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Jimidan
Posted on Wednesday, March 14, 2007 - 09:55 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

After spending nearly over $450 on gas to go from KY to Daytona and back in my 350 C.I. van, I started thinking of ways to increase its gas mileage. I changed out the mechanical fan for an electric one and picked up a couple of MPG.

I was also considering converting it to a 2 barrel carb. I can probably pick up a used carb/intake at a junk yard, as buying them new would cost around $700 (estimate provided by Pep Boys).

Would this conversion really help that much? I very rarely get into the back two barrels on the carb I have now (which came on the original 305 and is 25 years old-and has been rebuilt a few times). I was comparing an Edelbrock 300-500 cfm 2-bbl. carb to my carb, and it seems bigger than front two barrels on my carb. So would it really save me much? I would think that the more modern carb would be more efficient, but is that true? Have carbs really changed that much in 25 years?

The 350 that is in the van now has about 100,000 miles on it but burns very little oil and seems in good shape. I really like my van and would like to keep it, even though I know I could down size and get more mileage. Buying a new van would be way too expensive for the amount of use it would get. We use it for major trips and some around town hauling of large items and towing my bike trailer. Most of the time it sits in the drive, as I have another daily driver and motorcycles.

Thanks,
Jimidan
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Bomber
Posted on Wednesday, March 14, 2007 - 10:00 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

jimi -- if you don't get into the secondaries very often (I assume vacuum operated), a shift to a 2bbl carb won't get ya much, unless it's a MUCH smaller carb (cfi, measured using gthe primaries of the 4 bbl and the entire 2 bbl) -- in that case, your milage MAY increase a measureable amount, but you'd also be loosing power

my guess is that it would take a lot of miles to pay for the conversion
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Spiderman
Posted on Wednesday, March 14, 2007 - 10:08 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

You can get a 4bbl to 2bbl adapter plate so you do not have to buy a new manifold.

BUT
Like Bomber said above.

If you really wanna see an improvement do a re-build even if she doesn't burn oil there is 100k miles of crud on those pistons and in the chambers.

Do a port job on the heads so you get a little more efficientcey. Don't do a stage three or anything, just enough to breath better.

Put some headers on it with a decent exhaust and you should see a increase in your MPG.

A more efficient engine burns less fuel...
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Chasespeed
Posted on Wednesday, March 14, 2007 - 10:14 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Okay, is that a stock/factory 4bbl?

If so, its a Q-jet, which, though alot of people hate to rebuild them, they are a reliable carb..

If its a q-jet, you might as well leave it alone..

Ever driven a 350 with a 2 bbl? Not pleasant, most 2 bbl's just dont flow enough to feed that hungry motor, so, it wont rev up under a load etc...

Anyway, if you have an aftermarket carb, you MIGHT want to consider finding a edlebrock/carter/holley vacuum secondary carb.

But, you are also looking at a nice chunk of change for a new carb.

The best thing I can think of, is...

the obvious things, make sure everything is up to snuff...

CHECK YOUR TIMING ADN ADVANCE......

from there, do a few things to make it breathe better, the less the engine has to work pulling fuel and air, and expelling exhuast, the better off...

Might also want to look into your gearing.

do you just keep the van on the highway?

Or is it mostly around town?

ALSO, try some SeaFoam first... PERSONALLY, I would save the rebuild as a last resort, there are ways of cleaning things out...

And to TRULY make that engine more effecient through a rebuild, it would need to be ballanced and blueprinted.....

Chase

(Message edited by chasespeed on March 14, 2007)
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Djkaplan
Posted on Wednesday, March 14, 2007 - 10:37 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

If you stay out of the secondary, you essentially already have a 2-bbl carb. Quadrajets are pretty sophisticated carburetors, too. I think you'd have better luck at optimizing fuel mileage by making sure the ignition is dialed in and possibley recalibrating the jetting. Running too lean can hurt mileage by making you get into the accelerator pump all the time. Typically in late model carb applications, the jetting and ignition timing are compromised by factory EPA settings. I'm not saying you need to disconnect any emissions equipment, just optimize what you've got. Run as much vacuum advance as the engine can handle, mabye get a calibration kit for the carb from Edlebrock (it's excellent btw, it comes with lots of hangers, rods, jets and a great booklet with air/fuel charts of the different combinations).

It has been my experience that 2-bbls don't necessarily equal an increase in mileage unless your vehicle has a pretty high rear gear ratio. Lots of gear with the small primaries of a 4-bbl will give you a significant drop in manifold vacuum, whereas a 2-bbl with larger throat diameters just needs to have the throttles barely cracked and the carb stays closer to the idle circuit than a 4-bbl would.

