I replaced the 'stack' on my '74 duster since the manifold gasket was starting to leak on 3 runners...so while I had the stack off I decided to swap over to the super six setup that was previously on my Feather Duster, wrather than just bolting the 1 barrel stack back into place....
(Couldn't let my newly rebuilt BBD go to 'pot' on my work bench...either)

Previously this car got:
20.5 mpg with the 3.21 8 1/4" rear under it
then went to 21.3-21.5 when I upped the exhuast pipe to 2.25"ID
It remained there when I had to swap in a 2.94 7 1/4" rear, but my
highway rpm was lower.
That rear blew, so a 2.76 7 1/4" resides under there now (stop light starts
were clutch burner, high rev starts, but top end was nice on the highway when 'motivated').

Last night I took a trip to a training class and put in 151 miles before refilling on this setup.... It has lots of gump and doesn't 'clutch burn' anymore, motivates better, and baarely uses the pedal to keep 65MPH...
Current 95% highway mpg is 21.47...will try it again tomorrow night on my 'round trip'...
I'll also have to see if we can best the 15 mpg I was getting in town too...

-D.Idiot

"Sure I'll take anything that makes more power and keeps my mileage..."

Awesome! Keep us posted!

Reed

P.S. I recently learned that the jets in all post 1977 BBDs interchange with edelbrock jets. I don't know if you knew that already, but it might help you tune it a bit.

The Carter Super Tuning book said all post 1974 BBD's use carter/edlebrock jets and rods, so it's all good...I do have a Mr. Gasket #1937 adaptor and Holley 2300 I can alsa try too, but the engine is such a road oiler that I don't think I'll get any more MPG out of it (that and the direct gear A-230 3 spd tops things out at highway speed vs. say an OD...)

anyhow, never tryed the setup on a 'stock block', I last got to use it on a modified block and now have found it was a limiter for the mod-slant and a good improvement over the 1 barrel anything....

-D.Idiot

too lazy to do a search right now...

Where is that book available, DI?

_________________
I've been calling it as i see it for my entire life and that's not about to change. Take it or leave it.

I actually bought mine at the local book shop out of their Auto section, they had the Holley and Rochester versions too, the book mostly covers AFB and AVS's, but has a brief entry on the BBD...

-D.Idiot