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Thread: 250xs higher compression
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01-27-2019, 10:51 AM #15000 RPM
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250xs higher compression
The 2003-2005 250 xs had higher compression and required 91 while the later opti have lower compression and run 87 octane.
how much more compression do they have?
is it due to the heads? Will early heads bolt to a newer (2008) 250?
or is compression due to different shapes pistons?
Or a combination?
how much punch could be gained by swapping? If it’s possible?
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01-27-2019, 05:41 PM #2
I did a compression test on my 05 250xs's last week, 129 to 132 psi on all 12 cylinders with 320 hrs on them
Aaron
Fountain 38TE, quad 400 Verados
Talon F20 Flats boat, 250XS
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01-28-2019, 02:37 AM #36000 RPM
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Opti systems hate raised compression they are calibrated to low pressure barely above static compression psi. Ie raise it to much and they back flow.
The aire side functions like a supercharger and can bring operating psi to 160psi -180psi on a 3 cylinder. Think it’s 140-160 on most sixes. Fuels ok at 87 since it’s not heated by compression but added just befor spark( one reason they burn cold and dirty)
more effective power adding is standard turbo, supercharger methods, lowering compression and adding bost and fuel. (I only lost 500rpm at 7000ft but talk about a low end drop out).
See simmons, brat, DBR for real gains.
Never tried swaping heads and fuel air fuel air rail to a 3.2 hummm
many incounter it through shaving heads back in the day. Starved out every cylinder.
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