Has anyone dyno tested a quadrajet and B4B combo for the best angle on the secondary's? Some say that an extra 5 degrees over center from straight down, will direct fuel mixture toward the front and improve distribution. Not talking about the air valve here, just the bottom throttle plates. Any input on this?
The Manifold wants a 1/2" open spacer under it if you can , and then leave the secondary throttle blades set as they are stock.
I've done some testing with spacers but not much with changing the open angle of the throttle plates. On single plane intakes they will require at least a 1" nicely blended open spacer to make best power. Spread bore carburetors on single plane intakes are very sensitive to this as the rear throttle plates hang down further into the plenum areas and create distribution issues. Right on the dyno I've witnessed HUGE gains in power running at least a 1" spacer vs no spacer at all. Open spacers on dual plane intakes and/or grinding down or removing the divider can lead to negative results. On the dyno and at the track I've tested four 1" thick spacers back to back on dual plane intakes. Four hole, fully open, fully divided and semi-open. The 4 hole and fully open were the worst. The fully divided and semi-open made the most power on the dyno and quickest runs at the track. Semi-open simply means divided with some material removed between the secondaries. You have to be stingy removing the material between the secondaries as doing so can induced a "stumble/hesitation/bog going quickly to full throttle even if it picks up a little more upper rpm power on the dyno or a little more MPH at the track. I've also tested every intake available for a Pontiac engine that will fit under the hood. The Performer and early P4B intakes are "turds" everyplace, at least on a 455 cid engine making around 550hp. A modified factory iron intake is excellent, as is the Edelbrock RPM. Problem with the RPM is that it is a little over 1" taller and slightly relocates the carb making it difficult to use with factory Ram Air and Shaker set-ups. Currently I'm using a CNC ported 1971 455 HO intake, which is pretty much a copy of the iron intake with taller runners for larger intake ports. It has the plenum areas opened up same as the RPM, so just two big holes, fully divided. I run a 1/4" thick open spacer on it. It runs equally as good if not a tad better than the RPM intake and no "cobbling" to make things fit. I was actually quite surprised when I made the swap as I ran the RPM for many years, then went to the HO intake. 1/8 mile times are virtually identical with a slight 60' advantage to the HO intake with maybe a 1/2 MPH loss on top end but as quick or slightly quicker in ET. I've always had great respect for the factory parts, especially intake manifolds and try to use them over aftermarket parts. They are very well designed and effective at feeding these engines from idle to at least 5000rpm's. Bigger and taller intakes don't always make more power. Case in point. A few years ago we built a Pontiac 428 engine for a customer. It was 10.6 to 1 compression, 260cfm KRE aluminum heads (unported), Oliver rods, Ross pistons and exactly zero decked. We topped it with a current reproduction factory HO intake, then my "modified" cast iron intake, then the big Edelbrock RPM intake, back to back with no other changes. The HO intake made 487hp, the RPM 491, and the iron intake 497hp. Goes to show how a bigger intake isn't always making bigger power, and that we see so many high rise intakes on these engines making a LOT less power than that build did. I would imagine most of those engines would have ran just as good with a factory iron intake if not a bit better......FWIW.......Cliff
Since we currently don't have an RPM for our engines, we have to use stock, Performer, B4B (they are roughly the same) or single plane.
