Holly 390/Offenhausen Set-up and Gas Mileage

the_mahout · #1 (**permalink**) 02-07-2006, 08:04 PM

I know this topic gets a lot of airtime but I still have some question after reading through most of the archive topics with Carb and Mileage in the subject line. Please bear with me.

Yesterday I got around to calculating my fuel mileage over the last three tanks full of petrol. Data is not good – 10.1 miles per gallon (337.7 miles traveled and 33.4 gallons used). I did a complete tune-up a couple weeks ago and everything is in order. I drive very conservatively and a good percentage of the mileage is highway - 60mph maximum speed. After the tune-up I realized zero increase in fuel mileage. My current assumption is that the culprit must be the stock 1-bbl Carter carburetor.

I have read through most of the posts in this archive on carburetors and fuel mileage. It seems like the group consensus is that the following combination is the best for both fuel mileage and performance:

1) Holley 4-bbl carburetor – 390 cfm

2) Offenhauser C-Series Manifold

3) EFI Exhaust Manifold

Here are some questions I am mulling over:

1) What kind of fuel mileage can I reasonable expect from the set-up above? I would like to be able to get 15-16 miles per gallon. I want to make sure the $600 outlay in cash is worth the investment.

2) When you all talk of the Holley 390cfm is it the Model 4160 that you are referring too? See at site: http://store.summitracing.com/default.asp?Ntt=HLY-0-8007&searchinresults=false&Ntk=KeywordSearch&ffice:smarttags" />>

3) What are these EFI exhaust manifolds? Can anyone proved a better description and a link to a source / vendor? I have done a google search and nothing definitive comes up.

4) Does anyone have any pictures of the Holley / Offenhauser set-up on their rigs?

5) What is a source for a rebuild kit for the original Carter carburetor?

Many thanks.

roscoe · #2 (**permalink**) 02-07-2006, 09:50 PM

Okay....I'll try to answer...being the newest member to the 4bbl-Offy-efi-300-6 club.
Mileage varies depending on alot of things including engine condition, axle gear ratio, transmission, etc.
I used the Holley 4160/ 390cfm 4bbl. carb and it has been pretty good right out of the box...so far....
Also using Offenhauser dual plane intake....Also using efi manifolds...no mystery here...they were used on 87-96 pick ups and they bolted right up to my 1978 300-6 head - no problem. Get them at most junkyards.
I have some pictures of my setup in my gallery...I'll put up some better pics soon.
Keep asking questions....someone on here must know something.

John

garbz2 · #3 (**permalink**) 02-08-2006, 08:25 AM

Using the setup John mentions with a heated base plate from a 63 galaxie for the carb ( a must for colder climates due to ice build up in th carb) here in PA i averaged 13 MPG with a 1986 F150 Ex cab 4x4 t-19 3.73 Gearing. A full tank 19 gallons would consitently run out after 245 miles. I live in the highest city in PA so within 100 miles of me its sea level to 1900 feet where i live.

I drove this truck to Iowa in 2004 and as soon as i hit the flat lands of Ohio the mileage jumped to almost twenty at steady highway speed of 60 to 65 and 2600 RPM.

I ran the 390 as recieved with the jetting but played with the vaccume secondaries with springs to have them come in later as i have a lead foot. It is a huge difference in the engine department after this modifications are made.

Problem is here is now a emmissions inspection is required for 85 trucks as a visual so no inspection if no emissions...Truck less motor is now happily residing at Harrys U Pullit after 309 thousand miles of service....

Engine will be set in a 64 F100 to haul some more..

Garbz

teds74ford · #4 (**permalink**) 02-08-2006, 09:30 AM

I bought my truck with this exact setup, but I have real headers. I have never had my carb tuned right. I just can't get it perfect. I now run a larger squirter and a stiffer secondary spring. Even with it not being right, I get about 13 mpg. I would say go to it because if you are only getting ten, you can't lose. I am hoping for 15-16, but can't seem to get there. One thing you will like is the HUGE increase in power. Your wimpy 300 will turn into a beast. It is really quite impressive.
The holley number is 8007. There is a pic in my gallery. Incase you can't get to it, here's a link
http://www.ford-trucks.com/user_gall...105670&width=2

goldenford · #5 (**permalink**) 02-09-2006, 12:18 AM

I have a stock carter 1bbl in my 75 supercab longbed, 3.25 gears + an enormous camper on back.
I average about 14-15 mpg and have gotten 20mpg hiway on longer trips many times. I rebiult the carb about a year ago and I am a firm believer in sea-foam.

