Miles per gallon

[rcarlisle]

Just to contribute, my 81 with 302 and M5OD-R2 gets 9 - 11 mpg. No tag on the rear end and the tag on trans was painted over so I have no idea the ratios of either. But it seems like a lower overall ratio. 1st is almost too low and short - like a granny gear and 2nd gear starts are a bit more slipping. Seems like it could have higher rear gears to improve the mileage. It will easily run up to 75 mph. At that point the steering gets too imprecise to be really comfortable, but I know 75 is solid and easily attainable with more left in it. 235/75-15s for tires. I haven't counted the wheel revolutions to driveshaft or anything like that. These first 8 months have been getting it more comfortable and safe. Truck has been as reliable as an anvil so far. knock on wood.

A tach is on the "to do" list soon. Might help me know a little better.

I'm also hoping to find a good Ford tuner locally as well. To get everything set as best possible. I need a "carb whisperer". I can tinker and experiment, but I'd prefer to have a good tuner lay magic fingers on it.

 

[85lebaront2]

Just to contribute, my 81 with 302 and M5OD-R2 gets 9 - 11 mpg. No tag on the rear end and the tag on trans was painted over so I have no idea the ratios of either. But it seems like a lower overall ratio. 1st is almost too low and short - like a granny gear and 2nd gear starts are a bit more slipping. Seems like it could have higher rear gears to improve the mileage. It will easily run up to 75 mph. At that point the steering gets too imprecise to be really comfortable, but I know 75 is solid and easily attainable with more left in it. 235/75-15s for tires. I haven't counted the wheel revolutions to driveshaft or anything like that. These first 8 months have been getting it more comfortable and safe. Truck has been as reliable as an anvil so far. knock on wood.

A tach is on the "to do" list soon. Might help me know a little better.

I'm also hoping to find a good Ford tuner locally as well. To get everything set as best possible. I need a "carb whisperer". I can tinker and experiment, but I'd prefer to have a good tuner lay magic fingers on it.

Too bad you're down there, I used to own a carburetor and ignition shop. BTW, that gas mileage puts you in the 460 range. 12.5 mpg at 70-75 mph with a 6400 lb F350 Dually.

[rcarlisle]

Too bad you're down there, I used to own a carburetor and ignition shop. BTW, that gas mileage puts you in the 460 range. 12.5 mpg at 70-75 mph with a 6400 lb F350 Dually.

Yep. Something isn't right or wasn't considered when the trans was swapped in. But I know how people around here think - "Hey let's put a 5 speed in it. That'll be great. My cousin has one that will fit".

I wish I honestly knew more of the history of the truck. PO said it was a farm truck. Not sure that holds water, but who knows. I have receipts for what the PO did and it did not include the trans. Just everything forward of trans.

It's great fun to drive. Probably has smoky burn out potential, but I can't afford to break it to find out. But it will get up and go when asked to. At the expense of gas mileage. It's longest trips so far are about 15 miles to the cruise in and daughter's house. Might do better on highway for longer trips.

[85lebaront2]

Yep. Something isn't right or wasn't considered when the trans was swapped in. But I know how people around here think - "Hey let's put a 5 speed in it. That'll be great. My cousin has one that will fit".

I wish I honestly knew more of the history of the truck. PO said it was a farm truck. Not sure that holds water, but who knows. I have receipts for what the PO did and it did not include the trans. Just everything forward of trans.

It's great fun to drive. Probably has smoky burn out potential, but I can't afford to break it to find out. But it will get up and go when asked to. At the expense of gas mileage. It's longest trips so far are about 15 miles to the cruise in and daughter's house. Might do better on highway for longer trips.

Randy, I would look at the distributor, vacuum advance and mechanical advance in particular. A bad vacuum advance will kill gas mileage as will a sticking ar flat out stuck mechanical advance mechanism.

[rcarlisle]

Randy, I would look at the distributor, vacuum advance and mechanical advance in particular. A bad vacuum advance will kill gas mileage as will a sticking ar flat out stuck mechanical advance mechanism.

Good ideas. It has a cheap chinese dist so probably do need to confirm it's working correctly. Truck runs well though. Just bad mileage.

[85lebaront2]

Good ideas. It has a cheap chinese dist so probably do need to confirm it's working correctly. Truck runs well though. Just bad mileage.

You have one of those Chinese Chevy distributors? Trash can is the best place for it. I personally would go back to a breaker point system before I would touch one of them.

Mechanical advance on GM distributors is under the rotor and is easy to check by removing the cap. with the cap off, grab the rotor and turn it counterclockwise, it should turn with some spring tension and return when released. Vacuum advance can be checked with a vacuum pump, or with the engine running fast enough to have vacuum at the hose, connecting and disconnecting it should bring a noticeable rpm change.

[rcarlisle]

You have one of those Chinese Chevy distributors? Trash can is the best place for it. I personally would go back to a breaker point system before I would touch one of them.

Mechanical advance on GM distributors is under the rotor and is easy to check by removing the cap. with the cap off, grab the rotor and turn it counterclockwise, it should turn with some spring tension and return when released. Vacuum advance can be checked with a vacuum pump, or with the engine running fast enough to have vacuum at the hose, connecting and disconnecting it should bring a noticeable rpm change.

It's not a coil in cap HEI. Looks like a regular old distributor from the outside. When I bought truck the #3 tower on cap was cracked on both sides and about to fall out, but the truck was running on all 8 like it should. SO I located the cap on line and replaced it. No difference except I don't have to worry about the cap falling apart. Looks like a cap off an old ford except the terminals are male instead of female.

