Let's discuss building a carburated truck for fuel economy

[zieg85]

I am about to start, believe it or not, to put together my long put off 86 C10.  I have some obstacles to contend with but I am OK with that.  First of all I have to go through emission testing which consists of a visual inspection of the presence of a catalytic convertor, a gas cap check and a run on the sniffer run through a simulated drive.  My truck originally came with a 4.3L 4bbl and 3 speed stick.  I have a 5.7L and the dual air pump set up from a 1986 C20 with factory dual exhaust with no cats.  I have 2 brand new 3" cats I will put in.  I am going to attempt to use the carb off the 4.3L but fear the jets will need to be changed.  I have a 2 to 4 barrel carb adapter and a clean early 70's rochester 2 barrel I could also try.  Skinny tires and properly geared truck is the key for gas mileage but more than that is how efficient the engine runs. 

Take my 85 C20 7.4L 4 speed with a 3.21 gear.  It has the stock size LT235/85/16 and I could get 16 mpg.  This truck is completely untouched and still retains all the emission controls including dual air pumps.  The truck takes very little gas to get it going and shifting into hi by 35 mph, never lugging it.

This 86 C10 has 2.73 gears and my goal is to pass emissions and top the 20 mpg mark. 

[Stewart G Griffin]

OMG!  i love this topic.   i don't have time right now to get into it whole-hog, but for the meantime some of my thoughts are:

1) Easiest/cheapest way to get over 20mpg with one of these trucks is to find a 6.2 diesel truck.  Yes, i know you said carburetor, but this is one of my answers.        In fact, i would/should do it, but i love my truck too much to switch right now.

2) HIgh-compression with water injection---maybe 14 to 1.   We/i would need to do more research.

Is the truck going to be used mostly for transportation and occasional hauling?  Or will it be hauling frequently?
3) If only occasionally, move down on cubes.    i've just gotten a nice 4.3 v-6, carbed which i haven't gotten around to tinkering with yet, but will.   And this engine will probably end up in the truck, soon.

4) Consider an LS swap, using carb.

5) i think big gains can be made----with AERODYNAMICS.  i know i keep saying i am going to start, but this time i really will.

Based on my limited "testing," using that 2G carb will probably not net much, if any mpg improvement over the quadrajet.   If you look at my MPG thread, i'm getting about the same overall mpg with the 305 2G combo as i did the 350 quadrajet combo.  If anything, i think the quadrajet would be the better bet as it is more advanced.   i just prefer the 2G right now because it's simpler.

P.S. why not leave the 4.3 jets in there for now----try to go as lean as possible?

[zieg85]

For some reason I thought you would be the first to respond Stewart.  The 4.3L although it runs great has a major oil burning issue and the block is cracked where the starter mounts so it is junk.  It took a lot of pedal to keep it going so I am thinking it would be worse in MPG than a V-8 that is running well.  I know Diesels are the way to go however I am going to work with what I already have sitting in storage a 5.7L out of a Suburban which really ran well when I drove it home.  I plan to try the 4.3L carb but have at least a dozen q-jets to play with.  Biggest concern as I have already stated was to pass emissions so I can actually legally register it and start driving it.  I am going to lower it some but still want to retain the trucks use.  If it sees a trailer it will be a lightweight snowmobile trailer used for hauling garden tractors as that is my other hobby.

[Irish_Alley]

dont know about where you live zieg or if you looked into it but around here with emissions. if your truck came with a 4.3 they will test its emissions for a 4.3 no matter what engine is in it and we all know a 350 will have higher emissions over a 4.3. so this increase could make you fail

[VileZambonie]

Why not slap a tbi on it?

[zieg85]

Why not slap a tbi on it?

I may end up having to if I can't pass emissions but right now I am trying to work with what I already have.  I've only had one TBI truck and never needed to work on it so I really don't understand it or know what it would take to "slap" it in...

[VileZambonie]

It's pretty straight forward but trying to get good tailpipe emissions and fuel economy out of one of these dinosaurs with a carburetor just doesn't sound like it will meet your goals. Even a factory tbi system is an easy affordable retrofit. You should give it some thought.

[Stewart G Griffin]

Even i'm thinking about going tbi and i don't like computers on cars.   Because tbi just runs too good.  Easy starting, MPG will probably be a little better etc.

If i were going to do it, i would contact howell.  They make it easy:
http://howellefi.com/

[Irish_Alley]

i understand what you guys are saying and i dont mind a tbi but  others have said they hate them. just because theres more to go wrong. i like the ideal of a fi intake on out motors but its way out of my price

[nlauffer]

I say take it a piece at a time and try to maximize efficiency with each part.  Like switching spark plugs to those E3, which have been proven to improve emissions testing.

I do think that the 350 and 4 barrel will be better than the 4.3 or 2 barrel.  With the wait of the truck the 350 will have to work less.

Something to look at pretty close would be the heads.  There might be a lot of improvement there.  Just like improving power in regards to the heads, some of the same improvements could net an improvement in emissions. 

Just think of improving efficiency on each part to achieve overall better drivability and efficiency.  And stay within your constraints (carb vs TBI) and just understand there is only so far you can get without changing parts all together.

I don't know much about it, but I had a buddy put a homemade system on his little 4 cylinder Nissan pickup and Dodge Durango.  For the life of me I can't remember what it was, but it used water, something else, and electricity to produce a gas and injected it into the intake.  He claimed huge improvements in fuel mileage. 

HYDROGEN, I just remembered.  But I don't know much about the pro's and con's.