A rep at the local Kragen Auto suggested I switch out my 750 edelbrock carb and install 670 Holley carb instead. He noted better response and that the Holley doesn't need the constant adjustment that the 750 requires...

But here's my question (and bare with me, I've been into wrenchin all of 6mos.), will installing the 670 Holley give me better gas mileage?

The car: '71 Chevelle SS. 350sb, 4barrel, 350TH
Thanks in advance!

Is the 750 on the car you have now a vacuum secondary carb? The 670 Holley is the Street Avenger Series, and it's a vacuum secondary carb. We have these carbs on all of our cars, (770 on our 383) and we absolutely LOVE them!!! They're the only street carb we would use. Responding to the gas mileage question, Most likely this carb will help you with your gas mileage, ESPECIALLY if the carb you have now is a mechanical Secondary carb. It also depends on how you drive it. The Street Avenger is just that. STREET, it's for the street and the occasional take it down the strip. Hope I helped you!

With it set up right, the Edelbrock "should" give the best mileage. If yours is stock out of the box, its more than likely not right for your car. Its much closer in design to the Q-jet wich is your best bet for mileage. I spent many hours on the Ebrock and if you can keep all trash and I mean all out of the needle and seat they are trouble free. I run Q-jets on my streeters and Holleys on my racers now.

Originally posted by J. Herer:

But here's my question (and bare with me, I've been into wrenchin all of 6mos.), will installing the 670 Holley give me better gas mileage?

The car: '71 Chevelle SS. 350sb, 4barrel, 350TH
Thanks in advance! Stick with your Edelbrock, or get a Quadrajet. I ran a Holley -vs- Qj comparison last fall. The worst Qj got appoximately 14% better fuel economy than my 600 cfm Holley. The best one got nearly 23% better fuel economy!

Mike

Disregarding models and brands vs. gas mileage, arent we over carbing that mill? I wold think unless it was a real stout lil mill that the 750 is too much carb. But without knowing the combo its hard to say, I suppose. I mean, I run that same carb on my 402 and my mill is a touch or two above stock.

Just wondering out loud for the sake of the poster, guys.

All carbs need adjustment from time to time but if you are constantly adjusting you either have carb hardware issues or your compensating for other tuning issues that may not even be carb related, Just my sloppy .02.

You guys rock! Thanks for taking the time fellas!

At any rate, the guy I bought the car from told me the the carb came brand new out the box. That's the only reason he installed it. He also told me that it wasn't quite the right size for the car (350).

Which is how I got here in the first place. The other day I ended up breaking the cam/choke connector rod (which was plastic by the way). Edelbrock claims they never made this peice out of plastic on any models. So, to compensate, they're shipping me out a new piece. The funny part is, the carb does seem too big for the car, which my mechanic says is part of the reason I was able to break the connector rod in the first place.

So, now I'm looking for a carb that gives me a combination of good response, gas mileage and SPEED!!!

Sorry for the lengthy post. Thanks in advance! graemlins/thumbsup.gif

Whats your engine spec, tire size and gear? What MPG would you call good? 50 bucks will get you an Edelbrock tuning kit that will let you set it up for your car, you will spend a bunch more than that to get a Holley, jets, power valve, pump cam and spring to make it just right for your car. People can say what they want about "out of the box" carbs but I have never had one or helped someone that did not need to tune a new carb to get it just right.

Hey Marty...Ever tried a 950HP? I don't think you could tune it any better for MY combo,outta da box,that carb is perfect graemlins/thumbsup.gif . When you throw that SPEED factor in there, I'd go 650DP Holley myself,you'll get the best performance, but you'll never get the best mileage out of a Holley graemlins/thumbsup.gif

Robert, my new carbs have been 2 650 dp's, 1 750 vac sec, 2 600 edelbrocks and 1 625 carter afb. I have also delt with some friends edelbrocks, Holley dp's and vac secs and one dominater. I have not gotten my hands on the higher priced DP's.

Hey Dragn70,
I'm runnin a 350 on 15" tires. Still not sure of the gear ratio but I want to say 4:11. 12mpg would be great!

If 12 is all you want the Holley should do it, the edelbrock would do better and the q-jet would be best. When mileage is not that big of a deal, I would go with Holley or "holley type", you can get more parts and find them everywhere.

Originally posted by J. Herer:
Hey Dragn70,
I'm runnin a 350 on 15" tires. Still not sure of the gear ratio but I want to say 4:11. 12mpg would be great! If you are not getting 12 m.p.g. with the Edelbrock doing average daily driving, something is probably wrong. What kind of driving are you doing - short trips or lots of wide open throttle? If you are in the throttle all of the time, you won't get 12 mpg no matter what carb you have. Same with a lot of short trips.

Bottom line is if your combo is only getting 12 m.p.g. driving back and forth to work, before I bought a carb I'd check out the float level of the Edelbrock, and go over the ignition system with a fine toothed comb. You might also make sure that your vacuum advance is hooked up and working.

Driving back and forth to work my 327 clicked off a consistant 15-16 m.p.g. with a 1969 Corvette Quadrajet (750 cfm).

Here is a little test I ran last fall re: mileage http://www.chevelles.com/cgi-bin/forum/ultimatebb.cgi?ubb=get_topic;f=29;t=003044

Mike

Thanks for that link! I've been driving the car to work daily. About 12-14 total miles per day. Not a lot of wide-open throttling. There's a realy long street I take to and from with about 3-4 stop lights. After doing some research (pricing etc.) I am thinking of going with the quadrajet.