318 2bbl to 4bbl: Is it worth it this time?

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MOPARJ

MOPARJ

What can I upgrade now?
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My 75 Dart with dual exhaust (2.25" piping) and turbo mufflers currently has a decent 2bbl on it and runs well. It averages between 13-14.5 mpg total for a full tank with 3.21 gears and mixed driving.

I have done many 4 bbl swaps, but is stepping up to a 4bbl this time worth it and will it help milage? It is just a travel to work 40 miles a day ride, not a drag car. If four barrel, I was thinking manual choke 500 cfm Eddie and ubiquious 2176 performer intake.
 
If you go to a square-bore carb mileage will probably get worse. It will only improve if you go to something with smaller primaries than the BBD you're currently running, such as a ThermoQuad (which is what I'm putting on the 318 in my '70 Duster on top of an '83 iron pickup truck manifold). You should also be getting MUCH better mileage than that, I've heard of people getting upwards of 20 MPG in their stock 318/727 B-bodies. I guess you keep your foot in it then.

I want to go to dual exhaust on my Duster too, what did you do for your exhaust? Muffler shop?
 
I just finished my swap from 2 bbl to an SP2P Edelbrock and an eddie 1403/500cfm ele choke.
Best thing I could have done..difference between us is probably that I had driveability issues that prompted me to make the change.
Gas mileage will be checked now and I will see how I do.
 
Bear this in mind:
With the 2bbl, there is a chance that you have to have the throttle open more to get going away from the stoplight then you would with the 4bbl. I like the idea of the small 4bbl, and the 2176. I would make sure to have a fresh tune, and if you do not have a dwell tach, borrow or buy one and adjust the carb, via the air fuel mixture screws, for the highest vacuum/rpm possible, before adjusting the throttle screw. I would also check timing, because a little more advance could add some pep, and throttle response, requiring less actual throttle to get the vehicle moving, and ultimately better mileage.
 
I got 20 MPG Hwy. in my 360/904/2.76 rea with 26 inch tires Dodge Magnum.

If a 318 can't do it in an A body, you ethier need to go back and tune that baby up or replace the engine or trans cause something aint workin right.

The T-Q should be the smaller primary unit. Get ahold of Demonsizzler for tuning jets. (And advice on a T-Q carb to look for. I don't know if a smogger T-Q would be OK) Advance the timing some and a great MPG netter would be a MSD or equal. The multi spark really helps in mileage.

Between the smaller primary of the T-Q and multi spark, you'll gain mileage. If you had a 2.76 gear out back, you would do really well.
 
rumblefish360 said:
I got 20 MPG Hwy. in my 360/904/2.76 rea with 26 inch tires Dodge Magnum.

If a 318 can't do it in an A body, you ethier need to go back and tune that baby up or replace the engine or trans cause something aint workin right.

The T-Q should be the smaller primary unit. Get ahold of Demonsizzler for tuning jets. (And advice on a T-Q carb to look for. I don't know if a smogger T-Q would be OK) Advance the timing some and a great MPG netter would be a MSD or equal. The multi spark really helps in mileage.

Between the smaller primary of the T-Q and multi spark, you'll gain mileage. If you had a 2.76 gear out back, you would do really well.
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I had one of the old style MSD boxes on the car, the old type that you hook the existing wiring pigtail and connector from the original ecu. Its a simple plu in and play type, not requiring any wiring. It must be a mopar specific box. The why I took it off is because after I hooked up the tach to the coil, I would get erratic inaccurate readings after 5 minutes of run time. Took the box off and am running the stock ecu and the tach works fine. Its a shame, as it ran smoother, cleaner, and did get slightly better mpg with the MSD box.

I noticed a small plug in section on the opposite side of the box. Could this be where the tach lead that normally connects to the coil should go??? How can I get the tach to work normally with the box?

As far as milage, its a combined total. My hemi charger with cylinder deactivation gets 17 mpg mixed over a full tank. I seriuosly doubt that the teen will do better than that. Maybe 20 mpg on the highway, I know I am getting near that, but as an entire tank average, mixed driving, between 14-15 mpg total average at best.

