I currently have a 82 F-100 with the 300. I am thinking about changing out the 1bbl carb for a 2bbl 390cfm when I put split exhaust manifolds on. My question is will I get better gas mileage? I have been told that a 2bbl and even a 4bbl(if you keep your foot out of the gas) would get better gas mileage. Any info on the subject would be greatly appreciated. Also since I am switching to the split manifold I thought about taking the cat out and running the exhaust into the torpedo tube and then back to dual out of the tube. The reason for not running straight duals would be to equalize the back pressure. Am I correct in this thought? Any help would be appreciated.


Steven Willis

 

I am currently running a holley 350 cfm 2bl on top
of a clifford intake - the carb works very well,
I get around 15mpg on the freeway and have so much
torque that I seldom shift out of 4th gear once there. Thats with a stock cam.
Holley makes a 390 4 bl - is that what you are talking about? I have heard nothing but good about using the 390 with a clifford or offy intake. I ran a 450 4 bl for a while - could not
get it to pass smog checks so went to the 2 bl.
I understand that the Edelbrock (carter) 500cfm 4 will also work well.

 

I was talking about the holley 390. But also refering to a carb that O'Reillys carries a rebuilt motorcraft 2bbl 390cfm. This carb has been remanufactured by Holley.

Steve

 

[font size="1" color="#FF0000"]LAST EDITED ON 24-Aug-00 AT 06:22 PM (EST)[/font][p]Never heard of the O'Reillys 2bbl - but should work. Cliffords has an inline forum - maybe somebody there will have more on that carb.
It is possible to get a bit better fuel economy from a 4 bl that is the right size for the engine.
If using vacumn secondaries a stiffer secondary spring helps. I had major problems resisting - too much fun to open the secondaries and fly.

 

[font size="1" color="#FF0000"]LAST EDITED ON 24-Aug-00 AT 06:56 PM (EST)[/font][p]Yes it is easy to open up the inline six especailly when taking somebody at a red light and surpring them by leaving them behind. Also do you have any idea as to how the exhaust would work the way I described. Before I get everything welded up I thought about running the truck down the road and back and trying to see which side of the debates that have been going on are true. As far as how open you can run the engine and still get performance. I just can't decide whether or not to go without the cat. I plan on changing to the split manifold on the weekend of the Sept 22nd. After I get my paycheck I had a friend give me the manifold off of a newer 300. Thank you for the response it is greatly appreciated.


Steve

 

As for your exhaust you should be fine as long as you don't go above 2"s on you dual outlets. Also remember without a catalytic converter you will have to find the sweet spot to place your torpedo muffler. It's placement will affect the note of the exhaust on your truck. I believe the closer you put the torpedo to the exhaust manifold the lower the note will be(to a certain point).

 

No experience with that type of exhaust - sorry -
I agree on the 2 in limit - if you run true dual
exhaust. From what I read you could loose some
low end with too large an exhaust. Also adding a
cross-over to equalize the sides seems to improve
performance. You have smog restrictions where you
live?? If not ....
Forgot to mention - with the clifford manifold
(just in case you plan on one) and the holleys I
had to add the 50cc accel pump to get rid of a
major bog off the line - do not know if the offy
would have the same problem.

 

Mine has the offy manifold and I had to go up to a .35 shooter(from .28stock) to get rid of the bog on mine off the line.

83' Ford Bronco, 6" of lift, 35x12.5x15" thornbirds, and a 230HP I6
84' Ford Bronco 2" DROPPED custom 2X4, Soon to be 460/500hp.

 

Hey I got an '84 I6 with both clifford manifolds. Seems like the motor is running rich at some points and lean at other points. I got a 465 cfm holley four barrel. I also have the bog off of the line... Any help?

 

I went all the way up to a .4 shooter on the holley 450 cfm 4 barrel I started with and still had a major bog off line. Had to go to 350 2 barrel for emissions - had the same problem. Added the 50cc accel pump and it was gone. I will have to check but I believe I put the stock shooter or very close back in. I think the 450 also needs a stiffer secondary spring - not sure. I do not have to emission the truck after next year so will be able to put the 450 back on and play with it some more.