Woohoo, my Ross pistons came in yesterday! As soon as I unwrapped the first one I was struck by how light it felt compared to the old Jahns, and it had been weeks since I last touched the Jahns. So of course I had to compare them. The Jahns is 28% heavier than the Ross. And looking at the pics you can see why. 162 gram difference! Puts the claim of "lightweight" into perspective. The Ross is a jeweled beauty too. Since I'm a custom jeweler I can state that with some authority.
What doesn't show in the pics is the pin oiler, there's a hole from the oil groove thru the boss over the pin. I'm curious about the shallow groove between 1st and 2nd compression grooves. And you can see how Ross moved all grooves up a little bit.
These Ross pistons have 10.5:1 CR with 97cc heads. I know that's borderline concerning detonation but I can drop it down to 10:1 by using thicker gaskets if it turns out there's a problem. The Jahns just for reference I believe are 11:1, just eyeballing it.
This thing ought to spin pretty good. It occurs to me that besides less power loss due to reciprocating weight, the lighter piston will also put less stress on the connecting rods at higher RPMs, don't you think?
Finally I'm starting to make progress on the project. Feels good after picking your collective brains this past year. Many thanks to all!
Piston comparison
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Piston comparison
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Re: Piston comparison
As far as comp ratio goes I would think you can go 12-1 on premium pump gas without fear of detonation...it's a Hemi not a wedge.
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speedicusmaximus
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Re: Piston comparison
NE57,
True, with the drop in piston weight, there's less stress on the con rods etc. But whether that produces more noticeable power I don't know. You should get the whole reciprocating assembly (re)balanced though: the drop in piston weight, no matter if it's equal on all pistons, means it'll be out of balance.
I'd have thought that somewhere between 10.0 and 10.5:1 would be OK for every day use, more for weekend warrior stuff. It'll depend on your cam shaft spec's, gas grade, altitude etc.
Post more when you get the chance !
Mike
True, with the drop in piston weight, there's less stress on the con rods etc. But whether that produces more noticeable power I don't know. You should get the whole reciprocating assembly (re)balanced though: the drop in piston weight, no matter if it's equal on all pistons, means it'll be out of balance.
I'd have thought that somewhere between 10.0 and 10.5:1 would be OK for every day use, more for weekend warrior stuff. It'll depend on your cam shaft spec's, gas grade, altitude etc.
Post more when you get the chance !
Mike
Beep ! Beep !
Re: Piston comparison
Supposedly 10.5 on a hemi will be OK on the same octane as a 9.5 Wedge.
Re: Piston comparison
Way back in the seventies I had a 354 with 11:1 Jahns cast pistons. Well, they were advertised as 11:1 but I couldn't say what the actual CR was. Anyway, I experienced no problems with the gas back then, but who knows how that compares to today's gas and what kind of pump gas we might have in the future. I thought this was a good compromise, and I have room to back off half a point, if need be. Wiggle room, a nice thing when you can get it.
The rotating assembly is at the machine shop now along with the block. I have my fingers crossed to get it all back within a couple more weeks.
The rotating assembly is at the machine shop now along with the block. I have my fingers crossed to get it all back within a couple more weeks.