I have a 1992 F250 4x4 with the 5.8 liter engine. I have put a Flowmaster muffler and K&N airfilter to help increase power and help gas mileage. Well these improvements have helped the horsepower but my gas mileage is still hurting. I'm getting 13.5 m/g on the highway. I was wondering if putting a high flow catalytic converter would help with gas mileage? I was also wondering if anyone had any suggestions on which brands they have had success with, or any other suggestions to help with this gas guzzler. thanx

 

By opening up the exhaust system you are removing restrictions which will improve exhaust flow through the engine. At the same time the flow in the inlet side of the engine is slightly improved. That's why the horsepower is up, but improving the flow won't help gas mileage.

If you have fuel injection, lowering the fuel pressure in the system slightly will reduce how much gas the fuel injectors spray. You will probably want to change the sparkplugs one step colder if you go this route. Also, they make fuel injectors that run at different pressures just for making changes like this. Check with performance shops and they can help with the fuel pumps/injectors. Remember not to starve the engine of fuel.

If you have a carb. Try re-jetting to a little smaller jet and do the same with the spark plugs.

There is a cost. You will probably lose some horsepower. but if gas mileage is what you are after the above should help and not cost to much. It all comes down to a balance of hp vs fuel consumption and its a difficult battle as auto engines are only about 18-20% efficient.

Howard

 

Generally if you want to open up one part of a system you have to do everything in order to really see results. For instance you have a highflowing muffler, but the cat is still slowing down airflow. Once you get the cat taken care of you still have the exhaust manifold. There are debates on whether or not headers are worth the pain (rusting out every 3 years) but you get my point.

The trick is that once you get a performance mod, you tend to use it. Ideally your engine is only going to get a certain mileage pushing your truck down the road. If you take off restrictions on the motor (mufflers, cats, exhaust manifolds, disconnecting alternators, fans... all of which is a bad idea) when you take these restrictions off, the engine doesn't have to put energy into them, so you get better performance and same mileage, or better mileage and same performance. It all depend on your right foot. You can't have your cake and eat it too.

Be warned that there are bull(can't say it or Ken will kick me off) products. Pulleys, flex fans, ... yeah these help HP, but they underdrive the alternator and don't cool the engine at high rpm sufficiently. Buyer beware.

Daywalker
92' F-250 351 4x4 xlt 4.10 5spd supercab longbed

Sound System: Stock Stereo, RockfordFosgate 800 watt amp, Vega 18" sub (400 watt rms), one Cerwin-Vega LS-12 3 way floor speaker with the Vega sub removed (because I blew it) and a RockfordFosgate 12" sub (500 watt rms) in its place. And one Boise floor speaker with a 75 watt power capacity (you know it ain’t gonna last).

Performance Mods: K&N Air Filter.

Cosmetic Mods: Black Grill Guard, 5% window tint, bug guard, bed liner.

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