I have a f350 crew cab 4wd with 351 electronic fuel injection, automatic three speed, 315 75 16 tires.  I have no power, it's a dog.  I have hollowed out my muffler but the exhaust noise barley got any louder when I put it on.  Any ideas?  

chrislinggi1:
I have a f350 crew cab 4wd with 351 electronic fuel injection, automatic three speed, 315 75 16 tires.  I have no power, it's a dog.  I have hollowed out my muffler but the exhaust noise barley got any louder when I put it on.  Any ideas?

The cure is simple in concept here (there is some work involved) Your F350 CC was a bit under powered before you put even bigger tires on it which raised effective gear ratio and made it a bigger slug. Muffler mods, tunes and air cleaners is not going to fix this. A set of 4.56 or 4.88 gears would though. You could install a BB in it but 351 will move it okay if you give it a bigger "lever/pry bar" to work with. (ie deeper gears). Those trucks were not really geared properly from factory with that engine for their load potential.  

If I did that wouldn't I be really revving it out at 60mph?  As it is I only get 9 miles to the gallon.  

Not really. You tires are about 35 inches and with 4.56's you would be turning about 2800 at 65 which is not a problem for a 351 and engine will be turning at close to its torque peak where it will use the least amount of fuel for work delivered under a moderate to heavy load. HD P/U's used to cruise at this RPM and higher for many years before OD trannies. BTW, you MPG would likely improve because right now it is laboring badly at times. Forcing a engine to labor because you are worried about RPM will not improve MPG at all. This is a HD truck, not a car and it needs to be geared accordingly. You could do 4.56 if you cruise a lot but if you tow some too you really want 4.88's.  

thanks  

Take time to regear it and you will think you had a engine transplant.  

You didn't say how many miles. The timing chains usually stretch out by 50,000 miles. Install a new modern timing chain, not a napa special. Clean your sensors at intake with alchol/Q tip. Scary simple stuff just takes a little time. Also good maintenance like plug wires and check sparkplugs and distributor cap/rotor. scary simple stuff. O'yeah fuel filter to.  

wyomingtrailheader:
You didn't say how many miles. The timing chains usually stretch out by 50,000 miles. Install a new modern timing chain, not a napa special. Clean your sensors at intake with alchol/Q tip. Scary simple stuff just takes a little time. Also good maintenance like plug wires and check sparkplugs and distributor cap/rotor. scary simple stuff. O'yeah fuel filter to.

I love these. Always looking to tune their way out of it. Save your money on this stuff. This is simply physics here. This is a big heavy truck with big tires and tall gears relative to tire size, engine and weight. I am always amazed at the lengths many go to to try to avoid the obvious here. You see it a lot. It needs new gears!  

wyomingtrailheader:
You didn't say how many miles. The timing chains usually stretch out by 50,000 miles. Install a new modern timing chain, not a napa special. Clean your sensors at intake with alchol/Q tip. Scary simple stuff just takes a little time. Also good maintenance like plug wires and check sparkplugs and distributor cap/rotor. scary simple stuff. O'yeah fuel filter to.

SnoMan:
I love these. Always looking to tune their way out of it. Save your money on this stuff. This is simply physics here. This is a big heavy truck with big tires and tall gears relative to tire size, engine and weight. I am always amazed at the lengths many go to to try to avoid the obvious here. You see it a lot. It needs new gears!

i agree with both of you it should get the correct gears. but also a tune up, a fuel infected 351 should be getting better mileage, the both would do wonders and a tune up is fairly inexpensive  

You are wrong to assume the tuning is the problem causing poor MPG. The reason the MPG is bad because of 35 inch tires casing engine to labor a lot and therefore killing MPG. Many seem to miss this though and think lower RPM and lugging is the route to best MPG.  

i did not say that, i said he needs to gear and do a tune up. i know that by adding bigger tires causes your motor to work harder. but a tune up is also most likely in order and what could it hurt? but if he has limited $$$ then just try and do the gears  

If we had this conversation 30 years ago I would place more value on the need for a tune here but modern FI engine generally need little tuning other than plugs and wires and such and even then not often and when you do need them is is because of other issues other than lack of power (like missing or running very poorly from injector or sensor failure) BTW, I was not trying to say a tune has no value but simple physics here tells you a F350 CC with a 351, stock gears and 35's is going to be a slug unless your regear it or swap on much smaller tires.  

At these high gas prices, I would stick with the smaller tires and the money you save at the pump will pay for your gears in about 12k to 15k miles (exageration, or is it?). I would get 4.88s. Your truck is pretty damn heavy and the lowers gears will do better for the engine, especially when pulling a trailer or itself up a hill.