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73-87 Chevy _ GMC Trucks => 73-87 Chevy & GMC Trucks => Topic started by: cherrycj7 on April 20, 2010, 06:42:51 PM

Title: Early Chevy 305 Gas Mileage??
Post by: cherrycj7 on April 20, 2010, 06:42:51 PM
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.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: Stewart G Griffin on April 21, 2010, 08:00:27 AM
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.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: cherrycj7 on April 21, 2010, 07:40:51 PM
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
Title: Re: Early Chevy 305 Gas Mileage??
Post by: VileZambonie on April 21, 2010, 07:47:14 PM
What's your gear ratio?
Title: Re: Early Chevy 305 Gas Mileage??
Post by: cherrycj7 on April 21, 2010, 08:28:34 PM
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
Title: Re: Early Chevy 305 Gas Mileage??
Post by: VileZambonie on April 21, 2010, 08:43:19 PM
What size tires?
Title: Re: Early Chevy 305 Gas Mileage??
Post by: cherrycj7 on April 21, 2010, 08:46:18 PM
31" Goodyear MTR's.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: Stewart G Griffin on April 22, 2010, 08:55:07 PM
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.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: cherrycj7 on April 22, 2010, 10:25:15 PM
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.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: Stewart G Griffin on April 23, 2010, 08:08:42 PM
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.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: VileZambonie on April 23, 2010, 08:38:04 PM
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.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: cherrycj7 on April 25, 2010, 03:23:14 PM
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
Title: Re: Early Chevy 305 Gas Mileage??
Post by: Stewart G Griffin on April 27, 2010, 10:58:50 AM
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.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: jaredts on April 27, 2010, 12:52:35 PM
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.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: Stewart G Griffin on April 28, 2010, 09:01:03 AM
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.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: VileZambonie on April 28, 2010, 03:21:46 PM
Stewart, I understand you would like me to provide you with links and articles to prove this notion however I do not have time to do this. You can easily find this info yourself if you do some research. If you have your doubts look around online but do it in reputable places not like that link you posted of that messageboard, with a ghetto rigged air cleaner. Don't believe everything you read on the internet as there is a lot of false information repeated out there. Pick up a book on Automotive Technology like the Erjavec 5th edition
Title: Re: Early Chevy 305 Gas Mileage??
Post by: Stewart G Griffin on April 28, 2010, 04:28:08 PM
Yes, i think this topic is not cut and dry and will require more research.  i can't get a clear answer;  Some say yes, some say no.

This will take more time to uncover as i am busy too.



And i know about the trustablility regarding wikipedia entries, but for now:

