Slant Six Forum
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I'm new to this forum. And got a couple questions.
https://slantsix.org/forum/viewtopic.php?t=45425		 Page 2 of 2
Author:  ESP47 [ Tue Jun 28, 2011 9:42 am ]
Post subject: 
Is it normal to drop from 19 or so all the way down to the 12mpg range during cold winters? Our winters are relatively mild here and I don't really notice a difference in fuel economy whether its 50* or 95* out.

I definitely need to do a recurve on mine to see if I could up my mileage. Thats about the last thing I can do to this car short of installing an overdrive.

I don't know if I believe the Feather Duster claims. Here is an except from Valiant.org

"The Feather Duster included aluminum replacements for the inner hood, trunk bracing, bumper brackets, and intake manifold, cutting weight by 180 lb (around 5%). It had a smaller single barrel carburetor, economy distributor calibration, large exhaust, and a 2.8:1 rear axle ratio, with a choice of three-speed automatic or four-speed overdrive manual transmission.

While acceleration was compromised, the Feather Duster was now rated at 22 mpg city, 31 highway with the automatic (a stunning 24 city, 36 highway with the manual), and was larger inside than many other economy cars"

22 mpg city and 31 highway with an automatic is a huge difference. How come we don't see those kinds of splits anymore? Does it have to do with todays modern gas? I only get 1-2mpg difference from city to highway. Also it says "It had a smaller single barrel carburetor". Are they just talking a standard 1bbl or an even smaller specialty 1bbl thats different than the usually Holleys and Carters we see?

Either way those numbers, especially the highway mpg's are way up there. I just don't know if I believe those claims. Sure modern fuel has taken a toll on fuel economy, but to the tune of 10mpg's on the highway?
Author:  SlantSixDan [ Tue Jun 28, 2011 10:14 am ]
Post subject: 
Quote:
Is it normal to drop from 19 or so all the way down to the 12mpg range during cold winters?
On an olde-tyme carbureted car? Yep. You spend a lot more time with the choke on, dumpin' a lot of gas into the engine. It gets worse if engine oil isn't thoughtfully selected; many people choose too heavy a viscosity grade.

It's my understanding that Feather Duster/Dart Lite cars with automatic transmissions, at least late-production ones, got 2.45 rear axle ratio and not 2.76 (non-Feather/Lite cars got 2.76). Not sure what ratio was used with manual transmission, but my guess would be 2.94 (non-Feather/Lite cars got 3.21).
Quote:
22 mpg city and 31 highway with an automatic is a huge difference. How come we don't see those kinds of splits anymore?
Well, for one thing, automatic transmissions now have more than three speeds, so the engine can be kept closer to its optimal RPM range over a greater percentage of overall driving. Also, we waste a lot less gas when accelerating with fuel injection than we did with carburetion.
Quote:
Also it says "It had a smaller single barrel carburetor". Are they just talking a standard 1bbl or an even smaller specialty 1bbl thats different than the usually Holleys and Carters we see?
The Feather/Lite cars got a specific Holley 1945 carb with a smaller venturi and leaner jetting, similar in concept to the economy-configured carburetors that had been installed on slant-6 taxi/fleet cars since '62.
Author:  ESP47 [ Tue Jun 28, 2011 1:53 pm ]
Post subject: 
Quote:
Quote:
Is it normal to drop from 19 or so all the way down to the 12mpg range during cold winters?
On an olde-tyme carbureted car? Yep. You spend a lot more time with the choke on, dumpin' a lot of gas into the engine. It gets worse if engine oil isn't thoughtfully selected; many people choose too heavy a viscosity grade.

