Hi Guys,

Let me first say I have gone through endless search pages to find answers to these questions, but I am not 100% satisfied yet. So please bear with me.

I have a 94 F150 with the 5.8 in it. Everything is stock (except for tires) and I'm looking for an exhaust system for it. I've been waiting for the stock muffler to go out, and thank god, last week a baffle broke loose inside. Now for the important part.

I want to do this right the first time so I really don't want to deal with just replacing the muffler. I want loud, but not straight headers loud. What I really want to do is run true duals, without cats, with an H-pipe, 2.25 pipes, and flowmaster 40's straight out the back with about 8" x 3" tips. I think this would bring great sound out of the 5.8, and the stock pipe size along with the h-pipe should retain most of the low end torque so I wouldn't feel much of a loss.

Does this sound like an ideal setup? I know that not having cats raises a lot of questions, and it might be hard for me to find a shop that will do it, but I'm affraid that having cats only on one side will produce different tones out of the tail pipes, and I don't want that. I guess if it came down to it, I could purchase two high flow cats and put one on each side, but that's only if I can't find anybody to do it without cats.

The last question I have is if I'll have a problem with the O2 sensor. I remember it as being before the cats and after the y-pipe. So the shop can work around the O2 sensor, but will it detect a decreased exhaust flow since it will only have half the cylinders going to it? I don't want any check engines lights coming on, or any codes showing up.


Thanks for any help.

 

2x4 or 4x4?

 

inski21,

4x4

 

Well all I did was replaced the stock muffler with a flowmaster 40 selta flow and love it. But later down the line I am thinking about putting true duels. I have spent alot of time under the truck trying to figure out a good system to go with and have come to the conclusion that you can't have equal length pipes because the gas tanks are in the way. You would have to run down the passenger side with the pipes and have them exit wherever you want. I figured that I would get them to remove the front cat (y-pipe cat) and chop the rest of the exhaust off. From there have those two pipes from the mainfold go into their own high flow cat and then either get 2 mufflers or a DI/DO muffler. From there on you could get it to exit wherever you want. I want mine to exit before the rear tire like the Lightnings and have to nice Stainless Steel Tips. I'll draw up a diagram to further show this

 

Here is a diagram a just drew up. The front cat on the stick exhaust is wierd so I made it as good as I could. On the duel configuration the pipe that normally leads to the front cta will have to be shortened so that the pipes will be far enough away from each other. I hope this helps. You could put an H or X pipe in their but I think they are only good on equal length systems.

 

Thanks for the help guys.

I am heading away from true duals, and am going to make it cleaner and easier by taking off my two cats, adding a high flow, and then running one muffler with dual outs. The only problem is that I want to use a 40's series flowmaster, but they don't have a di/do setup. I would have to get a 50's series for that. I can get a 40's series that has a single 3" in/dual 2.25" out though. Does anybody think I will have problems with a 3" pipe in regards to low end power?

 

Just look at it like this. You will have 3" pipe goin in and then having a total of 4.5" exiting so there will be no resistance to give you back pressure. You will have high end but will loose some low end. I love what I did by just replacing the muffler and I retained all my low end I think I might have actually gained some because I left the stock pipe. Take a look at my gallery and see my setup. At 1600 rpms the 40 series sounds great real DEEP

 

My recipe isn't the easiest but its cheap and probably offers the best in performance if that interests you..

Summit Racing Hedman Long Tube 1.5" headers: approx $130 for the pair. NOTE: They are SUPPOSED to have an Oxygen Sensor Bung but mine didn't. Summit happily sent me one for free that the exhaust shop welded on to the collector. To answer your question you retain the 1 O2 sensor just put it in the collector.

Must Extend your O2 sensor harness; cut and solder the connection, use shrink wrap and electrical tape. Extend it a total of approx 12", this will give you plenty extra. Use approx 18 gauge stranded copper electrical wire.

I bought 2 Catco 2.5" in/out 3 way catalytic convertors from Summit: $59/each. I reused 2 Flowmaster 2 Chamber 2.5" mufflers off my Mustang. Use anything you'd like here, Summit sells some Super Turbo's for like $15 (their own house brand).

My first step was to have the exhaust shop make me to "S" bends that would bolt up to my longtube headers 3 bolt flange and allow me to slip-fit the cats on temporarily so I could drive it over there "quietly".

