I am looking to upgrade my exhaust system and add a programmer. I have an 01 5.4 4x4 and am looking to get rid of the 4 cats and go to 2 high flow units with a little larger diameter pipe. I will probably go with PHP for the programmer. Any reccomendations for the exhaust upgrades would be appreciated. Also are there any "real" benefits for shorty headers?

 

For truck application where low end torque is needed to move the weight, short headers would be no better than stock iron headers for flow at the lower RPM.
Long tubes would be the better way to go.
3:73 gears would be a good investment to improve overall performance.
Good luck.

 

JBA Shorty headers will gain "at least 10 hp" and the SS one won't rust out like the OE cast iron does.

 

Ok, you are going about this all wrong. The stock pipe is already more than adequate. Any increase in pipe size results in an increase in peak HP, but a loss of low end torque. You are basically just shifting the powerband. Great if you plan on using the truck on a race track, bad for everything else. Stick with stock sized pipe. Yes, even the JBA shorties will give a mild torque increase, and have the benefit of being compatible with all the stock pipe, which is a strong consideration when you consider that the stock setup is both mandrel formed and stainless steel. Anything you have most muffler shops build will either be aluminized, which is a major downgrade from stock, will be crush bends, also a major downgrade from stock, and if it is stainless and mandrel formed, you will pay an arm and a leg, and possibly some other body parts, to get.

There are real benefits to shorty headers over stock, but they are marginal. 10 hp will barely be felt. You spend an awful lot for such a small gain.

Likewise for high flow cats. You have to know what a high flow cat is in the first place before you can get one. Real high flow cats are expensive. How much gain will you see over stock by using one? Probably between 5 - 10 hp. High flow cats real strengths is an increase in sound output, and that they will support more horsepower than you can make on a stock motor. This means if you add real performance mods to make the engine produce more power, the high flow cats will not hold you back.

Realistically, the best setup is stock, there is little reason to mess with it unless it is damaged or defective, or you are trying to get more sound out of it. Its your truck and your wallet, you can do whatever you please so long as its legal. From my perspective, I view it as a really poor return on investment.

The programmer can give you a bigger bang for your buck. It can deliver the same basic results with or without the exhaust mods. Why, because regardless of changes in the timing or mixture, the engine is still moving the same amount of air. It takes real modifications to the airflow (porting, cams, valves, forced induction, etc.) to affect real changes in performance. Changes in timing and mixture off stock without regards to emissions can get you probably close to 30 hp on your truck, but even thats a theoretical number, actually achieving it can prove difficult without tuning on a dyno. No out of the box prepackaged tune will give you that. What most tunes do is change the timing to make the engine growl more.

 

I was not planning on putting on a larger diameter exhaust. The plan is to get rid of the 4 cats and replace them with two higher flow units and put on a better muffler. The shop that I have talked to has a unit with a built in X pipe. I understand that I will mostly get a better sounding note out the back but if I get better flow of air in and out of the engine won't be more efficient?

 

Ok, running an X-pipe implies you are planning on running duals. Explain to me who more than doubling the contact area with the exhaust improves performance? More contact area means more friction, more friction means more backpressure. Also you increase the mass of the exhaust gas, which means the motor has to work harder to push it out.

This is why all Ford trucks come stock with a single exhaust (it is not only cheaper and lighter, it flows better and retains a smoother powerband.) Mustangs come with duals strictly for sound, a sound you cannot easily duplicate on a truck.

What 2 higher flow cats, most cats on the market that claim to be high flow are inferior to the factory units in just about every way. If you don't know what cats they are, don't touch them. If they are Magnaflow, or Dynomax, or Cherrybomb, don't walk away, run.

If you want a better sounding note out the back, get a good straight through muffler. It will be louder and deeper if you run a dual outlet muffler with dual tailpipes. This can be done without any modifications to the cats, manifolds, or any other expensive components that are already the best parts for the truck.

