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Power 201, Intake
By: Ron Lee

          I hope that you at least glanced over the first power article before jumping here. This article will cover more modifications for a normally aspirated Mustang. These modifications do not have to be done in any particular order, but I will put them in the order of my preference, for a fuel injected 5.0 from a power making standpoint. I have grouped all the intake ones here and put the exhaust ones together in a separate article. Remember to make maximum power requires not only getting the air into your engine (intake), but also out of your engine (exhaust). Somewhere along the way, unless you start modifying the exhaust, you will basically hit a wall where you cannot make any more power no matter what you do to the intake side. Ideally, you would do all of the modifications together, but most of us are not made of money, nor do we have the proverbial money tree in the back yard. Mine died a long time ago. Therefore do the ones you can afford. You will notice an improvement from each and every modification you do. Note that doing some of them together (heads and intake for example) will save you time and money, especially if you are paying to have someone else do the work. Also note that the increased power numbers I give are much smaller than what you see advertised. These are real power increase numbers for a relatively stock motor. Advertisements are based upon the best possible scenario for the particular part involved, which is not the real world. If you do all (or most) of the modifications listed, you will gain far more horsepower than I list for each individual modification. Exceptions to the order listed will be noted, but in particular note the following two factory stock limits. The factory (fuel injected) fuel system is good to about 300 horsepower. Going above this limit without modifying the fuel system will result in melted pistons among other broken engine parts. If you think you are near this limit, you better put in a larger fuel pump and larger injectors (which also requires modifying the mass air flow sensor). On the other hand, do not waste your money installing a larger fuel system when you don't need it. Instead, spend your money on a modification that will increase your horsepower, or make your car handle better. Second, the stock engine short block is good up to about 400 horsepower (only 86-92, the other years are lower). Going above this limit will result in broken engine parts, not the first time down the track, but sometime soon. The factory rating was only 225 horsepower (87-93). I will also add that if you have a factory T-10, 5 speed transmission, and you have increased your engine horsepower output, do not speed shift or power shift your transmission unless you want to replace it. It will not take that abuse for very long. On the other hand, I have owned 4 Mustangs (5.0 cars) with 5 speed transmissions and I have not destroyed one yet. Don't abuse it (too badly) and it should live a long and happy life.

          Replacing the engine heads is the single best improvement you can make to increase the power of your engine (normally aspirated). A good set of aluminum heads will give you an additional 30 horsepower (or so) on an otherwise stock engine and reduce your car (front end) weight by about 50 pounds. The difference in the way the car will drive is just simply amazing, at least to me. The additional power will be higher on a modified engine. Aluminum heads will set you back about $1000 (cast iron heads will be about $700) plus about another $100 for miscellaneous parts such as gaskets, sealer, anti-freeze, etc. To have them installed will cost you about $500 unless you can do it yourself. Installing engine heads is not overly complex, but it certainly is not an easy task. This should not be your first under the hood experience, and even for a fairly experienced person, this is an all day job. The Trick Flow Twisted Wedge heads are the only heads that I'm aware of that have 2.02 inch intake valves that do not require flycutting the pistons. All the other heads will limit you to a 1.94 inch maximum intake valve size to clear the factory pistons. One surprise I got is that changing my heads (Aluminum Trick Flow Twisted Wedge) increased my gas mileage by about 1.5 miles per gallon. Since you have to remove and reinstall the intake manifold to replace the heads, it is advantageous to do them at the same time if you can.

          The factory mass air flow sensor (assuming you have one) is the most restrictive piece in the intake tract. It is only 55mm (except Cobras which were 70mm) in diameter while the throttle body is 60mm (58mm in 86). Ideally, the mass air flow sensor should be larger than the throttle body. For most cars, a size between 70mm and 75mm will work great. A 73mm sensor is 76 percent larger in area (roughly 76 percent more air flow) than a 55mm sensor, so the difference is more than it sounds. Bigger is better, but bigger than 75mm may require modification of the intake air hose. The more expensive mass air flow sensors usually include a new sensor while the cheaper ones usually reuse the factory sensor. Either way works fine. They start in price around $175 and they are relatively easy to install. You should pick up 3-4 horsepower with a stock engine, more if modified. Your gas mileage should not change. I've used a CL 73mm unit for years without any problems. One comment is that the mass air flow sensor must be calibrated to the fuel injectors. If you plan to change them out, you need to do these two items together, or somehow recalibrate your mass air flow sensor when changing the injectors, which is not possible with all types. You will not need to change out your injectors unless you plan to exceed 300 horsepower (or road race the car), which will require virtually all the modifications listed here. One thing nice about the CL 73 unit is that I was able to recalibrate it later (to use 24# injectors versus factory 19# injectors) by replacing the flow tube at a cost of $30 (which sure beat buying a new mass air flow sensor).