At the house I unbolted/cut off the whole exhaust. Bolted on the headers, S tubes (needed to clear the tranny cross member on my 5 speed and cats (the collector hangs at the crossmember height, the S pipe routes the exhaust over the crossmember). I then drove it over to the exhaust shop. They welded in the cats and 2 mufflers and had them exit at 45 degree angle both in front of the passenger side rear tire. Yes there is room for true duals no problem, yes they both have to run down the passenger side, Yes there is room for an "H" pipe connection but its close. NOTE: Summit sells an H Pipe kit for like $35 that an exhaust shop can weld in. The whole exhaust cost me about $500.. lots more torque than any cat-back exhaust is gonna buy you and its emissions legal.

The headers are not hi-temp coated so they rust.. no biggie for me, its my 170K mile hunting/towing rig..

In the interest of making it COMPLETELY emissions legal they will have to weld the air pump pipe to one of the cats. The other cat they simply leave it plugged just like it came from Summit. NOTE: They are 3 way cats that can but don't have to accept the air injection from the air pump on our engines. When you have to remove the exhaust to drop the tranny, you cut that pipe and will have to slip some Very high temp silicone hose over it plus 2 hose clamps to re-seal it.. no biggie.

BTW: The compliments on the sound of my truck are constant. It has the same firing order as your 351 since I converted to a custom cam and the 351/H.O. firing order so it would sound almost identical.

If someone can host a vid I'll take a 10 sec video clip of it when I start it..


JerryK

 

The only thing I have against headers right now is that we just got new manifolds about a month ago, so I want to get my moneys worth out of those.

As far as everything else goes, I want to go from the end of the y-pipe so I only need one muffler, with dual exit. I will have a high flow cat before the muffler now, so that will give me some more back pressure.

 

If they are the factory cast iron log style exhaust manifold, you'll never get your money out of them.. if you replace them with even shorty headers plus the exhaust you describe you'll be much better off..

JK

 

Putting a hig hflow cat will actually decrease your backpressure. Its not the backpressure that your engine needs its the scavening (spelling???) effect that you want. At low rpms you want the exhaust system to keep some resisance on the engine and at higher speeds you want it to to get out very fast. I have heard that the magnaflow mufflers do this the best. Im no expert but this is what I have gathered form these forums. The drawing I posted is something identical to what my friend did on his 94 f-150 with a 351 and it sounds deep at all rpms and when he steps on it it sounds great

 

What do you think about changing to a 50's series with a single 2.50" in/dual 2.25" out? This will creat more backpressure and scavenging. It's very similar to that drawing, just one less cat. The setup on the drawing looks like it would be more free flowing that even the single 3" in/dual 2.25" out flowmaster 40 I was talking about.

 

The setup I have drawn up probably would loose some low end but it would have great high end. the drawing is really for a truck that has more hp than stock alot more.

All I can say about going to a 50 series is that it will be quieter and i dont think my 40 series is that quiet. I have a sound clip but I dont know where to get it hosted if you or anyone else knows I will post it. Ive heard that flows have the worst scavenging of all the freeflow mufflers but from my own experience I like mine and have gained power throughout the rpm range. This is probably due to me keeping the stock exhaust. Do whatever you would like. If I was to do mine again I would do like in my drawing. Who cares if I loose a little low end the exhaust would be kick *** and have the potential to handle lots of HP. Also down the line you could still bolt on some shortie headers.

 

On the Flowmaster site I see that they have a 40 series with a single 2.25" in/dual 2.25" out. I'm going to go with that and see what happens. I think I'll be happy with that, and it has a smaller pipe size so I think I'll be alright on the low end. Thanks for your help guys, I appreciate it.

Does anybody know some large sites that sell Flowmasters? I have been to Summit Racing and cannot find the particular model I'm looking for. Truck performance also didn't have it. I want to purchase online because it is so much cheaper than the stores are selling them for around here. They are asking around $120 here, where as online most stores are asking around $60-$70 for a 40 series.

Thanks.

 

You don't have to worry about the O2 sensor, it measures the stuff in the exhaust, not the flow of the gas. As for going without cats, thats no problem along as you have a friend with an inspectors license. At least here in NY you won't pass inspection without them.

-Jon