http://en.wikipedia.org/wiki/Heated_air_inlet
Title: Re: Early Chevy 305 Gas Mileage??
Post by: VileZambonie on April 28, 2010, 05:44:11 PM
Again, what it is saying to you is in order to atomize the fuel when the engine is cold it is heating the air. When the engine is up to temp the thermostatic air cleaner no longer draws in warm air. The factory set up on our trucks draws the air in at the grill when the mode changes.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: jaredts on April 28, 2010, 08:07:10 PM
Stewart, I found the links interesting.  Thanks.  Not sure I buy it, but what do I know.  As for the thermostatic air cleaner, like said before it doesn't draw in warm air for very long anyway so I'm not sure its relevant to better mpg's.  Back to 305 fuel economy:  You'll be lucky to get 15hwy/11 city.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: Lt.Del on April 28, 2010, 10:21:41 PM
all the trucks i have owned have had hoses that lead from grille for fresh "cold" air to the air cleaner, that are about 4 inches in diameter.  The Feds have been putting pressure on manufacturers since the oil crisis of '73 to increase mpg's.  Why would they put in a fat hose to feed the carb clean cold air if it would decrease mpg?
Title: Re: Early Chevy 305 Gas Mileage??
Post by: cherrycj7 on April 28, 2010, 10:30:45 PM
Jaredts, 11 city, 15 highway, why do you say that. I mean, is that from expierience? With around 10mpg's now with my 232 I-6 wouldnt the better power to weight ratio with the 305 give better results? like 13 city? torque would be going from around 190 to 240ish foot pounds. Do others agree with this thought? Would the early 80's 305's have any better gas mileage do you think? I do not want to go fuel injection and feel the 305 is the perfect size for the cj7. Do the years matter with gas mileage? Would the "newer" carbed 305's have better MPG's than the older? Thanks
Title: Re: Early Chevy 305 Gas Mileage??
Post by: jaredts on April 29, 2010, 05:48:34 AM
Jaredts, 11 city, 15 highway, why do you say that. I mean, is that from expierience?
My answer was a cross between an educated guess and a little experience.  I've owned several cars with 305's.  Never had a truck with one.  The numbers I posted are about 1 or 2 mpg's less than what I generally got from 305's with a quadrajet in a heavy old car.  My '87 camaro got closer to 18 or 19 hwy, but they are light and it had overdrive.  Go to tbi and my '89 caprice got a little over 20 hwy. and that's a big heavy car.  If you have a 4x4 and you're expecting better than 15 hwy on a carb'ed v8 I think you'll be disappointed.  The inline 6's usually do produce a little better economy, despite having to work pretty hard.  Oh, and years aren't going to matter much.  There are differences in heads and cams, but I'm assuming you're not going with anything too out there (rv cams and such).
Title: Re: Early Chevy 305 Gas Mileage??
Post by: jaredts on April 29, 2010, 05:51:13 AM
Woops!  I missed the TH400 part (assumed TH350).  Knock 1mpg off my estimate.  Get a 700R4 if you're concerned with economy.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: Grover 1 on April 29, 2010, 06:33:01 AM
I agree with Jaredts.  If you get 15 in town, let me know how you got it.  I get 10 town 14 hiway with my 305.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: VileZambonie on April 29, 2010, 09:05:21 AM
If your main concern here is fuel mileage your set up is going in the wrong direction. Your 6 cyl will get better fuel economy, an overdrive trans will give you better fuel economy and EFI will give you better fuel economy. What is your goal with this vehicle? What are you going to use it for?
Title: Re: Early Chevy 305 Gas Mileage??
Post by: Captkaos on April 29, 2010, 01:52:33 PM
I get 17/22 with my R10 305TBI/700R4...
Title: Re: Early Chevy 305 Gas Mileage??
Post by: cherrycj7 on April 29, 2010, 07:50:22 PM
Thanks for the replies. This jeep is going to be my daily driver and weekend trail rig. I was hoping for more power and have wanted a V-8. But mileage realistically is a concern. What would the MPG thoughts be on a TBI 305 engine?? I really want to have a v-8 that gets better than my I-6 is getting and close to 15 city. I realy want a carb for its simplicity but have heard that the chevu TBI system is pretty simple as well. What are your thoughts on this. Is the 305 the right way to go with a V-8? Thanks for all of your imput.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: Stewart G Griffin on April 29, 2010, 07:52:20 PM
The other factor is how much money do you have budgeted to spend initially?
Title: Re: Early Chevy 305 Gas Mileage??
Post by: cherrycj7 on April 29, 2010, 08:13:35 PM
For the engine, headers, possible need of a rebuild, adapter to the AMC TH400 and engine mounts i have about 1000 dollars figured for it.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: Stewart G Griffin on April 29, 2010, 08:25:08 PM
i'll get back to you on that.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: choptop on April 29, 2010, 08:32:25 PM
