Early Chevy 305 Gas Mileage??

[cherrycj7]

Hey Guys, First post here. I am getting a 1976 chevy 305, 2 bbl. Everything is stock on it. I was wondering what a good estimate on the gas mileage might be? It is going to be in a 4 wheel drive jeep Cj7 about 4200 pounds. I have seen a lot of posts with the 1980's carbed 305's but nothing really about an earlier 305. Any thoughts would be greatly appreciated, thanks.

[Stewart G Griffin]

i will respond shortly(within 2 months) with a very detailed measurement as i have the same engine with same carb now installed in the truck.

Keep in mind that with the new E10/E15 gasonlines that are so prevalent nowadays, gas mileage for these types of engines will probably not be stellar.

[cherrycj7]

Not looking for anything great really for mileage. Just hoping for around 15 city. Do you think this is possible with this engine with the TH400 tranny and it being a 4X4? Thanks

[VileZambonie]

What's your gear ratio?

[cherrycj7]

Not 100% sure, either 2.73 or 3.54. I have to check it out this weekend. It seems as though it would be 2.73 because it struggles going up hills, struggles a lot! What would your thoughts be though with either? I will let you know what it is for sure this weekend if it does not rain. Thanks

[VileZambonie]

What size tires?

[cherrycj7]

31" Goodyear MTR's.

[Stewart G Griffin]

15 in the city i don't think is going to happen with that setup, but you never know----what's your exhaust setup?

More realistically, 15 highway maybe, just maybe.

With a 350 crate, i was able to get 15.8-16-ish with a high of 17.2 on the highway.  Here is the link to that scientific study which is continually on-going:

http://forum.73-87chevytrucks.com/smforum/index.php?topic=8474.0

Again, the study is on-going and my latest theory as to why the fluctuating figures is my usual fillup station had E10 blend while some of the other stations i used had pure 100% gas.  They were, however, all EXXON stations.

Because the 350 bent a valve among other things (not sure how that happened) ,Now i've got a  78 305 out of a 78 malibu in the truck.  It also has the 2G two barrel.  And i will report on MPG ASAP, probably within 2 months.

Now, with your 4200lbs weight, 4X4 and 31" tires and the move to E10/E15 (which i actually think is a good idea although it really hurts mileage i think) i don't think you'll get higher than 17 on the highway, but you never know.

[cherrycj7]

My exhaust will most likely be headers, no cat, glass pack muffler. Is there a differance between a quadrajet and the 2 bbl carb in mileage? I have heard mixed results, but mostly that it is a little better because of the small primaries.  Thanks for the thread. i will look at it tomorrow.

[Stewart G Griffin]

i think the quadrajets going to be better for mpg not so much because of the smaller primaries, but because the quad has metering rods in the jets whereas i don't think the 2G has them.   i still think the 2G is an interesting carb and that's why i'm using it now(it came with the engine, so i decided to go ahead an use it), but may switch back to quadrajet later.

i think the other important thing for mpg is to use the stock air cleaner assembly vs. an open element type aircleaner;  The stock air cleaner assembly is designed to have the incoming air at between 84-120 degrees at all times---warmer air = less dense air = less fuel burned =better mpg.

[VileZambonie]

Stewart, You want as much Oxygen as possible in every gulp of air you can get. When you have to demand more throttle to get the desired speed/acceleration you are being less efficient. The idea behind a cold air intake is to get more oxygen. Air = 78% Nitrogen and about 21% Oxygen

The thermostatic air cleaner is mainly for emissions purposes.

[cherrycj7]

Turns out that I have the 3.54 gear ratio. Would you think that with a manual overdrive transmission and 4.10 gears the gas mileage may be closer to the 15 city?? Thanks

[Stewart G Griffin]

Stewart, You want as much Oxygen as possible in every gulp of air you can get. When you have to demand more throttle to get the desired speed/acceleration you are being less efficient. The idea behind a cold air intake is to get more oxygen. Air = 78% Nitrogen and about 21% Oxygen

The thermostatic air cleaner is mainly for emissions purposes.

Please provide more info/links/articles/sources to support this notion as i can't get a clear answer and i have also read in many places that the thermac does improve mpg.  i will provide my sources if requested later as i am very tired right now.

[jaredts]

Stewart, I don't understand how a thermostatic air cleaner could improve mpg's.  It pulls in warm air when its cold to reduce emmisions, but after that it does the same thing as an open element air cleaner--just more restrictive.  If you find a link to some info. on that I would be interested to learn something here.

[Stewart G Griffin]

OK, i don't have very much time to provide links, because i got switched to night shift and also i can't seem to find most of the links i read.

But for now:
http://www.gassavers.org/showthread.php?t=244


More to come.