Seriously, the difference between the 4 cats and the single cat is only about 5 hp peak. That is a meager difference of 1.5%. You are not going to notice a 1.5% increase in performance. And no it does not increase efficiency, because an increase in flow at WOT does not translate to an increase in flow or efficiency at 10% throttle. If you do get more air in and out of the engine, the computer will add more fuel in, which would (and does) negate any economy benefits.

 

The JBS SS shorties can add a little milage as well and I mention them because here in MN and across the rust belt, the cast iron exhaust manifolds rust out. Going too big on an exhaust pipe will have the result of loosing hp and milage along with the other disadvantages of muffler shop pipe.

Q: Given your opinion of aftermarket cats, does anyone make one of QE quality or better?

 

They do exist. Its not a quality issue, it is rare that you can ever get an aftermarket of truely equal quality to an OEM. But you can get aftermarket cats that will outperform OEM. You just have to get past all the brand name marketing and BS to find cats that are actually high flow.

Catalytic converters contain a substrate called a honeycomb because of its cell structure. This honeycomb is designed to maximize the reaction sites or contact the exhaust has with platinum group metals that coat the honeycomb. These metals act as a catalyst (hence the name catalytic converter) and allow the remaining unburned fuel to more completely burn at far lower temperatures and pressures than would normally be required.

The more dense you make the honeycomb, the more surface area you get, but more surface area and density also means that you get more restriction to flow. True high flow cats use lower densities than factory. This allows more flow and lower backpressures. The tradeoff is that you loose a lot of surface area too, and less surface area means higher emissions and less catalyst efficiency. The way to compensate is to increase the amount of platinum group metals to help increase the efficiency. Since platinum group metals are quite expensive, this means that high flow cats also get to be quite expensive very quickly.

Many companies do make high flow cats, but they get lost in the brand name image. For example the vast majority of Magnaflow cats are ordinary 400 cpi cats, the same density as factory. This means from a performance standpoint, they are identical assuming the cross section and length of the cats are equal. In most cases they are either the same or smaller than the OEM, which means either no gains will be had, or the aftermarket "high flow" is actually more restrictive than the factory one.

Does Magnaflow make a real high flow cat? Yes they do. The problem with the Magnaflow units is they use cheaper platinum group metals and do not increase the concentration of the metals enough to make them work properly on OBD-II vehicles. Even on older vehicles, they often only pass marginally, making them suitable pretty much only for vehicles that can pass emissions without a cat but are legally required to have one.

Dynomax and Cherrybomb also both make real high flow cats, and several other companies as well. The Dynomax ones are ok, most other brands are pretty shoddy overall. They just don't have enough platinum to work effectively.

The only high flow cats are use are brand named as Tru-Performance, and all the cats in the Tru-Performance brand are real high flows. They have much higher loadings than other high flow cats, and in my own experiences with them, they work fantastically even on very new models that are known to be picky. Its the only thing I would even consider using.

But as I stated above, on your truck, unless you do real performance mods, they are not going to translate into any real world gains over the factory units. The engine performance is basically a function of how much air and fuel you can get into the engine. That is in turn a function of volumetric efficiency and compression. Volumetric Efficiency (VE) is determined by valve size, number of valves, port size, smoothness of the intake and exhaust surfaces, smoothness of transitions, runner length, cam profile, etc. The size and backpressure of the exhaust is often of very little consequence so long as it is not restricting the motor.

In almost all factory setups, the manufacturer selects a cam profile that will be a compromise to provide good power across the powerband, good fuel economy and throttle response at low RPM, and is almost always timed to work in concert with a catalytic converter. These cam profiles are generally very good compromises that are hard to beat in terms of maintaining good fuel economy, emissions and still have good performance overall. The catch with such cam profiles is that performance does not vary much when intake or exhaust modifications are made. If you want significant changes in performance, very often you have to make actual changes to the engine in order to increase the amount of air it will flow. Changes to the intake and exhaust have very little positive effect, and can often have a negative effect by fighting what the cam was designed to do.

