MPG experiment, 1976 Dart Lite

[Backtobasics]

The mechanical fan is king of my wild card, I expect it to show decent gains. It is a fixed blade 4-6 (don't remember) fins unit. I am going with a larger single puller setup with temp switch, so it only runs when needed. I also want it to pull well once the turbo is in place, particularly for air flow over the intercooler core.

I will set tires at 40 cold, to see what it does.

[ALS]

A 4 speed and 2.73 gears in the rear end should give you the best highway mileage. Best all around gears would probably be a set of 3.23's.

That Chrysler Automatic transmission is the biggest drain on your fuel mileage.
One the HP loss is probably close to 20%, and the auto box weighs an extra 100 lbs over the manual box.
The other factor is it doesn't have a locking torque converter. Slippage in the torque converter is killing your highway fuel mileage. The transmission swap should be good for at least 3 mpg maybe 4 if you get lucky.

[Backtobasics]

Originally Posted by Frank Lee

Why put in a bigger rear end? Bigger gears turn harder.

Why put in a bigger exhaust? Velocity is good and small dia is it for low rpm.

Don't even bother with decimal point claims with short fills. In fact don't bother with short fills at all. Run it down to at least 1/4 tank before filling to have any semblence of accuracy.

The 7.25 rear end with 2.94 gears is whining currently. Ususally a sign of improper setup if recently rebuilt or wear if not recently rebuilt (most likely), so the rear end is showing its age. I do not expect it to explode, but this particular differential has shown to be weak, and has a joking reputation that is is known to fail behind grandma and her slant 6.
The 8.75 housing I have is direct bolt it, and stronger, and I have both 3.23 and 3.55 gears accessible, and the gears change in an hour, so I can see which works better once the 4 speed OD unit is in place.

Exhaust: I am going to have a 2.5 run from exhaust manifold, to trans, and step to 3" from there back. Muffler will be a straight through Magnaflow, and exit just under bumper.
This goes against basic ecomodding theory. The reason is, this car will get a turbo down the road, and the 3" is sized for the turbo. It might be overkill in the short term while naturally aspirated, but the stock 1 7/8 stuff coming off the manifold chokes these engines. The head has terrible flow characteristics stock, and drinking straw sized exhaust does not help. The most common sizing on n/a is 2 1/4 or 2 1/2 so I am not overdoing it too much while n/a but will be sized right when turbo comes, and I don't want to do it twice. The existing set up is ok, but bangs and clangs, and is pinched over axle, through restrictive glasspacks.... not the model of efficient flow.

Originally Posted by ALS

A 4 speed and 2.73 gears in the rear end should give you the best highway mileage. Best all around gears would probably be a set of 3.23's.

That Chrysler Automatic transmission is the biggest drain on your fuel mileage.
One the HP loss is probably close to 20%, and the auto box weighs an extra 100 lbs over the manual box.
The other factor is it doesn't have a locking torque converter. Slippage in the torque converter is killing your highway fuel mileage. The transmission swap should be good for at least 3 mpg maybe 4 if you get lucky.

Right now it has the 3 speed manual. It was supposed to have 4 speed OD as part of the Dart Lite package, but mine is a very early unit, and got out the door with non Dart Lite options.

I have another /6 that I am going to build. Basic rebuild, with some internal tricks for oil drainback, reduced oil windage, etc. I will get it built, and swap the engine, trans to the OD, and rear end in one big swap, sometime next spring?

[ALS]

Sorry I miss read the original post and thought it was a three speed auto box.

[Duffman]

Its because he said 3 speed was one of two options, a 3 speed manual is never an option, if it exists then its standard (hence the term).

[Backtobasics]

Originally Posted by Duffman

Its because he said 3 speed was one of two options, a 3 speed manual is never an option, if it exists then its standard (hence the term).

OK I am confused.

The Dart Lite and Feather Duster were supposed to be either the 4 speed overdrive, or 3 speed torqueflite. Since mine was such an early model, it escaped with 3 speed manual.

[Duffman]

An option in car terms is something you pay extra to get, the 3 speed manual costs no extra, hence it is "Standard" equipment.

The 4 spd OD would be a nice addition to your project I think.

[ceej]

Interesting.
Are you sure the Holley is the original Dart Light unit? Sounds like your timing chain has had it. 20 mpg with that car is pretty low.

Check the list number to see if the carburetor is the correct one. If there is a Holley 1940 or Carter BBS on there, it's not right.

SlantSixDan up on slantsix.org had some special Holley 1920's at one time, NOS. I bought one for the build on my wife's '63 Dart GT. I have the correct Aluminum 1 bbl intake. One that isn't cracked in the plenum floor. (A rarity.) I've got a Feather Duster 2-1/4" head pipe that came off when I installed Dual Dutra Duals into twin 2-1/4" head pipes on my drag car.