It's my understanding that Feather Duster/Dart Lite cars with automatic transmissions, at least late-production ones, got 2.45 rear axle ratio and not 2.76 (non-Feather/Lite cars got 2.76). Not sure what ratio was used with manual transmission, but my guess would be 2.94 (non-Feather/Lite cars got 3.21).
Quote:
22 mpg city and 31 highway with an automatic is a huge difference. How come we don't see those kinds of splits anymore?
Well, for one thing, automatic transmissions now have more than three speeds, so the engine can be kept closer to its optimal RPM range over a greater percentage of overall driving. Also, we waste a lot less gas when accelerating with fuel injection than we did with carburetion.
Quote:
Also it says "It had a smaller single barrel carburetor". Are they just talking a standard 1bbl or an even smaller specialty 1bbl thats different than the usually Holleys and Carters we see?
The Feather/Lite cars got a specific Holley 1945 carb with a smaller venturi and leaner jetting, similar in concept to the economy-configured carburetors that had been installed on slant-6 taxi/fleet cars since '62.
Dan, I meant such a large city/highway split now with our sl6 cars, not modern ones. I only get a couple mpg difference whether I'm driving city or highway in my Duster.

If a Feather Duster had a 2.45 rear end ratio, that would cause a larger city/highway split but it seems like it would be too much of a bear to drive around town and in turn would waste more gas. If they did in fact get those numbers, they had to of been taking forever to accelerate and driving in the absolute most perfect conditions. I bet they even had a 95lb girl driving :)

Thats interesting about the economy Holley 1945. You probably can't find those anywhere huh?
Author:  lancer61 [ Wed Jun 29, 2011 12:23 am ]
Post subject: 
I got two of them.

With manual transmission the difference between city/highway is smaller, an automatic will waste much more fuel at read lights and so on compared to a manual.
Author:  SlantSixDan [ Wed Jun 29, 2011 12:53 am ]
Post subject: 
I know a guy locally here who has, if I'm not mistaken, at least one brand new Feather/Lite carburetor and possibly more than one.
Author:  exoJjL [ Tue Oct 11, 2011 2:22 pm ]
Post subject: 
I read somewhere the slant around '73 got 18 highway 15 city right out of the factory. These numbers are from Chrysler 1973 or 74.
Author:  Aggressive Ted [ Tue Oct 11, 2011 3:28 pm ]
Post subject:  Feather-lite 1945
Dan,

As you know I have been running the Economaster version 1920 Holley from a taxi cab the past few years. Do you think the Feather-Lite 1945 would be better? or the same on mileage? It came with a #53 jet in it however, for more performance I bumped it up to a #57 to keep it around 16 to 18" on the back roads along the foothills.

My local driving has been a very consistent 22.6 mpg. On the freeway it jumps up over 25.5 mpg.
Since my 74 Swinger is very boxy and heavy (3300 lbs.) I keep it around 60 mph on the freeway.

The current engine is a stock 1979 SL6 barn find with my good recurved distributor, 0-30W Mobil 1, large exhaust, etc..
Author:  olafla [ Tue Oct 11, 2011 9:26 pm ]
Post subject: 
I really don't see why you guys keep this thread going.

You already succeeded in scaring away Dartlan, who opened this thread and made his first - and so far, only - post back in June, and mostly got a lot of different and therefore confusing feedback to his questions.

You're all free to be as pissed as you want to, for me mentioning this. :P

Olaf.
Author:  SlantSixDan [ Tue Oct 11, 2011 10:35 pm ]
Post subject: 
Quote:
I read somewhere the slant around '73 got 18 highway 15 city right out of the factory. These numbers are from Chrysler 1973 or 74.
Keep in mind the test protocols used back then were wildly unrealistic. They used 100-octane fuel completely unrelated to anything you could (or can) actually buy at the pumps, and the driving cycle didn't even remotely resemble anyone's real-world conditions.
Author:  SlantSixDan [ Tue Oct 11, 2011 10:37 pm ]
Post subject:  Re: Feather-lite 1945
Quote:
Dan,

As you know I have been running the Economaster version 1920 Holley from a taxi cab the past few years. Do you think the Feather-Lite 1945 would be better? or the same on mileage?
Tough to say. Best way to check would be to find one and try it out! There are some design aspects of the 1945 that are better thought-through than the 1920.
Quote:
My local driving has been a very consistent 22.6 mpg. On the freeway it jumps up over 25.5 mpg.

Good going! If I were getting mileage like that, I would spend my time and effort on things other than swapping carburetors in hopes of better mileage.
Image
Author:  Aggressive Ted [ Tue Oct 11, 2011 10:54 pm ]
Post subject: 
Thanks for the advice Dan......

Yes, been doing lots of body work so I can get it repainted and finish the interior.
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