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Wikipedia lists 490 kN (110,000 lbf) thrust for BE-3 at sea level and 710 (160,000 lbf) kN in vacuum. BE-4 is listed at a stupefying 2.4 MN (550,000 lbf) at sea level.

But no numbers are given for specific impulse. Are there any estimates for this parameter?

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A few years ago I estimated 315s SL and 340s Vacuum:

https://forum.nasaspaceflight.com/index.php?topic=39674.msg1504802#msg1504802

The main things that affect this are chamber pressure and expansion ratio. As far as I know the chamber pressure hasn't been increased and that also sets the upper limit for expansion ratio on a first stage engine and therefore also Isp. They may be able to improve the vacuum isp without increasing chamber pressure if they use an altitude compensating nozzle.

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