I'm going to leave it alone as it is working properly - I want to check the advance operation as recommended above. But no point in changing something that's working. The duraspark box is still on the fender but not plugged. Have no idea if it works or not.

https://swperformanceparts.com/product/r2r6702bl/

[Rusty_S85]

With my new engine, replacing my excessive slippage C6 for a aftermarket C6 and switching over to a 3.25:1 axle ratio I hope to be in the area of 18 mpg city and 24 mpg highway.

Rusty, I wish you all the luck in the world, but I have a hard time imagining a 302 running 3000 RPM with a C6 and 31" tires hitting 24 mpg.

Even if you consider the 1987-1996 trucks, with speed density or later on MAF, with 5spd's and 3.08 gears, most of those trucks could barely even hit 20mpg on the highway. They surely wouldn't do in 4th gear at 1:1 ratio like a C6. I can see the Holley Sniper being better technology...sort of...but it's still throttle body EFI, and not multiport EFI.

To throw my old truck into the MPG mix for the OP, it was an '84 2wd Flareside with a mild built 302, a 1991 M5OD 5spd trans, and original 3.08 rear diff. No AC, and no other options really. Truck weighed 3500 lbs. I drove it on the highway quite a bit, and the best I ever got with it was around 18.5mpg...maybe it kissed 19mpg one time, but I'm not sure...my memory is getting fuzzy.

That was at around 2000 RPM in OD, running between 60-65 mph. My AFR was usually a little over 14:1 when I was cruising easily. I did try some highway trips at faster speeds and higher RPM's, and depending on the day it never really hurt my mpg too much...sometimes 1 or 2mpg less, but I think the wind drag negated any efficiency I might have gained with the higher RPM's.

I never did try running the truck up in the 2500-3000 RPM range in 4th gear on the highway to see if the MPG would improve. Maybe that's the answer to getting better mileage...higher RPM's and lower gears...I've never thought to try it.

That is my hope, I would be happy with 20 highway even. I know my '78 Mercury with a 351W would average 26 highway at 75 mph and it while having a smaller front end height wise, still had the brick like front end. Once I get my build finish I will be doing some logging of economy and seeing what kind of economy I am averaging. I know for me the roller cam I have for my build is for a 2,400 - 3,000 rpm cruise range and with the axle ratio I am looking at it would put 65 - 75 with in this 2,400 - 3,000 rpm range so here in Texas I should be able to drive just about any highway in the cam`s sweet spot. The gears I am looking at should put me at 81 mph at 3,000 rpm and 65 at 2,450 rpm

[66gtk]

With my new engine, replacing my excessive slippage C6 for a aftermarket C6 and switching over to a 3.25:1 axle ratio I hope to be in the area of 18 mpg city and 24 mpg highway.

Rusty, I wish you all the luck in the world, but I have a hard time imagining a 302 running 3000 RPM with a C6 and 31" tires hitting 24 mpg.

Even if you consider the 1987-1996 trucks, with speed density or later on MAF, with 5spd's and 3.08 gears, most of those trucks could barely even hit 20mpg on the highway. They surely wouldn't do in 4th gear at 1:1 ratio like a C6. I can see the Holley Sniper being better technology...sort of...but it's still throttle body EFI, and not multiport EFI.

To throw my old truck into the MPG mix for the OP, it was an '84 2wd Flareside with a mild built 302, a 1991 M5OD 5spd trans, and original 3.08 rear diff. No AC, and no other options really. Truck weighed 3500 lbs. I drove it on the highway quite a bit, and the best I ever got with it was around 18.5mpg...maybe it kissed 19mpg one time, but I'm not sure...my memory is getting fuzzy.

That was at around 2000 RPM in OD, running between 60-65 mph. My AFR was usually a little over 14:1 when I was cruising easily. I did try some highway trips at faster speeds and higher RPM's, and depending on the day it never really hurt my mpg too much...sometimes 1 or 2mpg less, but I think the wind drag negated any efficiency I might have gained with the higher RPM's.

I never did try running the truck up in the 2500-3000 RPM range in 4th gear on the highway to see if the MPG would improve. Maybe that's the answer to getting better mileage...higher RPM's and lower gears...I've never thought to try it.

That is my hope, I would be happy with 20 highway even. I know my '78 Mercury with a 351W would average 26 highway at 75 mph and it while having a smaller front end height wise, still had the brick like front end. Once I get my build finish I will be doing some logging of economy and seeing what kind of economy I am averaging. I know for me the roller cam I have for my build is for a 2,400 - 3,000 rpm cruise range and with the axle ratio I am looking at it would put 65 - 75 with in this 2,400 - 3,000 rpm range so here in Texas I should be able to drive just about any highway in the cam`s sweet spot. The gears I am looking at should put me at 81 mph at 3,000 rpm and 65 at 2,450 rpm

My all stock '83 with original exhaust and all original unrebuilt powertrain gets about 12-14 mixed city/highway (mostly hwy) with the AC off. 302, AOD, 3.55:1, SWB, EEC-3 all stock and all plumbed/intact original. NOTE: This is on non oxygenated fuel and tires inflated properly with no little to no load.

 

[Gary Lewis]

My all stock '83 with original exhaust and all original unrebuilt powertrain gets about 12-14 mixed city/highway (mostly hwy) with the AC off. 302, AOD, 3.55:1, SWB, EEC-3 all stock and all plumbed/intact original. NOTE: This is on non oxygenated fuel and tires inflated properly with no little to no load.

Where's the picture I saw in the email? I like the deux chevaux in the background. But your truck is beautiful!