All Big Six Which setup for best chance to control fuel milage and torque: 300 I6

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snakebit

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Which set up woud give me the best chance to control fuel milage and best torque. ? Offy intake with holly 390 4bbl or clifford intake with weber 2bbl. How would these choices compair to stock intake and carter yfa 1bbl. all setups with headers for dual exhaust.
Some one please elaborate.
Tks
snakebit
 

pmuller9

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Welcome to the Big Six section.
First question.
Did you replace the 1986 distributor with a distributor that has mechanical and vacuum advance?

The stock 1 bbl carb and intake manifold are a restriction even for the stock engine with a stock cam.

I'm assuming you are referring to the Clifford dual Weber carburetor setup.
That setup comes with two Weber 38/38 where all 4 barrels open together.
Not good for low throttle control.

The Holley 390 would be alright but it is expensive.

The best 4 barrel carburetors for control and mileage have a small primary with a larger vacuum operated secondary.
The engine cruises on the small primaries which will have high velocity for good fuel atomization and the large secondaries are there for the extra airflow to make power. The vacuum operated secondaries won't open further than the engine requires to maintain good manifold vacuum.

The Autolite 2100 2 barrel carb is also a good candidate for fuel mileage.
They vary in size from 190 to 474 cfm.
 
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Big six Farmer

Well-known member
The Q jet carb. mostly used on GM poducts is known for fuel economy, and im sure would work well if you wanted to endure the Q jet issues.. Holley used to make a line of Economaster Carbs., that out performed them all... I am very happy with my standard Holley 390 on my Offy dual port. Plenty of power, and has got 19-20 mpg from my 4x4, no overdrive. I have some Holley 450 Economaster carbs here, ( spread bore replacements ). Curious how that would perform on my 300 six... The key for smooth running and gas mileage is to have heat to the intake manifold hot spot, and pipe hot air into the air cleaner off the Exhaust manifolds... Here in Nebraska, i have hot intake air all year round going to the carb.. Its impressive how smooth and responsive it runs... If your not sure, look up Smokey Yunicks heat engines from back in the day. You want a mini version of that for street performance. He was really on to something back in the 80s.
 

pmuller9

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The difference between any carburetor getting good mileage and performance is the ability to tune it.
Most of those here that are still using carburetors install an air/fuel ratio meter.
Then you can optimize all the circuits for best economy and performance.

The rest have gone to Throttle Body Injection systems that will maintain the proper Air/Fuel mixture over a wide range of elevations

The Edelbrock AVS2 has smaller primaries than secondaries and is a metering rod carb like the old Q-jet.
It has Annular discharge boosters which does a better job at atomizing the fuel.
It has a very good tuning chart and the different needles and jets are available for tuning.
 
Last edited:

snakebit

New member
Welcome to the Big Six section.
First question.
Did you replace the 1986 distributor with a distributor that has mechanical and vacuum advance?

The stock 1 bbl carb and intake manifold are a restriction even for the stock engine with a stock cam.

I'm assuming you are referring to the Clifford dual Weber carburetor setup.
That setup comes with two Weber 38/38 where all 4 barrels open together.
Not good for low throttle control.

The Holley 390 would be alright but it is expensive.

The best 4 barrel carburetors for control and mileage have a small primary with a larger vacuum operated secondary.
The engine cruises on the small primaries which will have high velocity for good fuel atomization and the large secondaries are there for the extra airflow to make power. The vacuum operated secondaries won't open further than the engine requires to maintain good manifold vacuum.

The Autolite 2100 2 barrel carb is also a good candidate for fuel mileage.
They vary in size from 190 to 474 cfm.
tks so much. this is getting me headed in the right direction.
I am replacing the dest w/vacuum & mech adv. and I forgot to say that when I rebuilt the engine several years ago I installed a COMP towing cam.
What I'm talking about is that there is a clifford pkg that has headers and intake for 1 webber 2bbl. (expensive for my budget)
But the reason for my question is because you stated, as I thought, the 4bbl will use only 2bbl til throttle is opened calling for the other 2. I've been told 4bbl will get better ecconomy if you can keep your foot out of it.
Do you have any suggestions for 4bbl with small primaries and vac operated larger secondaries ?
How would the autolite 2 compare to the weber 2 any idea ?
tks again.
snakebit
 

snakebit

New member
The difference between any carburetor getting good mileage and performance is the ability to tune it.
Most of those here that are still using carburetors install an air/fuel ratio meter.
Then you can optimize all the circuits for best economy and performance.

