MPG for a 402

[70cst]

After reading this thread I have gleaned the following info: If MPG is a major concern...then our trucks are not going to offer a solution. The 402BB's will offer 8-10 average and the 350/327 will offer 13-15 on highway. The rear gears can offer some relief in improved MPG but...for the most part our trucks are great for work and play but...not for great MPG as daily drivers. JMHO. Good luck with your quest.

[69GMCLonghorn]

As Andy said, it's a toss up between getting crap mileage and spending 3-4 years worth of gas money to NOT use so much gas.

On that note, something to think about is the fact that all someone in the middle east has to do is SNEEZE wrong and gas is going to hit $5 a gallon again... or more. So maybe that 3-4 years' worth of gas money to drop an O/D in it would pay for itself quicker than you think.

In addition to that is the driveability. Forget the MPG for a moment, a truck that's taching 2000 RPM at 70 is going to be much more relaxing to drive than one that's taching 2500 - 3000 RPM.

[Jim_PA]

Good mileage from your engine is all about fuel and ignition tuning. 7/10 city/highway MPG in a truck with a small block means you have a tuning issue, or you have pretty bad driving habits.

I bought a wideband, a Qjet, and set up the timing. Set the cruise ratio somewhere around the low 16.x:1 range. I'm running 16 initial with 36 total timing and 10 degrees of vacuum advance.

I have 30 miles on this most recent tank. Looking inside the tank, it's just a hair below the filler neck. At the very most, I'd have to put 2 gallons in to bring it back up to the top.

7,8,9,10, 12 MPG isn't normal.

[mclairmo]

12 mpg sounds normal to me. I think any amount of spritited driving will lower fuel economy. However, if you really value fuel economy, then it might make sense to install an O2 sensor in the exhaust, hook up a wideband, run a Q-Jet or fuel injection and tune for economy. Also, as I have read about the hybrids, you would have to drive the vehicle for an abnormally long time to recover any extra money you spent to increase the fuel economy. Most hybrid owners won't drive their vehicles long enough to recoup the extra they spent for the hybrid engine in the first place. It's wasted money, for now. However, if a gallon of gas hits $6 then maybe it would make sense to pay the extra for better fuel economy. Not now, though.

[Jim_PA]

Originally Posted by mclairmo

12 mpg sounds normal to me. I think any amount of spritited driving will lower fuel economy. However, if you really value fuel economy, then it might make sense to install an O2 sensor in the exhaust, hook up a wideband, run a Q-Jet or fuel injection and tune for economy. Also, as I have read about the hybrids, you would have to drive the vehicle for an abnormally long time to recover any extra money you spent to increase the fuel economy. Most hybrid owners won't drive their vehicles long enough to recoup the extra they spent for the hybrid engine in the first place. It's wasted money, for now. However, if a gallon of gas hits $6 then maybe it would make sense to pay the extra for better fuel economy. Not now, though.

I have $150 in my wideband, and maybe $100 in my carb.

You can do this for little money, and performance doesn't suffer. Not tuning for efficiency is just an excuse, for not knowing how, or you just don't care.

[mclairmo]

Sounds like a good deal. I guess some of us are just reluctant to try out new technology. Don't you also have to weld a bung onto the headers or the exhuast pipes? I think that would deter some of us who cannot weld or don't want to drill a hole into our headers and hire an exhaust shop/welder to weld it up for us.

[Mburgess57]

LOL I have a '71 with a 402/400 and I get 10 mpg it doesnt matter if I am trying to push a dent in whats left of the floor pan or if I am driving 30 around town. My saturn that I am forced to drive every day gets on average 33mpg. So I get 21.5 mpg LOL!

[Jim_PA]

I put my fitting in the pipe right behind the collector. Yes, it needs to be welded, but this isn't more than a 1/2 hr job.

The wideband and my $10 89 Chevrolet truck seat have been the best value over all the things I've bought. Well, disc brakes is up there too but that was kind of expensive.

[mclairmo]

Wideband sounds like a great tuning tool for little money.

[WorkinLonghorn]

Jim PA, where did you get your MSD digital e-curve distributor? I see them all over for about $375. Thx.

[Jim_PA]

MSD 8394 -- Got it at the speed shop. I did send one back, but I think my starter was at fault. They need a certain number of RPM's before they will start throwing sparks. I originally had an off-brand mini starter that just wasn't cranking fast enough when the engine was warm. Haven't had a single problem since I replaced it for a late-model GM small block starter (about 4 months ago..)