I know your asking about the 4bbl setup (which I would like for more power) but thought it might be good info.

the_mahout · #6 (**permalink**) 02-09-2006, 12:01 PM

GoldenFord - I am actually OK with the 300ci engine’s current power. I am a long-time VW bus owner so I am comfortable with driving 55-60 mph on the highway and not enjoying lots of acceleration. I don’t like the 10mpg from both a financial and environmental standpoint. If I could get 14-15 out of the stock 1-bbl by rebuilding it I would probably stick with the original factory set-up. I bought the truck to use as a daily driver for 3-4 months this spring while I convert the engine on my current daily driver. After that I will use the F150 occasionally as a work truck for hauling gravel, dirt, plywood… and in foul winter weather.

Where do you purchase the rebuild kits for the stock carbs?

What is this sea-foam you speak of?

Thanks.

Boss50 · #7 (**permalink**) 02-09-2006, 12:43 PM

I put on Holley 390, Offy DP, and EFI's and I gained about 1-2mpg from what my 1-barrel got. Currently averaging 13mpg with a '81, 2wd, 2.75's and auto.

garbz2 · #8 (**permalink**) 02-09-2006, 01:16 PM

Most auto parts stores will carry rebuild kits, Napa usuall has them in stock.. you will need the year and tag info off of the metal tag on the carb to get the correct kit.

Sea Foam is a canned spray penetrating fluid. Awesome stuff. Works really well in clearing varnish and crud from the carberator and intake and valves while the engine is running....Spray it in according to the directions on the can in an open area and notify all the neighbors first as it smokes like heck... I find it at most of the auto parts retailers.

Garbz

goldenford · #9 (**permalink**) 02-10-2006, 12:01 AM

I've never seen spray seafoam before, I've only bought it in cans you pour in. A majority of chemical cleaners are just kerosene and alcohol. I don't know what is in sea foam but its great. I usually dump a can in my oil about 100 mile prior to an oil change.
The best way to clean your carb though s to warm up the engine, take off the air cleaner cover, and while the engine is running pour about half the can slowly into the carb. pour slow or it will kill the engine. Then at the end give it a big glug to kill the engine - if it doesn't kill, quick turn it off. This lets the seafoam sit in the carb disolving crud.
After about 5 minutes, start er' up and laugh at the blue cloud rising over the horizon- thats all the burning crud -don't breathe it in, I assume its bad.\

I bought a rebuild kit for my carb for about $20 at bumper to bumper. There should be a tag on your carb that will identify what model it is. As far as I know all 300's used the carter 1bbl but i don't know if there are different varieties of them. The kit didn't include the float but that was available for a few more bucks.- rebuilding this thing was simple, about as complicated as a lawnmower

BentonCityRanger · #10 (**permalink**) 02-14-2006, 02:58 PM

Thanks for asking your initial question, and thanks to all of you who have responded. It's been really helpful to get a big-picture view of this situation.

Thanks much!!

the_mahout · #11 (**permalink**) 02-14-2006, 08:27 PM

How many hours of labor are involved in the swap from the standard carb and manifold set-up to the Holley 4160 4-bbl 390cfm with Offenhauser?

Any tips to pass on?

Thanks.

Boss50 · #12 (**permalink**) 02-14-2006, 10:18 PM

I took the old stuff off, put the new on in a total of about 4-5 hours. Not bad at all. Thats putting on EFI's too.
As for tips, you can do it by yourself but its alot easier putting the manifolds on if you have someone to hold them in place. And GO SLOW so you only have to do it once. Lokar throttle and kickdown cables are your friend. I think thats about all the advice I have for now....

bbf150 · #13 (**permalink**) 02-15-2006, 04:47 PM

i wonder if a holley 500 2bbl would run stronger and better mileage than the 390 4bbl? also wondering which offy to run the c or dual port for max power-looking for best power gains and driveability,header,intake,and cam swap?

scottfreeman · #14 (**permalink**) 02-15-2006, 05:40 PM

I have the same setup on my 300 that has been worked to over to 300 hp and 300 ftlbs and pull 35in tires with 3.54 gears. I get 15 mpg at 80 mph on the freeway. only get 10mpg in town though.

teds74ford · #15 (**permalink**) 02-15-2006, 07:33 PM

Not to hijack, but scott, is your truck off white with 8 lug axles? I am going to Boise state for CE, and there is a nice one there.
As far as the question, I would think the c series is better because it is open and flows to all the ports. I am in the process of putting on a motorcraft 2150 because I am fed up with the holley. I am not saying it isn't great, but it takes so much fine tuning, and I am sick of it. I am going to try the 2 bbl and see if it is more user friendly. The holley 390 sure makes plenty of power. I would think a 500 2bbl would run plenty strong, and get decent mileage. The thing is, the bigger the primary bores, the more flow. Assuming a 4bbl is tuned right, the primaries are the only ones open most of the time, so a bigger bore 2bbl wouldn't get as good as a smaller 4bbl. Of course, this is all theory. My experience is that fine tuning is tricky. Either way, good luck.