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Fuel mileage on L6's


olie05

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Guest bastaad525

Well this seems to be common of the 240 tanks and gauges then... that's good to know. Okay, so, 16 gallons it is then. I'm not really using my fuel gauge to really measure anything, other than to know when it's time to fill up again. I just make it a habit of filling up whenever it gets to about 1/4 tank. To measure mileage all I do is top it off (verified visually... I fill it until the fuel starts to come up the fuel filler neck and wont go down any more. Drive it however far (again, usually to a 1/4 tank, but it doesnt' really matter for the purpose of calculating mileage) and top it off again. I take however many gallons it takes to refill it and divide it into the amount of miles I drove. I'm relatively sure my odo is correct, I have used the transmission calculator to verify the speedo's accuracy and it is dead on, verified as high as 90mph (as it should be as I'm running the whole zxt drivetrain along with the factory specified size tires).

 

I'm pretty sure everyone here knows enough about the stock 240 gauge being none-too-accurate well enough to not trust it as a way of calculating anything :D

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Guest Mateo

Don't know why you don't think you cannot get more than 25mpg out of a 6 cylinder engine. I remember one of my dad's older friends that he had a 70s model Duster called a Feather Duster. These cars had highly tuned slant 6's that got rated at 23 city/ 30 highway from the factory. He having owned one testified to it. Even though only a few were sold, its also proof that even back then a carbed highly tuned, probably with more breathing add ons, can get good gas mileage. My theory is that when FI was just coming around in late 70's, 80s, and even 90's cars they weren't as efficient as todays. They probably didn't research enough or had good ECUs to control each injection as well as today. Now that we know more about FI, things are starting to get more efficient and see the benefits of FI. But thats just me :-D

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Guest bastaad525

kewl thanks... well fuel gauge is definately off by a mile then and I probably do have a good 4 gals left in there by the time the gauge says empty.

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  • 11 months later...

My 280's gauge isn't the most accurate either, but at least they never claimed it to be.(The owner's manual actually states "The fuel gauge indicates the APPROXIMATE fuel level in the tank.") I DO know that that car is very, very pessimistic. The gauge will actually go below the final hash mark and point at "E". I decided to experiment and keep driving. About 30-50 miles later the "low fuel" light will come on, but only if you're on the highway and not sloshing the gas around in the tank. As soon as you hit a corner, it will go out for another 20 miles, then come on again. Keep being stupid (like I did), and eventually it will stay on. I finally got scared and stopped for gas. I put in 17.15 gallons (It's actually pretty hilarious, getting weird looks from people in thier SUV's seeing me put 35 bucks worth of gas into a Datsun!) and realized I might have gone another 2 or 3 miles! So at least the light is accurate!

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  • 5 weeks later...

my camed 82zx with headers and intake ran rich as hell at a idle and i got 12 15 mph in town. i went to great fall montana form spokane when speed limit was lifted with my brother and got 25 mph based on distance not odm......ps ran rich at idle cuse not enough vaccume pressure to the sensors from cam my 83 get about 28 to portaland with eledtric fan for radiator and intake done......soooo huh

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I have 13 years of weekly documented fuel economy data on my '77 Z. I have it with the original 4-spd and 3.54:1 R200, later with an '83ZX 5-spd and 3.90:1 R200, and finally with the LS1, T56, and 3.70:1 LSD R200.

Again - I'm talking about recording the mileage traveled on each tank, the tank filled to visual sighting each time in the fill neck and a calculation rounded to the nearest tenth of an MPG. Yes, I also use a calculator to do the computation each week.

Did I mention that I have been doing it for 13 years?

Bottom line is that they all get about the same combined city/highway mpg which is in the 18-21 mpg range depending on time of year, and the exact mix of city and highway. Straight highway the best I ever got out of the L6 was 24.5 with the 5-spd and with the LS1 24.3. Biggest difference is that the L6 ran on 87 octane while the LS1 runs on 93.

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well, Ill chiime in here.... I get about 21~22mpg with 70% in town/30% highway under normal usage. ON the recent trip to Cali for MSA I got about 27mpg, judging on distance, not odometer readings, because my odometer stopped working, HA ha! also, we were doing about 100mph 3/4 of the way, ooooops. this was verified by my freinds MEGASQUIRT tach and tire combination and back calculating and what not. on the way back I only got about 24 to 25mpg doing a little more sane speed. of course on the way back, its all uphill.

 

I have an 83 that would get about 30 on the highway. I know that for a fact because I could drive from fargo, nd to minot, nd and back on one tank of gas (290 miles each way) and still have change left over.

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I did a three month fuel economy study with an '83Zx one time. I went from driving "normally" to shifting at no more than 2,500 RPM and accellerating gently. That resulted in a 17% increase in fuel economy. As I once said "Fuel economy is directly related to the gas pedal - as one goes down - so does the other".

