Bringing this thread back up  

I'm wanting to get similar mileage and power gains for my 72 Vette.  

I have a 87 Chevy Caprice Wagon which is about 3900-3950lbs after all the stuff I have taken out. It has a ZZ4 350 with Heddman Hedders and 2.5" true duals. Got a built up 200-4R and 3.42's in the rear.
Now I drive this car like I stole it from someone I hate. Absolutly no mercy. and I still get 11-12mpg on average!!

I took it up to the White Mountains this summer and on the way up (at 10pm) I comfortable cruised at 85-90mph the whole way up at around 2100-2200rpm. when I filled the tank I was amazed to find out I had managed 17.2mpg on the ride up!

I am curious to find out what kind of mileage I could get if I kept my foot off the pedal, but I am just simply incapable of doing so.

So I get about 11-12mpg around town and can get 17 on the highway. Not bad for a car that was only getting 13/16mpg when it was brand new and only making 140hp vs the hefty 380ish its making now.  

Ok you asked for thought, but this thread is 3+ years old so it is probably dead. Anyways I think you may be going in the wrong direction somewhat. You need to montor manifold vacuum, timing, and performance. You don't need computers and O-2 sensors to build a V-8 that gets decent mileage on both the highway, and in the city.

Forget fuel injection. Go with the carb. A well tuned carb will let your engine run more efficient than a computer anyday. Carbs operate on vacuum to mix air and fuel. Injectors spray a fuel mist into the cylinder. Fuel in liquid form is not more volitile than the vapors. So biglock's uncle probably COULD get 100 M.P.G with that set-up.

I have a 1980 Chevrolet Malibu with a 267 V-8. I bought the car it was averagng less than 14 MPG. I have swapped the 2 barrel for an Edelbrock 1406(600cfm) carb the Performer series intake, a clutch fan, Flo-Tech's afterburner headers with 1 5/8" primaries, dual 2" exhaust, and advanced ignition timing. I am using two stages lean on my secondaries, and 8% lean calibration on the primaries for both power, and cruise modes. I have a THM-350, no lock-up converter, and a peg-legged 3.08 axle. I recently took a trip to Pittsburgh, from Warren, Ohio. The total trip was just under 187 miles. I used less than 7 gallons of fuel. My cruising RPM was anywhere from 2400 to 3000 RPM. My manifold Vacuum ranged from 16" Hg to 13" Hg, from speeds of 55-65 mph. I can only run 93 octane from timing, lower octanes knock. I have the metering rods in the carb set for power staging at 4" Hg. I did all of this on guessing from monitoring my engines performance and economy overthe last 4-6 months. My detent cable is set so perfectly, that youwon't feel my tranny shift at part-throttle acceleration. I may not run 13s, but my car has gained performance over stock. When I bought this car, a STOCK 4-DR Cobalt LS series could beat me in top-end. No My car is faster than most small V-6's with power ranging from 140-170 HP in their top-end RPM. My engine poops out after 4000, but it runs to almost 6 before shifting.

You want economy and power, look for ways to improve the EFFICIENCY of your engine. Also, your most EFFICIENT speed, is the RPM at which your engine makes it's peak Torque. This is also the speed the engine was designed to run at. Peak HP is made by spinning the engine faster than it's most efficient speed, but still making power to overcome the loss associated with incresed engine seeds. Remember, as engine speed increases, engine torque decreases.  

"Forget fuel injection. Go with the carb. A well tuned carb will let your engine run more efficient than a computer anyday. Carbs operate on vacuum to mix air and fuel. Injectors spray a fuel mist into the cylinder. Fuel in liquid form is not more volitile than the vapors."

I have a problem with this statement.  A well tuned carb can run as well as an EFI system, but definately not more than a well tuned EFI system.  An EFI system will take into account small and large changes in air density from elevation or weather changes and make corrections accordingly. A carb is set to ONE elevation/air density and works less than optimal from that (though a Q-jet try's and close is usually good enough).  As for liquid vs. vaporized fuel... better atomization burns better and more completely, it's a simple surface area reaction, more surface area exposed better/quicker the reaction takes place.  The intake runners give the carb's fuel time to atomize on the way to the cylinder.

