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Where is my dang MPG?
#1257067
06/25/12 01:28 PM
06/25/12 01:28 PM
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Joined: Jul 2011
Posts: 817
Eugene, Oregon
Secret Chimp
OP
super stock
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OP
super stock
Joined: Jul 2011
Posts: 817
Eugene, Oregon
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I'm still searching for decent MPG on my 318. I've asked this question more than once on this board but I'm back again to see if there are different thoughts after my most recent change.
My most recent update was going to a clutch fan to a fixed fan - some improvement, but not the 19+ mpg people are getting with less mild setups than what I have.
Here's my setup:
1967 Coronet station wagon (about 3,800 with me and gasoline)
318/727
Split dual exhausts with Flowmasters of some kind ahead of the rear axle on the stock manifolds
2.93 rear
Summit 6900 cam
Edelbrock Performer intake
MSD 6AL ignition on older Mopar Performance distributor
625 cfm Carter AVS 4966S leaned down to a rod change away from a light lean miss at cruise on a 4 hole spacer
Here's my distributor curve/setup:
15 initial
15 degrees vacuum at 18inHg
19 degrees mechanical all in by 3100
(this was set up by FBO)
The absolute best I've gotten out of this car is around 14.5 mpg all highway at 60-65 mph and around 2100 rpm.
What else can I try? I'm out of ideas short of just trying a different carburetor ($$$ with unknown benefits, unless some western WA Mopar people have something I could borrow). I fiddled with a strip kit but I can't lean the carb any more than it is already. Choke comes off all the way.
1967 Dodge Coronet Deluxe station wagon
1.03" T-bars, QA1 arms/rods, Cordoba/GM Metric/Volare brake & knuckle, XHDs, Hellwig rear sway, 318 Magnum w/ air gap, 727, 3.23s
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Re: Where is my dang MPG?
[Re: stumpy]
#1257070
06/25/12 02:28 PM
06/25/12 02:28 PM
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Joined: Jan 2011
Posts: 492
Kansas
BEINGmeISaCRIME
mopar
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mopar
Joined: Jan 2011
Posts: 492
Kansas
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I got a 70 coronet 4d myself and get around 22 mpg highway. Mine is a complete bone stock 318, 2 bbl carb,mopar electronic ignition and 2.76 gears. The timing on mine is set at 10 degrees initial, never bothered to check my advance or anything. Next week I'm putting in a 318 magnum with a 4bbl carb and headers for fun. Will prolly say goodbye to my mpg as well
Edit: if it makes any difference my 318 is 8:1 compression and open chamber heads.
Last edited by BEINGmeISaCRIME; 06/25/12 02:30 PM.
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Re: Where is my dang MPG?
[Re: stumpy]
#1257072
06/25/12 02:50 PM
06/25/12 02:50 PM
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Joined: Jul 2011
Posts: 817
Eugene, Oregon
Secret Chimp
OP
super stock
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OP
super stock
Joined: Jul 2011
Posts: 817
Eugene, Oregon
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Quote:
14-15 mpg should be about the best you are going to get with that heavy a car. 
I'd expect that much around town, but I don't need much throttle to keep it going at 60 and we have relatively flat highways here.
I'm wondering if I got a couple of bum carbs. Another fellow posted here about significant mileage differences between his lean-as-possible Thermoquad and an AFB that got another 3-4 mpg over it.
1967 Dodge Coronet Deluxe station wagon
1.03" T-bars, QA1 arms/rods, Cordoba/GM Metric/Volare brake & knuckle, XHDs, Hellwig rear sway, 318 Magnum w/ air gap, 727, 3.23s
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Re: Where is my dang MPG?
[Re: tcat446]
#1257073
06/25/12 02:51 PM
06/25/12 02:51 PM
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Joined: Jul 2011
Posts: 817
Eugene, Oregon
Secret Chimp
OP
super stock
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OP
super stock
Joined: Jul 2011
Posts: 817
Eugene, Oregon
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Quote:
I calculated mine yesterday at about 7mpg. 1973 318 4 bbl. I have the larger cc heads on mine lowering the compression with a trailer tow cam in it and 3:91 gears. I know mine has a few issues with the valves leaking. I would do a leak down test to determine if the engine is up to snuff. Have been told that if compression is down you mileage will suck. Not sure but have been told that. Worth a check. One other thing to try is do a compression test to see if you have a few cylinders low.
I ought to, it runs strong and doesn't blow smoke when I run it up but it's the one major aspect of the engine I haven't checked.
1967 Dodge Coronet Deluxe station wagon
1.03" T-bars, QA1 arms/rods, Cordoba/GM Metric/Volare brake & knuckle, XHDs, Hellwig rear sway, 318 Magnum w/ air gap, 727, 3.23s
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Re: Where is my dang MPG?
[Re: JohnRR]
#1257074
06/25/12 03:04 PM
06/25/12 03:04 PM
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Joined: Jul 2011
Posts: 817
Eugene, Oregon
Secret Chimp
OP
super stock
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OP
super stock
Joined: Jul 2011
Posts: 817
Eugene, Oregon
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Quote:
Thermoquad ...
I've been curious about those things for awhile but it seems easy to get into a money pit with them. Where would I want to start, especially for a non-emissions car?
1967 Dodge Coronet Deluxe station wagon
1.03" T-bars, QA1 arms/rods, Cordoba/GM Metric/Volare brake & knuckle, XHDs, Hellwig rear sway, 318 Magnum w/ air gap, 727, 3.23s
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Re: Where is my dang MPG?
