Gas mileage

[try2pas]

I have an 80 vette with a 3 speed automatic, ZZ4, 650
Demon and I think a 308 rear end. I now get about 15 mpg on the hiway. If I were to put in a 700R4 with the .70 overdrive what would my hiway mileage go to? 16, 18, 20 or ? Would a different carb help any? If I modified the ZZ4 to a ZZ430 with the fast burn heads and hot cam would my mileage go to H in a handbasket or not change much? With gas probably hitting $4 + bucks this summer just need to try and figure out my options.

 

[Art Jett]

I've got a TPI 383 with a 700R-4 and used to have a 3.08 rear. I changed it to a 3.70 cause it was just too tall for me. At 60 MPH the engine was only running 1500 RPM. When I would get into town at about 40 MPH or so it would only be running at about 900 RPM and start bucking. I would have to drop it into 3rd. Much happier with the 3.70 and still getting 18MPG.Art

 

[Bill75]

I have a ZZ4 with Brodix IK-180 heads, a Qjet, 3:36 gears, a cam very close to the "Hot Cam" and a Tremec with .68 OD. I get over 21 on the highway at 70 mph with the A/C on.

Based on my experiences I would expect the most mileage improvement could be made by switching to the OD. My motor justs loafs along on the highway at 70 mph. BUT, the mileage isn't that great around town so unless most of your driving is highway you might never see a substantial overall cost savings at the end of the year by making a trans. change. My OD is pretty useless under 55mph

I know you don't want to hear this but you might look into a good Qjet vs the Demon, when set up properly they are very economical.

 

[Hib Halverson]

Two things will improve your car's mileage
1) Switching to the 4L60 automatic (aka THM 700R4)
2) Properly calibrate the Demon for part throttle, or better yet, switch to a Quadrajet.

That said, there's also the economic aspect. Converting to an OD or a different carb will cost a fair amount of money. It is unlikely you will recover the cost of those modifications with the better mileage, unless you plan to drive the car a very long time. So, in the duty cycle typical of most older Vettes, over time, the mods will cost you more money than the car does now.

 

[gmjunkie]

I know you don't want to hear this but you might look into a good Qjet vs the Demon, when set up properly they are very economical.

 

[J Koehler]

Another way to look at it is..... Will you recover the money you spent to get better gas milage. I would put money into toys that will be more fun to you like more HP. Unless this your daily driver.

 

[THORIN]

I am a bit of a greenie. It cost me about $3000 to switch my 76 to a 700 R4. I know I could have bought a lot of gas for that amount; but I wanted a little more guilt free driving. Mine got 12 mpg when I first got it. Now depending on AC and freeway conditions. Mountains vs flat land I get between 20 and 24 mpg. I really like that at 70 mph I am turning about 1700 rpm. When I take trips with the younger vettes I have no problem keeping up. My next big thing is I want to switch to Fuel Injection that may get me pushing 30 mpg. I'm not into big engines and going fast. I just want to enjoy driving .
Last fall I installed a cruise control, so now I am interested in how that will affect my millage.

 

[Art Jett]

I wouldn't count on fuel injection increasing your mileage by much. I have a brand new TPI setup on my 383 and from what I've read they get about the same fuel economy as a well tuned carb. Art

It's too bad about your cruise setup. I just removed a perfectly functioning system cause I didn't use it.

 

[try2pas]

Q jet vs the Demon

So If I go with a 750 Q jet it sounds like it will improve my gas mileage some for sure over the Demon 650 but will I loose "horsepower" in the trade because the Q jet is more fuel efficient and won't dump the gas in that the Demon is doing now (when I get on it) so a resulting loss of power but better mileage? Or would the 750 cfm vs the 650 cfm make up the difference at wide open throttle? And if a guy could afford to add a FI system that should give better mileage yet and not suffer any power loss? I see there is a ram jet, ram port, tuned port and multiport fuel injection systems that can be purchased. Which would work best on the ZZ4?

 

[KANE]

So If I go with a 750 Q jet it sounds like it will improve my gas mileage some for sure over the Demon 650 but will I loose "horsepower" in the trade because the Q jet is more fuel efficient and won't dump the gas in that the Demon is doing now (when I get on it) so a resulting loss of power but better mileage? Or would the 750 cfm vs the 650 cfm make up the difference at wide open throttle? And if a guy could afford to add a FI system that should give better mileage yet and not suffer any power loss? I see there is a ram jet, ram port, tuned port and multiport fuel injection systems that can be purchased. Which would work best on the ZZ4?

I wouldn't say you'd lose power with a properly tuned Qjet. Remember, the primaries are smaller on the Qjet... you use those until you drop the hammer. Then, the larger secondaries kick in and you lose just as much fuel as the Demon (and have as much power!)....

