[trshman]

I've got a '66 LeMans with a '70 GTO engine with heads from a '78 TransAm, TH350, 2.93 rear, Edelbrock 600 carb, Performer manifold, and cam.
During a recent trip from Tennessee to Miami and back I checked mpg for the first time and found I'm getting around 10.5. averaging 75mph with an occasional burst to 100.
I'd like to go on some serious road trips with the car, I'm talking the Grand Canyon, Pacific Coast Hwy, etc., besides I love driving the car
and would drive it more but at $4.00 a gallon this kind of mpg gets expensive and I can't afford to drive it as much as I'd like.

Would fuel injection appreciably improve my mpg? I think they go for around $4K so I'd have to do a LOT of driving or get a helluva an increase to justify that cost. Any feedback about this or anything else that might. I'd be a happy camper if I could get up to about 15mpg.

Any thoughts are appreciated. You all gave a good day.
trshman

[Half-Inch Stud]

no. Highway MPG is a direct relation to inhaled air. So your "variables" are reduced engine RPM (rear gears or OD), and Exhaust Gas Recirculation (more Overlap with exhaust system designed to EGR a reflected signal, or an EGR intake manifold with some ability to control the ERG amount at highway cruise.

Weight reduction not likely to move the HIGHWAY MPG as much as the above changes.

[67drake]

For the price of the FI unit,I'd try a Quadrajet at a fraction of that price.
I had an E-carb on a little 327 Camaro years ago and it only got me about 11 MPG!
My GTO with Q-jet pulled down almost 16 MPG with the A/C on when I had the 3.23's gears in

[Cliff R]

I've had customers using our q-jets on 455's and rear gears in the 2.73-3.08 range report as high as 17mpg's without overdrive. Many years ago, I used my Ventura to commute back and forth to work, with a mild 400 engine in it, and 2.73 gears, 1973 Q-jet, and a Street Dominator intake, it never got under 14 mpg's no matter how I drove it.....Cliff

[goatwgn]

For the price of wasting money putting fuel injection on the car, I'd switch back to a Q jet. Your car is also a good canidate for an overdrive unit (such as gear vendors) or an overdrive transmission. I get almost 20 mpg on the highway (at 65 to 70 mph) with my '66 Tempest wagon with a 2004r,.030 455 with 4x heads, a quadrajet on a GM 1 intake, a melling 041 (RA IV) cam, and 3.42 gears. Used one of Cliffs kits in my carburetor, and it starts and runs as well as fuel injection. One pump of the gas when cold, a twist of the key and it fires to life. No "rich smell" out of the exhaust, but doesn't run lean either. Call and tell him what your "setup" is, and he should be able to set you up with the right idle bleeds, metering rods, jets, and a good ethanol resisitant accelerator pump assy.

[Half-Inch Stud]

Originally Posted by Cliff R

I've had customers using our q-jets on 455's and rear gears in the 2.73-3.08 range report as high as 17mpg's without overdrive. Many years ago, I used my Ventura to commute back and forth to work, with a mild 400 engine in it, and 2.73 gears, 1973 Q-jet, and a Street Dominator intake, it never got under 14 mpg's no matter how I drove it.....Cliff

Cliff; your Stop&Go MPG is amazing.

My 12.0 ET combo was atrocious stop&Go MPG (like 6-8MPG), but absolutely north of 17MPG (thin ice claim is >20MPG) at 65-75MPG sustained Highway driving. I attribute the "Overlap EGR" effect from Cam, header//exhaust, compression, & rear gear to the great Highway MPG, but not able to explain the stopNgo gas hog.

[Steve C.]

Can MPG increase ?
The answer is YES under certian circumstances and depending on the type instalation.

Appreciably improve mpg?
Depends, and subject to opinion.

Dec 2011 issue of Hot Rod magazine.
Test of Holley's Avenger EFI system.
The test was a '67 Impala with 383 cid small block, 231/236 hyd roller cam, Edelbrock Performer RPM heads and intake from Smeddding performance. advertised at 450 hp. Transmission is a 700-R4 and 3.08 gears. With driver and gas it was 4200 lbs.
Tested with 2 differant carbs and the EFI system.

MPG in hideous traffic:
Stock carb 9.0-11.0 mpg
Tuned carb 9.5-11.0 mpg
Avenger EFI 10.0-13.0 mpg

MPG at flat, 60-mph cruise*:
Stock carb NA
Tuned carb 17.7 mpg*
Avenger EFI 21.3 mpg*
(* these are best-ever numbers, and atypical)

If you go on the internet and do searches within various automotive publications you can find other testing also suggesting that MPG can be improved with various types of EFI systems !



( Keeping in mind some here feel many, if not all, aftermarket performance products featured and tested in auto magazines is simply all lies and decet, and only for the proffit of the manufacture and the magazine itself. Therefore the information posted above was intended for general interest only and not an indorsement or recommandation )



.

[68 Firebird]

I have been running a cliff built Q-jet since april of this year and it gets
around 14 mpg consistently. Probably would be better if I could resist
opening it up every now and then.

Also ignition curve is a player too. Once I converted to an HEI I had suntuned
setup and with the Q-jet from Cliff I found the car ran too cool. I thern put in a 180
t-stat and swapped to a 7 blade AC fan with a heavy duty fan clutch. Car was
excellent all summer and fall. Did not have to touch Carb or ignition
It is a total package!!!!!!