The car is not driven hard unless needed, always under 3,000 rpm, except for freeway driving, which at 65, is right at 3,000 with 235/60/14 tires.

Timing is advanced as far as possible with it on the ragged edge of detonation. I just tuned it up too with plugs and wires. Believe me, its tuned well, with the exception of the carb.

The motor is 20,000 miles old, along with the trans, and has great oil pressure, even ridiculously high, 90 lbs when cold, 75 warm on highway.

Any other suggestions??
 
MOPARJ said:
My 75 Dart with dual exhaust (2.25" piping) and turbo mufflers currently has a decent 2bbl on it and runs well. It averages between 13-14.5 mpg total for a full tank with 3.21 gears and mixed driving.

I have done many 4 bbl swaps, but is stepping up to a 4bbl this time worth it and will it help milage? It is just a travel to work 40 miles a day ride, not a drag car. If four barrel, I was thinking manual choke 500 cfm Eddie and ubiquious 2176 performer intake.
Click to expand...

It's definitely worth it. Your mileage will drop in the 1st couple of weeks because you'll be flooring it more O:) All kidding aside. The mileage shouldn't change. You only use the primaries during cruise anyways.
 
MOPARJ;
I noticed a small plug in section on the opposite side of the box. Could this be where the tach lead that normally connects to the coil should go??? How can I get the tach to work normally with the box?
Click to expand...

Yes. IIRC, the tach hook up is at the other end of the MSD box, a little male connector counter sunk inside the box's housing. That should set it straight.

The list or search for extra mileage is long. Some if not many you have done;

From top to bottom, front to rear;

Open air cleaner. I like a large diameter and as thick as one can squezze under the hood. It's simply more area, thats all.

No matter the carb, though I prefur a T-Q or simply a Carter, it needs to be dead balls on. F.I. would be best, because the carb will fall in and out of tune with the days heat or lack there off.

Upgraded intake. Blocked heat cross over. Sometimes a spacer can help between the carb and intake. A single plane should, in my head at least, get better Hwy. mileage.

Heads...well, actually, VALVES and seats. Even a simple clean up by your own hands is great on older engines with alot of miles. Since yours in new/rebuilt, a back cutting of the valves and seat work to improve flow can help breathing.

Cam...OOOOOO, tricky one. The thing with stock engines is the exhaust. It is in need of help. A split duration cam can help it breath easier. One day I'll have a few spare hundred bucks to have made a few custom grind cams with really small intake durations in a search for more mileage, but with extended exhaust duration which will not only help power, but IMO, mileage as well.

Headers, X pipe, dialed in distributor, and upgraded ignition,, parrasidic lose minimized, mechanical fan deleate, P/S delate, O/D tranny, or beter yet, manual O/D conversion, Hwy. gears, taller thinner tires, fiberglass wieght reduction and anywhere else you can get it on the body or drivetrain and wheels. Sythn. oils

The list goes on and on and on and on.......
 
You could also get into some unconventional stuff, like combustion chamber edging and Somender grooves. These mods help dramatically improve flame travel and combustion speed, boosting efficiency and allowing one to use much higher compression and less timing advance.
 
Ahhh HA! Piston top coating and cylinder head chamber smoothing and coating! Open up spark plugs wide!
 
Just slap that sucker on there, and have some fun. Your mods will never end after adding a 4 barrel, but it is a great start.
 
MOPEkidD-3 said:
Yeah, that too. Also "concave radius" the spark plug electrodes and drill a small hole in the ground prongs.
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I have never heard of that one....

MtNemoMopar said:
Just slap that sucker on there, and have some fun. Your mods will never end after adding a 4 barrel, but it is a great start.
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Amen! LOL, just have fun.
 
rumblefish360 said:
I have never heard of that one....
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Another trick thought up by Mike Holler. The "radius"-ing of the electrode makes it easier for it to "broadcast" a spark, and the hole in the ground prong lets the just-ignited fuel/air "shoot" through into the chamber as a jet of flame instead of having to go around the prong. Pretty unconventional, but makes sense to me. I see it as one step further from indexing plugs.
 
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