The rest have gone to Throttle Body Injection systems that will maintain the proper Air/Fuel mixture over a wide range of elevations
 

snakebit

New member
I guess I'm old fashioned. want to try to make the carb set up work.
tks for your input. I do need to learn more about tuning. and tks for for the air/fuel ratio meter tip.
 

pmuller9

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Clifford wants a lot of money for their stuff.
I don't remember anyone here posting experience with the Weber 38 so I don't have a comparison.

The Autolite 2 barrel has annular boosters which does a very good job atomizing fuel and many here have had good results.

The Edelbrock AVS2 has smaller primaries than secondaries and is a metering rod carb like the old Q-jet.
It has Annular discharge boosters which does a better job at atomizing the fuel.
It has a very good tuning chart and the different needles and jets are available for tuning.
It doesn't have vacuum secondaries but the 500 cfm version is small enough to work.

The Street Demon has tiny primaries and a huge secondary which is vacuum operated but I don't know about it's economy performance.

Again to get best results from any carburetor an air/fuel ratio meter is recommended.

Also Big Six Farmer's recommendation for heated intake is good but you will find that a long tube header will take care of that
 

Big six Farmer

Well-known member
Reading Spark plugs, and changing jets is a lost art anymore... I dont own a scanner, or an A/F ratio meter yet. I know i will need one if i ever built a Turbo setup, to get the most out of it safely... I have worked on and built many Carbs. over the years. Alot of tuning a Carb., is from driving and a lot of time... An A/F meter is sure the fast way there.
 

snakebit

New member
Reading Spark plugs, and changing jets is a lost art anymore... I dont own a scanner, or an A/F ratio meter yet. I know i will need one if i ever built a Turbo setup, to get the most out of it safely... I have worked on and built many Carbs. over the years. Alot of tuning a Carb., is from driving and a lot of time... An A/F meter is sure the fast way there.
Sounds like an art i'd like to hone. reading plugs and changing jets--i've got a grandson that can help.
 

pmuller9

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By the way someone posted a used offenhauser intake for sale and now i cant find the post again. anyone have suggestions.?
 

sdiesel

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dump the offy ,is my opinion if you can get an aussiespeed.
sean murphy can dial a q jet to the letter for you, if yu give him the info he requests. the q jet is very hard to beat for NA application and over-all performance. i love them. even so i use a FISH on mine with fantastic result. its an odd carb, like me, and hyper efficient in the performance dept, marginally better than factory 1 barrel in economy.
be sure that whatever you decide on can be tuned and understood easily by yourself. or set up professionally by one who does.
i believe i personally would go with a sniper on an aussie speed were i you.
 

Blairsville Ed

Well-known member
tks so much. this is getting me headed in the right direction.
I am replacing the dest w/vacuum & mech adv. and I forgot to say that when I rebuilt the engine several years ago I installed a COMP towing cam.
What I'm talking about is that there is a clifford pkg that has headers and intake for 1 webber 2bbl. (expensive for my budget)
But the reason for my question is because you stated, as I thought, the 4bbl will use only 2bbl til throttle is opened calling for the other 2. I've been told 4bbl will get better ecconomy if you can keep your foot out of it.
Do you have any suggestions for 4bbl with small primaries and vac operated larger secondaries ?
How would the autolite 2 compare to the weber 2 any idea ?
tks again.
snakebit
I am using a Weber 38 clone on a 240. Although I have not used a 2100 carb it appears that the Weber design is highly adaptable to any engine if your willing to learn how to set it up for your application. The 2100 was used on many engine and vehicle combinations. The carbs have removable boosters and different bore sizes which were matched up by the factory for the engine size and vehicle weight. If you buy a used 2100 if difficult to know which engine and vehicle weight is was optimized for. There does not seem to be a way to compare the booster part numbers, so the 2100 becomes a generic fit with the only variable being the Venturi size and the main jets.
Tuning a Weber involves main fuel jets, main air jets, idle jets and emulsion tubes. I’m currently experimenting on a annular discharge booster for the Weber 38.
My experiments with a stock manifold, modified to accept a 2 barrel carb, indicate that filling the plenum or stuffing the plenum to reduce it size results in a good increase in low end torque but it will reduce top end performance. Economy is a combination of engine, transmission, rear axle ratio and vehicle weight and driving style, etc.
 

