Here is a GREAT reference piece compliments of CAR CRAFT. This article will help us weed through the marketing pitches and see actual dyno results (AND PRICES TOO !).
It is an in-depth tech review with actual testing of 23 different dual plane intake manifolds of the style we would potentially use on our Chris-Craft boats. Of course for all out racing or offshore high performance use, some would opt for the single plane intakes but those are not considered in this particular test because they are basically for "racing only" and very high horsepower and rpm use.
Here is the good stuff just looking at performance, and I'll tell you now just forget about the one at the top, AFR (Air Flow Research). AFR is always better than anyone else when it comes to air flowing through an intake and a cylinder heat, but they are always far more expensive than anyone else as a result, and this intake is a composite, and OUCH, it is way expensive.
Interesting thing about the chart, when it comes to TORQUE, certain Edelbrocks fare well.
However, the delta between the top performing intake and the worst is 23 footpounds, and that is a unit of measure you would actually be able to feel in the boat (ability to spin a bigger prop, or cruise more comfortably at a given speed, etc.).
Then quite astounding, we see the delta between biggest and lowest horsepower is a whopping 48 horsepower. So guys, don't anyone buy a Professional Products Intake, they're at the bottom of horsepower and torque curves, but most likely they are better than the generic iron production intake we have on the boats.
If you have the clearance in your engine compartment or engine box, a 1" or 2" phenolic 4-hole carb spacer will provide even more torque to any of the intakes noted above. It will also help a bit in keeping the carb from cooking during operation and when the motor is shut down. Don't make the mistake and use an open spacer for your marine appliction, use the 4-hole in the rpm ranges we'll see.
So maybe I'll make a swap here sometime on my 327F, but I will probably grind off the brand identification and paint it to match the rest of the motor