7.4L MPI loud at partial throttle

[Sicktght311]

I have a 99 Sundancer 270 with a 7.4L MPI B3. This motor is new to me as i primarily dealt with smaller motors in the past. Everything runs very smooth, correct RPMs where they should be, no idle issues, no audible misfires or anything, but between 2000 and 2700-2800 RPM, around 50% throttle or so, the motor has a noticeable change in sound, that can best be described as a very loud air sucking sound. Above this at cruising speed or WOT its gone, and at lower RPMs its gone. Thoughts?

 

[scoflaw]

Normal, big motor breathing.

 

[Sicktght311]

Even though its only apparent at lower RPMs/Throttle? Once i get up to cruising speed, and 75% or higher throttle, its completely gone. I would think if its the massive V8 pulling in air, it would be the same at higher RPMs as well

 

[Wanderer 290]

Air flow sounds different at various velocities.

 

[scoflaw]

Not sure about your boat but at WOT I hear more wind than motor

 

[Bill Watson]

I thought I heard a higher-pitched sound last Sunday, at around 3000 RPM on my stbd 8.1. I quickly slowed down to where I had been running, 2200, and it disappeared. After docking I realized that I had left my blowers on. Would they be the possible source? Thanks!

 

[Nater Potater]

...between 2000 and 2700-2800 RPM, around 50% throttle or so, the motor has a noticeable change in sound, that can best be described as a very loud air sucking sound.

At that RPM, the engine is in the fat part of its torque curve, meaning that the intake manifold vacuum is at its highest. Combine that with the butterflies being that far open, there's a substantial pressure drop across them which makes for some pretty obvious sucky sounds. Since we don't draw air through a conventional air filter, the intake noise is much more obvious than you'd experience in a car.