Fuel consumption...no not a tree hugger, just FMI

[Wietse]

Hey guys,

Just looking for some figures from your cars average fuel consumptions.
Mine drinks like an absolute boss, like there is a hole in the tank.
I drive a '69 Coronet R/T, 440 with 750 CFM Holley 4-barrel (4150), Edelbrock Performer RPM intake, cam unknown but looking at the piss poor vacuum readings i have it's a heavy one
727 tranny and a 4.10 8-3/4" rear axle.

As far as i came it runs about 8 MPG, is that a reasonable figure for my car?

Future plan is to change the rear ratio to 3.55, to increase a bit on cruising comfort and obviously will help a bit on the fuel consumption as well.

Not complaining in any way, but just want to know it runs about right.

 

[miller]

Yep.

 

[Wietse]

Yep.

Short and sweet!

Reading up on the guys here who have or are installing EFI only reduces fuel consumption a little, but does brings some benefits with it i guess.
Thinking about doing a EFI upgrade as well in the future, but just wonder if with that system the engine is still so aggressive on the throttle as with normal carb? (i really like that, no lag, reaction time of the engine. There is no modern car who does the same)
And could an EFI be run with a RTR MSD distributor with a MSD Blaster SS?
In that case i would not be able to let the EFI control the ignition right? Do i need to?

Advisable upgrade for a street car? Or money that can be spend better elsewhere?

 

[moparwacko]

Holy cow, 8 mpg!!


You get that much?
I mix aviation fuel, leaded 100 octane with ethanol free 93 for my 383 (475 hp) at a 2 to 1 ratio.
And I get a whopping 5mpg
But that 5 miles is full of smiles

 

[Wietse]

Here i am buying RON 98 fuel for the Dodge.
I do have a few bottles of octane booster at home for any time i go for a long tour and might not come across a petrol station that sells 98 fuel.

According me, my fuel gauge is not showing really accurate so i had to do the math myself. (think it shows Empty a bit too early, or not?)
As the tank is 72 liter (19 US gall.), i filled it up full with 56 liter (14.8 US gall.) when the gauge was showing a hair of Empty, which leaves me 16 liter (4.2 US gall.) of backup.
After driving around for about 60 miles the gauge is almost showing half again and i was kinda shocked it burned 28 liters (7.4 US gal.) on 60 miles (96 km).
So in conclusion, it's not the consumption...it has a small tank
Same as with me, everybody always talks about my drinking, but never about my thirst.

 

[Demonic]

You have a 4150 - a double pumper and an automatic? How do your spark plugs look - are that black or sooty? I would go with a vacuum secondary carb for a street car unless you go tot he track a lot. Maybe try jetting down a size or two if the plugs show rich.

 

[Wietse]

See the last time i pulled the plugs, i did up the heat range. (was 6, went to 5)
I don't do any track, just a street car.
Currently i have a 5.5 power valve (used to have a 6.5) on the primary with .78 jets and a blank power valve with .84 jets on the (mechanical) secondary.
The engine does not pull much vacuum, maybe around 7-8 Hg at most at idle but it is a steady reading.

I do have the feeling a PO did go to the race track with it but i have nothing to back that up, apart from the setup of the car.

 

[JB400]

Best I've heard out of a 440 was 23 mpg with a 6 pack. But, average seems to be 8-15 mpg, depending on how the car is built

 

[moes]

an AFR gauge is a great product to help with tuning a carb

 

[Wietse]

an AFR gauge is a great product to help with tuning a carb

Things like that, i would like to get in to and set it all up myself and have the know how in the pocket.
This makes life so much better knowing 100% were you are talking about and is so easy to troubleshoot once you got the hang of it.
Installing 1 AFR gauge on 1 of the headers? So measuring on 1 bank only makes no difference right?

To me it is either investing in a EFI setup or get to know all ins and outs on good ol' carb tuning.

