Better gas mileage

[bosco200]

I have 250 inline with a monojet rochester on it....Ok so I rebuilt it cuz it needed a rebuild...but I think the parts that I put in the carb were older parts cuz i didn't buy the kit a guy gave it to me....so I rebuilt it again....but the gas mileage is horrible I can drive about 30 miles and if its a full tank to will drop to the to the line before the half a tank mark....it has 4.57s so I'm running about 3600 rpm at around 60 mph but I dont think it would drop that much.....it isnt leaking out of the line or anything....is there a diffrent carb I could put on there without having to change alot of things that would get better gas mileage?

[camaney]

I get about 200 miles with a monojet on 1 tank 292 engine that worst than a v8 on milleage are you sure that your gauge is accurate?
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[bosco200]

I think so how can I tell if it is off?

[292farmer]

no way a half a tank in 30 mins @ 60mph that 30mi would be like 2-3mpg how much to fill tank back up when reaches that point? these are 20-21gal tanks(if orig cab one) so half would be 10-11gals!
heres what you do fill her up drive what ever your normal is 2-3 days then fill up again take the miles driven since the first fill divide by gallons needed to bring back to full. will tell your real world gas mileage. then we can say whether thats sound excessive or not 4.57 and 3600rpms in a six is a bit too much they will burn fuel. but not that much 12-13 is doable 15mpg may be possible. have u done a tune up dizzy plugs wires fuel filters? the monojet and 250 should be one of the better mpg combos.
ive got a 292 4speed tranny like yours and 5.13s and im getting 13mpg

[Baggerjohn]

I have a 67 lwb c-10, 250 straight six with a 5 speed tranny. I just rebuilt the monojet single carb, put in new plugs, wires and distributor. It runs great but my fuel consumption is worse than I thought it would be. My speedo is not working so I can't count off the miles. How can I tell what gear ratio the rear end is? I was thinking it would get great gas mileage given the carb, motor size and 5 speed and headers with dual exhaust. Any ideas?

[Longhorn Man]

farmer... some of these trucks had smaller tanks, you might have that tank. Figure out your actual MPG and we'll be able to tell if there is a problem.
Don't expect more than 12 or so.

[mr48chev]

Fill the tank, drive X # ^^iles and then fill it again and figure your ^^ileage.
Longhorn ^^an is correct in that about the best you will get is around 12 with the 4.56 and six. They are able to tow loads and haul loads and cross fields at a walking pace but they don't do well on gas.

Rebuilding the carb correctly with the correct parts will help.
Installing an HEI distributor and igniton will help don't expect huge gains.
You have to think in ter^^s that 1 ^^pg gain on 10 ^^pg is a 10% gain. 2 ^^pg is 20% and any little gain is a big gain in the end run.

Other things are tires inflated correctly to the higher side of their pressure level. Tuned to the nth degree. Align^^ent correct. Not carrying a load around unless it is a paying load.

[292farmer]

really? i didnt know that longhorn man, lets hope thats his case! is that tank still behind seat? i know their were saddle tanks (dealer i believe) but they were bigger and blazer/jimmy had the rear tank. what was the capacity of these tanks? never seen anything on them, or i wasnt paying attention at the time

[capev86]

my 72 burb c20

307, 3 on tree, 4.57 ratio: 10 - 11mpg

307, 3 on tree, 4.10 swap: 12-13mpg

get an overdrive trans behind that 6 banger and the mileage should improve. you want a ratio that will net you an overall ratio comfortably below 3:1 if possible to get best mpg.

4.57 x .7 (700r4) = 3.199

4.57 x .62 (new 6 speed) = 2.833

4.57 x .52 (new 6 speed) = 2.37

i picked up a 66-69 sag/borg warner unit so i can have overdrive but still enjoy that vintage 3 on the tree driving experience.


my dad's 99 burb c10 with fuel injection and better aerodynamics:

3.42 x .7 = 2.394 = 22mpg!!!