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Bottom line is that they all get about the same combined city/highway mpg which is in the 18-21 mpg range depending on time of year, and the exact mix of city and highway. Straight highway the best I ever got out of the L6 was 24.5 with the 5-spd and with the LS1 24.3. Biggest difference is that the L6 ran on 87 octane while the LS1 runs on 93.

 

Phantom, Isn't the corvette with an LS1 rated at somewhere closer to 30mpg highway? How do you explain the mpg you got with your set up? Do you use a 5 or 6 speed? What measures were taken to keep the odometer correct with the differential swaps? Not trying to call you out or anything, I'm just looking for some more information.

 

When I'm trying to save gas I set my mental shift point for 2,000rpm. As phantom pointed out, The more you use the gas the lower your mileage goes, so I try to stay light on the pedal, but I don't even try to document my mileage, because I have different outside diameter tires and a 3.9 diff. and the speedo gear is not right for my setup. I really want a 6 speed transmission to drop the rpms down when I'm cruising on the freeway. I see about 2,700-3,000rpm keeping up with the flow of traffic (speed limit is 65... I think...) so a 6 speed would keep my gearing with the 3.9 and give me cruisability.

-Oliver

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  • 2 weeks later...
Guest Z Draci

Sorry to revive this post, but I think I have some valuable info on this.

 

My 240Z is stock except for the E88 head (car is manufactured in 10/70 so I'm expecting an E31). These figures were also with the 4-speed gearbox.

 

One of the previous owners of the car was so anal that he had recorded mpg figures for every fill-up at the petrol station. I have these numbers from 1989 through 1994. They are anything between 18-26mpg. I don't know what percentage is city/highway.

 

When I initially bought my car in Sacramento, I drove it back to Los Angeles. I got a little over 400 miles with about 2-3 gallons left in the tank. This is about 28-31mpg. I know my speedo error so I'm certain I was going mostly 70-75mph for the entire trip.

 

Right now, I get anything from 11-16mpg with 90% of the miles in the city. I know my carbs need a rebuild. I suspect that the float bowls may be dirty, among other things.

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  • 1 year later...
  • 1 month later...
Guest 240ZPompanoFlorida

Since its asked again.. the 240 Z gas tank is just under 16 gal capacity. I have a 72 240Z rebuilt 30,000 miles ago with only mod 6 into 1 header 2 1/2 in exhaust with Dynomax turbo muffler , stock4 speed and rear last trip running 70-75 ( 80 mph is close to 4000 with speedo adjusted ) I got 22 mpg. a/c not on.

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dude phantom you need to get out more lolololololololol 13 years of checking your gas guage lolololololololololololololololololololololol J/K

 

have any of you read the factory adds on these cars ?

i have one on my wall here ..i found it in a old 81 playboy .

it reads and i quote.

 

"This year's 280zx boasts a 10% increase in horsepower , just for the thrill of it .yet this fuel injected , 6 cylinder ohc powerhouse delivers [21] epa estimated mpg ,[32] estimated mpg highway milage with 5-speed transmission.

based on these figures , an estimated mpg of [443] miles and a highway range of [675] miles awaits you ."

 

add.jpg

 

we where in a gas shortage back then lolol....that was part of datsuns suck you in bit ..

"are cars will get you there and back with gas left over" .lolol lololololol nothing has changed much sence then same bulls@#$ war ,same talk of no gas or oil ..lolololol

same s@#$ differnt day ......they just moved the price in gas up higher .

but its still the same game , same players , same people running the game .they just got smarter with it ....

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phantom,

not sounding like a jack ass but you should have tuned your carbs a bit lean -- it does help. I am an aerospace engineer and I had 2 240Zs

 

first one 73 -- with five speed (early) and 3.9 diffy

going to florida and back to san diego I would compare mile marker indicators and my gauge (it would be off by maximum 2% i.e. 5-6 miles on 300 mile tank)

I averaged 24-25 mpg going crazy (average speed of 80-85 mph)

I got 28 mpg going 65 mph (there were two sections like that)

 

second one is a 71 with late five speed and 3.36

I managed to get a 28 mpg going average 85mph from SD to San Francisco

the odometer with within 1% error of the mile indicated by state (mile markers)

 

Also I aways fill the gas tank to the same level --- 6 inches from the top of the filler neck -- can't get any more fuel (say within 0.1 gallon error)

 

also there are 16 gallons in a 72 tank

1 gallon is unsuable period.

2nd gallon only if you are flat and level

other 14 no problem

and don't ask how I know, let's just say I have had enough expereince on that matter.

 

My current one 260 2+2 is in high teens (work in progress)

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