carb options for Dodge 318

[unknown]

Hello,

I've got an old Dodge truck has a 318 w/ the original 2 barrel. I'm
thinking of changing to a 4 barrel - would it give me any more gas
mileage over a 2 barrel? If so which one?

I have a square bore intake manifold.

I was thinking of maybe one of those smaller Holley 600cfm vacuum
2ndary carbs?

Or how about a spread bore intake and a QJet?

I was thinking a carb w/ small primaries might give me a tad better
mileage if driven mildly and a little extra power when towing/passing.
I'll also be adding a dual exhaust (no headers keep the manifolds)
maybe 2" each.

thanks!

[Larry Smith]

I hate to be negative, but I really don't think you will see too much
improvement in gas mileage in your truck if you put on headers and
install a 4 BBL. It could easily get worse, but will not likely get
much better.

You may enjoy driving the car a little more with a mild hopup though.

I have the fuel injected 318 in my van. Great engine, plenty of power
for an old fogey like me. Depending on how I drive it, I get 15-17 mpg.

[Daniel J. Stern]

Post by unknown
I've got an old Dodge truck has a 318 w/ the original 2 barrel.

That covers a lot of different trucks, made in a lot of different years,
and equipped with one of two kinds of 318 engine and a lot of different
"original 2 barrel" carburetors made by one of three different
manufacturers. Can you be a little more specific about the year and model
of the truck, and the make and model of 2bbl carburetor you're starting
with? If the truck is newer than '69, also note whether it's a 49-state,
California, Canada or rest-of-world-spec truck (emissions system), and
whether it has an automatic or manual transmission.

Post by unknown
I'm thinking of changing to a 4 barrel - would it give me any more gas
mileage over a 2 barrel?

A brand-new economy 4bbl on a good manifold compared to a worn-out 2bbl on
a poor manifold? You bet.

A brand-new too-large 4bbl on a poor manifold compared to a worn-out 2bbl
on a poor manifold? A used too-large 4bbl? Also, how is this truck used?
Highway flyer/unloaded? Heavy hauler, rock climber, grocery getter? Lots
of variables here. It sounds like the goal is better mileage, so don't get
too hung up on swapping this carb for that carb -- spell out what the
truck is and how you use it and then we can discuss how to make it get
better mileage.

Post by unknown
I was thinking of maybe one of those smaller Holley 600cfm vacuum 2ndary
carbs?

600cfm is not "smaller". 390cfm is "smaller".

-Stern

[unknown]

On Thu, 27 May 2004 12:58:13 -0400, "Daniel J. Stern"

Post by Daniel J. Stern
That covers a lot of different trucks, made in a lot of different years,
and equipped with one of two kinds of 318 engine and a lot of different
"original 2 barrel" carburetors made by one of three different
manufacturers. Can you be a little more specific about the year and model
of the truck, and the make and model of 2bbl carburetor you're starting
with? If the truck is newer than '69, also note whether it's a 49-state,
California, Canada or rest-of-world-spec truck (emissions system), and
whether it has an automatic or manual transmission.

'82 automatic. I don't know off hand what 2bbl but yes it's seen
better days. The block is out of a junker and I'm not sure of the year
it's maybe a mid to early 80s 318? It's been machined/overhauled
recently w/ fresh cam etc... the orig 318 had been rebuilt several
times and it was time to replace it.

Post by Daniel J. Stern

Post by unknown
I'm thinking of changing to a 4 barrel - would it give me any more gas
mileage over a 2 barrel?

A brand-new economy 4bbl on a good manifold compared to a worn-out 2bbl on
a poor manifold? You bet.
A brand-new too-large 4bbl on a poor manifold compared to a worn-out 2bbl
on a poor manifold? A used too-large 4bbl? Also, how is this truck used?
Highway flyer/unloaded? Heavy hauler, rock climber, grocery getter? Lots
of variables here. It sounds like the goal is better mileage, so don't get
too hung up on swapping this carb for that carb -- spell out what the
truck is and how you use it and then we can discuss how to make it get
better mileage.

