I finally took my freshly rebuilt engine on its first "longer" trip.  I've done several 5-10 miles journeys, but this was a 50 miler.  I started with a full tank of 91 octane fuel and went out on the expressway to meet up with some Chicago Z guys for our monthly club meeting.  I kept it around 55-60 mph (even with the semi's passing me) and it drove very well.

 

To my surprise though, upon my return home when I refueled to allow me to check my mileage, I got over 30 MPG!  Is this possible?  I'm running a rebuilt stock 1972 L24 with N58 needles (I know they're lean) and with a pertronix ignition.  I did put a wide-ratio 5 speed, along with my stock 3.36 rear end, which I know makes for very high gearing.  Guess I must have gotten the old engine put back together correctly.

 

What do you guys see for MPG?

My first long haul with my fresh L24 to Zcon 2010 I got over 30. SU's running very lean running max or 37 total advance. Amazing was that fuel gauge was dead nuts accurate using my CJ 5 gas tank -

This was with a 480 lift cam and headers and electronic ign.

Im seriously thinking going back to SU's, because its crazy expensive to drive with triples. Some have suggested that with well tuned triples you could get to the same levels (on highway) but i doubt it...

Unless you got a turbo no need for 91 octane. 

If you want accurate mpg drive little more like 120 miles then check by refueling.  

Do this 10 times then take average of all the fill ups.

if you want to measure gas mileage using a cell phone app, there is one called gasmate that will do all the math for you.

 

Yea its possible to get over 30 but you've gotta drive slow  and accelerate slow and have a lot of flat terrain and a strong tail wind and

no rain.

 

i've been trying to get 50 mpg with my vw diesel. I've done everything possible from tweaking the computer to overinflating the tires.

I've only achieved it once and let me tell you its not easy. You have to drive like a 100 year old. Hype-r-mile-ing really pisses off

other drivers too

 

my efi 78z gets about 20-24

Edited May 4, 20159 yr by hr369

I also was running 54 gears and a T5

The diff ratio and the five speed are playing a big part in achieving 30mpg. You are running 3.364 with a five speed which gives you long legs and the best chance of getting 30mpg on the highway. If you had 3.54, 3.7, 3.9 or 4.11 you can forget it.

The pertronix ignition would also be an improvement over the points system.

 

Keeping the speed down and no hard acceleration also helps a lot. Once you go over 50mph the wind resistance its devastating to your milage.

 

Anything performance wise done to the engine is generally a big negative for economy, but thats not the objective when fitting up for performance.

 

Im running a stock L28 with efi and getting nowhere near 30mpg. More like 20mpg, but then Im not all that much on the highway. I like cruising the back roads and its not a daily driver.

 

I think Black gold man has a good point. Multiple fill ups will give you a more accurate reading although it will be average milage.

 

Chas

i've been trying to get 50 mpg with my vw diesel. I've done everything possible from tweaking the computer to overinflating the tires.

I've only achieved it once and let me tell you its not easy. You have to drive like a 100 year old. Hype-r-mile-ing really pisses off

other drivers too

 

I have Skoda (wich is Volkswagen, basically) with 1.9TDI and i get easy 50mpg with it, on the highway even more.