General Category > Quadrajet Carb Talk and Tips

Exhaust crossover in intake

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tayto:
Looking for recommendations on what to do with the exhaust crossover in the intake manifold. I daily drive my truck and do not live in warm climate (west coast of Canada). My Qjet has an electric choke, I am running stock "log" exhaust manifolds with NO heat riser valve and currently my intake has no provisions for an EGR valve. While most say to just block them off completely, I do not think this is the way to go. An intelligent source said to block one side complete and restrict the other side with a 1/4" hole. I think the intake gaskets I got sent 2 plates with a 1/2" hole in them.

Any suggestions here?

Kenth:
You need to understand the principles of the internal combustion engine to make the right decision for the use of the car.
Heat is a factor of three that converts liquid fuel into a combustible gas.
The others are the amount of fuel and the air velocity through the venturi.
If you remove or reduce one of the factors, you must increase the others accordingly.
This does not worry race guys as they start at 3000 rpm or higher and drive only 1/4 mile at a time. For them, driveability and fuel consumption are not a priority.
The crossover channel is there for a reason.

FWIW

Cliff Ruggles:
For what you are doing leave the exhaust crossovers open in the intake.  It's a wet-flow system and heat is your friend with these things.  Heat improves thermal efficiency and allows for faster warm-up of the engine and eliminates problems associated with fuel globbing up on the cold intake runners until the engine fully heat soaks.

You will so a lot of conflicting information on the subject, and a high percentage of it is highly inaccurate.  There is NOTHING waiting for you but issues, especially in cool/cold weather if you block off the crossovers.  I'd like to have a nickel for every person who has build a 350 SBC with the later "Vortec" heads and calls up here complaining about poor performance in the Fall and Winter months bit don't have too many issues in the summer........Cliff

tayto:
I had no intention of blocking it, so don't worry about that! I am just curious, I guess, of why they used restrictors, if at all. Two 1/2" diameter restrictors were sent with my intake gaskets, so that's what I used. I recently acquired a 14096242 "bowtie" intake that i want to try with my setup, so would like to "correct" anything while i'm in there.

old cars:
Here's what Brzezinski Racing has to say:

In stock form it will produce more power between 4500 and 7000 rpm than any other stock Chevy manifold. Commonly referred to as a “Marine” intake, this manifold is a cast-iron copy of a Z-28 high rise aluminum intake. The marine intake is equipped with both carburetor bolt patterns, is 1.250" taller than regular intakes and was not available – in cast iron form – on any production cars.

In stock form this intake will out perform stock Q-Jet and 2 barrel manifolds in most applications where the engine is running between 4500 and 7000 rpm. Because of its huge internal volume, the Marine Intake lacks throttle response below 4500 rpm compared to other stock intakes.It is equipped with Holley and Q-Jet carburetor bolt patterns.  It will not bolt to Vortec or Vortec Bow-Tie heads.

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