I like EFI. That is why I swapped to it.

 

[THORIN]

DarkShark and Art Jet. The second reason I want to go to EFI is not having to wait for the carburator to get off choke and the engine to warm up. With your TPI and EFI can you just get in and go? If you don't mind me asking, what did it cost to convert? I am expecting between three and five thousand.

 

[Art Jett]

My system was right at $2000.00 without the powder coating. the system was complete with injectors, sensors, fuel pump, filter, computer and wiring. Get on the web and look up Affordable Fuel Injection. If you call, talk to Norm and tell him I said hello.

 

[THORIN]

My system was right at $2000.00 without the powder coating. the system was complete with injectors, sensors, fuel pump, filter, computer and wiring. Get on the web and look up Affordable Fuel Injection. If you call, talk to Norm and tell him I said hello.

Thanks, that helps.

 

[KANE]

...I am expecting between three and five thousand.

I did mine for around $1,344 complete....

- Ebay
- Off-brand sensors (they work and have warranties!)

Below is the list of parts- rounded to the nearest dollar.

Item / Cost / Source
Plenum, baseplate, fuel rail, TB $150.00 Ebay
Fuel pump $90.00 Pep Boys
EGR block off $10.00 Ebay
TPS $20.00 O'Reillys
IAC $70.00 O'Reillys
MAT $12.00 O'Reillys
MAP $45.00 O'Reillys
IAT $12.00 O'Reillys
Harness $245.00 Ebay
O2 $25.00 O'Reillys
Fuel hoses & AN fittings $100.00 Jegs
Gaskets $25.00 O'Reillys
Distributor $90.00 Ebay
Injectors $100.00 Ebay
Cables, clamps, bolts, misc $100.00 Various
Fuel pump bock off $10.00 O'Reillys
Radiator hose, T-stat, housing $40.00 O'Reillys
ECM / chip $200 Ebay
Total- $1,344.00

You can listen to it through the links below...

 

[try2pas]

Is stock '80 carb a 750 Q Jet?

I am convinced I should go with the Q jet. But how do I know one when I see one and was my (which I still have) original '80 vette carb a 750 Q jet?

 

[Koop]

You could install a Honda in your driveway right next to the Vette.

I have the fast burn heads on my 383 with a Qjet, it gets poop for MPG.

TH400 doesn't help it either.

And of course my foot is in fact made from solid lead.

 

[Glensgages]

..... in late '78, I bought a brand-new '79 Z28 off the showroom floor, and began modifying it for better performance at the drag-strip:
2 buddies from high-school (Class of '77) also bought new Z28s, one a stick-shift '78, the other an automatic '80, but refused to modify them, fearing they'd get terrible mileage.

When we'd go to the strip, I'd run low-14s at 97 MPH (junk-yard 64cc heads, 268H cam, factory dual-plane intake, 650 double-pumper, open headers, with the original 3.42 gears), while they were content running 16.20s @ 84 MPH, but they were content, figuring they'd get much-better mileage on the open-road.

In '83, we all made a 330+ mile one-way trek to a car-show, and to 'prove' how-much better mileage they'd get, we all filled-up at a local SUNOCO station, and pulled-out, nose-to-tail, begiining our trip:
they kept asking me on the CB-radio if I 'needed-to get-some-gas', but I told 'em I was doing just-fine, and we kept-on going down the Interstate.....

When we arrived at the town hosting the Car Show, we pulled into another SUNOCO station, and began filling our tanks simultaneously, with them supremely-confident their pumps would shut-off long before mine did


My pump shut-off first, followed by the '80, and finally the '78.....
:W

I got just-over 19 MPG, the automatic '80 got over 16, and the stick-shift '78 (with OEM 3.73 gears) got over 15


That Winter, we rebuilt the '80 into a clone of my Z28, except for an L-82 intake/Q-jet induction:
it wasn't surprising that the '80 didn't run quite-as-good as mine did, but I still got better mileage when we made the same trip the next Summer.

2 years later, we installed 4.11s, and never looked at mileage again.


28+ years later, I still have the Z28, which now runs 12.80s @ 105+ MPH, and uses a gallon of gas per run
;help

My bone-stock (Cross-Fire, 700-R4, 2.87:1 gears) '82 Corvette once got 23+ MPH, running with the AC blowing ice-cubes, T-tops off, at 75+ MPH, over the Alleghany Mountains of Western Taxylvania, on a 230+ mile round-trip, most of it highway/Interstate:
after switching to 3.73 gears, it returned an amazing 17+ MPG over a 440-mile trip, equally split between sustained Interstate cruising, city-driving, and 2-lane country-roads over the mountains, following the old road-bed of the Pennsylvania Railroad (often getting-lost when losing sight of the tracks) between Pittsburgh & Huntingdon, Pa., again with the AC on.