snakebit

New member
The Q jet carb. mostly used on GM poducts is known for fuel economy, and im sure would work well if you wanted to endure the Q jet issues.. Holley used to make a line of Economaster Carbs., that out performed them all... I am very happy with my standard Holley 390 on my Offy dual port. Plenty of power, and has got 19-20 mpg from my 4x4, no overdrive. I have some Holley 450 Economaster carbs here, ( spread bore replacements ). Curious how that would perform on my 300 six... The key for smooth running and gas mileage is to have heat to the intake manifold hot spot, and pipe hot air into the air cleaner off the Exhaust manifolds... Here in Nebraska, i have hot intake air all year round going to the carb.. Its impressive how smooth and responsive it runs... If your not sure, look up Smokey Yunicks heat engines from back in the day. You want a mini version of that for street performance. He was really on to something back in the 80s.
Big six tks for your response.
As a recap : I'm new to the forum and I'm a low info. carb person, and a slow learner, but getting educated on this site. Please excuse any dumb questions and responses.
I'm after low end towing torque and quick off line starts with reasonable fuel millage. (Best of both worlds). I'd be happy with 15 to 19 mpg. I'm low budget also.
I'm interested also what your holly 450 ecconomaster would do. Do you have one for sale and if so how much ?
Also you have any suggestions how I can find the person that advertised the used offy intake on this site somewhere ??
In shopping I found the holly 390 was recommended for the offy intake(but so expensive) so i'm using 390 as a starting reference for cfm.
What do you think about your 450's ? Direction please .
Tks. snakeit
 

snakebit

New member
I am using a Weber 38 clone on a 240. Although I have not used a 2100 carb it appears that the Weber design is highly adaptable to any engine if your willing to learn how to set it up for your application. The 2100 was used on many engine and vehicle combinations. The carbs have removable boosters and different bore sizes which were matched up by the factory for the engine size and vehicle weight. If you buy a used 2100 if difficult to know which engine and vehicle weight is was optimized for. There does not seem to be a way to compare the booster part numbers, so the 2100 becomes a generic fit with the only variable being the Venturi size and the main jets.
Tuning a Weber involves main fuel jets, main air jets, idle jets and emulsion tubes. I’m currently experimenting on a annular discharge booster for the Weber 38.
My experiments with a stock manifold, modified to accept a 2 barrel carb, indicate that filling the plenum or stuffing the plenum to reduce it size results in a good increase in low end torque but it will reduce top end performance. Economy is a combination of engine, transmission, rear axle ratio and vehicle weight and driving style, etc.
Tks
I understand the elements of ecconomy you listed above. The combo i have re: c6 4x4 was rated around 14 mpg originally by ford. i'm getting 7 since rebuild. I am about to put the vacuum destributor on which may help. also on highway I never get the feel of cruse. I have to keep too much accelerator and have to nearly floor it on the slightest incline . I've played with timing some but nothing seems to help. Hence: snakebit
Any input will be appreciated. Tks again.
 

pmuller9

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The carb and ignition are tied together electronically.
One will not work without the other.
If there is a problem the carb will stay rich and the ignition timing will not advance.
 

Big six Farmer

Well-known member
Well Snake bit, there are no dumb questions. Only bad moves, with out a plan. There are many on here that are sick in the head with good info. on the 240/ 300 6 cylinder, ( my self included. )... If your on a budget, and want better pep and mileage, this is how i would come at it. Keep your stock Intake manifold for now. Put on a rebuild YF Carter on from the 70s to about 83 ? ( stock carb. for a Ford Truck). Or get an adapter to mount a standard Ford or Holley 2 barrel carb. Many on here have had good luck with doing just that. You could get by with your stock Exhaust manifold, step up to a 2.25 or 2.5 pipe right off the manifold, to like a turbo style muffler dumping at least past the cab a foot or so. Look up my post on welding cast iron and my manfold set up. I could maybe be talked into making you one, but it would take some time... Yes get a Dura spark dist. with the vacuum advance, put lighter advance springs in and tune on that. A daily driver 300 six doesent need much Carb., but better exhaust and spark timing curve. You will be only running from idle to about 3800? rpm . work off what i advised, and you will get alot on the cheap. You can always upgrade to more performance parts later. Im not interested in selling my Holley 450 for now. They can be found on Ebay im sure.
 
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