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Carburetors Carb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.

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Old 10-12-2007, 05:41 PM   #1
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What is "normal" Mpg on stock 305 carb?

Just a simple questions since it is not much people here in Norway with GM Cars with V8 engines...

I have a 87 Camaro Sport Coupe..It is in stock condition and is running very nice..Carb is newly rebuilt...It is a 305 stock engine with computer controlled q-jet carb...

I figured out my Mpg is about 28 now...And that's is normal daily driving..From small villages to another one and so one..Cruising speed almost all the time...

My question is simple...what is about "normal" mpg on stock 305 (daily driving)???
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Old 10-12-2007, 05:55 PM   #2
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Re: What is "normal" Mpg on stock 305 carb?

28 seems a bit high... i was only getting 21mpg on a tbi 305. ive heard that the qjets get around 18-20 when running properly and not ******* the shat out of it.
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Old 10-12-2007, 07:35 PM   #3
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Re: What is "normal" Mpg on stock 305 carb?

What gallon do you use in Norway? Imperial or US?
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Old 10-12-2007, 08:55 PM   #4
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Re: What is "normal" Mpg on stock 305 carb?

Think I have the same engine and carb set up as you. Last December I got 25 miles per gallon on my carb at 55 miles per hour; 24.5 mpg driving at 60 mph. the best I ever ot was 18 mpg driving in the city stop & go traffic (usuall lower). 28 mpg is really good!
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Old 10-13-2007, 12:50 AM   #5
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Re: What is "normal" Mpg on stock 305 carb?

You guys that are only getting 19-20 mpg on the highway out of your carbed LG4 305 need to either do some work to your car, take you foot out of the gas, or slow down. Driving on highway trips with the cruise set @ 70 mph in my 1983 G20 Van with the stock 250K mile carbed 305, I could knock on 18-20 mpg all day.

I also had a 1988 Cadillac Fleetwood Brougham with the Q-Jet fed Oldsmobile 307 that would do an honest 27 MPG running 70 mph with the cruise set and the A/C blasting.
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Old 10-13-2007, 05:29 AM   #6
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Re: What is "normal" Mpg on stock 305 carb?

Quote:
Originally Posted by chesterfield View Post
What gallon do you use in Norway? Imperial or US?
Actually we don't use gallons in Norway...We say gas mileage in litres per 10km..So my car is using about 1,3litres on 10km (norwegian mile)

And I am very sorry guys but I have calculated wrong....

To calculate my MPG's i just do like this

US MPG = 23,6 / litres/10km

That means I use:

US MPG = 23,6 / 1,3 = 18 Miles per gallon (US gallon)


Now we are talking about the excact gas mileage on my car...So this is not a good gas mileage I guess?????
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Old 10-13-2007, 07:15 AM   #7
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Re: What is "normal" Mpg on stock 305 carb?

18 isnt bad still... the best i ever got on my TBI 5spd was 18mpg and with my carb 357 i get like maybe 10 to 13 im guessing.... no odo yet
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Old 10-14-2007, 08:16 AM   #8
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Re: What is "normal" Mpg on stock 305 carb?

ok..So I guess 18MPG on daily driving isn't to bad at all...
I thought mayby it was a little bit low....
That about 20-25 MPG were more normal but OK..
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Old 10-15-2007, 04:46 PM   #9
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Re: What is "normal" Mpg on stock 305 carb?

Just a question about imperial and US gallons, which one is supposed to be used to check mileage?
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Old 10-16-2007, 09:52 AM   #10
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Re: What is "normal" Mpg on stock 305 carb?

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Just a question about imperial and US gallons, which one is supposed to be used to check mileage?

I guess European Car dealers use this Imperial gallons to check mileage...
After what I've been reading, all American cars use the US gallons...
isn't that right or??
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Old 10-16-2007, 10:22 PM   #11
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Re: What is "normal" Mpg on stock 305 carb?

Wow on my carb 305 I am getting 14mpg! how are you guys getting 18 and up!?!?!?

I keep it at 2000rpm and lower. Never exceeding the speed limit becasue of how many cops are around here!

What is wrong?!?!? Do you think my carb needs a rebuild? The gaskets seem to be sweating though.

How much would it cost for someone to rebuild it. I hate computer controlled anything I do not want to deal with it so I am not doing it. I like my Holley on my 78 Z. Dang compu q-Jets!!!

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Old 10-17-2007, 02:29 PM   #12
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Re: What is "normal" Mpg on stock 305 carb?

