Pontiac 400 Engine - Intakes?

[AM.MSCL]

No matter how cool this looks to people that look at the car :hooray:
I have to believe it is way too much fuel being put into the motor. Plus a lot of the other things on the motor just give the feel of show car.
I believe the carbs are both 600 cfms also a PVC is attached to the front vacuum port on the front carb.
https://static1.pt-content.com/images/noimg.gif
https://static1.pt-content.com/images/noimg.gif

The car does run decent and only needs a 30 second run to idle on its own. NOTE: 4 Speed Manual Tranny! I don't know the CAM specs.
No bogging or cutting out. Acceleration comments below.
Every great once in a while it will diesel (2 knocks and shut off)
In 2nd or 3rd gear and low RPMs: punch the pedal: wait a few seconds to get moving
In 3rd or 4th gear and High RPMs: punch the pedal: the front end starts lifting and responsive ass hauling
Start the car up (sitting a few minutes, an hour or two, day or more) 90% of the time have to crank the motor 30 seconds to a minute; with the pedal to the floor to start it up. Pumping the pedal makes it worse.
Another point of interest is it takes some major RPMs to get it moving from a dead stop at a light. (no tach but hearing the motor rev)

I am really thinking of switching out to a Edlebrock 2156 intake with what cfm carb?
Any other known intakes that are good that will still fit under the stock style hood?
Thanks
Ray

[wmhjr]

You're right - those are 600cfm E-brock carbs. And I'm guessing that it just might be more than the 400 can really use. It probably doesn't suck, but if you really want performance you'd be better off with something else.

I don't know what else is in the motor. Not knowing the cam, compression or what heads it's hard to say what the best solution would be. I "think" you're running cast manifolds (don't know if they're long branch, etc) and some sort of stock head.

For intakes you have only a few choices. E-brock has the Perfomer, the Performer RPM and the Torker 2. All of them should fit under the hood without a carb spacer - don't know about with a spacer. I think you have a '69 bird? Then you have the Tomahawk and Crosswind intakes.

So much depends on info you may not have. You just might want to think about pulling the cam if you're replacing the carb and intake. And see what you can about the heads.

Once you do that, you should email:

[email protected] (Jeff)

He will want a ton of info, but he can really set you up right. Jeff knows ponchos and he really understands what works best with what.

[AMC Racer]

Assume you're using the manual choke for starting and cruise until it warms up? Not sure if there's room, but phenolic or thermal barrier carb spacers may help the hot start issues. Swapping intakes won't likely fix this.

Two 500cfm carbs (Edelbrock AVS rather than AFB) would seem to be a better plan than the 600s and help the low speed response. This is their typical setup. May be good to do some tuning on the current arrangement before swapping parts as it sounds like an accelerator pump and lean/rich transition issue.

For a single carb, the RPM (7156) gets my vote ... but with the right carbs and tuning, the dual quad should work.

http://www.edelbrock.com/automotive_new/mc/carbs_acc/thunder.shtml
http://www.edelbrock.com/automotive_new/mc/manifolds/pontiac/pontiac.shtml

Hope this helps.

[AM.MSCL]

I don't have a manual choke or if I do I have not found the pull cable on the inside of the car. It does not look like there is cable on the carbs either.
The car has Headers (Doug Thorley I think)
https://static1.pt-content.com/images/noimg.gif

[wmhjr]

I'm not an Edelbrock carb fan. I'm also not a dual quad fan for close to stock pontiac street motors. But, the carb and intake will absolutely depend on the cam, heads, compression in addition to car weight and tranny. A dual plane will help with low end tq and may be where you want to be. It also depends on what you want to do with the car. Personally, I'd really want to know what cam is in the motor. Good weekend job! Of course, if you're just trying to solve the hot start issue, the recommendation to use a phenolic spacer might be a place to start. You'll just have to determine for yourself if you've got enough hood clearance.

[AMC Racer]

The first picture can see wires going to the choke arms? Maybe they are just holding the chokes open? A working choke is usually a good idea ... at least on one of the carbs. Probably a good sign that the carbs weren't tuned in properly. Part number should be stamped on the carb, to double-check which model.

[Roadrage David]

a tipicul 400 needs 750 carb. when its a soupt up engine a torker I ore II is the way to go when hood clearense is needed. a performer rpm gives more lowend torque but hase ahood clearense problem.
Edelbrock carbs in the pontiac world are notories for having a flatspot when giving the engine troutle. my sirguestion Holly 750 ho from AED....

[AM.MSCL]

Fired the car up this morning a 2 big black spots out the exhaust on the ground.
The rear carb has the mix screws bottomed out ( tightened all the way in).

[critter]

Mix screws affect idle. Jets control how rich or lean it is.

The PB4 dual quad intake is OK for car shows, as you've figured out, but not much for performance. A factory 4 barrel intake and a properly tuned Quadrajet would do a better job IMHO.

[79PonchoUK]

Generally, if you have two big carbs the fuelling is still dictated by the jets....so it won't necessarily be overfuelling because of that....just because it's not been jetted. Although, the jetting isn't going to be as accurate with that setup. It won't hurt your engine too much but you're right, it probably is for show more than anything.



I'm also a big fan of the stock Quadrajet.

Not only does it meter the fuel better than a Holley or equivalent, it's also a lot more fun to own.

The later pontiac engines had a quadrajet that was approx 800CFM as standard. More then enough flow for a mild street engine and bigger than the 750 holley people fit here as an 'upgrade'.
The fun comes from the stock carb being mechanical secondaries Vs most holley carbs being vaccuum. They're easier to tune too -

I put the quadrajet back on my car, bought a wideband lambda gauge and got the mixture 'about there' by changing the jets.....then I fine tuned it by taking out the metering rods (a single screw on the top of the carb) and filed them either at the top or the bottom (depending on where it was lean) until the gauge showed as spot on all the way up the rev/load range.

So easy to tune and you don't need to keep disassembling the carb to alter the secondaries fueling.

plus! everything fits....including the shaker. lol


Quadrajet FTW.

The only thing you need to watch with the Q-Jet is the leaky float bowls. Make sure they're sorted once and for all before fitting it and it's a better street option than any other aftermarket carbs I've laid hands on.....again, despite general concencus.