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gas mileage??

This makes sense. That 318 was probably working harder just to keep the van in motion.
This is the instance where a small engine in a heavy vehicle is a bad combination. You'd think that a 273 in a Satellite would get better mileage but if that engine is straining to maintain freeway speeds, the throttle opening is larger and the engine is working too hard to be efficient. A 360 could be used and even though the engine has more cubic inches to feed, the engine is barely working to move the vehicle.

Kern, agreed. The 360 took very little throttle to maintain freeway speeds (70+) without the trailer.
 
This makes sense. That 318 was probably working harder just to keep the van in motion.
This is the instance where a small engine in a heavy vehicle is a bad combination. You'd think that a 273 in a Satellite would get better mileage but if that engine is straining to maintain freeway speeds, the throttle opening is larger and the engine is working too hard to be efficient. A 360 could be used and even though the engine has more cubic inches to feed, the engine is barely working to move the vehicle.

Read the paper I posted. Thermodynamics is one thing that what seems like should be true is not really (understanding cooling system for instance is not intuitive). Look at the Engine Load Factory section. For a given engine speed and RPM a small engine operating at high load will have higher efficiency and fuel economy than a larger engine running at lower load.
 
The EPA paper is good when comparing theory and actual fuel consumption as measured, but there could be exceptions in some rare cases (like a larger displacement engine outperforming a smaller displacement engine-MPG wise). Unfortunately, the EPA did not find or mention any exceptions or state if cases might exist.
 
The EPA paper is good when comparing theory and actual fuel consumption as measured, but there could be exceptions in some rare cases (like a larger displacement engine outperforming a smaller displacement engine-MPG wise). Unfortunately, the EPA did not find or mention any exceptions or state if cases might exist.

Not sure what you are getting at.... I don't see how that could be possible with 2 engines on a dyno doing the exact same work. That what the paper is getting at. The magic in MPG is matching the entire system to put the engine/rpm/load in the optimal point to get the most work out of it at the highest efficiency.
 
Thanks for the paper, Jim. One thing I have realized about mpg is how you drive is the big factor. For example, my grand marquise will get 17mpg in town when my wife drives it, and I can get 19 easily with me behind the wheel. My 4 cylinder ranger gets 21 when my wife drives and I get 24. I drive three cars ahead in traffic watching the patterns, and that helps mpg. Going to fill up the road runner today I'll check the mpg and report back.
 
Thanks for the paper, Jim. One thing I have realized about mpg is how you drive is the big factor. For example, my grand marquise will get 17mpg in town when my wife drives it, and I can get 19 easily with me behind the wheel. My 4 cylinder ranger gets 21 when my wife drives and I get 24. I drive three cars ahead in traffic watching the patterns, and that helps mpg. Going to fill up the road runner today I'll check the mpg and report back.

Mmmmmm what do this say out your wife driving :). I think this was mainly concerning open road driving not city driving which can be drastically different based on operator.
 
I guess there is no way to manipulate the laws of physics. I'm running a 318 two barrel right now, converting to a 340 shortly, then I am going to de-stroke the 340 to a 305 (billet crank should be ready in another week or so). It should be interesting to compare my MPG figures and see which is more efficient. What may throw the whole comparison off is not changing the rear end ratios to match torque peaks of each motor.
My custom (longer) rods for the 305 are ready to go (see fotos):

DSC01169.JPG DSC01170.JPG
 
I guess there is no way to manipulate the laws of physics. I'm running a 318 two barrel right now, converting to a 340 shortly, then I am going to de-stroke the 340 to a 305 (billet crank should be ready in another week or so). It should be interesting to compare my MPG figures and see which is more efficient. What may throw the whole comparison off is not changing the rear end ratios to match torque peaks of each motor.
My custom (longer) rods for the 305 are ready to go (see fotos):

View attachment 541088 View attachment 541091

Agreed I think you hit the nail on the head. It is how you match system to the engine, the gotcha is that perfect spot may really suck anywhere else in the band. It really is an optimization problem with no real single answer.
 