Quote:
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Wow on my carb 305 I am getting 14mpg! how are you guys getting 18 and up!?!?!?

What is wrong?!?!? Do you think my carb needs a rebuild? The gaskets seem to be sweating though.
When was the last time the carb was rebuilt? I just rebuilt the carb for the first time on my '84 T/A and went from about 12-14MPG to well over 20MPG. If its never been rebuilt, its LONG over due for one. Chances are the throttle shafts are also loose in the baseplate and need bushings installed.

There is nothing more complicated in the CCC Quardrajet than a regular vacuum control Quadrajet. The only additional things is a mixture control solenoid in place of the old vacuum controlled primary metering rod power spring and a TPS sensor. Both are very easy to adjust.
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Old 10-17-2007, 02:38 PM   #13
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Re: What is "normal" Mpg on stock 305 carb?

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18 isnt bad still... the best i ever got on my TBI 5spd was 18mpg and with my carb 357 i get like maybe 10 to 13 im guessing.... no odo yet
wow my 91 TBI just git a tune up and i'm getting around 24 mpg.
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Old 10-17-2007, 06:05 PM   #14
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Re: What is "normal" Mpg on stock 305 carb?

It has never been rebuilt as far as I know. Wow, that would be a good improvement in mpg. Ill pay for someone to do it.
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Old 10-17-2007, 06:47 PM   #15
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Re: What is "normal" Mpg on stock 305 carb?

I have an 84 T/A with the L69 305, 700R4, 3.73 gears and and a Qjet. The carb was rebuilt last year. On the highway I get 23-24 MPG at 65-70mph and 18-19mpg when city driving.
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Old 10-17-2007, 07:08 PM   #16
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Re: What is "normal" Mpg on stock 305 carb?

i get anywhere from 15-25mpg when city driving..
25mpg is when i granny drive it, with nobody in the car (rarely happens), 15mpg is when i throw my lead foot on, and drive with the car full of people, and around 20mpg just regular driving(which for me is with my lead foot on :P)
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Old 10-17-2007, 10:23 PM   #17
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Re: What is "normal" Mpg on stock 305 carb?

WOW!!! I really cant wait until I get it rebuilt!!!! The estimate was 250 for rebuild but it will be worth it when I am saving in gas!!!!!!!!

SWEET!!!
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Old 10-18-2007, 03:27 AM   #18
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Re: What is "normal" Mpg on stock 305 carb?

Quote:
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I have an 84 T/A with the L69 305, 700R4, 3.73 gears and and a Qjet. The carb was rebuilt last year. On the highway I get 23-24 MPG at 65-70mph and 18-19mpg when city driving.
Darn, I also have an 84 T/A with the exact same specs (except for headers and shift kit) as yours but I only get 14mpg I already had the carb rebuilt last summer and there was no change. When I bought it, some vacuum lines were missing. I already put those in but i still have a very small vacuum leak going to the A/C controls. Could that be causing the drop in MPG? My TCC doesnt lock normally either (only under high temps). Would the TCC locking increase the MPG significantly?

Last edited by jaimegmr; 10-18-2007 at 03:33 AM.
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Old 10-18-2007, 07:36 AM   #19
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Re: What is "normal" Mpg on stock 305 carb?

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Darn, I also have an 84 T/A with the exact same specs (except for headers and shift kit) as yours but I only get 14mpg I already had the carb rebuilt last summer and there was no change. When I bought it, some vacuum lines were missing. I already put those in but i still have a very small vacuum leak going to the A/C controls. Could that be causing the drop in MPG? My TCC doesnt lock normally either (only under high temps). Would the TCC locking increase the MPG significantly?
Yes, if your transmission isn't lockng properly, it's slipping which is causing a drag on your driveline. I don't think it'll make up 6mpg, but it'll make up some. I know at 70mph I'm running about 2600rpm in overdrive. Also, find that leak....a vacuum leak will screw with your engines performance pretty badly.
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Old 10-18-2007, 09:28 AM   #20
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Quote:
Originally Posted by camaro87-alex View Post
I guess European Car dealers use this Imperial gallons to check mileage...
After what I've been reading, all American cars use the US gallons...
isn't that right or??
US cars are rated using the US gallon. An Imperial gallon should get you more miles per, because it is bigger than the US gallon.