[Longhorn Man]

http://67-72chevytrucks.com/vboard/s...d.php?t=172346

[Jim_PA]

Originally Posted by Longhorn Man

http://67-72chevytrucks.com/vboard/s...d.php?t=172346

There appears to be an epidemic of people who don't care about efficiency

[BBChevy71]

402BB 71 fleetside longbed and I've always told people I get 10mpg going up hill, and 10 mpg going down hill in neutral with a tailwind

[tim21391]

i drove 15 miles to school and 15 miles home from school and i had to put 20 bucks in every two days..

[Mburgess57]

But when you start it and you hear that rumble, or some punk pulls up beside you in a rice buggy and the light turns green who cares that it cost you $15.00 to dust him off all the way to the next light!

[tim21391]

thats no lie right there.. and when u start it up u always rev it a bit.. well i do anyways

[67ChevyRedneck]

I bought an S-10 for mileage. Even with a tree fiddy and OD my 67 only gets 11-12 around town and 15-16 highway, but I don't drive "highway" very much, so most of my tanks are around 12mpg.

[El Jay]

'72 GMC, LB; I average around 10 MPG, but I have (honestly) gotten almost 12 MPG on the freeway on a long trip while "feather footin'" the throttle.

BTW, my '69 with a 355 does just about the same. Both trux have 4.11:1 rear ends.

[67shortie]

Ya, mine with a 350, aftermarket heads, cam, Holley 1850 with stock 66 jetting with the 700r4 gets 12-13 average.

I have tried different carbs (tuned Qjet) and cannot get much better.

I do drive 65-75 on the freeways and have some fun around town once and a while but I have come to the conclusion that these trucks with the old school carb'ed engines are going to get bad gas mileage no matter what. There are exceptions but very few and I want to know thier secrets

Heck, even my Chevelle with a hot solid cammed 427 will get the same on the freeway. Maybe even better, but not by much....

[turp mcspray]

[QUOTE=Jim_PA;3469094]I have $150 in my wideband, and maybe $100 in my carb.

Jim, what kind of a wideband setup are you using? I see there are several in Summit. I am ABSOLUTELY going to do this! Thanks for any info!

[Jim_PA]

I am using a JAW 1.041 -- You have to build it yourself, or you can find them assembled for usually an extra $50 or $60. You literally get all the pieces plus a blank circuit board. If you've ever soldered anything, this isn't that hard to do. I thought it was kind of fun, but I'm a nerd.

They now offer it for $125 which includes an o2 sensor and display. I believe you still have to get your own project box ($4-$5 bucks from radio shack).

The best thing about the unit is that it takes input from other sensors (RPM, exhaust gas temp, etc...). Then when you log your run, you can see RPM vs AFR. I have never logged my data to a PC, I just drive around and watch the LED display.

You won't find the same features anywhere for this cost. Most units that take RPM or other input cost $400+.

This has saved me so much time in tuning, it's not even funny. It takes all the guess work out of it, and you can see what your carb is doing in every area.

http://14point7.com/Widebands/JAW_1_041/JAW_1_041.htm

I bought a stainless o2 sensor bung and plug for $5 on ebay.

[Naterman35]

Originally Posted by Mburgess57

LOL I have a '71 with a 402/400 and I get 10 mpg it doesnt matter if I am trying to push a dent in whats left of the floor pan or if I am driving 30 around town. My saturn that I am forced to drive every day gets on average 33mpg. So I get 21.5 mpg LOL!

Thats the way to look at it! LOL

[turp mcspray]

Thanks so much for the info Jim. I KNOW that you can decent mpg even with extra cubes and power! It's just a bit of work to find it. This should save a LOT of trial and error.

[mclairmo]

Originally Posted by Jim_PA

I am using a JAW 1.041 -- You have to build it yourself, or you can find them assembled for usually an extra $50 or $60. You literally get all the pieces plus a blank circuit board. If you've ever soldered anything, this isn't that hard to do. I thought it was kind of fun, but I'm a nerd.

They now offer it for $125 which includes an o2 sensor and display. I believe you still have to get your own project box ($4-$5 bucks from radio shack).

The best thing about the unit is that it takes input from other sensors (RPM, exhaust gas temp, etc...). Then when you log your run, you can see RPM vs AFR. I have never logged my data to a PC, I just drive around and watch the LED display.

You won't find the same features anywhere for this cost. Most units that take RPM or other input cost $400+.

This has saved me so much time in tuning, it's not even funny. It takes all the guess work out of it, and you can see what your carb is doing in every area.

http://14point7.com/Widebands/JAW_1_041/JAW_1_041.htm

I bought a stainless o2 sensor bung and plug for $5 on ebay.

I was wondering why your wideband was so low priced and now I know. Unfortunately, I am not good with soldering anything. I guess I am stuck paying $400 for one. you should start making these and sell them here.