Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
Dreaded nozzle drip 17056200
old cars:
“Modified plenum to make two sides and smoothed out corners. “
What does modified plenum mean? Can you post pictures?
“Checked intake machined flange and found one side to have high spot where heat riser port is.”
Similar to checking block deck and cylinder head surface this is done with a machinists straight edge/bar. How many thousands was it out?
“It never fit properly from the beginning, with filing bolt boss's and holes to fit.”
Have your heads been planed and/or engine deck?
Machining deck/heads can cause misalignment for the intake manifold including end end gasket squish / thickness required on chevy engines. Also BBC intake manifold gaskets come in different thickness and quality. Such as Felpro 1212 Printoseal .060”
thickness or Edelbrock 7203. End gaskets are not recommended. Use RTV Silicone 1/4” inch bead aprox.
This applies to both aftermarket and OE intake manifolds.
Cliff
If your example did not have rules to follow for his class that 750 Quadrajet on a dual plane aftermarket intake manifold would have been too small on cfm by a couple hundred . This is where the aftermarket manifolds shine / The cork in the system becomes
the carburetor, especially on a true dual plane intake.
68rs/ss:
Two photos of cast intake. Original and after. Used RPM as template to remove casting which pretty much went to floor of plenum. Just smoothed out transition to runners. Was pretty much at right angles to runners.
Block is not decked. Heads did have a few thousands planed off to make true. Edelbrock intake has four bolt boss's that interfered with ridge along top of mating surface, just below valve cover. Couple of holes needed to be enlarged to fir bolts.
One side has .010 high spot at heat riser. Yes, checked with straight edge. Used Fel-Pro .060 gaskets with silicon bead on end rails.
I did not check angles of machined surface on intake, when I get my other intake back from soaking, I will compare.
So, in my mind, for the amount of money spent for this product, I feel quality was pretty low quality for issues found. Will it may make more HP? Maybe....? Only way to tell is with dyno or strip time. Don't have either.
Phil
old cars:
What was the Edelbrock number?
Cutting the divider between the two plenums (moderate to ? ) , you allow cylinders to draw from all four barrels instead of just two. It converts a dual plane intake into a single plane intake that has longer but more tortuously routed runners. A true dual plane intake , where the left and right hand plenums are separated , each cylinder sees only half the carb's CFM capability. This is why a true dual plane can require a bigger carb than normally thought of.
Think of the Z28 1969 302 and 1970 350 which had a true dual plane fully divided intake and a 780 holley.
But you can always rely on the plenum cutout when the carb cfm falls short. Big blocks in the 454 cubic inch and up, are already hurting for flow.
If a certain power output is targeted , in practice , an oval port single plane intake with a short cam
( this is what I did ) makes as much or more low end output as a dual plane with a big divider cutout and a longer cam.
I think this could be a very good test of your cast iron intake.
Cliff Ruggles:
"Cliff
If your example did not have rules to follow for his class that 750 Quadrajet on a dual plane aftermarket intake manifold would have been too small on cfm by a couple hundred . This is where the aftermarket manifolds shine / The cork in the system becomes
the carburetor, especially on a true dual plane intake."
Some race Classes require the factory intake to be used. Nothing more, nothing less. My example simply shows that a flat iron big block Chevy intake is fully capable of making big power. It's not meant to compare it to anything else.
You also know nothing about the carburetor used, it was done here and specifically built for FAST Class racing. To maintain the privacy for my customers I will not reveal any details on those particular units. I have other Q-jets out there in FAST Class applications, several run into the high 9's and those cars do it on 8" bias ply tires, so the level of performance we are getting is most likely WAY above the vehicles owned by most who are reading this..
I'd also add here that on more than one occasion I've back to back tested intake manifolds with no other changes. I've also tested them in conjunction with 4 different 1" spacers.
On one outing (private track rental) I tested my "modified" cast iron Pontiac intake against the new (at that time) Tomahawk intake. I also added a 1" spacer to the Tomahawk as well for comparisons. The Tomahawk intake is basically a well modified Holley Street Dominator single plane intake professionally ported by Dave at SD Performance then used to supply the scan for the final product originally marketed/sold by Ace at Pacific Performance Racing.
Without a spacer it ran SLOWER everyplace, 60', 1/8th and 1/4 mile, worse in ET and less MPH.
With a 1" spacer and eventually swapping over to my very well prepared 4781-2 850 Holley DP carb it ran almost 2mph faster, but slightly slower in ET by .02 seconds to my factory cast iron intake with no spacer at all. I repeated the test and same thing buy .03" seconds slower but still almost 2 MPH faster.
Where it really gave up power was 60' and short times. Even with a stronger top end charge (it obviously made more upper mid-range and top end power) it was not enough to offset the loss of low RPM and average power.
So it was NOT hitting the converter as hard, the tires as hard, or pulling as hard off the line thru the 60', but pulling harder at the top end of the track.
I know testing like this is difficult for some folks to understand or accept. Edelbrock (and many other companies selling "high performance" parts) have to tell us how much better they or they'd have trouble selling them in the first place. So if you don't test anything you'll simply be like everyone out their and think that all of these products are superior to factory parts at every level.......FWIW
Cliff Ruggles:
"Cutting the divider between the two plenums (moderate to ? ) , you allow cylinders to draw from all four barrels instead of just two."
NEVER cut down or remove the divider in a dual plane intake. I've had to put dividers back in quite a few over the years.
It can help to remove a small amount of material between the secondaries, about have of a 50 cent piece, but removing part or all of it KILLS off more power and it can/will induce stumble/hesitation/bog going quickly to full throttle that is difficult and often impossible to tune out.
Yes, I've done a LOT of testing in that area as well and dyno and drag strip tested my Pontiac cast iron intake many times against aftermarket intakes. The final result will outrun Edelbrocks RPM intake on the dyno and at the track to engines making at least 500hp. Plus it fits under the hood just fine and doesn't require "cobbling" to use Shaker or factory Ram Air set-ups, or a drop base air cleaner (they can move the lid too close to the carb and rob power) for hood clearance.......
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version