Yes it was regulated, 10-14”

How about piston oilers ?

Engine masters have done a few episodes on vacuum pumps and the dyno results were always minimal if I recall correctly .
18extra hp is surprising

We run a 4 stage Peterson pump, we have it set for 10 inches of vacuum. But when designing the engine we planed for it. Piston oilers, coated pistons, bearings. We have many runs at 5800 to 6000 for 8 to 10 minutes long. I'm not sure I would just add one to a build that wasn't designed for one.

I hear about these dyno videos from my customers all the time I rarely watch them anymore because you never get all the specifics so I just do my own dyno test back to back to back . I was never convinced vacuum pumps did a whole lot my self until i dynoed with/without one. One of my friends who also has his own dyno and builds engines too says he will pick up as much as 40 hp with ring package/vacuum pump. so basically he lowers parasitic drag with ultra thin low tension rings then essentially gets them to seal by bandaiding them with a vacuum pump, nothing you'd do in a inboard boat engine though, Smitty

The engines in the planning stages, it will have some cool stuff done to it but IDK if will be as far as piston oilers, Smitty

Piston Oilers would be an absolute if your going to run vacuum in an endurance engine. IMO.

The following might be helpful re HP gains… some good information.

https://www.speed-talk.com/forum/viewtopic.php?t=52136

They were also running a really good Morosso oil pan that drastically reduced windage. I think reducing windage by running a vacuum pump is part of your horsepower gain. Personally my next motor will have ported rings with a really good windage control system. I think that's the best of both worlds.

So what would be the difference between a vacuum pump and a dry sump oil system that is creating vacuum in the crankcase? Nearly every form of motorsports racing run dry sumps with the loud pedal pushed to the floor for hours on end.