Hey all,

I have a '98 F150 4x4 w/ 4.6L motor. The exhaust is on its way out. I know the cats are junk, it's constantly throwing P0420s, and the manifolds are shot. This thing sounds like a tank fired up on a cold winter day. I'm know the 4.6 is somewhat slouchy during towing, so I was hoping to go for a little power gain with a good clean flowing exhaust. The problem is, what I know about exhaust I could fit into a thimble. So I'll toss out a few questions here.

1. Long tube or shorty headers? Is there a difference for power gains? Which brand? Painted steel or stainless steel?
2. Catalytic converters, I was looking at the universal application high flow from Magnaflow. (99176HM is the model number). Are these going to work? Will it quit throwing P0420s or will I introduce more problems?
3. I've ran across several catback exhausts for sub-300 price range. One I was looking at on ebay was a Flowmaster single 3 inch inlet and 2.5 dual outlet with mandrel bent pipes. Sound good? Or should I try to find a good dual all the way back?
4. I was thinking of having a local reputable shop slap together a Y pipe for me when they install the rest of the system.

I'm shooting for less than $1200 total exhaust bill here (including installation), hopefully with some power gains for towing use and a helluva lot better gas mileage than what I'm getting now (10ish with a bad exhaust). Wouldn't mind a little grumble to it either. I plan on having a reputable shop near me do the work, as I don't have the tools to clean up the mess of removing the old retarded manifolds that like to break off studs in the block.

Any help you can offer is greatly appreciated.

 

Be careful with headers. It's quite likely that they will move the power band up in the RPM range. Not exactly what you want when you're towing. I'm almost positive that the stock Cats are "high flow". You might want to try contacting "Bear River". He's a board member here at FTE. I got my exhaust from him a few years a go and he was very knowledable and helpful.

 

#1-Don't be so quick to jump to headers. If you pick the wrong manufacturer, or use it towing alot-you'll find out why. Cracks are very prominent on high EGT applications,and they're a PITA to replace. Lifetime warranties do you no good when you spend a lifetime yanking them off and shipping them for replacement.
#2-You're not gonna gain anything with a "high flow" cat over the stock pieces. They're not as bad as people would have you believe,and nowhere near as efficient as OEM pieces-meaning you'll likely fail and emissions test if they do them in your area.
#3-The most cost effective thing to do is to have the system built at a local shop using a prefabbed tailpipe. Magnaflow makes a SS mandrel bent tailpipe for an F150 that's very reasonably priced. Pair that with one of their XL series mufflers for a nice SS system that flows good, sounds good and last a long time. I used a dual in/single out XL series muffler on my old '98 model and it sounded really good,and the install was fairly simple.
#4-If you use a dual in/single out muffler that I mentioned above,it's really easy for the shop to do the install,and typically less costly and will flow better than most hacked together "Y-Pipes" that a muffler shop will make.
You're not gonna gain much fuel economy with even the best exhaust system out there. The state of the engine's tune, fuel quality, and your driving habits will dictate that.
JL

 

Some interesting discussion going on here. Let me add to this a bit.

You know the cats are bad, and that your performance has degraded somewhat. The cats didn't go out by themselves, something else has gone wrong, which has caused the vehicle to run rich, which has caused the cats to fail. This other problem may not have any codes, take a good look at the LTFT data. IF the LTFT is more than +3%, plan on replacing the O2 sensor, especially if you know it is original. If the value is more the +4% and replacing the sensor alone didn't resolve it you may have an intake leak or a fouled MAF. Also incomplete combustion may not trigger a mis code, but it will cause increased positive fuel trims. Make sure the ignition system is in tip-top shape with Motorcraft or Autolite ignition parts.

For headers, running shorties will gain power, but if you need to redo the cats anyway, go for a triple-y header or long tubes. Brand matters, as meantioned, the cheaper junk can crack and leak, or the gaskets will constantly leak, don't want that. JBA is a highly recommended brand, as are the Doug Thorley Triple-ys.

On the car, the Magnaflows are junk, and the part you are looking at is not high flow. It is an ordinary 400 cpi ceramic catalyst with a hyped up brand name. It uses a weak loading. In my area, muffler shops often refuse to install these anymore. Far to many repeat converter codes. Also the size you are looking at is wrong. The F-150 uses 2 1/4" pipe, not 2 1/2.

