So the 750 Holley that was on my car when I got it went down Sunday. I could break it down and try renewing it but it's an oldie and I'm a newbie.

I'm trying to learn what size (cfm) came stock on 400s with automatic trans. I felt the 750 Holley was too much but a buddy is trying to convince me to stay at 750 or go higher. I'm thinking that I will replace it with an Edelbrock.

I just put a Holley 670 Street fighter carb on my 400 auto. So far I'm real happy with it

Early q-jets where rated at 750 cfm.
But many claim they'r actually 780.

FWIW, Pontiac used 800 cfm q-gets on V8's from 75 thru 80.
Including 301's.

Thanks guys. I saw that 800 cfm carbs were used in the late seventies, which was surprising given the gas crisis then.

Ok, I guess I gotta listen to my buddy and stick with a 750cfm one.

a too big carb can get you to get gas in the oil, if its not all used....750 is border line imo...I have a 650 Holley on my 400....runs great....
I had a 650 Holley on a 302 once...wore out the engine based on my comment abv..switched to a smaller carb. got more power , and gas consumption went from 15 mpg to 19 mpg...and was faster. bigger isnt always better.

I agree. I was thinking 650 but I keep hearing 750 (or bigger!) in my ear.

My 400 was bored 30x and it has a mild cam (cower baja II). I wouldn't want to go lower than 650 or higher than 750, so it's between the two I guess.

Heres a helpful calculator

http://www.wallaceracing.com/intakecfm.php

I'd replace the holly with a 68-70 fresh built qjet... JMO

per that from Wallace I get for mine :
Required CFM: 592 to 753 cfm

I have a quadrojet, which I was told was the original, but if I'm reading the code stamping correctly, it's not.

I saw two codes (one on a circular pressed piece on the side) that had 7037202 and HO or HD with I believe M6 - and then one pressed into the metal on the back side that was 7032750

I googled 7037202 and from the results it looks like it was a '67 era carb for a 327 or 350 (I have a 400). Thing is, on the base is a stamping that I think is the date code, which reads 0318 (or 31st day of 68).

7037202 carb is a 1967 Chevy 4 barrel for a 327 or 350 auto trans as you stated. The circular tag is the carb code and date M6 which is December of 66. The baseplate has another date code of January of 68. When you say "pressed in" are you talking about the small 3/8" casting which is circular with 7 digits within the circle? Those can be found on the base, airhorn. Here is a pic



There were the first year Firebird carbs that had a round metal tag on the main body that had the carb number and date on it as well. After 67, they stamped the carb with the carb number and two letter plant code.

Here is a pic...



Don't confuse the cast part numbers for carburetor ID.

Here is the later 68 up carb number and plant code.



If you are racing a car, a Holley is the better choice. If you have a daily driver, go with the Q jet. You will be fine with any Q jet that is calibrated properly. These carbs are "on demand".

I had an 800 cfm Buick Q Jet on a 428 and used it on a 350 with no issues.

It's all about tuning jets and rods.

Thank you, good info. Just to clarify the plate (the picture with the pencil in it) is the carburetor ID? The casting number (the 3/8" circle with a 7 digit number in it) is used for what? My quadrojet has both, and that number I couldn't find in a Google search.

Why would the carb made in Dec 66 have a stamping of 03168?

I want something for a Daily Driver...maybe I'll shop around for a larger q-jet.

That carb is a 67. In 67, Carb ID was a circular disc with the carb number and date. Example, my 67 is 7027272 with a D7 date (April for D and 7 the year)

The baseplate had it's own casting number to differentiate some differences for specific applications. Some are interchangable, some are not. The baseplate appears to be a 1968 as evidenced by the date code you provided. This base is NOT original to that carb. You can sell that carb and probably fetch some decent money. I would sell the baseplate serately.

The airhorn, baseplate and bowl/body all have specific 7 digit castings per application. For example a 68 HO 400 4 speed will have cast in that small circle on each 1234567 for airhorn and 2345678 on throttle body/base. The bowl/body will also have a 7 digit casting number.

So...Essentially, you are looking to buy a rare carb. You have 3 main parts, each with their own specific 7 digit numbers. The body/bowl must have the correct 7 digit casting number AND 7 digit carb ID number (don't confuse the two) AND have the correct two letter plant code.

Here is an example of a restamped 1968 HO Firebird carb trying to be passed off. If you have been around carbs, you can spot incorrect fonts.



I wished I had a resource that identified the correct casting numbers for throttle bodies, bowls and airhorns for all carbs, but I don't.