Can I tune a QJet to obtain 18+MPG on a 383-406 Chevy in a Chevy II Wagon?

[AHotRod]

Cliff,
First off, I have purchased parts from you and built a #207 Qjet that works great, and also, THANKS for autographing your book that I purchased also.

Now, I'm ready to take my old Wagon back to the street as a daily driver. I've got most of the parts to build a 383 or a 406 small block for it so I can enjoy some nice power. It currently has a old 327 Super Stock engine in it with the #207 carb.

Some of my buddies are trying to push me into converting the car to a 5.3-6.0 litre late model EFI conversion, and maybe that is what I should do. But,..... I'd really like to know if it is feasable to obtain 18+ MPG with either a 383-406 CID engine?

I have Turbo 350 transmissions, and 3.55 - 4.30 gear ratios and the rear street tires are 27.5" tall.

I really have not found much discussion on fuel mileage setups, so I need to find out if this is feasable or A'm I forced into doing a late model conversion.

I look forward to any guidance that you or others may provide.

Best regards,
Glenn

[Cliff Ruggles]

You are going to find out that after all the time and effort, there isn't any more fuel mileage, total power, or any other benefits to the EFI set-up.

The only difference when it is all said and done is that you don't need a choke for cold starts on the EFI conversion.

Fuel milage is effected by a lot of things, including how the engine is built and set up for efficiency in the "normal" driving rpm range(s).

Ignition timing and fuel curves are part of the equation as well.  Both are fully adjustable with vacuum advance distributors and q-jet carburetors, so the tuner has full control of the outcome in that area.

Quite a few years back we restored a 1967 Impala SS.  It had a 300hp 327 engine and PG transmission with 3.31 gears.  It was capable of 16-17 mpg's for "normal" driving. 

I decided to install a 4L60 OD unit to lower engine rpms in high gear, and provide a lower first gear.  It worked out better than I had expected.

We consistantly got 18mpg's city, and mid 20's on the highway cruising around 65-70mph.

My Ventura has a 455 cid engine making over 550hp, with 3.42 gears and a 10" converter.  It gets around 13-14 mpg's if you have enough willpower to run thru a tank of fuel without a few full throttle blasts.  It runs nearly into the 10's in full street trim.......I have yet to make it thru a tank without a couple of runs thru all the gears at full throttle!....LOL.....Cliff