Max MPG

[1978Bonanza]

I have a 1978 C-20 with a 350 4 barrel and a th350. It has an edelbrock 600 and thats it performance wise. I put a new rotor, new wires and plugs, and new air filter. I have no clue what my mpg is. I would be driving about 40% city and 60% highway. I have no clue what my gearing is. It is a 14 bolt and thats all I know about it. What gearing and other things would get me the best mpg? What do you think it would get now? Thanks.

[Stewart G Griffin]

This is a fascinating topic and the one the interests me the most.  i am obsessed and very anal about this.  As soon as i get my digital speedo installed i can report back on exact mpg figures:

350 crate engine (260hp version)
Th-350C
2.56 rear
true dual exhaust

i feel you should be able to get 15 easily.  But tell me about your exhaust system. 

Some improvements could be adding a tonneau cover;  Tests are saying 11% improvement.  Blocking off the front grill sort of like what the nascar racers do.  But this is tricky---don't want to block off too much so as to cause overheating.  Streamling the  underside of the chassis;  i will report back on this after i attempt it.

Another thing i was looking at was a tailgate device that supposedly makes better aerodynamics than having it completely closed or open:
http://www.droptail.com/index.htm

The other thing i was looking into was designing a front end/nose, probably out of fiberglass, similar to the ones found on the superbird/daytona charger:
http://en.wikipedia.org/wiki/Plymouth_Superbird

i feel this would really improve mpg.

[eventhorizon66]

The other thing i was looking into was designing a front end/nose, probably out of fiberglass, similar to the ones found on the superbird/daytona charger:
http://en.wikipedia.org/wiki/Plymouth_Superbird

i feel this would really improve mpg.

It would also reeeeeeeeeeeeeeeally look goofy. 

[Captkaos]

trucks get the best gas mileage with the tailgate up, this has been debated over and over.  Drive around on a tank of gas with it up and then drive around on a tank with it down, you won't see an improvement.

The Superbirds were not designed to be fuel efficient, they were designed like that in a wind tunnel because Ford was coming out with a more powerful motor and they new they couldn't come up with the necessary power to compete in that same amount of time without reworking the engine, so the put the car in a wind tunnel and increased its aerodynamics which was equivalent to gaining the power they needed.

For driving around at 55mph, doing that kind of aerodynamic changes won't help..


I would think you would be around 15mpg with optimum settings, depending on the rear ratio...

[1978Bonanza]

What rear ratio would get me the best mpg? I have not the slightest idea on the ratio I have now. My exhaust consists of stock manifolds and 2 3/4 inch pipe cut right before the bed. It has no cat no muffler but and thinking about glasspacks and put the tailpipes back on.

[VileZambonie]

There are too many variables to say without knowing what you have now for final drive ratio, trans, tire size, what type of driving you do etc. First thing, get a decent exhaust system and make sure you're tuned up well. The amount of $ you'll spend on a ratio change you'll robably never see vs fuel mileage $$

[zieg85]

What rear ratio would get me the best mpg? I have not the slightest idea on the ratio I have now. My exhaust consists of stock manifolds and 2 3/4 inch pipe cut right before the bed. It has no cat no muffler but and thinking about glasspacks and put the tailpipes back on.

I would guess you have a 3.73 gear being a 78.  In my case, I get 15.5 with my 3.21 gear in my 454 on the open road with the tailgate down.  I have 133K and every emission control device installed from the factory is still on it and I assume functioning even the dual air pumps.  My tire size is stock LT 235 85R16.  In my case my engine is not working hard at all, tons of power even with the highway gear.  I am in 4th gear by 30 mph and I drive mine very easy.  I can say it doesn't take much gas and I am up to 60-70 very quickly.  I have

[1978Bonanza]

My 350's only emission control is a pcv valve and soon that is going to be gone for a breather. My tires are 8.75x16.5 lt. It has 120k or 220k. I will try to keep my foot out of it when I can. It has a 350th tranny.

[VileZambonie]

My 350's only emission control is a pcv valve and soon that is going to be gone for a breather.

Why would you want to do that? Do you like diluted oil, carbon build up and sludge in your engine?