If you want a real high flow cat, this part should do well for you. Item Details It also has the precious metal content to keep your CEL light off, and because it is a real high flow cat, you will have noticeable sound and power gains versus a stock cat. If you just want a cat that will keep the light off but is roughly equivalent to the stock cat in terms of flow, this will fit the bill. Item Details

Which catback system you go with is up to you. I wouldn't go with a Flowmaster if I wanted maximum flow. The straight through mufflers to me sound better. Check videos on Youtube and see if there is something you like. You really don't need to replace the entire catback, the stock pipe is mild stainless and will last a while, you can get good results just replacing the muffler. When you buy a catback, you get stuck with that brands muffler, which may not be the best choice.

You are not going to get better gas mileage till you fix the underlying rich condition that wiped out your cats.

 

at my local muffler shop i can get a cat back dual system installed for $250 out the door

 

The truck has 145k miles on it. The exhaust iis worn out from manifold back. The manifolds are junk as they are cracked and dumping right out the side of the motor. The motor runs fine, and the O2 sensors have all been replaced as part of a troubleshooting stwp for the p0420 codes. Ive never had any other codes than the cat ineffiency code. Why wouldn't I want to jump to headers to improve exhaust flow? The MAF is clean as a whistle.

Basically this truck has lived in the snowbelt its entire life and the exhaust is hammered. I don't tow often, but id like to get a few exta horsepower when I do tow.

 

Ok, you didn't mention your old manifold were cracked, or if you did I missed it. I say if your old manifolds are toast, you definitely want to replace them with header. The Doug Thorley Triple-y's are not available for your motor, so looks like these are the best all around header for our application
JBA Headers 1677S - JBA Headers Cat4ward Headers - Overview - SummitRacing.com
They are a compromise in the price while keeping the quality up. Most other headers are either cheap, or have those lousy flanges that warp and leak. These will bolt into an otherwise stock system.

To replace the cats, here are two recommended routes. If you just want to resolve your P0420 code, and never have it come back, but keep the cost down, this is the part I would recommend.
Item Details
I know that there are lots of companies selling converters cheaper than this. I also know all of them do so by reducing the precious metal content, and that is exactly what makes them work and keeps the CEL off. Thats why this converter has a full 5 year warranty, while everyone else has only 2 years.

If you want to get the most possible flow and sound from the converters, this is a real high flow converter. Don't assume because companies like Dynomax and Magnaflow has high performance brand labels that their converters are automatically high flow. All their standard products are ordinary 400 cpi ceramic that is identical flow wise to a good OE converter.
Item Details

On your exhaust pipe, just cause it looks rust doesn't mean its shot. The factory pipe is made from 409 stainless steel, which does corrode, but does so more slowly than mild steel. It will basically just turn brown then slowly pit over time. It still lasts between 10 - 20 years even in snowbelt areas. I know, I live in the snowbelt. Salt Lake City didn't host the 2002 Winter Olympics because we don't get snow here. Only you can really decide if your exhaust really needs to be replaced, I can't see what condition your system is in. But it probably has a lot of life left in it. Once you replace it with aluminized though, it will only last a couple years then it will need to be replaced again. You definitely want to stay away from flowmasters if rust is a concern. If the pipe is still in good condition, it is suitably sized for a 4.6L. You can get fairly good results with just replacing the muffler will a good stainless steel one.

If you do want to replace the pipe, try to find a system that is stainless steel. If you plan on having it professionaly installed anyway, I know of a setup that should work for you. This company sells just the prebent stainless steel system with no muffler and no tips. Unfortunately it is only a dual outlet system that exits under the bumper, but it is ready to go with the addition of a muffler.
97-03 FORD F SERIES EXHAUST TAILPIPE KIT (304 STAINLESS - 2.5 INCH)

On the muffler, everyone has their preferences, I have my recommendation. I use this muffler myself. I have been let down by Magnaflow twice. Once on my mom's van, when their muffler, which was supposed to be quite, was painfully loud inside the vehicle. It sounds great from outside. The second time was on my Mazda pickup. The packing blew out and they wouldn't warranty it. I recommend the WickedFlow Max series.
http://www.bearriverconverters.com/I...e-7eb7ebf6a744

 

i got some pacesetter shorty headers, not to bad but like they said it helped with the higher rpm range. whatever you buy though i wouldnt recomend installing them your self.