I have a 1998 F150, 5.4L V8 with 305/70/17 (Nitto Terra Grapplers) and flowmaster 40 series exhaust. You would think with a 5.4 V8 the power would be really good, but its the opposite! i cant even get it to spin a tire from a stand still while its pouring down rain and the roads are wet!

I guess my question is why dont i have any power? I've had it looked at and they tell me its not the converters, its not the fuel pump or fuel filter, and everything else seems to be in good order. However, they did say the air flow was not right but they fixed it and the power still isnt there like it should be. I know the tires cut down on power but if they cut it down this much then theres no way i could pull a boat or anything.

ps. - i had to floor it to get up to speed to get on the interstate the other day.

any input would be greatly appreciated guys! also, is there anything i can do, or is there anything i can look at or check?

 

get rid of the SLOWMASTER and put on a real muffler. get anything with a straight through design and no chambers. also slap on a cold air intake.

 

I do plan on getting an intake, i would like to do the Gotts mod. Also, i feel like there is something wrong with the fact that the power is the way it is. I mean, shouldnt the tires atleast bark at me when i get on it with soaking wet roads?

is there anything i can check or get a mechanic to look at that they may have missed?

 

There could be a number of thing, your plugs are on there way out, injectors are clogged, your throttle body could be caked with carbon build up.

What configuration is your exhaust? Ex. Single in dual out, true dual, single in single out.

The Flow-Master is contributing to your trucks weakness, so look into Magnaflow, Borla, Dynomax Bullets, anything that does not have baffles and plates inside the muffler.

 

x2. Also these trucks aren't the quickest off the line, the torque doesn't instantly pick off. Custom tuning changes everything.

 

thanks guys, i am gonna check all of those things and hopefully ill get some improvements.

anyway, today i did the Gotts mod and put on a K&N filter. I haven't noticed much difference at all to be honest. I unhooked the battery and everything and it does seem to get up a little faster but there is still this lag, especially going up hills.

i have 2 pipes coming into the muffler and one coming out and splitting off into duals, straight out the back. (forgive me i dont know a whole lot about this stuff!)

What muffler would you guys recommend me getting if i did change it? All i want to do is change the muffler.

 

Now we know a little more about your truck.

Firstly, you have a 98 5.4 with non-PI heads. That alone means your motor is quite underpowered.

You also have a SIDO exhaust with a 40 series. 40's are great for sound but lousy for performance. All Magnaflow mufflers are straight throw but vary in size. The shorter and slimmer they are, the louder. What about your pipes, are the crimped and crinkled on the inside of the bends or are they smooth? Crush bent is an exhaust nightmare while mandrel bent is a wet dream.

If you haven't had your plugs changed, it sounds like it's time for a tune up, plugs, COP's, and maybe injectors.

The Gotts Intake Mod alone isn't going to boost performance, but with a free flowing exhaust and a custom tune it really helps.

 

IMO the best thing you could start off with is, what 4.6punisher said, making sure the truck is up on maintenance(plugs, clean maf, fuel filter, clean throttle body, maybe throw a bottle of a good injector cleaner in the tank, etc). then exhaust and an intake can add power. a pi(power improved) head swap would be your best bet though as far as mods(IMO anyways). or get a used 99-03(or 04 heritage) 5.4 2v. tunes dont do a whole lot for the non pi engines compared to the pi engines.

 

If your converters are fine, then your exhaust is not your problem. If your truck is really that under powered then you have other problems much larger than the style muffler you are using. I would recomind a good tune up, and maybe find some pi heads and a tuner.

 

your muffler isnt going to make that big of a difference. Dont expect to go out and change the muffler and expect to spin the tires a whole block. I would look more towards the maintance then the muffler. There are haters on here about flowmaster and some people love em. Your MUFFLER is not the problem!!!!

 

X2. all the flowmaster haters are loving this. gettin to blame the ''so restrictive'' design of flowmaster for your truck not bein able to spin the tires. if a muffler swap made this much difference in power id put money on it flowmaster wouldnt exist anymore. so when you go buy the ever so wonderful magnaflow and still cant spin your tires, not to mention have less exhaust volume, dont blame me

 

driving everyday unloaded wont make a noticeable difference but towing with flowmaster vs. stock or magnaflow will. towing is how you really notice torque differences. and mine has lost a decent amount of torque when it comes to towing with my knockoff flowmaster vs. having that glasspack that my truck came with. hell i notice a difference while towing a little lawn mower and my atv at the same time. but sound wise flowmaster is definately the best IMO.

 

Whoa whoa wait.......... You have a Flowmaster 40 series.. with dual pipes coming INTO it, and a single pipe EXITING it?

Your muffler is installed backwards. Climb under and look at the front and see if it says "Inlet" facing the front side of the truck. If its on the back of the muffler, your installer smoked crack before he installed it, or never learned to read. Chambered mufflers are not reverseable, and if this indeed is the factor here, the point that he cut your Y pipe out and ran dual pipes to it makes him the most un-skilled installer ever.

 

I'm not blaming the Restrict-Master for his poor performance, I blame his non-PI 5.4 and lack of maintenance.

 

thats hilarious if thats the case...it would suck but still be pretty funny
easy fix