Post by unknown
I was thinking of maybe one of those smaller Holley 600cfm vacuum 2ndary
carbs?

600cfm is not "smaller". 390cfm is "smaller".

I was thinking 600 cfm as an absolute max. In the Holley line it's 600
or step down to 390 I think - nothing in between...? I believe it's
their 4160 that comes in either flavor w/ vacuum 2ndaries for a mild
street application. Not looking to win any races - just good fuel
economy for daily driving and some added oomph for passing/towing once
a month or so. No headers - retain the exhaust manifolds but will add
a basic 2" dual exhaust.

The (Edelbrock) QJet might work nicely too but I don't see those on
much outside of GM applications.

What about the (Carter AFB) Edlebrock Performer? I think it can be had
in 500cfm tuned for economy. Should bolt right onto a square bore
intake mani.

Anyway after thinking a bit on it I'm thinking a 4160 @ 390CFM or
Performer at 500cfm maybe... thoughts?

[Daniel J. Stern]

Post by unknown
'82 automatic.

Oof. OK, next question: What kind of emission tests do you have to pass?
The '82 wasn't necessarily just a plain old carb, on many trucks it was a
feedback carburetor. Unless you are prepared to rework the entire engine
management system, such as it is, you can't just swap the carb and expect
to (a) gain mileage or (b) pass a smog check.

Your '82 could have had either a Carter or a Holley carburetor from the
factory. Of these, the Carter is superior. If you are trying for better
mileage, you might still find one of the Holley "Economaster" new carbs on
Ebay or from one of the carburetor houses, but don't look for this to
improve performance.

Post by unknown
I was thinking 600 cfm as an absolute max. In the Holley line it's 600
or step down to 390 I think - nothing in between...?

Don't think there's anything in between, no. The 390 is more than plenty
on your '82 318 truck. I'd put it on an Edelbrock Performer intake. If I
needed to retain the feedback system, my strategy would probably change to
a small Quadrajet. But I'd rather have a Carter than either a Rochester or
a Holley!

Post by unknown
economy for daily driving and some added oomph for passing/towing once a
month or so. No headers - retain the exhaust manifolds but will add a
basic 2" dual exhaust.

Good thinking, headers are a pain.

Post by unknown
The (Edelbrock) QJet might work nicely too but I don't see those on much
outside of GM applications.

Chrysler used them on '80s M-bodies (Diplomat, Gran Fury, and in Canada
the Caravelle) with Cop-spec 318 4bbl engines.

Post by unknown
What about the (Carter AFB) Edlebrock Performer?

I like this thinking better than "Rochester" or "Holley". Better than the
AFB: the newer Edelbrock copy of the Carter AVS. I forget what Edelbrock
calls it -- Steve should chime in here -- but you get better mileage and
driveability out of the AVS design than out of the AFB.

-Stern

[Steve]

Post by Daniel J. Stern
I like this thinking better than "Rochester" or "Holley". Better than the
AFB: the newer Edelbrock copy of the Carter AVS. I forget what Edelbrock
calls it -- Steve should chime in here -- but you get better mileage and
driveability out of the AVS design than out of the AFB.
-Stern

They call it the "Thunder Series AVS"

http://edelbrock.com/automotive/carb_thunder_series.html#650cfm


I see they build it as a 650- should be PERFECT for a 318. Now I need to
go buy one myself... :-)

[Daniel J. Stern]

Post by Steve

Post by Daniel J. Stern
I like this thinking better than "Rochester" or "Holley". Better than
the AFB: the newer Edelbrock copy of the Carter AVS. I forget what
Edelbrock calls it -- Steve should chime in here -- but you get better
mileage and driveability out of the AVS design than out of the AFB.

They call it the "Thunder Series AVS"
http://edelbrock.com/automotive/carb_thunder_series.html#650cfm
I see they build it as a 650- should be PERFECT for a 318.

And I was just gonna comment "Shoot, they don't make a smaller one?".

-Stern (How 'bout quad SUs?)