Also check your distributor and vacuum advance can to make sure they are the correct ones. The vacuum amplifier that runs the EGR may have problems. If it isn't there, you sure don't want to run the Feather/Lite distributor curve. You'll jack the Cylinder head temperatures through the roof with 52 degrees total timing and no EGR.

Got some pics of the engine compartment? Unmolested Feather Dusters and Dart lite's are cool! And Rare!

CJ

[Backtobasics]

Originally Posted by ceej

Interesting.
Are you sure the Holley is the original Dart Light unit? Sounds like your timing chain has had it. 20 mpg with that car is pretty low.

Check the list number to see if the carburetor is the correct one. If there is a Holley 1940 or Carter BBS on there, it's not right.

SlantSixDan up on slantsix.org had some special Holley 1920's at one time, NOS. I bought one for the build on my wife's '63 Dart GT. I have the correct Aluminum 1 bbl intake. One that isn't cracked in the plenum floor. (A rarity.) I've got a Feather Duster 2-1/4" head pipe that came off when I installed Dual Dutra Duals into twin 2-1/4" head pipes on my drag car.

Also check your distributor and vacuum advance can to make sure they are the correct ones. The vacuum amplifier that runs the EGR may have problems. If it isn't there, you sure don't want to run the Feather/Lite distributor curve. You'll jack the Cylinder head temperatures through the roof with 52 degrees total timing and no EGR.

Got some pics of the engine compartment? Unmolested Feather Dusters and Dart lite's are cool! And Rare!

CJ

I recognize the screen name.
I futz around over at .org from time to time.
20 isn't great for sure. I had not considered timing chain. Original motor has fair amount of blow by so I know it is aged.
Carb is a 1945 if memory serves. I rebuilt it when I first got the car. The bolts holding lid to main body AND bolts holding base to main body were stripped. I tapped them out and rebuilt. I sorely need to find or build an accellerator pump rod, it has no acc pump shot right now.

I might need some help with the distributor and EGR curve stuff.

I will get some engine shots.

[ceej]

Your user name looked familiar!

Yeah, typo on the 1945. I gave my last one to DusterIdiot over on dot org. See if Dan still has one of the Holley economasters. He seems to have quite a few interesting tidbits squirreled away!
The 1945 wasn't well regarded by the mileage or power folks. DI was experimenting to see if he couldn't get one to run well. He may be able to supply you with the accelerator pump rod. You should be able to find a ton of 1945's in the junk yards though.

For the power fiends, best economy tends to be with the BBD or small Holley four barrel. I was in the 24 mpg range with the 8007 Holley 390, converted to a jetted secondary metering block.
For the HyperMiler, the Holley 1920 or the BBS would probably be a good carb to play with, except in a heavier vehicle, then the 390 Holley would likely give the best balance. Staying in the small primary venturis will give excellent results. DusterIdiot was bumping 26 mpg with his Hyperpak car with a split plenum and 390.

The 1 bbl economaster should emulate the original Feather/Lite carburetor. The main jet was pretty small. I think DI told me they ran a 48 jet. Something to that effect. I'd have to take a look at what's in the Economaster I have. It got installed on THOR's race car for a while, so he likely has a 56 in it. I'll have to fix that.

Do you have the FSM for the '76 model year? The EGR will likely be very similar, if not identical to my '74, but I just don't know. The biggest issue is finding a properly working vacuum amplifier. Mine was junk on the '74. DI got me one, which I returned to him when I started farting around with four barrels. (No EGR provision on the Exhaust setup I run.)

Have you found a build sheet? They normally were in the rear seat back, or taped up behind the glove box. That will tell a tale. Be careful with it! By now it's going to be old and crunchy!
The gears and transmission seem a bit odd. As an early car, it's very possible though. DI has a Feather Duster that has a factory Sun Roof! Want to talk about a rare car! It's 1 of 3 IIRC.

If you can get somebody with a distributor machine to take a look at the distrubutor curve, we can see if it's correct for the Dart Lite. The governor should be rediculous, like a 15R. Huge advance. It won't be all in till 3400 or something like that. So if you cruise around at 90 you'll get all of your timing.

The advance can is pretty radical too. DI has all the specs, and may have some bits and pieces for the Feathers and Lites. His Hyperpak car is a Feather Duster with much of the Aluminum bits and pieces. The optioned car he has includes the Aluminum trunk lid, so is a tad lighter yet. Not all the cars came with all the good bits.

The quiet chains are generally a 100k mile item, but time and rust will loosen them up pretty badly. Even a low mile car that's this old will have a worn out chain. It'll give you a chance to degree the cam to make sure it's where it's supposed to be.

Fun project!

CJ