I kind of doubt your van has a high enough rear gear to take advantage of that.
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Djkaplan
Posted on Wednesday, March 14, 2007 - 10:49 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Rebuild that Quad, too. If it's an electronic one, you might want to convert it to an earlier model with vacuum operated APT rods. This gives you another parameter to fiddle with (and possibly make worse, of course).

It doesn't make any difference in mileage, but also make sure you set the secondary air-valve properly. The first time you gas it to pass on the highway, you'll be glad you did... ecstatic maybe.
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T9r
Posted on Wednesday, March 14, 2007 - 10:51 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Changing out the differential gear can help, with fuel economy depending on what gearing you have in it now.

Get away from the carb. and go fuel injection, or throttle body injection. Yes, you'd have to pick up a new intake manifold, throttle body and injection, possibly fuel pump/pressure regulator, computer and wiring but if your talking Chevy, it might be easier to find.
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Justin_case
Posted on Wednesday, March 14, 2007 - 11:02 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

After market port fuel injection. My brother-in-law's 400+ HP '07 Vette gets 25 MPG .Unreal.
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Xl1200r
Posted on Wednesday, March 14, 2007 - 11:11 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Get away from the carb. and go fuel injection, or throttle body injection. Yes, you'd have to pick up a new intake manifold, throttle body and injection, possibly fuel pump/pressure regulator, computer and wiring but if your talking Chevy, it might be easier to find.

I would not recommend this. The intake gasket angle on the heads of a fuel injected engine are different, meaning you would need to get a new intake, new heads AND all the EFI stuff. There may be adapter plates out there for this, but you're going to give up quite a bit of effeciency doing it.

On top of that, the TBI system used on the Chevy trucks is not terribly effecient and I don't think you'd see a measurable increase in mileage.

Has anyone though to ask what kind of mileage you're getting now? How heavy is the van (1/2 ton, 3/4 ton, etc.)? If you're getting 12mpg on the highway, then I'd say something can be done. If you're getting 20, I'd say count your blessings and forget about it.

Going off assumptions, I'd tell you to stick with the Q-jet. People bitch and moan about them, but the bottom line is they're an excellent carb, with only one little think that makes them a pain in the to rebuild. I think the Q-jet is probably the best and most cost-effective street carb out there, even today.

An Edelbrock carb is essentially the same thing, but they moved the gasket higher so they are less likely to leak. I do not like Hollys for street applications. It seems anytime you hit a bump the settings go all out of whack.

And as has been saod before, a typical 2bbl is going to be a higher cfm than the primaries on your 4bbl.
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Firemanjim
Posted on Wednesday, March 14, 2007 - 11:15 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

No way that a 2 bbl can equal mileage on a properly working Q-jet. Just turn one over and look at the size of the primaries---tiny compared to a 2 bbl carb.They were designed to be miserly and still get good performance when called upon(mashing the throttle)A good tune-up with carb rebuild should help,but really,a van was designed to haul stuff so probably has low gears in rearend.And it is not very aerodynamic so mileage suffers here,too.Not a commuter.
Buy a little beater,they are out there cheap.Look on Craig's List.30 mpg from a Civic or Tercel will save the purchase price pretty quickly.
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Etennuly
Posted on Wednesday, March 14, 2007 - 11:32 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

I have had many of those aero-pig full size Chev vans. You are pushing a large square box through the air.

I had a G20, 3.55 gears with a straight six, 9 MPG. a little torque no speed.

A G20, 2.76 gears, 305 TBI, 14 MPG. no torque WFO to do 75 MPH.

A G20, 3.08 gears 350, 4 bbl, 12 MPG. OK torque, had to run hard for speed.


A G20 3.08 gears 400, 2 bbl(dual jet), 14 MPG. Big torque, ran easy at speed, pull big things.(kind of like a Ulysses)

If you want fuel economy with the 350 drive with the wind with a large sail on top. Or try running at 55 MPH for a while. Run standard height tires and go narrower for less rolling resistance and keep your air pressure at max for the tire. Accelerate easy, cruise lightly with the right foot, use down hills to your advantage to get a run on the up hills. Don't use cruise control, feel how much throttle you need to use on hills and against the wind, draft other vehicles as much as possible(at a safe distance). Try moving up a grade on gas.
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Chasespeed
Posted on Wednesday, March 14, 2007 - 11:51 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

In other words, give it a good tune up, rebuilt the Q-jet, and LOWER the van, chop the top...6 inches.............

Seriously, the TBI, while being simple, and relatively easy to swap, is probably more effort than it will EVER be worth...


Holley makes a bolt on system for carb'd intakes...

Another thing, IF you decide to go into the motor, snag a set of Vortec heads from a boneyard.... re-furbish them(at the least new valve seals).. and get a Edlebrock intake to match those heads...

Those heads are great bolt on iron heads, great swirl, etc

Anyway....