You are definately right about using vacuum as a measure of efficiency.  Higher the better, and adjusting your primary's and secondary metering accordingly (like 4" for vacuum secondary opening).  

Hmmm, well yes todays cars get very good gas mileage, and today's cars tend to blow engines moreso than older cars. Very few engines have the dependability of cast iron for the past. I work, once again in a salvage yard. If it doesn't sell, that means it does not break. Alot of newer engines just don't last. I believe with tuned EFI, this is part of the problem. Automakers, in order to get vehicles t operate more efficiently and with less emissions, have leaned out fuel alot. After spend 2 1/2 hours under the hood of a 96 Skylark, with a FORQ 4(2.4L Twin Cam, or the #$%%ed Over Rebuilt Quad 4) and looking at the distance from the injector to the valve, and there isn't much. A mist spray of fuel is still liquid. As for te vapors? Vapors are what combust. a minimum % of vapors has to concentrate the area with at least 19% or something like that. Don't quote me there, I didn't research it, yet. In reality, apuddle of gasoline will snuff out a cigerette, before igniting it, if the fuel vapors weren't present. So for ideal conditions, you want the fuel as vaporized as much as possible, before combustion. You also want it evenly mixed throughout the cylinder with the air. I don't not believe with EFI that is possible.  

New engines break more because more of them push the limit of cost vs. power output and todays engines work harder on smaller displacements than older lazy larger displacement engines.  As for EFI and emissions, actually OEM's have to richen the mixtures up to meet emission requirements on NOx so they are not leaned out very far (not much over 15:1, and engine can usually cruise at 16+:1), you rarely get burned exhaust valves (the first thing to go when too lean while cruising), they do shut fuel off entirely when coasting though. As for fuel vapor, the heat of the cylinder head, valve and combustion chamber very quickly evaporate any liquid fuel into vapor. Especially many small droplets with large surface area to evaporate with.  The suction of the air/fuel around the valve mixes it pretty good, then by the time it's compressed the small area should be fairly saturated with fuel (12:1 to 17:1 air/fuel ratio) and not puddling in the combustion chamber due to air flow and heat.  

Fiero,

I don't know to say it other than you are dead wrong in almost all of the statements you've made here.

Fuel injectors do a better job of atomizing fuel, there is no discounting this. The fuel injector can do a much better job of breaking up fuel than a booster and vacuum signal can ESPECIALLY at low speeds. Better atomization means more fuel economy, better emissions, easier cold-starting etecetera.

The ideal conditions for making power is not a fuel that is completely vaporized before it reaches the chamber - that would make volumetric efficiency drop like a stone and power would fall with it. This is why a carb can compete with fuel injection for top-end power BUT it never can in terms of driveability, "tunability," economy, etcetera.  

Well more ppl are bulding high powered street cars with carbureted V-8's that are getting just as well economy as newer cars with E.F.I. Automakers have started putting variable valve-timing and displacement on demand to increase economy on newer cars, and their estimated EPA MPG aren't much better than what a well balanced V8 can produce with a 4 speed manual, or auto tranny. EPA measures fuel consumption based on to types of things, first they simulate driving in both city and highway on a dynometer for 10 miles for each test. Second they measure emmisions to get an idea of how much fuel is actually consumed by the engine. I saw a Hybrid GMC Envoy on a Chevy dealership that was rated for 20 MPG city and 20 MPG highway. A HYBRID!!!!! Wow looks like the 19 overall MPG I get outta my "stone aged" Carbueted 267, doesn't even compare. There is a difference here too. The Envoy has the "Hybrid Junk"....err I mean tchnology, and a 6 speed automatic transmission with lock-up torque converter. I have a THM-350 with only 3 gears, and non-locking torque converter. Technology does help, I will not argue that, but you can do with mechanical devices the exact same thing you can do with electronics. I don't care what your engine runs on for fuel or induction. Power is generated by flow and atomization, which is consistent with laws of physics, period. A carb can mix fuel just as well as EFI. EFI in theory, would be more conisistent, as it runs on a program. Carbs can run consistent, if the owner makes the adjustments for the environmental conditions. This requires keen observation of vehicle peformance and troubleshooting experience. I have always owned EFI vehicles, and I now onw my FIRST carbueted engine. I"d rather have the carb. It gives me the flexibililty of making minor adjustments whenever I need to, rather than relying on my ECM to adjust everything without burning out. FYI Now that I work in a salvage yard again, I should let you all know, alot of newer vehicles(post 1994) have problems with the ECMs burning out. See another law of physics here, heat. Electronics generate alot of heat, and if they do not dissapate that heat, just like an engine, they will burn up. EFI has better consistency, and less durability. Does anyone remeber a fuel pump for a SBC costing 200 bucks from AutoZone, or NAPA? If you can get one for a car with EFI for less, you got a steal on it.  