[Nate Nagel]

Post by Steve

Post by Daniel J. Stern
I like this thinking better than "Rochester" or "Holley". Better than the
AFB: the newer Edelbrock copy of the Carter AVS. I forget what Edelbrock
calls it -- Steve should chime in here -- but you get better mileage and
driveability out of the AVS design than out of the AFB.
-Stern

They call it the "Thunder Series AVS"
http://edelbrock.com/automotive/carb_thunder_series.html#650cfm
I see they build it as a 650- should be PERFECT for a 318. Now I need to
go buy one myself... :-)

Now if they just made a 500 or 600CFM version... (for a Stude 289...)

nate

[Steve]

Post by Nate Nagel

Post by Steve
They call it the "Thunder Series AVS"
http://edelbrock.com/automotive/carb_thunder_series.html#650cfm
I see they build it as a 650- should be PERFECT for a 318. Now I need
to go buy one myself... :-)

Now if they just made a 500 or 600CFM version... (for a Stude 289...)
nate

As I said, the AVS design is EXTREMELY flexible, and its very hard to
"over-carb" an engine with an AVS (or Thermoquad, or Quadrajet) as you
can with a mechanical-secondary carb or even a vacuum-secondary Holley.
I'm convinced that is part of the reason that GM used the Quadrajet
design so long and on so many engines (and I know its why Chrysler used
the Thermoquad on copcar 318s). A 650 AVS should be fine on a 289, and
I've run a 750 old vintage AVS on a 318 with no problems at all.

[Nate Nagel]

Post by Steve

Post by Nate Nagel

Post by Steve
They call it the "Thunder Series AVS"
http://edelbrock.com/automotive/carb_thunder_series.html#650cfm
I see they build it as a 650- should be PERFECT for a 318. Now I need
to go buy one myself... :-)

Now if they just made a 500 or 600CFM version... (for a Stude 289...)
nate

As I said, the AVS design is EXTREMELY flexible, and its very hard to
"over-carb" an engine with an AVS (or Thermoquad, or Quadrajet) as you
can with a mechanical-secondary carb or even a vacuum-secondary Holley.
I'm convinced that is part of the reason that GM used the Quadrajet
design so long and on so many engines (and I know its why Chrysler used
the Thermoquad on copcar 318s). A 650 AVS should be fine on a 289, and
I've run a 750 old vintage AVS on a 318 with no problems at all.

I didn't see that post until after I'd sent mine. I do have a 600CFM
Carter AFB (one of the newer ones) on the shelf, do you think the 600
CFM AFB or the 650CFM AVS would be a better choice? This will end up
being a "mildly warm" street motor and will probably never see over 6000
RPM. If the AVS would be better, I can always pass the AFB on to my
dad, he has a stock 350 in his pickup and the old Q-jet is about due for
retirement. I have no experience with the AVS carbs, are jets, rods
etc. available and how difficult are they to tune? How much tuning is
usually required or do they generally run well "out of the box?"

Also, I'll probably be running this on an Offenhauser WCFB manifold with
an adapter plate if that makes any difference. I'm not aware of any
good manifolds for a Stude for an AFB-style square bore carb other than
the factory cast iron one or the (pricey) aluminum recastings of the
stock manifold. Plus I got a good deal on the Offy with a matching pair
of valve covers.

nate

[Steve]

Post by Nate Nagel

Post by Steve

Post by Nate Nagel

Post by Steve
They call it the "Thunder Series AVS"
http://edelbrock.com/automotive/carb_thunder_series.html#650cfm
I see they build it as a 650- should be PERFECT for a 318. Now I
need to go buy one myself... :-)

Now if they just made a 500 or 600CFM version... (for a Stude 289...)
nate

As I said, the AVS design is EXTREMELY flexible, and its very hard to
"over-carb" an engine with an AVS (or Thermoquad, or Quadrajet) as you
can with a mechanical-secondary carb or even a vacuum-secondary
Holley. I'm convinced that is part of the reason that GM used the
Quadrajet design so long and on so many engines (and I know its why
Chrysler used the Thermoquad on copcar 318s). A 650 AVS should be fine
on a 289, and I've run a 750 old vintage AVS on a 318 with no
problems at all.

