If your car was overcarbed, you would be able to tell by...?

What are your feelings on Edelbrock?
I was seriously pondering a 750 on my 400 bored .30 w/ mild cam.

What about the perfomer series?

There are several keys to carburetor selection:

(1) engine specs (CID, cam, compression, max RPM, ec.)
(2) the projected environment (street, street/strip, race only)
(3) the tuner's knowledge and experience
(4) availability of tuning parts

In general spread-bore carbs work best for street and street/strip vehicles. They also work well for straight-line race vehicles. However,making a spread-bore work going around corners can be challanging.

The last two items are extremely important. NO carburetor is going to be perfect for a modified engine right out of the box. Someone (the owner, or the tuner) will generally have to modify a carb. Their knowledge of the specific carb, and the availability of parts will play a large role in the success of the installation.

Size will be a factor of the first two items. And remember it is MUCH easier to tune a carb for all-out race than for a high performance street engine!

Jon.

JB: I've heard one way you can tell if you are over-carbed is if the car is sluggish off the line.

You're overcarbed if your springs sag.

- Jake

the word "overcarbed" can have different meanings. It is quite possible to be overcarbed at high vacuum and undercarbed at low vacuum; or, just the opposite. The is why the desired environment is important to consider. As an example, I own a car with a 121 CID 4 cylinder that came factory equiped with 2 500 CFM 2-barrels. Is is over carbed? The factory evidently didn't think so.

But to try to answer the question: as a general rule too large a carb (high vacuum) will cause the engine to run lean (insufficient venturi air velocity) up to a certain RPM. Too large a carb (high vacuum) will also cause sluggishness at high vacuum. Too small a carb may have excellent throttle response (up to a point), but will fall on its face at some higher RPM.

Oh, and by the way, my own Pontiac 350 sits under an 800 CFM Carter TQ (and loves it ).

Jon.

Edelbrock performer #1406 is superb for the 350-400 HO, runs very nice out of the box. I've had one for two years now, replacing it with Quentons original 1968 carb he sent me. The problem I had with the 1406 was simple: GAS MILEAGE! **** thing sucks alot of gas, too much for my driver '68. And it demands 93 octane for an FGF configuration, nothing less.
Of course, my lead foot could be guilty to some degree for the bad gas mileage.....I suppose.

I also have a #1406 on a 68. Mine also pings on anything but 93. Nashville68, the pinging - Can that really be a carb issue? I thought that was usually a compression, octane, timing, or carbon issue. ???

Cheers,
Scott

A lean condition can cause pinging. It's possible those #1406's were set up too lean.

The carburetor cfm required for a street engine is calculated by the following formula:

cfm = ((engine cid x max rpm)/3456)* volumetric efficiency

((455 x 6000)/3456)* 0.80 = 632 cfm
((350 x 5000)/3456)* 0.80 = 405 cfm

The cool thing about quadrajets is that they have vaccum secondaries. Even though they typically are rated over 700 cfm, the engine only uses what it needs. If there isn't enough of a pressure drop to open the air valve - it doesn't open.

I've got a Q-jet on a 350 with the 2bbl heads and cam and a 2.78:1 gear. The secondaries aren't quick to open. When they do, I love the waaaah!

C'mon guys! That was a good line! Nobody appreciates my sense of humor. Sigh....

If you're over carbed I would recommend looking into the Atkins Diet. How's that for humor Jake?

There you go!