Fiero,

 You cite the new car EFI mileage vs Carb milage, what you are not taking into account at all is the tail pipe emissions. OEMs can't run full timing or as lean as the engines are capable of due to tail pipe emissions (Particularly NOx).  You can't tell me or prove for that matter any of those carb'ed car will pass a tail pipe test as clean (Low HC, Low NOx, etc) as a newer EFI.  I've hand built a Megasquirt ECU, when I want to make adjustments I simply plug my laptop into it and punch a few buttons and I'm good to go.  Once I have it dialed in though I should never have to touch it as it has an O2 and dual MAP sensor to make changes I've dictated automatically with air pressure and temperature.  Take any OEM ecu and re-tune it (like with HyperTech, etc) to ignore the tail pipe emissions and you can get 5+mpg more right off the bat.  

Are you listening to yourself? You're trying to tell me that average joe with his 30 year old carbureted 350 with a TH350 in some camaro is getting the same gas mileage as a vehicle just off of the production line - I don't think so, really, how ignorant are you?

Power is not directly dependent to how well you atomize the fuel - you go build a few race engines with this in mind and you won't be winning any races.  

My basicly stock 4400 pound 95 caprice wagon with the 5.7 lt-1 engine gets 21 mpg doing 75 on the highway. It has a 2.56 axle, but still runs 85 mph ( 16's) at the track on warm days. If I changed to smaller tires I could probably go faster through the quarter and put the tall tires back on for every day driving. Only mods are a cut out airbox, hocky puck, dynomax super turbo mufflers ands coolant bypass. I want to tune it to advance the timing to run on 91 octane ( 10+ more H.P. with 160 stat) and delete the speed limiter just in case some nut is chasing me ( it has happened once before)  

Yeah, Fiero's comments are wrong on a number of issues...and comparing to today's cars forgets one VERY important thing...

Today's cars tend to be heavy.  My Cutlass, from the factory, weighed in around 35-3600 lbs...the new Camaro, which is considerably smaller, weighs in at 37-3800lbs.  Old cars didn't have all the safety or emissions crap...didn't have all the electronics, the gadgets, the sound deadening, etc, etc.  

But in no way is a carburetor going to out-perform EFI in fuel efficiency...not even a quadrajet.  

As far as emissions goes, who cares? I read an article in the newspaper one time where the EPA, said that you cannot increase MPG by putting high performance air cleaners in, like a K&N, or from cutting off the catylitic converter. This would increase emission and increase fuel consumption. That is a load of bull. I had a 1993 Pontiac Grand Am, with a 2.3 SOHC Quad 4, with no catylist, and opened the airbox with a K&N. It turned 17.8 at the strip(V-6's with auto, stock, turn 17.4). I avg 35 MPG in the city. I managed anywhere from 440-520 miles per 15.2 combined city and highway. Now according to you guys and EPA, my emissions would be higher and therefore I'd be using more gas. So shouldn't I have lost MPG from the 26 I was getting stock???? Looks to me like the engine was making power more efficiently, if I was able to get more MPG. I alos romped that thing all the time, even tried to race BMW's and Mercedes with it. If emissions are so deadly then write your lawmakers and tell them to stop testing nuclear bombs and building reactors. I'm completely, sarcastically, assured that H-bombs have NO impact on the O-zone layer whatsoever.