I didn't see that post until after I'd sent mine. I do have a 600CFM
Carter AFB (one of the newer ones) on the shelf, do you think the 600
CFM AFB or the 650CFM AVS would be a better choice?

I just prefer the AVS all-around, at least the "real" Carter AVS and the
Edelbrock is an exact clone. The fact that you even HAVE a way to tune
the kick-in rate of the secondaries is the key, IMO.

Post by Nate Nagel
This will end up
being a "mildly warm" street motor and will probably never see over 6000
RPM. If the AVS would be better, I can always pass the AFB on to my
dad, he has a stock 350 in his pickup and the old Q-jet is about due for
retirement. I have no experience with the AVS carbs, are jets, rods
etc. available and how difficult are they to tune? How much tuning is
usually required or do they generally run well "out of the box?"

Almost all the "tuning" parts for an AVS can be borrowed from an AFB.
The old original Carter-built AVSes had 3-step metering rods instead of
the AFB's 2-step, but you could use the AFB rods in an AVS if you also
used the AFB-style cover plate.

But it doesn't matter, Edelbrock sells everything you need to tweak a
new AVS: http://edelbrock.com/automotive/carb_acces.html

As for "out of the box," I haven't actually tried an Edelbrock AVS yet,
but it should be pretty good. Their AFB was pretty close (although a tad
rich for a mild engine- but that's safer than too lean).

[Steve]

Post by unknown
The (Edelbrock) QJet might work nicely too but I don't see those on
much outside of GM applications.

Chrysler actually used Quadrabricks as original equipment on Police-spec
318s from about 85 through 89. Carter quit building the Thermoquad, and
the Quadrajet is really the closest direct replacement. Its a decent
carb overall, and because its an air-valve secondary spread-bore, it
works on a wide array of engine sizes, including smallish engines like a
318.

Post by unknown
What about the (Carter AFB) Edlebrock Performer? I think it can be had
in 500cfm tuned for economy. Should bolt right onto a square bore
intake mani.

Great carb, and I ran one for many years. But I prefer the new AVS
version. All the advantages of a Carter, plus its also an air-valve
secondary so it "sizes itself" to the engine much better than an AFB.

Post by unknown
Performer at 500cfm maybe... thoughts?

Well, Thermoquads and Quadrajets flow a LOT of air, but have small
primaries, air valve secondaries, and work well even on small engines.
IF you go with an AFB, go SMALL because it doesn't adapt as well. An AVS
also adapts well and you can use a 750 AVS on a 318 with no problem. In
fact, I think you'd like a 750 AVS better than a 500 AFB, even though it
would never flow near 750 CFM on a 318. The 390 Holley might be a bit
TOO small, IMO.

[Steve]

Post by unknown
Hello,
I've got an old Dodge truck has a 318 w/ the original 2 barrel. I'm
thinking of changing to a 4 barrel - would it give me any more gas
mileage over a 2 barrel? If so which one?
I have a square bore intake manifold.
I was thinking of maybe one of those smaller Holley 600cfm vacuum
2ndary carbs?
Or how about a spread bore intake and a QJet?
I was thinking a carb w/ small primaries might give me a tad better
mileage if driven mildly and a little extra power when towing/passing.
I'll also be adding a dual exhaust (no headers keep the manifolds)
maybe 2" each.
thanks!

If you can find a Carter Thermoquad in superb condition, that's the carb
for a 318. I'm running one now on mine, and IMO its the best carb design
ever- but its delicate and not many lasted all these years, and if you
don't know the design very well you'd be hard pressed to find the
potential faults with a used TQ. So I don't SERIOUSLY recommend it.

My first serious pick would be the new Edelbrock reproduction of the
Carter AVS. I've run the old Carter AVS on a 318 for many years with
excellent results. Better throttle response than an AFB, without the
Holley problems (blowing power valves, leaky gaskets, leaky accelerator
pump diaphragms.) Not quite the gas mileage of the Thermoquad, but
darned close.

