I've been recording my mileage for a few years now and thought I'd just share exactly what has happened to my mileage as I've made different modifications to my car. All of my driving is part city and part highway. I don't try and take 60mph trips down the highway to bump my mileage up because to me thats unrealistic. I drive 65-80mph on the highway (hey its California) and pretty normal on the streets. My car is a 71 Duster and started out bone stock from the beginning. All the mileage checks were done 3+ times so I could at least get an average. Anyway, here goes...

Starting out, the Duster had a 1bbl Holley 1920 and 75,000 miles on it, 7 1/4" rear end with 2.76 gear, 195/70/14 tires, stock exhaust. Car was very slow and sluggish.

--------------- 13 mpg

Somewhere along the line the carb started running very rich and I couldn't fix it. Gas mileage got much worse. I even found that the power valve check ball had fallen out of the metering block and gas was just spewing in. I reseated the ring and as a result, nothing happened at all.

--------------- 10.2 mpg

As a graduation gift, my grandpa had the engine rebuilt. Car felt faster and I was excited to see what I was going to get as far as mileage went. I was pretty disappointed. 100,000 miles on it now (few hundred on the rebuild)

--------------- 12.5 mpg (15 mpg on a highway run)

The Holley had a 52 jet in it and from reading here, some of the guys said it was most likely drilled out. So I went out and bought a 57 jet. Not much difference.

--------------- 12.8 mpg

Finally I decided to install a super six setup with a 2bbl Carter BBD that was remanufactured. My biggest project to date. Had lots of problems with vacuum leaks until I finally bought the Australian gaskets. Took the car to a shop because I couldn't get it to idle under 1000rpm. They said the distributor shaft was loose and replaced the distributor. It still ran like crap but the mileage jumped up a bunch. Also had a lot more power.

--------------- 15.4 mpg

At this point I finally figured out that it was my points that was causing the terrible idling problems. I replaced the points, set everything to specifications and set my timing to 10 BTDC. I also got rid of the remanufactured Carter and bought a NOS BBD, which ran much better.

--------------- 17.6 mpg

Now I'm thinking it's my cam that is causing all of my woes. The points keep getting to the point where they stop opening up all together. It only takes about a month before they go from .020 to .000. I decide to do the HEI conversion to get rid of the points all together. Mileage goes up a bit. Power goes up as well.

--------------- 18.5 mpg

Even now with the HEI conversion, the engine is starting to idle rough again and I'm almost positive it's gotta be my cam because whenever I would fix the points and when I first put the HEI on, this thing ran perfectly smooth for a few days and then slowly went downhill. It's not running nearly as bad with the HEI but it's definitely getting shaky again.

--------------- 18.5 mpg

Adjusted the valves looser, .010 and .020. Motor now runs free and doesn't rough idle at a stop. No gain in mileage but can definitely feel a difference. 109,000 miles.

--------------- 18.5 mpg

Ended up getting a 2 1/2" exhaust from the manifold all the way back with a flowmaster. Sounds great and I definitely can feel the difference in power. No drone on the highway either. Mileage jumped by 2. 109,000 miles on it by this point (9,000 on the engine rebuild). Car has been pulling to the right for about a year now.

--------------- 20.5 mpg

Front end needed a rebuild kit, so I replaced all the ball joints etc. Got an alignment, steering feels much stiffer and it goes in a straight line now. Mileage jumped up by 1. 110,000 miles (11,000 on engine rebuild).

--------------- 21.5 mpg

So thats it as far as exactly what I've gotten out of each of the modifications. I bought this car for $1000 when I was 16 and I'm 23 now. The only thing left that I can really think of is recurving the distributor. I don't totally understand how to do it yet but I'll keep reading and figure it out eventually. Hopefully that can get me closer to 23mpg and I'll be done with it.

None of this stuff is 100% accurate. While I do average out my mileage gains before I post, there is still the coincidence factor to this all. I can't tell you that putting on a super six exhaust will give everyone a 2mpg gain, but it did in my case. Maybe if more people put together timelines like this, we can get an accurate read on what each modification does. So when someone asks, we can tell them what kind of mileage gain they'll most likely get if they do X to their car.

What would be neat is if we could also get a chart of what each mod costs and will save you per year. That way we can calculate out how quickly the mods will pay for themselves and then some. Now if the average american drives 15,000 miles/yr and lets say gas is $3.50 a gallon. You save $478 a year per 1mpg you gain. So for some of my mods, here's what I saved per year.

Engine rebuild = $1100
Super Six = $2294
HEI = $430
Exhaust = $956

Is my math correct? That seems like an awful lot of money I'm saving. I think I'm wrong, so please correct me because none of that money has been appearing in my wallet

ESP47,

Good history, don't stop there......my Dart started out at 17 to 18 mpg when I first got it too!

When you rebuilt the engine, did you upgrade any internals? or just used the same pistons and cam and only did the rings, bearings, oil pump and timing chain?

What is your rear end ratio?

How many rpm are you turning at 60 mph?

Would you say the car is still sluggish as well as shaky?

When was the last time you lashed the valves?

Have you rewired the engine harness?

Do you know how much mechanical advance your getting? you said the initial was 10 degrees.

Do you know what vacuum pod your running?

A good VC-208 pod and valve lash of .010 and .020 should easily get you into the 20 mpg range.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

How much of your mileage is 'intown' vs. highway? If it is in-town, how much 'bumper to bumper' or idling do you do?

When you rebuilt the engine, did you rebuild the head and have the valve seats replaced? Did you degree the cam, or do the 'dot to dot' method?

What distributor did you use when you upgraded to the HEI?

How's the color of your plugs when pulled after it shakes? What plugs are you running?


-D.Idiot

'Just making suggestions not based on the user's data is not very scientific... maybe we should just forget considering physics all together at this point...'

Nice writeup of your sequence of events.

Poor mileage and rough idle are both clear symptoms of tight valves (possibly due to seat recession). Adjust the valve lash and you may get a new running condition!

Lou

_________________
Home of Slant6-powered fun machines since 1988

Finally got some time to work on it today and adjusted the valves. The intake valves were too tight initially. I ended up adjusting them to the .010 and .020 but I did more of a loose fit with the feeler. I know valves that are too tight can cause worse economy and even burn them, but can a slightly loose condition hurt anything other than being noisy? As it is right now they still sound pretty quiet. Took it for a test run and the engine shakiness calmed down by a lot. I still have to go take it on the highway and see how it runs afterwards. But for now when I'm idling at a stop light, it doesn't have that annoying shake anymore.

As far as the questions, I'll try and answer as many as I can.

The spark plugs look great.

I had the motor rebuilt by a shop and it's basically a new long block.

2.76 rear end gear.

Havent rewired the harness and I don't know the advance or pod that I have.

The distributor was a NOS one from a late 70's mopar. I posted the ebay link to it months back and Dan said it was a good one with good advance curves.

I'm running the NGK ZFR5N plugs gapped to .40

I'd say that 2/3 of my driving is in town driving. Im basically in Sacramento so there aren't many open roads. I'm curious to see what the mileage is now with the valve adjustment. I'll definitely post an update when I find out.

Added a couple of extra mileage gains to the original post if anyone is interested.

What front end kit did you use?

I used this kit off of ebay. Whether or not it's of good quality is up in the air. The parts are made in america but I had to buy two more tie rod ends because the kit only comes with two. The seller is a good guy though. He forgot to send me some of the bumpers. I emailed him and told him about it but said it was ok because mine were still in good shape. I was just letting him know for future sales. He ended up sending me another box full of bumpers a week later.

http://tinyurl.com/5ofaft