Personally, Id hunt for a 350. It has more power on demand, no physical difference exterior wise, and can be made to perform better with simple upgrades. That being said, my 86 extended cab gets about 19-20 hwy with the 305 /700r4 combo unless its windy. then it get down to about 15. Keep in mind its a 2wd tho. I really am not sure what mileage I get out of my 85 k10 with the 350 because due to rear axle issues, I havent had a chance to really find out. I would definately ditch the 2 barrel when possible and upgrade to a 4 barrel, with a rv cam. This will help you both on and off the trail. The 6 is a better trail engine in my opinion because they are notorious for low end torque. Yes the 305 has more, but it will be at a higher engine speed, and may result in more wheel spin than beneficial.
  As far as the cold air induction, for years I drove Oldyellers 81 C20 with 350/400/4:11s with the air cleaner lid flipped. It was what everyone was doing for supposedly more horsepower. The I had an old man tell me to put it back on right, and hook the tube back up. With just that, I went from 9 mpg to about 11mpg. It seemed to run better too. Later, he rebuilt the carb for me and I got almost 15mpg. I was very happy, plus it ran like a striped ape. If I can get close to 15 with a 6000 lb 3/4 ton truck, your jeep should be fairly simple to get there. Main thing is a properly tuned engine, with a properly setup drivetrain. On your Jeep with 31's, I wouoldnt go more that 3:73s and that jsut because it seems the next upgrade is always larger tires. That engine with 3:73 should turn 33s pretty easy and not hurt your mileage too bad. Most economy is ruined because the final drive ration puts the engine in a lug condition under normal driving situatuons.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: VileZambonie on April 29, 2010, 08:44:54 PM
How's the body on this jeep? Is it worth putting the time and money into? A friend of mine just did a TBI 350 with a 700R4 and he loves it. But if it were me I'd do a TBI 4.0L Jeep and Aisin Warner Trans with a 242 tcase.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: cherrycj7 on April 29, 2010, 09:19:11 PM
The body is pretty good. The frame is the main thing I am holding onto.It is extremely clean. So, yes, it is worth it. I just want a V-8, haha. The 4.0 is a great engine and all, but the  "cool" factor just isnt there in my eyes. Its in almost all of the cherokees and wranglers from 1990-2000 somethin. I want this jeep to be something that people look at and are impressed about, gets decent gas mileage and is good off road. I think with a V-8 i could accomlish these thngs. Its a classic (1979) so i am going to take it to car shows too.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: 1980c10 on April 29, 2010, 10:06:25 PM
a 305 will give you reasonable mileage for a regular driver. I would definatley go with the quadrajet.  Then tune it perfectly and you should be able to see 15 mpg. My 82 lwb c10 had a 305 w/ a quadrajet, 4wd, 4 speed manual trans no od, 31x 10.5 15 bfg's would get me 18 no matter where or how i drove. The engine never missed a beat and ran like new. I had it tuned and vacuum lines routed some what differant from stock and timing set by a guy who is known for tuning these stock engines and carb. best of luck. btw he recomended stock air cleaner housing.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: cherrycj7 on May 01, 2010, 01:37:46 PM
1980c10, Thanks for your responce. You have been one of the only positive ones reguarding the 305. I am guessing that the 18 is highway? What it get city? thanks
Title: Re: Early Chevy 305 Gas Mileage??
Post by: Stewart G Griffin on May 02, 2010, 11:12:57 PM
In the meantime, this article should give you some hope.  Their tires are close to yours too:

(may need to scroll down)

http://forum.73-87chevytrucks.com/smforum/index.php?topic=14391.15
Title: Re: Early Chevy 305 Gas Mileage??
Post by: jaredts on May 03, 2010, 06:31:16 AM
I said nothing bad about the 305.  I think your biggest hurdles to economy are in order:  The TH400 tranny and carbureted fuel delivery.  A TBI 305 with 700R4 transmission should yield you over 20mpg's easily.  The TH400 is a great choice for serious off roading, but economy is not its strong suit.  TBI compared to a carburetor will yield a couple of mpg's, a 700R4 compared to a TH400 will yield????  My guess is 4 to 5 extra mpg.'s.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: 1980c10 on May 14, 2010, 12:53:47 AM
I would always get 17.5 to 18 mpg city or highway, maybe because It didn't have an OD. If power is your priority I would go with a 350 ci. If mpg and budget are of more concern I would go with the 305 ci. You will be able to find a 305 much cheaper than a 350 due to demand. an overdrive trans would also be worth the extra money spent for sure.
Title: Re: Early Chevy 305 Gas Mileage??
Post by: Stewart G Griffin on October 07, 2010, 05:01:45 PM
Last 3 fillups:

15.14 mpg

16.72 mpg

16.10 mpg.