods if you run out.

Thanks, now I know. I'm not sure if I'll ever use them, they weigh a ton.

Yes they do. They never wear out, break or loose barrel and cam either.
I’ve seen more than few come in with a broken valve stem sticking out of the dome. I honestly believe I could have removed that stem and cleaned the dome up and put it back in service.

Diamond used to have a program to lighten those pistons up under the dome, the pin tiers, and use light wrist pins.
They won a lot of Super Stock and early Pro Stock races with those pistons.

This same piston design ran and won in NASCAR for years.

Today, just spend $1500. For a new set of Diamond pistons

And I wonder how much HP difference there is between them

Some people that have used both say 30.

Modern rods and pistons will save at least 10 lb of reciprocating weight. Imagine how much power it takes to move 10 lb up and down almost 4 in 7,000 times a minute.

10 lbs

What would be a typical bobweight for an old school 426 with those pistons and the rods of the day?

My 572 came in at 2439.1, I was told that's not too shabby, but don't really have anything to compare it to.

I'll get some weights and post them. I remember about 15 years ago, I compared a set of stock Hemi rods with a set of Manley sportsmaster I beams, it was 6 pounds.

omg....

I’m thinking centrifugal effect, kinda like those 283 Modified Production cars with the 40-50 pound flywheels. Once it’s ‘up’ there it ain’t coming down.

The reciprocating weight of the pistons and top half of the rods has no momentum like a flywheel. It has to stop and start twice per revolution, and that takes a lot of energy.

In a one cylinder engine that would be true

Just for fun, I threw some stuff on the scale. I didn't take the time to disassemble the other stuff, and don't have an apples for apple comparison.

This 12.5:1 4.25" piston with pin and rings is 1107g. The 6.86" rod with bolts, cap and bearing is 1117g. Total 2224g.

A 15 year old eagle 7.1 H beam with a 4.5 Ross 13.5 to 1 racing piston, .990 pin, rings, cap, bolts, bearing is 1835g.

For a set of 8 that adds up to 6.8 pounds difference. Not as much difference as I thought it would be, but still a lot. But the difference in piston size and rod length makes this only entertainment, not a real comparison.

The theory the movement of the pistons up and down carries flywheel like momentum is a new one to me. It would be interesting to see some test data.

I knew some racers that race SB Chevy with really short strokes, John Dieanna and Ed Hamburger did similar things on their SB Mopar Modified programs and later Comp eliminator 4 speed SB Mopar motors. Lots of RPM and very slow to rev up or down, I remember John saying he would floor it on the first yellow (back when we still had 4 yellows bulbs on Xmas the tree) and let the clutch out on the last yellow, multiple short burn out hops behind the starting line, the motors would rev way up and then slow down real slow after putting the clutch pedal back in after the dry hop with the gas pedal off all the way, those where the days

Yeah, I've got to let myself off the hook (7.100, 4.500 and just a street piston)