Time to hit the gym...

Chase
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Strato9r
Posted on Wednesday, March 14, 2007 - 12:20 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

A properly tuned Q-jet is going to work better than a 2 barrel. Make sure the welch plugs in the bottom of the main body arent leaking. Then concentrate on making sure the distributor is working properly; a stuck mechanical or vaccuum advance can really mess things up. A free flowing exhaust will help, and as strange as it might seem, so will going to a shorter (higher numerical) gear ratio.
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Djkaplan
Posted on Wednesday, March 14, 2007 - 12:55 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

I did not realize there were so many Q-jet men here.

"I do not like Hollys for street applications."

Neither do I. Unless the only thing important is to go WOT, a Q-jet is going to be better than a Holley in just about any street application... if you know what you're doing. Anyone who ever complained about "Quadrabog" didn't have a clue.
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Chasespeed
Posted on Wednesday, March 14, 2007 - 02:10 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

I personally love q-jets...

If anyone plays offroad, especially rockcrawlin, these carbs are the SHIT.. I love them...

I can remember being handed a q-jet back when I was a kid, (had a bad body), and a bunch of old needles... and being told...

"Dont bother me until you can tear it down, and reuild it with your eyes closed.. AND WITHOUT BEND ANY NEEDLES or boogering the seats..."

hahaha

Needless to say... my dad wasnt bothered for quite a while.. I was maybe...12

And Holley's???

I will leave that alone...

Chase
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Etennuly
Posted on Wednesday, March 14, 2007 - 03:17 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

I used to race dirt ovals with Q-Jets, they could be tuned to work really well and my salvage yard sponsors had tons of them.
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Cochise
Posted on Wednesday, March 14, 2007 - 05:50 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Holley SUCKS! I had a Quadra-Junk on my '67 Chevelle SS, set it once and pretty much leave it alone. I have a Holley on my '70 Chevy C-10 and I hate it. I want an Edelbrock. Anybody want to trade?

On the 2 barrel thing, I had a buddy that gave his daughter a GTO and he put a block of wood where the rod for the accelerator comes back so the rod would hit the wood and the secondaries wouldn't open.
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Jimidan
Posted on Wednesday, March 14, 2007 - 06:07 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Thanks for all of your ideas and insights.

It looks like a little more info is needed here:

The van is a 1982 Chevey G20, that weighs 6000 lbs empty (actual).

The sticker that is still on the underside of the hood says that the rear axle is the "standard". It will cruise 60 mph on flat ground with just a little pressure on the accelerator, barely pushing it down. I have pulled a 21' cuddy cabin Starcraft boat in the hills of KY with it effortlessly. Power has never been the problem.

The 12.5 MPG was taken over several tanks coming out of FL, GA on I-95, I-10, and I-75, cruising as economically as I could (drafting big trucks where possible) at 55-60 MPH. It got worse in TN and KY, but not much as I really wasn't pushing it.

The carb is the original Rochester 4MV Quad that came on the original 5.0 V8, and was used with the new GM 350 that was purchased in 1999 from the factory. When we put it in, we lost the knock sensor, air pump, most of the superfluous vacuum hoses, the stock air cleaner (replaced with K&N), the stock exhaust (replaced with twin free-flowing mufflers and cross-over pipe), and cruise control...I honestly cannot say what happened to these components as they just disappeared out of the garage during the interim.

So the engine is pretty free-flowing as it is, and has oodles of power...the sum'bitch will get up and romp if you put your foot into it...at a significant $$$ penalty BTW. The shorty exhausts exit right in front of the rear wheels, so there isn't much restriction there...it sounds like a freakin' cigarette boat!

I have actually been looking at some used TBI's off of Cameros and Firebirds like this:

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?Vi ewItem&ih=005&sspagename=STRK%3AMEWA%3AIT&viewitem =&item=150100860252&rd=1&rd=1

They should fit the heads on my 1999 350, I think. These TBIs have two injectors and support 250 HP, according to the seller. My 350 with carb is only supposed to be 210 HP, according to GM when I bought it. It sounds like a good idea, if I could figure out the wiring and how to incorporate it into my van's harness.

What do you think? FI has to be better as it can lean itself out while the jets are still pumping gas at high load levels.

This isn't my daily driver, as I have a Mitsubishi 3000GT for that, which gets great mileage and will romp to boot. This vehicle spends most if its time shading concrete oil stains, but it is very handy to travel in, and with enough folks to pitch in, gets very economical. We took it to Utah on a raft trip with 6 folks and their gear and boats on top not too long ago, and it worked great. But draggin my tired butt to Daytona with the Buell in tow is another thing.

