I have done a mild performance mod on my 1980 Dodge D-150 truck (see description below). It has Holley 390 cfm carburetor on it and I am getting 13MPG in town and 15-16 MPG on the road. I was thinking of putting a Holley 2280 on it that I have in the hopes of improving the gas mileage. I compared the carburetor bore sizes between the two the 390 has 4-1 7/16" bores and the 2280 has 2-1 7/16" bores. I never get the thing above 3000 RPM. So should I swap carburetors or just put the black spring in the 390's secondaries and accomplish the same thing. Since I would be running on 2-1 7/16" bores either way.

BTW my old 1 bbl got 16-17 MPG.

bwhitejr

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'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

What is your rear end gear ratio?
If it is super low like a 4.10, that may be limiting your mileage.

What size is your exhaust system? If it is too small it could be off setting all your upgrades.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Is your truck auto or standard? Rear tire size? Just as a super low gear like 4.11 hurts you, so will a super hi gear like 2.80

BTW the best my 81 D150 long bed 225 2bbl 727 got 14-15, then again that is with me driving
I also have an 85 D150 short bed with a 318 2bbl, 999a lockup (all stock)that gets 11
A 92 D150 318 Magnum 518a, speedo is broke but we estimate no better then 12-13.
A 85 D350 enclosed utility bed dually 360 4bbl NP435 4 speed (big heavy truck) 6-7 towing or not.

These are heavy trucks with the aero of a brick. I would have been very happy with your 16-17 before I blew up the 81.


TopHat

The rear end is a 3.55 and the transmission is a A-833 OD. So final drive ratio is 2.52. So the mileage should be better than it is.

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

Have you checked the distributor curve, is the engine getting lots of advance?

What jetting in in the Holley?
DD

If that Holley has a power valve, make sure the diaphragm isn't ruptured. Also look to see what it's opening pressure is. It's been a while but I recall they should open at 2" vacuum less than the vacuum reading at idle for proper operation.

-James

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The distributor has 12* initial advance and a original small spring and a Mopar distributor spring from the recurve kit. I haven't mapped the advance curve, yet. But was toying with the idea of a super-six instead of a 4bbl for better gas mileage.

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

The Holley 0-8007 jetting is stock out of the box all around.

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

Hi Bwhite,

I dunno if you will get better mileage with a super six than with a properly adjusted 4bbl...I have a 8007 and am now getting 16 mpg with 3.91 rear end with an 833OD on my D100 on a road trip. Now, kicking it around town did drop me to 9 mpg! I put in a secondary metering block and a quick change spring kit. (Per advice from the forum, BTW). I am right now using an 8.5 power valve but because I am an endless tinkerer will probably slide in a 6.5 to see if it is too lean. The 10.5 was a tad rich. Now using 51 jet in primary and 57 in secondary with a 25 shooter. I had a 31 shooter but I wanted a different outflow. Be sure the secondary plates are properly adjusted so the idle transfer slot isn't "leaking". I idle at 750 rpm and 19 inches of vac, too. Oh, I did a high rise under my carb, too.

rock
64d100

I know that I can get better mileage than I am getting. I just don't know the steps to isolate each component and decide which way to go. Like the shooter, the primary jets, the secondary springs. The problem with Holleys is you have to completely take them apart to change the jetting. I have all the cams, the springs and some additional shooters I just don't know where to start.

bwhitejr

_________________
'72 Duster (Performance 360)
'83 Ramcharger (Performance 318)
'80 TrailDuster (360)
'80 D-150 Truck (See Below)
CompCams 252S, Holley 390cfm, Offy manifold
Ported, Polished and Gasket Matched
P4286813 Springs,0.040 Overbore,
0.090 Shaved Head

