3500 Plenum

[Fireball]

So I just went from a 3100 plenum (ported and polished with 65mm tb) to a 3500 plenum (gasket matched, light porting) with TCE phenolic gaskets.

Anyways,

I'm undecided as to what I like better. The 3500 plenum has had moments that make me think it provides superior pull across the band. There have been other moments where I've felt it's lacking. The performance has been inconsistent (Car seems to take quite a while to adjust).

One thing I did notice is that the car is significantly quieter on hard acceleration... does anyone have any insight as to why? Just curious on peoples insight and opinions on this.

[NateD4]

I assume you are using the 3500 throttle body with this as well?

If so, the quieter sound is probably due to the reduced air speed into the larger throttle body.

If you look at a throttle body like GM uses from an aerodynamics point of view the fastest the air can enter a naturally aspired engine is just below the speed of sound. At the speed of sound (local to the throttle body) the air is said to choke whereby no more airspeed can be had (and thus flow). A a larger throttle plate gives you more flow at a lower speed comparatively.

The only other explanation I could venture is that the chamber harmonics (and thus RPM tuning) of the plenum are different for the 3100 compared to stock.

[Fireball]

I actually have the same TB (From the 3.5 L on the Intrigue).
I had a 65 mm TB for both plenums.

I think your explanation of air velocity makes sense as the runners are much shorter/practically non existent on this plenum?