What do you think?

jimidan
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Mikej
Posted on Wednesday, March 14, 2007 - 06:55 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Funny, I used to run a 650 Holley on a '67 Chevelle 396 and it never gave me a bit of trouble. Kind of like a Buell, some like them, some don't, some have problems with them, some don't. Oh well.

Probably about the only way you'll get better mileage is to get a different rig. I'm guessing you'll be able to get it up into the 15-16mpg range playing with stuff and settings, but beyond that you might have to upgrade, or get into cam swaps and such.
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Etennuly
Posted on Wednesday, March 14, 2007 - 06:58 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

It sounds totally normal comparing it to the ones that I have had.

The injection is usually better for fuel mileage. The only way to properly retrofit a used one is to swap-out the entire wiring harness, computer, sensors, etc. The computer needs info from all of its sensors to make the injectors, timing, and such work in harmony.

I 've done it a couple of times, and I'm doing one now on a Corsica '94 to '95 engine and trans swap, harness, computer and all.

I say get more people to chip in and leave the dinosaur alone. If you spend all of the time and money to make it happen you might gain one or two MPG and it would take years to recover the economic savings you are looking for.
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Hughlysses
Posted on Wednesday, March 14, 2007 - 07:27 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Jim,

It seems to mean your main impediments to good gas mileage with that thing are (a) aerodynamics (it's a big brick) and (b) weight. Can you get a front air dam for it? That might improve the aerodynamics marginally. I doubt you can do much about the weight unless you want to build a full carbon fiber body for it..

One thing I can think of that hasn't been suggested is to change to synthetic fluids (engine, tranny, and rear end) if you're not running them already. That might be worth 2 or 3 MPG, but switching to synthetic in a 100k motor is a little risky if the seals are at all questionable.

Finally, one easy thing that can help you identify what helps your mileage is to install a vacuum gage. They used to be pretty popular as "fuel economy" gages. For a given speed/grade, the higher the vacuum, the less your engine is working so the better the gas mileage. For instance, when you're drafting an 18 wheeler, a vacuum gage would help you find the "sweet spot" behind the truck where drag is least.
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Vegasbueller
Posted on Wednesday, March 14, 2007 - 09:46 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

I used to run Q-jets on an oval track car and loved them. That was until I bought an electric choke Edelbrock for my street hot rod. I put the Edelbrock on a 350 punched .060 over, w/292 cam and flat top pistons, etc and LOVED it. It never gave me an ounce of trouble and got superb mileage even pushing a 78 Olds Cutlass down the road.

Nick
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Gearhead
Posted on Wednesday, March 14, 2007 - 10:12 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

As many have mentioned above the Q-jet is an excellent street, mileage carb.

The TBI conversion is relatively simple, especially if you have a complete donor vehicle. There are several aftermarket companies that supply stand alone harnesses for this conversion as well, Howell, is one of the best. If you're going to this much work/trouble I'd recommend a Tuned Port injection instead as it was the next generation injection after the TBI. The TBI was used for trucks while the TPI was used on cars. Guys I know who converted their TBI trucks to TPI have been very happy with the switch.

TPI complete set-ups are easily found on ebay and there is a lot of info out there on this conversion since it was very common on street rods a few years back.

I have a TPI waiting for my next hot rod project but my current builder, a '62 Chevy Biscayne, 400 SB, 4-speed has a Q-Jet!
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Djkaplan
Posted on Thursday, March 15, 2007 - 09:13 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Does your distributor have a vacuum diaphragm on it or is it an electronic distributor? If you tossed the knock sensor and kept the electronic distributor, you lost the electronic advance for high vacuum, low-load conditions (highways).

Sounds like your timing is way off (retarded) for cruising conditions. What's the deal with the distributor?

Also, make sure the heat riser in the intake manifold hasn't been blocked off - carb heat (and hotter intake temps) are good for mileage. Blocking the riser is an old hotrodders trick that really isn't good for a daily driver.
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Rick_a
Posted on Saturday, March 17, 2007 - 12:00 am:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

The best way is to keep everything in a good state of tune then tune it on a dyno. Try all you might, but you have to be damn good and a bit lucky to get a good proper a/f across the board on a car. I don't understand why it's so common for people to dyno tune bikes but not cars. A good 4-barrel spread bore carb (small primaries and larger secondaries) is the best compromise there is in carburetors.
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Jimidan
Posted on Tuesday, March 20, 2007 - 03:30 pm:   Edit Post Delete Post View Post/Check IP Print Post    Move Post (Custodian/Admin Only)

Thanks for all of your suggestions. I will check out the distributor, timing and also TPI systems.

Like I said, I really would like ot keep the van as I have sunk $3500 in it recently for a body restoration. It looks pretty sharp too. It has a rebuilt T350 tranny, and new starter, alt, water pump, belts, hoses, etc., and it drives great.

jimidan
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