Next would be an Edelbrock AFB, then after that a Quadrajet (or
Edelbrock repro Quadrajet) and finally a small vacuum secondary Holley.
Holley carbs perform great, but they're just too maintenance-hungry for
me. Especially with todays gasolines that might eat all the rubber parts
right out of one.

[unknown]

Thanks! That nails thigns down nicely.

FYI No there are no emissions equip on the truck and no requirements
around here.

Could I expect much if any mileage improvement over an original 2bbl
with any of these options if driving conservatively?

thanks again,

Post by Steve

Post by unknown
Hello,
I've got an old Dodge truck has a 318 w/ the original 2 barrel. I'm
thinking of changing to a 4 barrel - would it give me any more gas
mileage over a 2 barrel? If so which one?
I have a square bore intake manifold.
I was thinking of maybe one of those smaller Holley 600cfm vacuum
2ndary carbs?
Or how about a spread bore intake and a QJet?
I was thinking a carb w/ small primaries might give me a tad better
mileage if driven mildly and a little extra power when towing/passing.
I'll also be adding a dual exhaust (no headers keep the manifolds)
maybe 2" each.
thanks!

If you can find a Carter Thermoquad in superb condition, that's the carb
for a 318. I'm running one now on mine, and IMO its the best carb design
ever- but its delicate and not many lasted all these years, and if you
don't know the design very well you'd be hard pressed to find the
potential faults with a used TQ. So I don't SERIOUSLY recommend it.
My first serious pick would be the new Edelbrock reproduction of the
Carter AVS. I've run the old Carter AVS on a 318 for many years with
excellent results. Better throttle response than an AFB, without the
Holley problems (blowing power valves, leaky gaskets, leaky accelerator
pump diaphragms.) Not quite the gas mileage of the Thermoquad, but
darned close.
Next would be an Edelbrock AFB, then after that a Quadrajet (or
Edelbrock repro Quadrajet) and finally a small vacuum secondary Holley.
Holley carbs perform great, but they're just too maintenance-hungry for
me. Especially with todays gasolines that might eat all the rubber parts
right out of one.

[Steve]

Post by unknown
Thanks! That nails thigns down nicely.
FYI No there are no emissions equip on the truck and no requirements
around here.
Could I expect much if any mileage improvement over an original 2bbl
with any of these options if driving conservatively?
thanks again,

Kinda depends on the manifold you choose, as well as the rest of your
combination. The only carb that gave me a real noticable improvement was
the Thermoquad, and only when being careful to stay OUT of the
secondaries. One or two wide-open romps will pretty much erase the
slight benefit of the small primaries for that tankfull. But as I think
Dan said, old 2-bbls tend to be in mediocre condition and a brand-new
4-bbl might well do considerably better. Especially once you get it
dialed in.

[Kingsway]

I think it will help , got a 76 Malibu with a 350 2 bbl was getting about
14 -15 mpg , change to a factory 4 bbl intake and Qjet carb from a 83 and
fuel mileage has gone up to 17-18 and when i need to pass and open it up ,
lots more passing power ..
i personally stay away from the dodge 4 bbl thermoquads myself ...but that's
my experience
i still think a 600 cfm edelbrock would be ok , but the carter 500 vac
secondarys would work good too

"pgtr" <pgtr(deletethisandsubstituteatsymbol)bigfoot[ot]com> wrote in

Post by unknown
Hello,
I've got an old Dodge truck has a 318 w/ the original 2 barrel. I'm
thinking of changing to a 4 barrel - would it give me any more gas
mileage over a 2 barrel? If so which one?
I have a square bore intake manifold.
I was thinking of maybe one of those smaller Holley 600cfm vacuum
2ndary carbs?
Or how about a spread bore intake and a QJet?
I was thinking a carb w/ small primaries might give me a tad better
mileage if driven mildly and a little extra power when towing/passing.
I'll also be adding a dual exhaust (no headers keep the manifolds)
maybe 2" each.
thanks!