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70 351W. Edelbrock Performer 1405 carb and intake. Mallory distributor and ignition. MSD Blaster 2 coil.

since the valve job, the car has been running really well. but i'm only getting around 12-12.5 mpg. back in the 80's and 90's, with the original setup - points, condensor 2bbl Autolite carb - i averaged between 14 and 15 mpg, sometimes more.

i'm not concerned so much about the extra few dollars to run the Cougar. just curious if this is normal for my setup, or is the lower mpg an indication of some other problem. yes, the 1405 is a 4 bbl carb but i rarely get into it to involve the secondaries. appreciate your thoughts-

billy
 

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could be just as simple as the gas today sucks compared to the 80s and 90s gas w/o all the ethonal crap....
 

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could be just as simple as the gas today sucks compared to the 80s and 90s gas w/o all the ethonal crap....
That would be my guess.
 

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I would be very surprised if it were that simple, GAS TODAY.

Something else is going on, IMO. How do the plugs look? After a good drive, what does the tail pipe interior look like?

I wouldn't just write it off as TODAY'S GAS.

Dale in Indy
 

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I would be very surprised if it were that simple, GAS TODAY.

Something else is going on, IMO. How do the plugs look? After a good drive, what does the tail pipe interior look like?

I wouldn't just write it off as TODAY'S GAS.

Dale in Indy
plugs look fine. nothing weird like black and sooty or burned. but at least my records point to the carb change when the mpg went down and stayed down ever since (that is a long time! owned the car since 1979).

the interior of the tail pipe has always been relatively black. is that normal? should my mpg be better? this is the second Performer 1405 on the car. replaced the first one under warranty soon after the install in 1999.
 

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My guess is the carb is running too rich. Wasting gas, especially if there's black on the ground from the exhaust. Adjust the air and fuel mixture , and maybe the fuel line is causing high fuel pressure due to inside corrosion or all gunked up.
I found a crushed-in section of fuel line on one of my cougar's and it was causing the pressure to be very high.
 

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I think today's gas DEFINITELY plays a part in poor mileage, that is the same car on no methanol added fuel will get better mileage. I'm getting around 10MPG and it seemed (or seems) weird to me too. However, I have not played around with tuning beyond getting it "running good" during the build. I plan on doing that (along with a lot of other little things on the to do list) over the winter.

Regards,

Bob
 

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Discussion Starter #8
I think today's gas DEFINITELY plays a part in poor mileage, that is the same car on no methanol added fuel will get better mileage. I'm getting around 10MPG and it seemed (or seems) weird to me too. However, I have not played around with tuning beyond getting it "running good" during the build. I plan on doing that (along with a lot of other little things on the to do list) over the winter.

Regards,

Bob
curious what kind of set up is getting you 10 mpg - engine, carb, etc.

in general, assuming i engage the secondaries very rarely, would you expect the 4 barrel Edelbrock to get about the same mpg as the 2 barrel Autolite?
 

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You guys are lucky, I think I am only getting about 5 at best. I am on my fifth tank of fuel, and still havent broken 500 miles yet.

The ethanol will absolutely cause poorer fuel milage. It takes not quite 2 times as much ethanol to produce the same power that gasoline does. Since the fuel is 15% ethanol, you are basically loosing 50% power on the 15% of that fuel, or about 7% all together, therefor, it take more throttle to maintain the same speed as without the mixed stuff. I am thinking it is a combination of both that is causing the fuel milage to decrease.
 

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Discussion Starter #10
You guys are lucky, I think I am only getting about 5 at best. I am on my fifth tank of fuel, and still havent broken 500 miles yet.