Next race engine aren't very efficient at producing power. All they produce is high amounts of flow, fuel consumption to make power. Most race engine aren't very efficient, if they get driven on the street. I haven't seen many 9 second cars getting more than 12 MPG, if they CAN run on pump gas. I never once stated anywhere about building race engines. My initial post here, and following are comments/opinions on how to make an "EFFICIENT" street engine. There are many ways to do things to an engine, to make efficient power. The more fuel you burn, with proper air/fuel ratio will generate more torque(power). You can do other things as well, roller rockers/cams, full engine balancing, 3 angle valve jobs, pocket ported heads, higher compression ratio, removing catylists, open intakes, and less resistent air filters. All of these can make and engine more powerful on the street where you need it, low to mid RPMs. Also since they increase flow over stock, they'll increase High RPM performance slightly. All these things help reduce engine load on bearings, and air fuel flow. When done right they can improve atomization to. Carb adjustments, proper timing can help burn more fuel. This is where AIR pumps came from. They pump atomosphereic air into the exhuast to help burn up some of the unburned fuel, to reduce emissions. Wasted fuel increases emissions far worse than burned fuel, without catylists. Torque(power) is generated by burning fuel and pushing the pistons downward.

Asmuch as I hate fart can mufflered cars, I'd like to state that import automakers make very efficient STOCK engines and with their caytlists, and emissions control devices, are why they are ULEV vehicles. In simple terms, a Honda Accord with 125 HP wastes less fuel, than a stock ECOTECH 2.2L Cobalt. The Cobalt has more HP, but has higher emmisions from wasted fuel. I haven't seen the BIG 3 put out many ULEVs compared to imports. Heck a Ford Mustang with a 302 V-8, has 8 catylitic converters from the factory, on the 1995-to 1997 models. They have 6 O2 sensors between them. Not only do they only have like 260 HP, but they avg 12 MPG city, and 21 Highway. To me, that is a powerplant that wastes fuel. Cut off those catylists, throw away the EFI and ECM, slap on a well-tuned carb, and true duals. Not only will you get better MPG, but you'll see more power, and surprisingly not much higher emissions. That Mustang is a prime example of how well technology benefits economy from EFI. I'd much rather have 12 MPG with 260 HP, than say 18-20 MPG with 392 HP(CarCrafts build) and a Carb.

Lastly I could careless about RAT engines and full blown race engines. If you cannot drive it daily on the street, the vehicle doesn't serve the purpose it was designed for. Race engines waste fuel, simply put, they flow so fast, that air/fuel do not have time to mix properly. This is why a drag car uses 5 gallons of fuel to run a 6 sec qtr mile. At $6 a gallon for race fuel, I would want to make as much power as possible with as little fuel consumption as possible there too.  

The EPA is correct about those things.  A CLEAN paper air filter will flow about as well as a K&N.  Changing the airbox is an entirely different thing.  And the catalytic converter is hardly the dominant restriction on a stock exhaust system.

EFI will always get better mileage than a carb because it atomizes the fuel better.  EFI can run at leaner A/F ratios than a carb can, meaning better mileage.  Thats a fact that cannot be disputed.  EFI also optimizes that A/F ratio regardless of weather (including atmospheric pressure, humidity, temperature, etc), altitude, or operating conditions.

You are also confusing mileage with emissions.  Emissions are the products of combustion.  Perfect combustion yields carbon dioxide and water.  Car engines do not produce perfect combustion so you get NOx, carbon monoxide, and a host of other byproducts of the combustion.  That stuff is emissions...that is the stuff that the catalytic converter, AIR system, EGR, and a ton of other emissions equipment are designed to reduce or eliminate.  Fuel mileage is just that...how much fuel you use over a given distance.

Pretty much every point you are trying to make is completely wrong...and shows a complete lack of understanding in how this stuff works.  

Another point...nuclear reactors emit steam...that is it.  They are the ultimate form of clean energy.  The ONLY issue is putting the waste somewhere for it to decay (everything on the planet is radioactive...this stuff does not hurt the environment if stored properly).  Also, the US hasn't tested a nuclear bomb above ground in 50 or so years.

So stop...go read up on this stuff, see how it ACTUALLY works...then come back.  

Fiero,

CSIROC is right, you are waaaaaay off in your thinking.  There is more to bad emissions than pumping unburnt fuel out the tail pipe. As CSIROC stated there are a number of other gases that come out from combustion that the OEM's have to content with by law. You may not give a dang about them, but by law the OEM's do, and to mitigate them they have to De-tune the engines, pull some timing and add fuel to lower combustion temperatures and lower unwanted tail pipe emissions.