Carb for mild 400
 

I built a mild 400 for my street car last year. I am running a performer rpm intake. Right now I am running a 750 holley vacuum secondary. Performance is not a primary concern. I would like to get decent fuel milage out of it. I plan on taking some long road trips (+500 miles) with it.
I have a 76 quadrajet and a 600 holley laying around. Do you think I am giving up some milage with the 750? or change carbs?

I have to add the 2004r trans is great with the 3.73 gears.

Quadrajet would be my pick. Be aware 76 model quad has the single rod APT style and is not very friendly to any performance apps.
I would look for a later model BOP unit that came from something with the 200r4 to reduce head aches with the TV cable set up.
Even the 301 units are 800 CFM and quite a few had 200r4's in original application.

Run the q jet. Properly set up, of course.

I believe the `75 is the oddball. `76 and `77 carbs are some of the best ones.

Might be good to post carb number to be safe. Or take op of carb, and show picture...

I bought one of those goofball carbs (salvage yard), It looked like the later units, until I got it home and cleaned it up and took apart...........

:gag:Might be good to post carb number to be safe. Or take op of carb, and show picture...

I bought one of those goofball carbs (salvage yard), It looked like the later units, until I got it home and cleaned it up and took apart...........

Although I usually run Holley carbs, a well setup up Quadrajet will do much better on mpg.

I would also put the factory intake on it. For a mild 400 the RPM is not a good match.

Mike,
Do up the 76' Qjet, smaller primaries will give you better gas mileage and it's 75' only that has 3rd metering rod deal so your good to go!
Jeff

If your looking at putting a cap of 5500 rpm on this 400 then your average power band will be better served with a iron intake and fortunately leaves you with the Q-jet as the way to go.

Any 1976 M4MC/ME is good except 1976 Olds still using the auxilary power piston.

FWIW

LOL, the "goofy" carb I bought was from a 76 Olds...now I know better.

I knew there was an odd duck there.
Must be because my driver is an Olds.

How is your 750 Holley? If it works well leave it.

I had a 750-3310 Holley on the Performer on the mild 400 in the 81 TA. Bad mileage. Threw on a '73 750 cfm Q jet better mileage and same performance.

You didn't say what car or I missed it but a 750cfm AFB would be good also. The AFB isn't as tunable as the Holley or Quadrajet but is less complex than either of them and more reliable IMO. GM went to the quadrajet from the AFB because of government emissions requirements which the AFB wasn't engineered to cope with. If you switch to the AFB use an old early to mid 60s original and not the Edelbrock copy. A '65-'67 cast iron factory intake will bolt up to '65> heads.

17057274 I s the carb you want!
This is the Carb Cliff R ran on his Ventura.
1977 GP 400 cid.
Not a rebult (replacement) carb, try to find orginal piece.
Get a rebuld kit from cliff and be Happy!

Speaking of Cliff. If you dont already have the 'Quad bible' of Cliffs, pic a copy up and learn all you can.
Cliffshighperformance.com gets the book and the best parts and tech help with the set up of Quadrajet carbs.

The quadrajet is from a 77 Pontiac If I read the numbers right. I know the rpm is the wrong intake but I used a lot of parts I had laying around. I have the Holley tuned pretty good and runs great. I can tune Holley very well but never tried to tune a quadrajet. Mabey I should do some milage runs before I do anything.

The car use to run 11.7's with the 455 at 3900lbs. But decided to make it basically a stock cruiser. It's a 72 Lemans.

You can certainly start off with the RPM and Holley you have on hand,and see how well it works for you..

if you have enough snap to burn well into second gear then I guess it boils down to what might be the want for better fuel mileage.