The two LG4's that I'm most familiar with are: 1) my nephew's '86 with TH700 and 2.73 gears. It quit on him on a road trip, it was towed to the nearest dealer, who discovered a bad ignition module and coil (one will often take the other out). They did a tune-up as well, and suddenly he started getting 27 mph highway with it. I never heard how it did around town after that. 2) my own while still stock. The torque converter lock-up never worked (figured out why after it was no longer a stock LG4). I got 26 mpg on the one road trip I took with it, and got around 20-22 around town, depending upon how much "fun" I had. I had 3.08 gears at the time.

I just bought an '82 with stock LG4. It has the TH200C transmission and I believe 3.23 gears (need to verify that). I haven't driven it enough to know what kind of mileage it will get, but I'll have the opportunity when I drive it from California to Colorado, about 1200 miles. I expect that to take 4 tankfuls, somewhere between 20 and 25 mpg.
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Old 10-18-2007, 12:12 PM   #21
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Re: What is "normal" Mpg on stock 305 carb?

Ok..I am not sure of what is wrong with my engine or carb....
Because my car is running on about 18-20mpg and that is with "normal" driving with medium acceleration and most of time a cruising speed of 1500RPM in 60MPH.....Of course since there is small distances between the towns around here I often stop and have to accelerate again, so a little bit City driving appears...

Anyone have an idea of what could be wrong??..My carb was overhauled/rebuilt 2months ago but no difference...Mayby something on my choke is sticking...I think so....
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Old 10-18-2007, 10:20 PM   #22
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Re: What is "normal" Mpg on stock 305 carb?

I usually get around 23-24mpg highway and 17-18 city. Usually around 19-20 mixed driving. The only times my milage was bad was when my O2 sensor started going bad or when I was flogging the pedal and having fun. You guys gotta remember everything could be in perfect working order and still get 12 MPG if your secondaries are opening up at every green light
Alex your milage sounds acceptible. 24 MPG was traveling only on highways doing a constant speed for a long trip. It sounds like you do a lot of mixed driving conditions where 20mpg is pretty good.
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Old 10-18-2007, 10:52 PM   #23
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Re: What is "normal" Mpg on stock 305 carb?

come on ppl its a CAMARO (or Firebird) a muscle car (or pony cars or sports car, depends on who you ask according to the other thread) the point is, its made for performance, if you care about gas milage go buy a honda. LOL
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Old 10-18-2007, 11:44 PM   #24
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Re: What is "normal" Mpg on stock 305 carb?

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come on ppl its a CAMARO (or Firebird) a muscle car (or pony cars or sports car, depends on who you ask according to the other thread) the point is, its made for performance, if you care about gas milage go buy a honda. LOL
So you wouldn't care if your car got 5mpg when its supposed to be getting 20mpg right? After all its a muscle car.

Your statement that we should not care about gas mileage because the cars are made for performance is illogical. It is known that a car will use more gas if you upgrade the engine from 200HP to 400HP. But a car SHOULD NOT be using MORE gas for the LESS horsepower (because obviously something is wrong with the motor if its getting bad gas mileage).
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Old 10-19-2007, 12:39 AM   #25
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Re: What is "normal" Mpg on stock 305 carb?

Dude calm down I was just Joking
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Old 10-19-2007, 01:17 AM   #26
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Re: What is "normal" Mpg on stock 305 carb?

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Dude calm down I was just Joking
I'm calm now. I've read so many posts before saying the same thing you said that I kind of went nuts after reading your post. My 14mpg problem probably contributed, slightly. I could have saved at least $450 since I got my car if I were getting 18mpg instead of 14mpg, which could have been used for some upgrades.
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Old 10-19-2007, 06:58 PM   #27
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Re: What is "normal" Mpg on stock 305 carb?

Ok....I can see here is a lot of meanings about this subject...
And I also guess that 18MPG on Mixed driving isn't to bad

I was just curious on this question because we don't have a lot American cars with V8 around here so therefor I was very curious...

The best gas mileage I have ever got on my engine was a long summer trip with almost 1500rpm all the time in 60MPH on a long trip..
Then I got my mileage to 27MPG so that time I was VERY satisfied....

But that is almost half year ago so mayby some few things have changed...
I think 18MPG is a little to much because I don't hit the pedal to the medal very often...Some few acceleration's of course but no big deal...
I also have some troubles on my choke so mayby it is sticking or something..Have to take a look....I have newly changed my O2 sensor also so everything in the Emission system works perfectly....

My dwell readings are fine, and my timing is fine...The sound is fine and everything seems fine...Only a little bit to much gas I think...
But what the heck, gotta have some fun also...