Ok my 2cents worth. I've been a Holley man since the Mayflower came over with the first one. However, while trying to get my sl6 running good I finally got mad and tried an old carter afb,bingo ran great. So picked up a new edelbrock 500 thunder series and TaDa,I like it. Everything that may need tweakin is right on top so no more benching the carb to play with it. The 2ndary opening is adjustable with a screw while carb is on the manifold(which is where it belongs). No I'm not saleman for edelbrock or a parts man,just some old guy who likes it simple and dependable PS I gave the holly and all the extra parts I bought to a chevy friend,I will not go back to a holley again

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83 B-150 slant 6,4 speed. 79 B-300 360 pathfinder 4x4. 74 W-300 318 4x4 git-r-done 80 B-100 sl6,4speed

bwhitejr,

Since you mentioned it.......

Where did you get the MOPAR distributor recurve kit?
I have been looking far and wide for one!

What color is the spring you replaced the heavy one with?

Is that a 9R governor in your distributor?

Do you know how much vacuum advance your getting?
I am able to get 13 degrees out of a 11R advance. That helps to buy a few miles per gallon at cruise.

Don't give up on the Holley even though it's tempting to just bag it and use a 500 Edelbrock. They are so easy to dial in.

You should be able put a heavy spring in to keep the back barrels from coming on to help focus on the jetting and power valve. Sort of like using it as a two barrel only for awhile. The mileage doesn't sound all that bad, do you have other issues? like stumbling or bogging? or just fine tuning?

Thanks!

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

6shotvanner-
What do you think about the build quality on that Thunder series carb? I got a little excited to see my second favorite 4bbl carb being built again. Now if Edelbrock would only see fit to offer a new Thermoquad...

Agressive Ted-
Summit racing lists the MP distributor spring kit on their website, although it's a bit spendy at 12 bucks. Sucks Crane Cams used to sell a kit for the small block mopars that would work on the slants. Perhaps there is another vendor out there that has a similar kit for sale?

-James

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James,I like the fit and finish of the thunder. Not one complaint from me on this carb Oh and bwhitejr, as far as mileage goes I've got no complaints on that either. I didn't build this puppy for mpg but it seems to be doing ok. The odo took a dump before I got the edel on so no real #'s but it's doing as good or better than the stock 1brl just by seat of the pants figren

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83 B-150 slant 6,4 speed. 79 B-300 360 pathfinder 4x4. 74 W-300 318 4x4 git-r-done 80 B-100 sl6,4speed

Hi again, Bwhite

In no way is this note an attempt to try to convince you of my pointo f view., rather after reading this thread, and because I have done a lot of d100 playing, I moved to the Holley. In retrospect it is because I learned enough to understand Holley vs. the Eddy I used to start with. Eddy is probably a good carb to start with. As others have said, bolt er on and go. It is not, however as infinitely tunable as the Holley. If you turn into a tuning nut like I am, you can really zero in on "tune" for any reluctor, cam, advance can, and spring combination with the Holley. The metering rods in an Eddy would seem to offer the same possibilities, but you will find it not as sensitive as the Holley with the 4150 conversion. Now if you are not a tuning nut...the Eddy is a great carb...I kept mine on the shelf.

With the Holley first ya gotta set the throttle plates correctly with the carb off. Then, put in say, a black spring to keep the secondaries closed. DI (Duster Idiot) gave me the skinny on springs and 4150 upgrade and it works. I run the purple spring some and the yellow spring some, but get yiour primaries set with a black spring in. Til I rebuilt some Holleys I was afraid of the Holley (Hmmm, rebuilding one may be a good way to understand a Holley). And in truth I had to use 3 books at the same time, each telling me more of the puzzle.

Rejetting doesn't really require taking it all apart, only removing the float bowl to get to the plate. You do need reusable gaskets and I put PAM on mine so they wouldn't stick. To start with, put in a 51 Primaryand a 57 Secondary jet to dial in. I am using a reluctor filled and filed to 9R now.
Just another truckers' 2 cents worth..a trucker who was CONVINCED he'd never use that Holley he had on the shelf!

rock
'64d100