 

[moes]

your plugs are running rich with all that soot

 

[moes]

yes 1 gauge will work, your carb has the same jets and metering rods on both sides of the carb. Unless someone has installed two different jets or metering rods in your carb. So your AFR gauge reading will be the same whether the 02 sensor is installed on the drivers side or passenger side header. If you sell the car you can remove the AFR gauge (install a plug in the 02 bung) and install it in your new car, I"ve had the same gauge in 3 different cars now.

 

[Wietse]

your plugs are running rich with all that soot

I must say, this is what i found initially.
After i have rebuild the carb, changed the power valve and adjusted the timing.
It runs very well and as i was so proud of myself to get it going the way it is i forgot all about after care and double checking on my work.
Bear in mind, i never got there without this forum!
I should pull the plugs again and check, also still want to do a compression test at the same time.

Now driving about and looking the fuel meter dropping like a 200 ft tree that was cut i started to wonder if i was accurate enough or if there are still things to improve.

I runs great atm, starting it is a bit of a trick and once running you need to keep the rpm up for a minute to warm up a bit, after idles fine.
The throttle response is instant and goes like an absolute rocket.

Then again, someone spend some good time and money on it in the past.

 

[moes]

read this it will explain somethings to you, it's a good writeup about reading spark plugs

http://www.4secondsflat.com/Spark_plug_reading.html

 

[threewood]

My 440, 800 cfm Eddy, 3.55 rear, 727 gets 10.6 mpg on the highway.

 

[Brewzer67]

My 526" 850 cfm 4.30 geared 67 Coronet got 13.8mpg on the freeway. I was surprised as hell since the 440 it replaced only got 10.

 

[Wietse]

Decent figures there, better then mine.
Although i have not driven it highway much yet.
Whenever i will go for a meeting or so i will try and keep a record of consumption on the highway.
Guess it is more rpm’s but no start/stops for traffic lights etc.

 

[coloradodave]

A few things in your post got my attention: The gear ratio, the carburetor and the 'unknown' camshaft.
First, have you tried advancing your timing to 'up' the vacuum reading?
Second, as was stated, the 750 Holley is a performance oriented carburetor. You definitely would find better mileage in a vacuum secondary carburetor. Meanwhile, reduce the primary jets two steps at a time until your plugs clean-up.
Third, as you stated, changing out the rearend gears will help mileage if you do more highway driving verses stop and go.
In my experience with running EFI instead of carburetors, I did not see an improvement in mileage. However, the throttle response is as good, if not better, than with well set-up carburetors.
The main consideration is what YOU want out of the car. If changing the timing doesn't appreciably increase your vacuum, it could be an indicator of a camshaft that will never allow you a mileage increase. In that case are you willing to change it? I understand that you are just wondering, but the best combination is one that has been tailored to a particular use; that is, racing, street/mileage or street/performance. Glad you're a member; you're a long ways away...lol.

 

[Wietse]

The current initial timing is 18 deg, where i found it to be spot on for starting (hot and cold), idle smooth and be very responsive so i did not change it again.
Never considered a vacuum secondary as i did not know any better but when looking at the distributor i wonder if it would fit on there. (Space wise, as it does have an option for a vacuum canister)

The engine had been modified by a PO, not the shop i bought it from, and have no back ground or history.
As you mentioned the carb is a performance type, and with all other types of setup i have a feeling this thing spend quite some time at the strip.
Untill the day i “need” to pull the engine for overhaul or so i am not planning on doing any major changes, it is what it is.
I can enjoy it as it is, but in the meantime make the most out of it from what i can.
If it’s thirsty, it’s thirsty. (Know the feeling LOL)
I will have a look for a AFR meter and some different jet sizes and start with that and see how it works out.
Any recommendations on AFR meters? (Something from Summit, they are my fastest and most reliable source for stuff)

 

[GetX'd]

I’d like to get 8 mpg. I’m running a stroked 440 to a 494 with a six pack. I only get about 6 mpg. It’s well tuned but drinks like a pig in heat. I have 3.91 gears and wish I had put 3.55 or 3.21 gears in when I rebuilt the car.