But with gas prizes that is about 7,50 bucks per gallon you have to think a little bit on how much you can drive....
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Old 01-23-2009, 07:26 PM   #28
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Re: What is "normal" Mpg on stock 305 carb?

OK I am bringing up a dead thread because I got a rebuilt carburetor now. Averaging 72mph on the highway and a little bit of town driving I got 19mpg. That still seems low compared to you other guys. The car runs great for the most part. I had the tranny flushed also. I dont have a smog pump(Like that from previous owner), but all the hoses are still connected and all plugged up as far as I can see.
Would an Old cat converter hurt mpg? Is there anything else I can do?
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Old 01-24-2009, 12:13 AM   #29
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Re: What is "normal" Mpg on stock 305 carb?

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OK I am bringing up a dead thread because I got a rebuilt carburetor now. Averaging 72mph on the highway and a little bit of town driving I got 19mpg. That still seems low compared to you other guys. The car runs great for the most part. I had the tranny flushed also. I dont have a smog pump(Like that from previous owner), but all the hoses are still connected and all plugged up as far as I can see.
Would an Old cat converter hurt mpg? Is there anything else I can do?
I am hoping that 72 is really a typo and you meant 27mpg. If you are getting 27 mpg on the highway, you've got your ride tuned very, very well. Before I swapped in my 350, I had a carbureted 305 and I was lucky to hit 24mpg at 55mph for a road trip (yes, I did the math 55mph one way and 70mph the other for a full tank of gas). Now with the 350, I'd love to get back to 20...I think I need to get it tuned. hehe I think I'm getting about 15mpg right now on the highway.
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Old 01-24-2009, 01:53 AM   #30
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Uh, he was saying driving an average of 72 miles per hour and getting 19 miles per gallon.
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Old 01-24-2009, 09:28 AM   #31
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Re: What is "normal" Mpg on stock 305 carb?

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Uh, he was saying driving an average of 72 miles per hour and getting 19 miles per gallon.
Crap...well I can't read.

Based on the re-read, then a little tune would help maybe, headers, more free-flowing exhaust. I do think 19 was about average for the time though. Of course the speed limit was only 55 back then so slowing down might help it creep back up a bit.
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Old 01-24-2009, 09:53 AM   #32
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Re: What is "normal" Mpg on stock 305 carb?

Is your converter locking up at cruise? Won't affect mileage much but it will indicate that the engine is going into closed loop at highway speeds.

An old O2 will richen the mixture, hurting mileage. Normal tuneup items, plugs, cap, rotor, wires, air filter will all affect mileage if these items haven't been replaced in a while.

I would suspect that a restrictive exhaust system would cause loss of power issues before significantly affecting mileage during low rpm, low flow cruise conditions.

In my 85 TA I noted a significant difference going to electric fan. Only other diff is an open element air cleaner that seemed to help (although it was installed along with replacement of ignition parts/pieces). Best I averaged was 29 last Summer, but that was non-stop from this side of Memphis to Columbia, SC-down hill the whole way.

Noted you have a TA. I've always felt that the air hose routing to the air cleaner was a severe bottleneck in the TAs. The ducting placement doesn't seem to get the air flow that the camaros have with the opening mounted above the charcoal canister. Try an open element cleaner for a while if you haven't already.

Last edited by naf; 01-24-2009 at 09:58 AM.
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Old 01-24-2009, 10:51 AM   #33
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Re: What is "normal" Mpg on stock 305 carb?

Quote:
Originally Posted by naf View Post
Is your converter locking up at cruise? Won't affect mileage much but it will indicate that the engine is going into closed loop at highway speeds.

An old O2 will richen the mixture, hurting mileage. Normal tuneup items, plugs, cap, rotor, wires, air filter will all affect mileage if these items haven't been replaced in a while.

I would suspect that a restrictive exhaust system would cause loss of power issues before significantly affecting mileage during low rpm, low flow cruise conditions.

In my 85 TA I noted a significant difference going to electric fan. Only other diff is an open element air cleaner that seemed to help (although it was installed along with replacement of ignition parts/pieces). Best I averaged was 29 last Summer, but that was non-stop from this side of Memphis to Columbia, SC-down hill the whole way.

Noted you have a TA. I've always felt that the air hose routing to the air cleaner was a severe bottleneck in the TAs. The ducting placement doesn't seem to get the air flow that the camaros have with the opening mounted above the charcoal canister. Try an open element cleaner for a while if you haven't already.

