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.

I bought Cliff Ruggles carb book 20 years ago. Even though I've been dealing with carbs for 60 years or so I purchased his rebuild kit. I told him the how my engine is configured and he sent me everthing I needed to make it the best for my engine.

What 301 cars had a 200r4 OD trans?

Cant say for sure. Guess I connected the fact that the 301 was a 800cfm, not meaning a 200r4 was available behind one.
If possible I would think later model Grand Prix, Lemans.

Thanks for the clarification, just curious since Ive never heard of any 301 cars with an OD trans. The way it was worded saying the 301s had 800cfm carbs (which they did) and "quite a few had 200r4's in original applications" implied 301s had 200r trans. The 301 was done in 1981 & all previous year cars had non OD transmissions like the th350 or th350c that was a first year lockup converter in 1981 on the computer control cars. After that it was all corporate GM engines that did get OD trans like the 200r4s & 700r but no BOP engines/carbs.

Just did a quick search over on Cliffs site. OD equipt quads used a bolt on TV bracket and he recommends that or not a hard fab job. Thought I read there was a factory primary shaft you could swap. Maybe even a later CCC shaft will swap. I will dig a bit more and see if I can find where I saw that.

Later CCC carb throttle shaft wont work due to acc pump linkage differs.
200r4uses same geometry as 700r4.
This from Cliffs site.

Does your carburetor have a provision on the linkage for hooking up a TV cable? Most Chevy carbs will have one, as they typically used the TH350 transmission.

We use the univeral cables here for the 200's and 700 overdrive units, with come with several different ends making them easy to hook up to most carburetors.

Several companies make kits to add the parts to the linkage as well.

The factory snap-on type hook-ups are the best, IMHO, and most later carburetors have the provision already on them for the cable end. When they don't, we usually rob the parts from a mid-1980's unit and put them on the end of the throttle shaft of the carburetor we are setting up.....Cliff

I did a mild buildup of my 400 in my 69 Bird last year...10.6: 1, Kauffman heads, recommended cam/roller rocker arms, RA exhaust manifolds. Went to the Holley 750 with vacuum secondaries instead of the Q-jet (since rebuilt by SMI for 5500 ft elevation).

The Holley is just a gas hog, plain and simple. The Q-jet got 11/12 mpg around town and 15 mpg on the highway doing 80 mph with the AC on.

The Holley was so bad I did a test driving 52 miles, 1/2 city, 1/2 highway. I drove like an old lady. And I mean slow AF. It was torture for me to drive the Bird that way for 52 miles. I filled it up after that and it took almost 7 gallons to drive, which was 8.3 mpg.

The Bird is back in the shop to get that dialed in. My mechanic hates Q-Jets, but this Holley has been a huge disappointment compared to the Q-Jet. The Q-Jet was better on mpg and it launched and accelerated quicker at high speed, too.

Just my .02

Jim

A word to the wise , avoid mechanics who say they hate the Q-jet!

That’s a flat out sign of how ignorant they are!

Perhaps you're right. If he can't get that Holley going a lot better, I'm putting the Q-jet back on and getting a refund (or credit towards future upgrades) on the Holley and the labor.

To be fair, the linkage on the Q-jet was messed up and wasn't opening the secondaries fully when he recommended the Holley. SMI has fixed that, so I'll make a decision about that after I test drive it late next week.

I don't drive my Bird anymore, I just visit it...sigh.

Maybe check the sparkplugs color and a jet change. go at least 2 sizes down.

Did that already, still no joy. I think there's a leak somewhere in the fuel system. I can walk out to the shop and it smells faintly of gas even in the car has sat for a few days. It's maddening.