The ethanol will absolutely cause poorer fuel milage. It takes not quite 2 times as much ethanol to produce the same power that gasoline does. Since the fuel is 15% ethanol, you are basically loosing 50% power on the 15% of that fuel, or about 7% all together, therefor, it take more throttle to maintain the same speed as without the mixed stuff. I am thinking it is a combination of both that is causing the fuel milage to decrease.
i am sure the quality of the gas has something to do with it. however, i doubt that when i changed carbs from the two barrel Autolite to the 4 barrel Edelbrock is the exact same time the country started putting ethanol in the gas.

i always assumed a later engineered carb would be more efficient than something from 1970. but maybe not...........
 

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almost hate to suggest it but the old gas was also a minimum of 89 octane and now regular is only 87. Not exactly sure how much difference that make but I run only 91 octane in my bike. It runs like crap and get a lot worse mileage with the lighter stuff. My wifes jeep get worse mileage with regular than it does with the higher octane also. Enough to justify the price of the higher octane.
 

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i always assumed a later engineered carb would be more efficient than something from 1970. but maybe not...........
What makes you think that the Edelbrock carbs were 'later engineered'?

The Eddy carbs are simply newly manufactured/licensed versions of Carter AFBs that are from the '50s and early '60s. That same metering rod tuning approach was used in both GM Rochester and Ford Autolite factory carburetors after the mid-60s when they quit using Carter-built carbs, although Chrysler continued to use Carter until the end of V-8 production in the late '70s.

Nothing 'new' about Edelbrock engineering at all. Just re-badged old technology.

You can tune an Edelbrock/Carter carb by changing metering rods/jets. It is just a slightly different method of tuning compared to a Holley. NO carbs are simply 'bolt-on and go' one-size/calibration fits all. All will need some tweaking.
 

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I think that isn't too bad. My 67 with a 289, mild cam, stock heads, intake/headers 600cfm carb got 13 mpg highway.
 

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curious what kind of set up is getting you 10 mpg - engine, carb, etc.

in general, assuming i engage the secondaries very rarely, would you expect the 4 barrel Edelbrock to get about the same mpg as the 2 barrel Autolite?
351C w/302C closed chamber 2V port heads, a true measured 10:1 compression, XE262H cam, full length headers and 2 1/4" SS exhaust w/SS magnaflow mufflers. Holley 4777 List 650 DP w/mechanical secondaries (and I believe the secondaries should be opened early and often!). Edelbrock Air Gap manifold. 4 speed with 3.25 gears.
 

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Billy if your getting 14-15 your right in the ballpark for what it was in the day. You can improve it simply by changing your gear ratio's however...either rear gears or trans (both) Like Mike points out ethynol is not a good buy (it's cheaper here and still not the nest value)b
 

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Discussion Starter #16
Billy if your getting 14-15 your right in the ballpark for what it was in the day. You can improve it simply by changing your gear ratio's however...either rear gears or trans (both) Like Mike points out ethynol is not a good buy (it's cheaper here and still not the nest value)b
i would agree. only i'm not getting 14-15. that is what i got with the old 2 barrel autolite carb. since i put on the Edlebrock 4 barrel Performer over ten years ago and recently had a valve job, i'm only seeing around 12-12.5.

so that is really the question - is 12-12.5 in the ballpark for my setup?
 

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it's likely that carb is not tuned as it should be to your car....you'll have to play with the jets/rods to get it better. It's really only a 2V until you mash it - so it's running a bit rich compared to your old one. See if they have tech support line that could lead you to the right parts.
 

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You guys are lucky, I think I am only getting about 5 at best. I am on my fifth tank of fuel, and still havent broken 500 miles yet.

The ethanol will absolutely cause poorer fuel milage. It takes not quite 2 times as much ethanol to produce the same power that gasoline does. Since the fuel is 15% ethanol, you are basically loosing 50% power on the 15% of that fuel, or about 7% all together, therefor, it take more throttle to maintain the same speed as without the mixed stuff. I am thinking it is a combination of both that is causing the fuel milage to decrease.

Had the same milage with my '68 with the Cleveland, 5MPG. Sure fun to feel the blood going up your legs though eh? :lolani:
 
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