That is some good info. The original cap and rotor are there "I believe" I have an IROC air cleaner set up w/ K&N filter from My brothers IROC, I actually swapped that from an open air cleaner that was on the car when I bought it becsuae someone told me that the car might run more rich with the open air element, I guess they did nto know what they were talking about.
I am going to get an O2 sensor now, new cap and rotor...would a control module help?

How do I know if my converter is locking up? Oh and the Highway speed limit is 65 so any slower then 70 and I am getting honked at, and causing traffic during the rush.

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Old 01-24-2009, 11:37 AM   #34
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Re: What is "normal" Mpg on stock 305 carb?

Open element won't cause it to run rich (or lean) the computer should fix that. It would tend to LEAN out a motor that had a mechanical tune when it replaces a more restrictive intake.

There is concern, however, that the open element will allow warmer, underhood air into the intake than a ducted system, which isn't as efficient (the warm, less dense air that is). The TAs just don't have good airflow to the factory snorkel opening IMO and the open element is the best compromise for me. I would still prefer a proper cold air intake but there are other more pressing issues on my plate.

Losing the factory air cleaner also means losing the thermac vent that provides exhaust manifold heated air into the intake during cold weather warm-up. I haven't had any problems with mine though. 'Course I live in SC, but even in the frigid, near 20 degree mornings we've experienced lately I've noticed no cold weather start or warm up issues.

To check your lock up: while at highway speed, keep your right foot on the gas to maintain a constant speed and gently tap the brake pedal with your other foot. The brake pedal switch will disengage the lockup and you should see the rpms flare up by 100 or so. Doing this while going up a slight grade will make the flare more apparent.

Control modules don't wear. They either work or don't work, usually failing when hot. No need to replace until failure.

Your TA has one of the lowest coefficients of drag for any production car, especially for its time. It should be happiest at 75-80 on the interstate.

Last edited by naf; 01-24-2009 at 11:41 AM.
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Old 01-24-2009, 11:38 AM   #35
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To test the converter lock-up:

On a steady cruise, keep your foot steady on the accelerator and slowly depress the brake pedal while keeping your eye on the tach. If the lock-up is working, the RPMs should jump up a couple of hundred when the clutch releases as the brake pedal is depressed.

Another way is to be cruising and depress the accelerator enough to just speed the car up a little. If the RPMs increase without really speeding up the car, the lock-up isn't working. If the tach and speedometer increase together, the lock-up is working.
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Old 01-24-2009, 11:48 AM   #36
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Re: What is "normal" Mpg on stock 305 carb?

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Control modules don't wear. They either work or don't work, usually failing when hot. No need to replace until failure.( I meant with an aftermarket one)

Your TA has one of the lowest coefficients of drag for any production car, especially for its time. It should be happiest at 75-80 on the interstate. (It deff. does seem to cruise easiest at those speeds)
Quote:
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To test the converter lock-up:

On a steady cruise, keep your foot steady on the accelerator and slowly depress the brake pedal while keeping your eye on the tach. If the lock-up is working, the RPMs should jump up a couple of hundred when the clutch releases as the brake pedal is depressed.

Another way is to be cruising and depress the accelerator enough to just speed the car up a little. If the RPMs increase without really speeding up the car, the lock-up isn't working. If the tach and speedometer increase together, the lock-up is working.
ill try that monday when I have to commute. thank you!

Last edited by KJZ28/TA; 01-24-2009 at 11:51 AM.
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Old 03-03-2009, 01:21 AM   #37
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Re: What is "normal" Mpg on stock 305 carb?

I know it sounds odd, but I seem to get pretty low gas mileage in town, but I do even worse on the highway when I'm going about 65-70 than I do about 35+ in town. I've got a high output 305 with an edelbrock intake and carb (dont have the part numbers at the moment). Going from here to Knoxville (about a 30 minute drive) and back to my house again (so an hours driving, over 50% of it on a 65mph highway) it takes me 1/4 of a tank. Should I be getting better milage than this?

I would have exact mpg numbers to post like the rest of you, but I still haven't found out what is wrong with my speedometer and odometer... they just don't work. So no way for me to calculate exactly how many miles per gallon I get.
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Old 04-22-2009, 11:16 PM   #38
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Re: What is "normal" Mpg on stock 305 carb?

I know this is an old post but I get 28 MPG and I calculated it using GPS and being on the HWY.

In the city I get 18 - 21.

I have an 89 Camaro RS 5.0/305 TBI

Just bought it too, so don't know what upgrades might have been done to it.
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Old 04-22-2009, 11:16 PM
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