Thanks for the paper, Jim. One thing I have realized about mpg is how you drive is the big factor. For example, my grand marquise will get 17mpg in town when my wife drives it, and I can get 19 easily with me behind the wheel. My 4 cylinder ranger gets 21 when my wife drives and I get 24. I drive three cars ahead in traffic watching the patterns, and that helps mpg. Going to fill up the road runner today I'll check the mpg and report back.
How is your wife on brake pads? Friend of mind changes pads after 15,000 miles on wife's car.
 
My 456 stroker went from horrible to 20mpg with just an overdrive, there is no better way then OD to add mileage. As stated matching your parts to the ideal operating range that your targeting is crucial. Knowing I'd be operating down around 2,000 rpm on the freeway I chose a cam that likes 1,800-5,800 rpm, used a 750cfm carb and put 3:55s in it. Wouldn't change a thing accept a Procharger lol.
 
Wrenchero, I have been down this road, listen up. I do not have all the golden ticket answers but I do think I can help a little bit. Since your doing pretty OK now, and do not mind experimenting which is key, I’ll tell you all what I did.
i dont have any experience with tq's. any good comments out there
Ether of the TQ’s you have there will be fine. IMO, the electric choke model would be better to use and easy to hook up. I managed a best of 18 but normally found 16-17 with that carb on a 400/727-3.55 set up in my B body. Only other mods were a Holley street dom & headers fired by a chrome box.

But truly, no matter the carb used, state of tune will rule.

i guess i shouldnt complain too much.it runs great,super low maintenance, and it runs great on 87 octane.i met a guy at a show with a challenger with a 2bbl 318 challenger who got over 20mpg.he told me i should put a 7 1/4 in it.too bad i threw one out 25 years ago??

No no no, stay away from that person! Post holiday s picture up so we know what *** hat to stay awat from.
Bad advise that will yield no real result.
Nothing like going backwards and paying a fee for it.
Revoke his MoPar card now!
Report him to ththe man club for review on his man card!

hello all.i know most guys are looking for more power but i am looking for better mileage.i have a 68 satellite convertible that i take trips with.it has a stock 318 2 barrel with stock cam,stock exhaust manifolds,dual 2 inch exhaust,8.75 rear with 2.76 gears and 904 trans.it gets 16-17mpg on the highway.should i be happy with that or should i try to do better.i have 2 thermoquads i was thinking of trying. a 9185 318 truck carb and 9801 mopar universal thermoquad with electric choke, and edelbrock performer intake.i dont mind messing with it because i can always go back to how it was.thanks for any input.

Cost vs. return? Do you care?
I didn’t. The search for knowledge is never cheap, and perhaps not easy at times.

What I did on my stock 360/904-8-1/4, 2.76 geared rear in my ‘79 Magnum to achieve a max of 20 mpg’s and normally 19, from top to bottom was;

Earlier OE trap door air cleaner
600 AFB on the OE iron 4bbl.
Dual exhaust @ 2-1/4 into twin high flow cats that were legally needed at the time, H pipe, turbo mufflers to the bumper. Ignition was a junk yard truck distributor fired by a MSD 6. I also installed a MP viscous fan. If that freed up HP, for mileage, IDK but I needed a fan so I hired that MP fan.
Tires were 245/60/15 on all 4 corners.

While this list is not a huge help I hope it helps. Obviously it has room for improvement!

If you drive your car everyday. As your main car even in the cold, I suggest a regular factory air cleaner to help in warming up the car. An open element air cleaner will deliver easier breathing which translates into more power and mileage.

The intake could be less restrictive. While the OE unit is a rock solid part, an aluminum unit can help with additional free breathing.

For the 318, I have found the Performer is as good as the OE iron. The LD4B is better. I would like to try the rpm up top myself even though there is a slight rpm off set. But IMO, an improvement will be found on the hwy. Around town, not so much. Again, IMO.

Exhaust. Headers should improve mileage. But I can not verify this on my engine testings. On your engine, I would move to a 2-1/4 pipe size with an H or X pipe into a Dyno Max super turbo muffler.

Again on carbs, no matter what carb you have on top, make sure that your cruising rpm state of tune is excellent!

The only draw back to the use of the TQ is tuning parts or there lack there of. And if the bowl brakes or warps due to heat, it’s kind of done then. A good working TQ is really hard to beat and if you have a good one, your in luck.
The TQ is my favorite carb hands down. Great for stock to the fun and flexible street strip rides.

