Is it possible to get good gas mileage with a carbeurator? I mean, if tuned by a professional, could I make decent power and get decent gas mileage? Anything above 20 on the freeway would be acceptable.

 

I get around 20 on the highway with my holley...it won't be that bad.

 

my holley drinks gas like crazy, but then again, it needs tuned...

 

i used to get 23 to 24 MPG with my Dell'Orto on the highway.

 

I'm thinking of going with a carb simply because it's so much simpler, there's bolt-in kits, it doesn't cost $2000, etc. etc. I have three RX-7s, so that's three times the normal sized hole in my wallet.

 

9 on my dellorto

 

If you are running FI now, get it tuned right and keep it. More reliability, less headache.

Coming back from Denver, I pulled 23 mpg on the interstate with the 12A-bp and Mikuni. It's also very easy to drop to 9 mpg in town.

Is it possible to have both, yes, to a point. More power=less mpg, usually. The biggest deciding factor is the foot.

 

A carb can be tuned to give you the best possible fuel consumption for any given power ouput. At the optimal condition there is not much difference between carb and FI. However outside those conditions FI is more tuneable with the result it is more fuel efficient by up to 12%.

Driving a carbed BP with 220 rwhp, consumption can fall to 6-7 mpg, one reason was the need to keep revs up at low road speed in city traffic. In contrast, my daily driver with an efi 12AT also with 220rwhp can get 27 mpg cruising at 65mph on the open road because it is using less than half power. Its worst fuel consumption is around 15mpg driving continually in the 5-7000rpm range on a 50 mile hilly curved road.

In summary, yes a carb set up will give you around the same fuel consumption at peak power as efi but at a much cheaper cost and quicker tuning. For economy over the whole rev range, efi is better.

 

I routinely get 23-24 with my stock Nikki in an 84 GSL, mostly on the highway. Considering Paul's comments above, I doubt I'd do much better with efi. The Nikki carb is simple enough that I have learned to fix it and tune it to keep it that way.

Ray

 

never tune lean though..


one detonation and your screwed/

 

with my driving style...i get 9-13 mpg out of my holley 650, depending on when and where i am. (gotta drive good in the local cop spots!)

 

A 650's venturi diameter is too big for the air demand of a 12a or 13b. The consequence is that the velocity of the air that is flowing through those huge venturis is so slow that it cannot atomize the fuel into the mixture.
You're literally dribbling fuel into your engine at anything under 5500 RPMs.

Even with vacuum operated secondaries, driving style plays a larger part of your fuel economy than jetting -unless your jetting is beyond the range of the carb.
I have mech. sec.s and driving like a complete ******* and lunatic on my local "Dukes of Hazard" back roads, I get no less than 12.5 MPG. I am spending all that time between 4800 and 7800 RPM.
But if I drive like there's a trooper around every bend, and shift @ 3200 RPM, I can get 17 MPG. Obviously open freeway travel would be even better, but I just can't keep myself from the pedal in those situations long enough for an accurate MPG calc.

 

I get ~23 mpg highway with my Dellorto and its still a hoot to put your foot into it too.

 

I am hoping to improve my highway milage by the '87 n/a tranny I am putting in. A .697 5th gear + a 3.909 rear end should give me a very good RPM for 80mph to increase MPG. The stock 83 tranny I am using is a far to low. It otherwise spins 4300rpm at 80mph, which is rediciously high for a car IMO. I really need to find ways to improve my blowthrough turbo highway MPG or I will not be driving it at all this coming summer.... Now city MPG- NOT going to be getting any better anytime soon.

 

My stock 12a 83 GSL gets 25 mpg all day long, I do have the 2GCDFIS which improved economy along with a good set of plugs and wires and quality oil.

 

While this is true for the turbos, the NA's can be leaned out more than stock. They tend to be a bit rich to help with emissions by adding extra fuel to burn in the cats to add more heat to burn off the pollutants.

With emissions and cats gone, leaning them out a bit can yield better economy. Just have to watch the egts, detonating an NA isn't as easy as one might think, unless the timing is way off.

 

Does the carb type affect gas mileage or is it just how well its tuned? I'm going to be running a stock port engine for now, but I'd like to use a weber 48IDA with a set of phenolic spacers to bring down the powerband a bit, but I'm not sure how well that'd would work.

 

Afr's are afr's. Fuel mileage will depend on how well the carb is suited for the application, the tuning, exhaust and position of the right foot.

 

I'll need to find someone who can tune a carb, as I have no experience. I don't think it's suited TOO well to a stockport motor, but with the plenum spacers the 48IDA should work alright, better if I get a clean-up port job. I'll have a collected exhaust w/ no cats and two mufflers at most, terminated before the rear axle. If I want to get good gas mileage I know how, but the biggest shortcoming is that I'll probably be using a regular 12A transmission.

 

I'm not that familir with the 48's, but you may be able to have smaller chokes put in. Too big of a choke, or carb, can reduce intake velocity and lower performance.