[Re: Secret Chimp]
#1257075
06/25/12 03:08 PM
06/25/12 03:08 PM
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Joined: Jun 2012
Posts: 123
Ripley, NY
tcat446
member
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member
Joined: Jun 2012
Posts: 123
Ripley, NY
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Quote:
Quote:
I calculated mine yesterday at about 7mpg. 1973 318 4 bbl. I have the larger cc heads on mine lowering the compression with a trailer tow cam in it and 3:91 gears. I know mine has a few issues with the valves leaking. I would do a leak down test to determine if the engine is up to snuff. Have been told that if compression is down you mileage will suck. Not sure but have been told that. Worth a check. One other thing to try is do a compression test to see if you have a few cylinders low.
I ought to, it runs strong and doesn't blow smoke when I run it up but it's the one major aspect of the engine I haven't checked.
MIne runs strong too. No smoke that I have ever seen either. Worth a check.
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Re: Where is my dang MPG?
[Re: Secret Chimp]
#1257077
06/25/12 05:00 PM
06/25/12 05:00 PM
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Joined: Jan 2003
Posts: 1,307
BC, Canada
Black_Bee
pro stock
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pro stock
Joined: Jan 2003
Posts: 1,307
BC, Canada
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I daily drove a '67 Coronet 2door HT for a couple of summers. 318, auto, 3.23. It was a stock (except as noted) 100,000+ mile 1970 318 with a 600 Edelbrock carb on a LD4B intake. Pertronix ignition, single exhaust through a Dynomax muffler that dumped at the axle. Anyway, I consistently got between 17 and 19 MPG. I drove pretty much 100% on the highway going between 55 and 60 MPH. I tried all kinds of driving styles and carb/ignition tuning to bring the numbers up, but that was it... the weather made more of a difference than anything else. ***EDIT.. Sorry, I was looking at my fuel logs, and that 17-19 was my imperial MPG calculations (I'm in Canada)... I actually was getting 14-16 US MPG.
Last edited by Black_Bee; 06/25/12 05:05 PM.
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Re: Where is my dang MPG?
[Re: Fury Fan]
#1257079
06/25/12 05:44 PM
06/25/12 05:44 PM
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Joined: Nov 2006
Posts: 2,256
IL
furious70
top fuel
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top fuel
Joined: Nov 2006
Posts: 2,256
IL
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did u degree the cam when you built the engine?
70 Sport Fury
68 Charger
69 Coronet
72 RR
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Re: Where is my dang MPG?
[Re: Dodgem]
#1257081
06/25/12 07:49 PM
06/25/12 07:49 PM
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Joined: Jul 2011
Posts: 817
Eugene, Oregon
Secret Chimp
OP
super stock
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OP
super stock
Joined: Jul 2011
Posts: 817
Eugene, Oregon
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Quote:
So your running 34 deg mechanical total and 15 more vacuum? for 49 deg at light cruise??
No, I'm not cruising on my full mechanical, it comes in at 3100.
Would excessive timing be masked by a rich mix though? Maybe that lean miss was the right mix with too much vacuum advance.
1967 Dodge Coronet Deluxe station wagon
1.03" T-bars, QA1 arms/rods, Cordoba/GM Metric/Volare brake & knuckle, XHDs, Hellwig rear sway, 318 Magnum w/ air gap, 727, 3.23s
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Re: Where is my dang MPG?
[Re: Secret Chimp]
#1257082
06/25/12 08:08 PM
06/25/12 08:08 PM
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Joined: Sep 2007
Posts: 14,889
up yours
Supercuda
About to go away
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About to go away
Joined: Sep 2007
Posts: 14,889
up yours
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Sounds to me to be a timing issue. 3100 rpm for max mechanical advance is way too high of an rpm for your combo.
They say there are no such thing as a stupid question.
They say there is always the exception that proves the rule.
Don't be the exception.
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Re: Where is my dang MPG?
[Re: Secret Chimp]
#1257083
06/25/12 08:27 PM
06/25/12 08:27 PM
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Joined: Mar 2008
Posts: 5,746
Ontario, Canada
Dodgem
master
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master
Joined: Mar 2008
Posts: 5,746
Ontario, Canada
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Quote:
Quote:
So your running 34 deg mechanical total and 15 more vacuum? for 49 deg at light cruise??
No, I'm not cruising on my full mechanical, it comes in at 3100.
Would excessive timing be masked by a rich mix though? Maybe that lean miss was the right mix with too much vacuum advance.
Well that is where you gas mileage is you probably set it up By FBO's instructions he's wrong period.
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Re: Where is my dang MPG?
[Re: Dodgem]
#1257084
06/25/12 09:48 PM
06/25/12 09:48 PM
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Joined: Jul 2003
Posts: 1,212
Canton, Ohio
Crazy68Dart
pro stock
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pro stock
Joined: Jul 2003
Posts: 1,212
Canton, Ohio
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Need to see what your timing is... get as much advance as the car will handle at light cruise. If mechanical is not all in until 3100 and you have 15 initial and 15 at cruise (assuming you have that vacuum you posted at your cruise RPM) then you likely only have 30-34 degrees of advance which is not going to help your MPG at all.
What is your cruise RPM? What do your plugs look like?
383, Hemi 4-Speed, AlterKtion, D60
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