Re: Carbruator for best gas mileage
 

That's awesome!
Every time I tell someone I'm running a small block 327, they always tell me to expect 10 to 15, 15 if I'm lucky.

Re: Carbruator for best gas mileage
 

So what Carbruator were you using?

Re: Carbruator for best gas mileage
 

Rico, I'm sure you've heard the old saying " figures never lie, but liars figure". :devil::lol: Anyhow my formula was when we used adding machines:waah:, so I would probably go with the newer computer one. Also wanted to add that on my truck I have a 350 (325 hp), 350 turbo and 2:56 Nova rear axle. I run an Edelbrock 600 CFM carb and have 235/55/17 tires that are 26.7" tall. Running at 70 MPH (GPS) I pull around 2400 rpm and get 17 mpg with the AC on (and really watch how I accelerate, going up and down hills) . The only time I check it is going to the Nats in the summer, otherwise its just gas and go. I've been told that a 350 best performance and gas milage is between 2000 and 2200 rpm. So if you could get your set-up in that range at 70 mph, you might get close to 19 or 20, just a guess. I'll keep my mouth shut for awhile now..Jim

Re: Carbruator for best gas mileage
 

Ricos54;

The 350 was set up with rodchester 2bld from the factory,I got the whole engine assy from a 76 chevy Nove that had been hit in the rear end.

I also know that sometimes you can over do the carb n that is when you get in to trouble with gas mileage.
Cams, heads n carb all make it run right n perform.

I working on a 305 V8 sbc for the project that I'm working on.
I'm also trying to work out a 350 V8 sbc(76 yr) going to try to put votex heads,stock 4bld intake, Q-jet carb with HEI dist.

Have always been a SBC person.
First car was a1959 chevy biscayne 6 cly 3 speed,just back from viet nam n needed a car. yr was 1970.

Tim

Re: Carbruator for best gas mileage
 

You need to tune your carb to your motor. I putan edelbrock on an 81 blazer I had years ago right out of the box, set idle and mixture screws and it ran great. However where a tank of fuel used to last a week and a half or two I was filling up every 4 days. A jet kit and some fiddling and I had it getting better mileage than with the original carb.

Re: Carbruator for best gas mileage
 

The Quadrajet is a staged carburetor with a fairly small diameter primary venturi. Air passing through does so at high velocity and fuel is drawn into the venturi with a strong vacuum signal. This does a better job of shearing the fuel as it's introduced into the incoming air. Once fuel is introduced into the air it must be heated before it will turn from small droplets (atomized) into combustible vapor (vaporized). The smaller the drops to begin with, the faster they will vaporize. Unlike Holley or Edelbrock carbs, Q-jets have several additional features which attempt to compensate for some temperature and / or airflow variations as the throttle opening changes. Q-jets were OEM and needed to meet emissions and fuel economy standards where the others were performance replacement versions. Non-electronic carbs from the late '70s to early '80s are usually my choice when retrofitting as after about '83 or '84 GM was really trying to make the Q-jet do more than it was designed to do.

There are huge amounts of data around for the Q-jet carb. If you're going to get into tuning one for mileage, an excellent reference book is Doug Roe's "Rochester Carburetors." Although many of the part numbers listed are NLA, there's still a ton of wealth for a guy wanting to make a good carb work well. And these carbs can be tuned well. I had a Buick 455 in a '79 Monte that would pull 18 mpg on the highway. It took a bunch of work and the car was a long way from stock, but we're talking about an engine that normally got 8-12 mpg. I used 2.26 rear gears, 235/75 15 tires, a switch pitch 400, and a low end cam to make that combination.

EFI has upsides and downsides. I tend to recommend using stock GM parts for a conversion because you can usually find them cheap at wrecking yards, on CL, at swap meets. But unless you have a stock engine that's similar to the one the EFI came from, chances are you'll end up getting a custom tune to get best performance. When combined with electronic spark control EFI gives a whole new level of performance if properly tuned. EFI can be better than a carb for being able to deliver exactly the amount of fuel needed at exactly the right time even with temperature and weather changes but there's more complication and there can be more frustration during the tuning process. There are plenty of guys on gearhead-efi that have done EFI retrofits including a guy putting TBI and distributorless ignition on a Corvair and a 4.3 Vortec engine installed in a VW Vanagon.

The Holley spreadbore carb was a decent unit but I don't believe it was designed as a stock replacement for emissions applications. It was larger and provided slightly better response than the Q-jet although I never tuned one for economy and don't know if it was very flexible that way. I've worked on a couple of them and even owend one but ultimately once I learned to tune a Q-jet that was my preferred street carb.

Cylinder heads and compression play a huge part in getting good economy. TBI truck heads are not great for performance but they'll do 200+ hp and have special ports designed to get better mixing and combustion. Vortec heads are even better by a long shot. Combining either of these heads with an aftermarket aluminum intake and a Q-jet can give a decent response and economy. Pick a cam that makes peak power at low rpm with the 700R4 and a set of numerically lower rear gears and you'll have good acceleration and acceptable performance while retaining good fuel economy. The stock cams from the '70s often liked to run at 2800-3200 rpm while a low end grind can have a peak from to 2200 - 2600 rpm.

Re: Carbruator for best gas mileage
 

,I've used q jets , and Holley , liked them both, I have an edelbrock that I'm hoping to try on the 51....
Qjets are awesome, had them on a 454 vette, and a 455 olds jet boat, even though the small primaries, get good mileage, it was too much fun keeping all four flowing ! Pretty easy to adjust and rebuild, but watch out for old carbs cheap, usually the throttle shafts wear, and you suck air around there, ...but here is something I've run across, and would use in a second...
http://www.ebay.com/itm/Holley-Reman...item20dca4757a

Holleys are good, easy to adjust, never had any problems, but ,,I never cared about mileage...