The Q-jet should be classified as a musical instrument.
Scooterwrench, I happen to be in violent agreement with your statement. :0)
I still remember the first night I ever flipped the lid on the air cleaner atop a Quadrajet and went for a drive.
('74 454/Turbo 400 C20 8-lugger Camper Special.) Teenager Road Trip had goosebumps on his arms before the end of
the highway onramp. (Insert the Deep Purple song "Highway Star" being played on an 8-track here. :0)
Here's a photo showing where the source of where that bellowing intake roar originates:
You must be registered for see images attach
(credit: ebay auction for a NOS Quadrajet throttle plate.)
Check out those glorious secondaries.
Twin 2 1/4" diameter throttles.
Each one is the same diameter as a American billiard ball! (See attached.)
Over time, I've come to realize that my choices in life are driven by the associated sonics much more so than
most of the well-adjusted folks in the audience. :0) So when working on a Bucket List powerplant project,
(assuming all other things being equal) whichever solution is going to bring the most memorable intake tone
is the way that I can't help but choose.
Even if it means more fabrication/effort. Because a lot of my touchstone memories include stuff like an afternoon
thunderstorm at the Grand Canyon, the infrasonic rumble while riding in the Maid of the Mist at the base of
Niagara Falls, or the full-throated roar of a WOT Quadrajet on a recently rebuilt V8 on a perfect summer evening.
Fortunately, given how much hood clearance there is in our GMT400s, we aren't force to run a stock,
low-profile spread-bore intake manifold. So our choices are anything but limited for our engines.
(
Endless Q-Jet intake possibilities) BTW, see attached for a couple of modern Q-Jet capable dyno-proven
front runners.
But in order to achieve that
complex, layered melody that will bring back the memories of your misspent youth,
be sure to adopt a high performance, high rise
dual plane intake, and avoid the sexier looking single plane offerings.
Not just for the better street-rpm performance. But to get that authentic tone. And if you believe this to be self-evident,
then you are done reading this reply.
**** (Optional Reading) ****
But if you are still wondering why I would use sound to eliminate the single-plane intakes from my Bucket List
Quadrajet-fed project engine? The answer will require a little math that will allow me to translate from motorhead
to audiophile.
Keeping things simple, let's look at the
3000 to
6000 rpm range.
This translates to a 50 to 100 crank revolutions
per second.
And since it takes
720° to complete all
4 cycles, we will therefore have an intake stroke every
25 to
50 cycles
per second. (ie:
25 to
50 Hz)
If we communicate these intake strokes through a
common plenum (either carb single plane or Vortec EFI manifold) then
the intake melody will be based off of these fundamental frequencies. (Note: Similar to the relative smoothness and
higher PRF (Pulse Repetition Frequency) of a single exhaust.)
And if you perch a square-bore Holley 4150 on top of this single plane intake, then the tone will be shifted higher,
partially because of the higher PRF from the single plane, and partially because the throttle bores are smaller,
causing the resonating tone to be at a higher audio frequency.
****
On the other hand, if you put a Q-Jet on top of a dual plane intake manifold, we now have two individual manifolds,
taking turns every
180° of crank rotation to feed the next cylinder in the firing order. So we end up with (2) intakes
running from
12.5 to
25 Hz, essentially halving the PRF. But there is a chorusing effect, because these intake tracts
alternate every
90° of crank rotation. (Similar to a true dual exhaust behind an engine with a flat-plane crank.) And
of course the larger the secondary throttle openings, the lower the resonant frequency of the air pulses passing
through. (Think carb design from a wind instrument perspective.)
Believe me, this sonic signature stuff is easier to pick out with the ears as opposed to trying to explain it via typing.
But after years of listening to all manner of intake setups on SBC/BBC engines, there *are* distinct sonic differences
between the main intake combos. In terms of personal preference, here's a list in order of increasing sonic excellence
for a street driven small block or big block Chevy V8:
* single plane intake fed by a square bore Holley
* single plane intake fed by a spread bore Q-Jet
* dual plane intake fed by a square bore Holley
* dual plane intake fed by a spread bore Q-Jet (lid flipped)
* IR (Individual Runner - Think max effort Can-Am big blocks.)
* dual plane intake fed by a Q-Jet drawing cold air from any of the cowl induction examples above. (!)
Given all of the above, I think that the Q-Jet is the affordable pipe organ of GM's induction setups. :0)
EDIT: Bonus reading. If you have ever sat in church and soaked up the sound of a large pipe organ...and
started wondering just how many cfm it took to drive the big bass pipes that shook the house of worship, then
you might also find the article associated with the last attachment of interest: (
What size fan or bellows for a large pipe organ?)