Need a new carb?
I suggest ether the AFB or better yet IMO a AVS. The tuneable secondary air door is a real nice item.

If your a Holley only guy, you’ll need nothing more than a simple 1850/600cfm carb.

Make the best effort in the carb tune and the distributor tune. Once you have all of that dialed in and running and operating at its best, I now say, add the MSD for the final edge.

Have fun and good mileage hunting!
 
just wondering about the guys getting 25 mpg.are you fishermen too? i live on long island where fishermen and stories are plentiful. haha! if you get good highway mpg give up some info!
 
i am by no means rich.just a struggling mechanic.dont mind spending money to improve my ride and learn something at the same time.i'll never claim to be a sensible person.i have a 1977 ariens snowblower with a tecumseh 4hp.i rebuilt the engine and had the cylinder sleeved.i could have gotten a knock off engine for a fraction of the price at harbor freight for $99 but......
 
how is the gear vendors unit.i know its expensive but does it make a big enough difference in mileage.would i need a 904 with lock-up converter for that to work best?? just throwing things out there but always interested in it.
 
Just filled up the road runner. Calculated 13.3 all city driving. I do drive like a old lady around town as I have no expressway. In fact my average speed in my work commutes is 22mph due to many long traffic lights. I'm in the habit of hyper mileing to the red lights.
 
just wondering about the guys getting 25 mpg.are you fishermen too? i live on long island where fishermen and stories are plentiful. haha! if you get good highway mpg give up some info!
Where are you located on theIsland. I'm at exit 62 of the LIE.
 
how is the gear vendors unit.i know its expensive but does it make a big enough difference in mileage.would i need a 904 with lock-up converter for that to work best?? just throwing things out there but always interested in it.
As I mentioned there is absolutely no better way of improving fuel mileage than an overdrive although it's probably the most expensive and labor intense way to get it. In my case I went from 3,100 rpm @ 70 mph to 1,700 rpm @ 80 mph, that's huge but I'm running a 6 speed standard (the hardest one to make fit). The gear vendors is probably the quickest and easiest OD you could install without going to a standard. As for mileage I took a 6 hour drive to a buddies place in Canada with 4:30 gears and consistently got 20mpg on the freeway with a 500HP big block 456. You can fine tune it, play with different carbs, etc but nothing will give you huge gains like an overdrive. I'm not super familiar with the gear vendors OD ratios but you could download the tremec app on to your phone which will allow you to quickly compare rpm differences. The other huge plus to OD is often you can lower your rear ratio for better out of the whole performance and still do great on the freeway.
 
As I mentioned there is absolutely no better way of improving fuel mileage than an overdrive although it's probably the most expensive and labor intense way to get it. In my case I went from 3,100 rpm @ 70 mph to 1,700 rpm @ 80 mph, that's huge but I'm running a 6 speed standard (the hardest one to make fit). The gear vendors is probably the quickest and easiest OD you could install without going to a standard. As for mileage I took a 6 hour drive to a buddies place in Canada with 4:30 gears and consistently got 20mpg on the freeway with a 500HP big block 456. You can fine tune it, play with different carbs, etc but nothing will give you huge gains like an overdrive. I'm not super familiar with the gear vendors OD ratios but you could download the tremec app on to your phone which will allow you to quickly compare rpm differences. The other huge plus to OD is often you can lower your rear ratio for better out of the whole performance and still do great on the freeway.


The paper completely agrees with this because of 2 things. 1 you are lowering RPM. efficiency drops FAST after 2000 RPM. 2 you are loading the engine more to do the same work. Having the throttle plates closed caused more work to pull in the air. Having them 1/2 open is more efficient.
 
I love overdrive transmissions to make driving at highway seeds much more comfortable. I doubt, however, that if you do it merely to save money, I doubt you will recoup your investment.

What I worry about in your case is that you have a 2.76 rear with a 318 2 barrel. I am not sure an overdrive is right with the gearing and power you have in your car...
That's why I mentioned helping low end torque a bit, and the OP said he was on a budget; which, to me, throws the OD idea out the window.
 
how is the gear vendors unit.i know its expensive but does it make a big enough difference in mileage.would i need a 904 with lock-up converter for that to work best?? just throwing things out there but always interested in it.
I'd go another route. Their OD is a mere .78.
 
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