That dual plane air gap is the manifold that's on my 355. I love it,it makes gobs of torque. The TB I've got is a 454 unit off an '87 1 ton and I got it with the factory spreadbore adapter GM used back then,the one that had water run through it. I had a crazy wild idea of running my A/C low line through it and really cool the inlet air,,,,,,,,,,,probably won't!!! I'm gonna give the TBI a whirl being I've spent plenty of money on the conversion but if I get too aggravated that $hits going up for sale and my good ol trusty Q-jet bull horn's going back on it. Only downside to the Q-jet is ethanol,it don't like it. Also there are no primary airhorns on my Q-jets so no choke or cold fast idle and I'm getting too old and lazy to sit there and tickle the accelerator pump for 30sec before I can drop it in gear.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 a 8-track here. :0)
Here's a photo showing where the source of where that bellowing intake roar originates:
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(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 projet 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.
(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.)
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 order of increasing sonic excellence for a street machine:
* 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)
* dual plane intake fed by a Q-Jet drawing cold air from any of the cowl induction examples above. (!)
So yeah, I agree that the Q-Jet should be classified as a musical instrument.
Now y'all see my dilemma.
TBI that has to be tuned and relies on electronic gizmos to work but plays well with modern fuel or reliable Q-jet that I have a coffee can full of jets and needles for but is temperamental with modern fuel.
I opened the hood this morning and there is a perfect spot right behind the center of the engine in the vent cowl that's just begging to have a breather inlet plumbed to it.