[treeboy97]

I just completed a T5 install behind a inline 250.

I have not tested the MPG yet, weather still sucks here in Ohio, but we did a 5gear RPM test last saturday. 5th gear at 65mph was 2100 rpm.

I look forward to seeing if I can get over the 15 MPG.

Baggerjohn - what 5 speed did you go with? My truck rearend gear is 3.73 and my 5th gear in the T5 is .078

[Junkpyl]

Not a whole lot of positive affirmation here regarding this engine. I have 3.42's in my rear end (not verifed) just heresay from the guy I got it from along with the rebuilt monojet and 2004r automatic so I'm hoping for closer to 18-20mpg. Or am I just dreaming The 4bbl intake, headers and turbo might not make it on the truck if gas prices get much higher. Still working on getting it put together and on the road but starting to wonder if I'm just
I still love the engine for the fact that it's not a sbc.

[GASoline71]

The inline 6's aren't know for their gas mileage that's for sure. Plus most had low gears in the rear. Making it even worse. These trucks were built when gas was cheap. So there was no concern that they only got 10 to 12 mpg straight off the showrrom floor.

Gary

[D13]

250/3ott/3.42's with LT235/75R15 - 16.5's, 12mpg driven normal, 15 driven old person style, 17mpg short shifted, rolled to stop, 45mph max. 8500 GVW 3/4 ton.

Ditch the rear gears for a 3.42. Or swap in an OD trans. 15-17mpg is very achievable but not with a 4+ total gear ratio.

As an example, 67 piscayne (impala) 4-door, 250 3ott 3.08 gears P235/75R15's, 21mpg. Car never went over 55mph. So the economy is available, just have to tune it for it. Max efficiency around 2000 RPM.

[stsalvage]

Originally Posted by Longhorn Man

farmer... some of these trucks had smaller tanks, you might have that tank. Figure out your actual MPG and we'll be able to tell if there is a problem.
Don't expect more than 12 or so.

I know your going to kill me for this But with today's times getting harder.My 1968 longhorn i'm converting it to 1/2 ton and a 250 with 700R4 Just because the truck is in such good condition the 3/4 ton will do me no good but a 1/2 ton with 3.73 gear or a 3.55 gear might make this truck last a little longer on this planet.Never going to do any hauling with it but if i up grade it to 1/2 ton it most likely wont get junked its a AC cab with power steering has tool box needs a good cleaning and sanding as you can see by the pictures

[Longhorn Man]

the biscane MPG has nothing to do with a truck MPG, and isn't worth compairing. Yes, same engine and gearing and weight, but the main thing in MPG is aerodynamics.
This is the absolute best way to describe it so anyone (even children) get it with no questions.
Get your car up to 60 MPH with the windows all the way down. Now, stick you hand out as far as your arm will reach (MUST be past the mirror). Open your hand, fingers extended and together, palm down.
Notice how much effort it takes to hold your arm out straight.
Now, turn your hand so your palm is facing forward.
Notice how much effort it takes to hold your arm out straight.
I don't need to tell you which is the Biscane and which is the pickup.
Can an old 4000 pound pickup get 17 - 20 MPG?
Yes.
Can it happen with an iron block/carb'd/non computerized inline or small block?
Yes.
Is it likely to happen?
Not very likely.
2000 RPM with an old school flat tappet cam, carb'd, cast iron, non electronic controlled inline or small block, is 9 times out of ten, going to be too low an engine speed with the barn door aerodynamics of a pick up.

[CaptRMW]

If yer done pullin stumps you need to lose the 4.57 gears. Each time the engine turn over the cylinders will require a mixture of air/fuel..Reduce the number of times the engine turn over in a mile and wa la.

[lilpoindexter]

For giggles I checked the mpg of my '78 1/2 ton 250/3spd shortie with 3.73's ....12mpg in mixed driving...I'm getting the parts together to swap in a t5 which should improve mpg a bit, but honestly I'm just doing it because it will be more fun to drive.

