I would like to redo the whole system at once, like you suggerst, but i don't think it would be awise choice for me financially, unless I win the lottery. But I'm not counting on it. What sixe pipe should I get for a dual exhaust?

 

Dual 2.5" should flow more than enough for your application. I just check the proficient site, and there Gibson duals dont list a pipe size. They also dont recommend duals for towing, but to each his own.


Rich

 

I wonder why that is. The reason I'm thinking duals is because that's what's on there now. I wonder if I should go to a single exhaust, since I tow regularly

 

Well all of the carbon and other exhaust gases leave their sooty deposits on whatever you are towing. Plus, if you haul for long distances, the heat from the exhaust may effect whatever substance is being towed. I believe that a single three inch, mandrel bent pipe actually has a greater flow rate than duals. Besides, a single 3" is good up to ~360rwhp, and I am guessing youre 5.8 doesnt put that out. Its all up to personal preference. Ive run duals on pickup trucks before, and I liked it. I have also run a single 3" too. When I own another pickup truck, I will probably stick with the single 3" at the stock exit location.


Rich

 

I like the look of duals, but if a single would be better suited for my appplication, then it wouldn't bother me. Are there any big price differences? I'd keep it at the stock exit, unless found a good reason not to. I don't think I'd like to see the exhaust exit in front of the tires though. And out the back I would think is a big no-no when towing.

 

I havent been exhaust shopping in a while, but I think duals normally run you about 50-75 more than a single 3". I have never been a fan of exiting the exhaust in front of a rear tire (unless its on a mustang or something). The exit behind the right rear is the optimal location to dump your exhaust for towing purposes. The exhaust gases will be pulled along the side of whatever you are towing.


Rich

 

btw i think knN fipk are way overrated, just get the knN filter and insulate the hoses to the throttle body

 

I bought the KnN filter last week, but when it came time to put it in, it was about 3 inches too short. And it was the one for my truck. So I went back, with my orig. filter, and tried evry box that was in the place, the closest one being 1/2 in ch too wide. Can I just just the short one and duct tape the air intake box, or do some other mod?

Sounds like I'm gonna shop for a single 3" exhaust. thanx guys

 

No, the filter really has to seal with the air box. Did you cross check the K&N part number with the motorcraft number?


Rich

 

No, I just looked up 1990 F250 5.8, and it gave me the short one. Guess I'll try that. thanx

 

I got 13+ with a '90 5.8L 4.10 open and 5sp. I removed the air tube from air box (filter) to grill, used Autolite Platinum plugs, Dual 24" glasspacks/no cats, and 160 degree thermostat. I also cleaned the throttlebody with spray type ChemTool B12. It went to 260K miles. I now have a F350 DRW 4x2 same drivetrain, running similar exhaust but 18" mufflers, same plugs, gets 11-12 mpg. The right K&N will fit, but I don't have one to get part #. I just change my stock filter often. I run offroad a lot and don't have time to properly clean the K&N.

 

has anyone tried the flowmaster universal tailpipe? I am thinking about buying the 3" kit to go behind a 3" dynomax muffler I have and was wondering how it fit up.
Matt

 

removing the air tube didn't suffocate the engine? How did it get air? I would think that it would get hotter air from the engine compartment, therefore reducing mileage. I added STP fuel injector cleaner last tank, but I'm not sure where to spray that B12.

 

Try replacing the O2 sensor if your truck has more than 80,000.
They slowly degrade and don't set trouble codes. they are real MPG killers.
I have no experience with O2 sensor on F-series but when I replaced it on my V8 sedan, it gave a 4-mpg improvement. Along with complete tune up.
Low MPG basically means you are running rich. If your sensors are bad, the computer will never get out of the "cold" mode and default to some number.

EGR valve is another good item to check after 100K miles. Clean it first with brake cleaner.

 

Why would the engine suffocate? There is oxygen in the air under the hood just as well as that in front of the grill. And at 70 mph, I doubt that there is much temp. difference. The opening at the filter box is larger than the opening at the grill. It won't have to suck air through the tube from the grill either. Of course this is theoretical and I can not tell you how much, if any that it helped mpg. You can always put it back on in 2 minutes. We had open air filters on top of carb. trucks back in the '70-'80's. When you "stomp" on it, the response is quicker and louder. Under normal driving, though sound difference is unnoticeable.

Remove the air hose at the throttle body end (2 clamps) and spray into the throttle body as the truck idles. It will try to die so spray slowly in strokes. You want the truck to keep idling and the cleaner to go through the throttle body to injectors. Check throttle body for tag (sticker) first. I have a '97 F350 that has a protective finish, supposedly to make it slicker and keep cleaner. B12 or carb cleaner on it will remove that finish. My other trucks did not have this finish.

The HEGO2 sensor will help mpg, esp higher mileage trucks. I get "back" 1-2 mpg previously lost from before (as sensor wears out/gets clogged). There are different wiring pigtails, so take yours with you or get a number off housing. If the truck runs in default due to a faulty HEGO2 sensor, there will be a code stored in PCM.

Timing doesn't have to be reset, if nothing has been changed before. If you check it, unplug SPOUT connector first. It looks like a big 2 prong fuse that will unplug. It keeps the computer module from altering timing while , you check/reset. If not you'll be too slow and run rich. I set at 10-12 degrees BTDC for 87 octane. If you run only higher octane, you can set 12-14.

Good luck with mpg. It is difficult to get decent mileage out of 3/4 4x4, especially if it has to work. I just try to make enough $$$ to keep it going. Diesels get better mpg but also cost more. I've got friends that don't get much better than 15 mpg with imports or Ranger 4x4. I generally fall sort but try to get 15 and end up 13-14. I would get better mpg with V6 F150 or if I changed to less than 4.10 or if I traded my MT tires for A/S but then my truck wouldn't do as much work either.