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Best SBC Aluminum Intake for Street/Strip Qjet 355?

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AHotRod:
Have you done any testing with carb spacers on a factory intake Cliff ?

77cruiser:
Is the GM intake similar to an Edelbrock performer or RPM?

Cliff Ruggles:
I've done extensive testing with spacers on various intakes.

ALL of the single plane intakes I've tested require one to get the most out of them, especially if you are using a spread bore carb on them.

The huge secondary throttle plates hang pretty far into the plenum area and can cause MAJOR distribution issues and considerable power loss.

One dual plane intakes I have tested a variety of 1" spacers in various materials, aluminum, wood, etc.

The only spacers that worked better than no spacer at all was a semi-open spacer, or basically one that divided the front barrels and was partially open in the back. 

Fully open spacers were HORRIBLE on every dual plane intake I tested one on and 4 hole spacers weren't much better.

A fully divided spacer worked pretty well but the semi-open is the only one that ran quicker in MPH at the track vs just one 1/4" thick stock Q-jet open gasket.  It still ran a little slower in ET as it gave up some 60' time but ran more MPH showing for sure it made more top end power.

I'd add here that I tested spacers on a 455 CID engine making around 514hp and 587tq, and didn't really see any benefits anyplace using one.  Not if you consider the problems they bring in associated with having to "cobble" things up some with the carb sitting that high.

I also found that having to use a shorter air filter which moved the air cleaner lid closer to the carb KILLED off a bunch of power, and flawed the testing so I had to make a customer filter for the opening of my Shaker assembly (1974 GTO) just to get good test results with the carb sitting up that much higher.

Anyhow, on one test outing I swapped 4 spacers back to back and made 2 runs with each one.  When the smoke cleared and dust settled the car ran the quickest ET with no spacer at all and just one 1/4" thick gasket.  The fully divided spacer was close but still a few hundreths slower in ET.  The semi-open spacer was just a tad slower in ET and just over 1.5 mph faster.

From what I saw on my big CID engine using one on a dual plane intake isn't worth the effort, and I'll bet the results wouldn't have been as close on a much smaller engine and slower car.

So bottom line, really not worth the effort on a dual plane intake at least to 500hp or so, and for sure you need to use one on a single plane intake.  On the dyno and at the track my engine lost a BUTT LOAD of power not using a fully open/well blended 1" spacer on both single plane intakes I tested.......Cliff

AHotRod:

--- Quote from: 77cruiser on November 02, 2017, 07:40:53 PM ---Is the GM intake similar to an Edelbrock performer or RPM?

--- End quote ---

Jim,
  My factory intake is similar to a Performer.
Glenn

AHotRod:
Cliff,
  Most excellent information and results regarding the spacer testing.

I wonder what the real life comparison of intake flow on your Factory iron intake is to a Chevy SB Factory intake.  I'm certain you know what I'm referring to.

I'll share this with you.  On our SBC "Stocker" engines, as you know we are required to use stock intakes and carbs.... as well as almost everything.
We are allowed to use 2 carburetor gaskets.

On numerous engine combinations from 305 - 350 CID, extensive testing was done on the Dynos as well at the strip. Four hole gaskets and open gaskets were tested in all thicknesses and all combinations.
To fast forward to the best results .... installing a FelPro 1908 ( 1/4" thick open gasket) on the intake manifold, then adding a FelPro 1905 (1/4" thick 4 hole gasket) on top of the other, then the Qjet. This combination yielded a increase in torque and horsepower of 6-10 HP depending on the specific engine, and quicker E.T.s.

In addition to this, every air cleaner base under the sun was tested, and nothing came close to the GM factory bases, all the aftermarket stuff hurt airflow, fuel curves and HP. 

We also tested the engines and cars with and without air cleaners. Some ran best with nothing but a base on the carb, some ran best with a K&N 4" filter installed. My belief is that different cars produced different under hood environments which produced different results.



Question: Have you ever experimented with a 2" - 2-1/4" or 2-1/2" header collector? 


Glenn

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