For example, most factory cams have a considerable overlap between the intake and exhaust valves. This is because the factory is considering that having cats might slow the exhaust down, so by having more overlap, you create more opportunity for proper exhaust scavenging. As a general rule this works very beautifully. But if you remove the cat, or if it does not slow the exhaust enough, you can get an over-scavenging effect, when the exhaust will actually pull some of the fuel and air mixture through the combustion chamber through the open valves, and straight into the exhaust system. Obviously this is a complete waste of fuel, and results in an engine that produces less power at certain parts of the power band and gets much worse fuel economy than one that was left unmodified. But it will be louder and make a deeper throatier sound, producing a perceived increase in power. The effect would be most noticeable at low RPM, as a loss of torque. As RPMs increase, the overlap period gets shorter and has less effect on the performance, so increases in peak HP might be had, but usually at a higher RPM than factory.

Almost all modifications have tradeoffs. Mods that increase total horsepower often decrease horsepower (torque) at lower RPMs. Likewise, such mods often decrease fuel economy, since they decrease VE at the parts of the powerband where the highest economy was to be had.

In my experience, I have never had a bad result from using a true high flow cat in terms of a loss of low end power or negative effects on economy. The main tradeoff in their case is cost and an increase in exhaust noise (a positive tradeoff for some). A high flow cat mostly just supports power increases, it doesn't really create them. What this means is that on a stock or even lightly modded motor, you will get almost inconsequential gains. But in cases, such as forced induction, or major cam profiles, the airflow can increase to where a stock cat would be a restriction, and in those cases, a high flow cat will have major advantages over a stock converter.

I use a high flow cat on my '87 Thunderbird 2.3L Turbo. It gives me basically the same power output as if I was straight piped, but it helps smooth out the exhaust note so it doesn't sound ricey. On this car, the high flow cat was very advantageous over the stock one. But this motor is not stock by any means either.

Yes, if I had to replace a manifold anyway, I would probably spend a little extra to replace it with a stainless header. That way I could get some mild gains and increased long term durability. But the cost of headers is hard to justify if your stock manifold is in good shape, because the gains tend to be so minimal. Headers, like high flow cats, tend to support power more than create it. So if you modify the engine to flow more air and make more power, the high flow components will not hold you back the way a stock component might.

 

Very informative Khan. Answers a lot of grey areas I've read about in posts over the last few years in a common sense way. After talking with several Ford A-techs, I'm told after-market cats don't work with the OE O2 sensors unless you install *dummy sensors available in the after-market. There's also a very informative article & chart on the "Walker": website about scavenging and exhaust pipe size concerning gains and losses in HP and torque unless they've changed there site again.

Q: Will *they affect and or destroy new or OE cats.

Another note on rust if your not familiar with the northern part of the US. My 98' F-150 has 198,000 miles on it and the cast iron manifolds are literally disappearing from heavy use of road salt up here. The nuts and studs are indiscernible mounds of rust and mostly all break off and start leaking. When I install my JBA SS Titanium coated shorties to replace my disintegrating OE manifolds I'll be using SS fasteners and lock (clip) nuts. Stage 8 used to carry them, but not that I've seen lately. The factory used too small of fasteners on the late 90's - 2000's. The newer engines have reverted back to the older standard approximate 3/8th size studs which hold up much better and provide more dispersal of torque across the E-manifold for a tighter leak proof fit. I had e-mailed Ford about that some years ago, looks like someone was listening. I'm waiting for an all SS F150 to hit the streets after I win the lottery to be able to afford it. I hear the aluminum bodies are coming, can't wait to see what the salt does to them??? Salt eats aluminum alive!

 

LOL, salt eats steel alive more. The cars will be painted and sealed the same way they are now, so long as it was bonded properly, and the truck is kept cleaned, rot on the body shouldn't be too bad.

I hear you on the manifolds. If you need to replace a manifold anyway, you might as well upgrade to a header.