[Junkpyl]

If mine's on the road before the world ends, I'll follow up with some stats on my combination. I just ordered a new HEI and wires for it. Does anyone have any input on whether I should leave the monojet and stock intake/exuast on it or put my header and 4bbl intake with a 2bbl carb. I'm thinking that breathing a little better might get it more mpg even with a 2bbl. Input please.

[Longhorn Man]

Good breathing usually helps more on the upper end. I've seen where a member on here had headers and a performer intake (can't remember what carb) and he lost MPG. Swapped back to stock 4 bbl intake and regained some, then manifolds, and regained more MPG.
A funnel ram adapter can't be good IMO. That's just hypothetical thinking, but I can't see it helping. Esp since a 2 bbl will suck more air/fuel than a 4 bbl (esp quadrajet) that's driven gingerly.

[roofingbloke]

Hi guys, good topic,

Just thought i would mention that petrol in the UK is £1.40 per litre,

But you cannot put a price on the smile you get on your face when you drive a classic car/truck.

[Junkpyl]

Longhorn man, what your saying is that I should just leave the factory setup on the ol' 292 for the best mileage?

[Longhorn Man]

Since I do not know much about inlines, I would recomend looking into it more before laying down the cash for expensive inline parts. The header could help with low end torque and actually help, or it may just be money spent that you won't see improvements on.
If you are looking to make power, then go for it, but for higher MPG, do some more research. I think there's an inliners forum that would be ideal for your questions.

[D13]

Originally Posted by Longhorn Man

the biscane MPG has nothing to do with a truck MPG, and isn't worth compairing. Yes, same engine and gearing and weight, but the main thing in MPG is aerodynamics.

2000 RPM with an old school flat tappet cam, carb'd, cast iron, non electronic controlled inline or small block, is 9 times out of ten, going to be too low an engine speed with the barn door aerodynamics of a pick up.

I learned to drive on a 69 C10 with 250/3OTT/3.43 that got 17mpg up until the day the cow went thru the bed floor. We drove the 67 Biscayne to 400,000 miles without pulling the head. We drove it's 66 PG equipped brother to 300,000 until the wiring shorted out and the frame cracked, and got only 19mpg (slipping auto trans). I made the 81 3/4ton get 17mpg just to prove it could be done, and belive me, that's about the most anti-aero brick available.

Aero is an exponential effect and very important, from 35mph up. By keeping speed reasonable and driving carefully you can easily make these trucks get 15-17mpg without an OD trans. Want to run 75 on the highway? Aero says you'll need a lot more HP and thus fuel.

Back to the OP, change your gears to get in the 3.2-3.4 overall ratio (trans or rear swap), slow down, and drive like your grand parents.

[Junkpyl]

I already have a really nice polished clifford 4bbl intake and a long tube header for it, just wondering if I would help or hinder the truck as far as mileage. I know it will give it a little more HP. I guess it will be good experiment to get a base line then swap the go fast goodies onto it and see what transpires.

['68OrangeSunshine]

Originally Posted by Junkpyl

I already have a really nice polished clifford 4bbl intake and a long tube header for it, just wondering if I would help or hinder the truck as far as mileage. I know it will give it a little more HP. I guess it will be good experiment to get a base line then swap the go fast goodies onto it and see what transpires.

Go for it man! The driving experience is so much better than stock, it's worth the effort. I went 4-barrel in 1978 on my '68 C/10 w/ L6 292 --SM465, 3.73 rear. They told me at the speed shop that I would get better mileage with a four barrel Holley[#R8007/4160/390 CFM], if I kept my foot out of it for the most part. Well, I still get ~12.5 mpg. Of course after 25 years and 250,000 miles and an engine swap, the Holley wouldn't hold a tune so I replaced it with a 500 CFM Edelbrock 1404 AFB clone. I do have some horsepower. It's real good uphill.