I briefly ran a Holley Street avenger when I first bought the car as I wanted a shiny
new carb. Yes is was more reliable than bastardized carb that was on the car, but
the car drank ALOT of fuel. Also my plans for the car changed and I went back to the
Q-jet. Holley did sell fast on ebay!!!!!!!

The great thing about this hobby is we can all do whatever we choose. It's your ride
to enjoy. Carb or fuel injection are both cool, just get out and drive it!!!!!!!!!!!!

[Pontirag]

your issue is that your rear end ratio is not compatable with your cam

I am just guessing that

I dont know your tire size or if you have an automatic tranny

but if your trying to get your engine to operate in the RPM range of your cam but that does not complement your rear end gears or the miles per hour operating envelope then you will find your self constantly shifting into second gear , accelerating up through speed limit until you shift into third gear where you let off.


essentialy your cam is fighting your rear end gears and your tranny it caught in the middle.

EFI wont fix that.

your tires, rear end ratio and cam should be chosen as a complementary, compatible trio. Again I dont know your cam choice but if its a performance cam, thats why your gas milage is suffering and you tranny spends too much time in second gear when it should be in high gear.

sort out your cam/ tires and rear. then fine tune your carb or re evaluate the EFI thing

I think some of the other responses are a little concervative in thier praise of efi

you can do much better but efi is costly. but its a one time expense with emeadiate benifits

there are excellent books from SA Design on EFI. read them and do your home work

[Cobrabill]

No real FI system exists for a "real" Pontiac.Actually, a real FI manifold doesn't exist.Any of the systems mentioned above are nothing but real expensive computer monitored carbs.

[NBF823]

I'd think the better atomaztion would help. Thinking port injector style would be best.

But I sort of think there's more mpg in that car with a carb. Theres something wrong. I had a '78 T/A with 3.42s and a 224@.050 cam and I got that kinda milage out on the highway. Maybe it's the bursts to 100 though. The key to good milage is staying out of the go-pedal. Just my thoughts.

[68 Firebird]

yes keeping your foot out of the pedal does help!!!!!

[A.W.Dille]

My 71 GTO with a 400 and basically stock 670 heads with a Lunati BMII cam (230degree@.050) with a four speed and 3.08's only got around 9 mpg with an 800 Holley spreadbore and switching to a 69 Q-jet now nets me around 15-16mpg out on the road. I'd have the heat crossovers filled in the heads and go with a 68-71 iron intake and a Q-jet with one of Cliffs kits and built by the guidelines in his book and you should see better results. Also in my 85 Grand Prix when I had a 75 400 with a 73 iron intake and 73 Q-jet with a 200-4R trans netted over 20mpg and that was with the carb needing rebuilt.

[smittyseng]

Can you get "better" mileage with efi over your carb, possibly, could you get better mileage with a efi over a "otpimized carb", barely, proper stoich is proper stoich, dosesn't matter how the air or fuel gets into the motor as long as it gets the right mixture. I just spent alot of time and money to put efi on a strong 455. I didn't really do it for mileage as much as I did it to have better overall driveability. For the 4000$ it would cost you to build a good efi sytsem (I have about that in mine, even more once you add in dyno time) you would probably NEVER save enough in gas to recoup your cost. Optimize your carb, put in a overdrive and you will see the biggest savings, Smitty

[74Grandville]

is your vacuum advance working?

[smittyseng]

I just re-read the original post, I doubt overdrive would do much for you with already being geared high at 2.93. I do think there might be more in your tune though, I had a 76 firebird with a 3.23 gear and a strong 400 motor, it ran 13.40's and I would drive it from Va to Mi between 65-100 mph and always got around 12.5 mpg so maybe your mileage could be tweaked a little bit better, Smitty

[jonathonar89]

I just want to be clear on this subject. I'm a novice to the efi subject. Is everyone referring to throttle body or direct port fuel injection for this mpg debate? Throttle body injection seems as though it would distribute fuel roughly the same as a carb (manual vs. auto tuning). I can see how a direct port setup would be more conservative with fuel usage...

[trshman]

Thanks everyone for the responses. Seems like the Q-jet is the most bang for the buck, besides I LOVE the look of an old carb sitting on top of these engines.

After reading these posts there's one more thing I want to mention that might be a factor. While in Miami a friend did a "mini" tune up and found that although the timing was ok at idle the advance timing was off by about 40deg. Unfortunately he didn't have time that day to check into it further and I left a couple of days later.
My question is could there be a problem with the distributor that's thrown the timing curve off? Aside from good wires and a Petronix Flamethrower ignition it's stock.

trshman

[Half-Inch Stud]

Timing off? Count on it. Post #2 assumed a proper tune. What am I supposed to do assumed a 70% tune?

[Ollie]

Originally Posted by jonathonar89

I just want to be clear on this subject. I'm a novice to the efi subject. Is everyone referring to throttle body or direct port fuel injection for this mpg debate? Throttle body injection seems as though it would distribute fuel roughly the same as a carb (manual vs. auto tuning). I can see how a direct port setup would be more conservative with fuel usage...

2X Jonathonar89,
Especially with sequential injection and COP ignition.