          If you are fuel injected and don't have a factory mass air flow sensor, you should add one now. The 86-88 Mustangs did not have mass air flow sensors and will not tolerate more than about 10 percent additional air flow (about 20 additional horsepower) before they start having problems running correctly. Just adding a good set of heads will put you over that 10 percent limit. Your engine will not idle correctly among other problems. You can get kits from Ford to add a mass air flow sensor to your 86-88 car for about $550 including the sensor, wiring, intake tract, and new computer. Another option is to get one from a wrecked car, but remember to also get the computer and wiring harnesses along with the intake tract. If you have a 86-88 Mustang, and you want to modify it very much, and you want it to run correctly, you must do this step.

          Replacing the intake manifold should be next on the list. There are a multitude of intakes to choose from. Unless you are building a race car, stay away from the box types. The box types do make more power, but only at high rpm's. The box types give up power at the low and midrange rpm band which is very important for a street car. For a street car, you need a plenum type manifold which will help build a broad torque curve. The Ford GT-40 intake has been the standard by which all others have been measured by for years, but probably is becoming a little dated. The Cobra manifold is a cheaper cast copy of it. Edelbrock and Trick Flow each now make several different types of plenum manifolds so that you can choose the one that fits your car (desired rpm power band) the best. If you have an 86, just replacing the upper intake with a 87-93 upper intake will make a big difference, and you can find a used 87-93 upper intake cheap (in fact, I'd be happy to sell you mine). The aftermarket plenum manifolds cost between $400 and $600. Installation is involved, but not overly difficult, because it requires removing/installing the fuel injectors, fuel rails, and other sensors. Remember to oil the fuel injector o-rings when you reinstall them in the new intake manifold. You should pick up 6-10 horsepower with a stock engine, more if modified. It should not change your gas mileage. They can reduce your bottom end torque if you select one that is intended to operate at high rpm's. Choose carefully based upon your application and don't be afraid to ask for advice

          Next on the hit parade are roller rockers, especially ones with a 1.7 ratio such as the Crane Cobra ones (original equipment on the 93 Cobra). The factory rockers are barely above junk and should not be on your engine (in my opinion). The factory rockers have a 1.6 ratio, so installing the 1.7 ratio roller rockers will make your cam act like a bigger cam. Your cam will open the valves 6.25 percent more and also hold the valves open a little longer. This will increase your power by 4-5 horsepower with a stock engine, more with a modified engine. On the down side, they cost me about 1.5 miles per gallon after I installed them on my car. They cost about $200 and are not overly complex to install (you will have to remove the upper intake manifold). You will have to modify a valve cover slightly, but it is explained and easy to do with no detrimental effects. If you are installing a new cam at the same time, you may want to use the 1.6 ratio roller rockers instead to match up with the new cam. I personally bought the 1.7 ratio rockers years ago and when I later got a new cam, I bought a cam that would work okay with those 1.7 ratio roller rockers (no big deal). The roller rockers reduce friction which is good, and are made of aluminum which takes weight out of the valvetrain, which is even better.

          I would change out the fuel pump somewhere in here. The factory (fuel injected) fuel pump is good to about 310 horsepower assuming the fuel pressure has not been raised and the engine is very fuel efficient (bfse = 0.46). Raising the fuel pressure typically causes the fuel pump output to go down about 30 percent. The penalty if you do not have enough fuel flow is melted pistons and other assorted engine parts. Fuel pumps are cheap insurance. The factory pump is rated 88 lph. Aftermarket (in tank) fuel pumps are available in 110, 150, and 190 lph. The 110 lph size is sufficient for most cars assuming you haven't raised the fuel pressure, but the 150 lph size will provide some extra insurance at very little additional cost. To flow much more than 150 lph really requires upsizing the fuel lines. With a supercharger or nitrous, I would ask the manufacturer what they recommend and follow it to the letter. Most fuel pumps are less than $100 but they are a hassle to install. Make sure your tank is almost totally empty. They do not require any special tools to install other than a brass drift (chisel) and you can do them in your driveway (I have). One further piece of advice is to have on hand the two different plastic fuel line retainers before you start the job. They are cheap and prone to breaking on removal, especially when you're trying to remove them with improper tools (like I've done). The one on the return line is especially tough to get off in one piece.

          Not next, but soon you should also change out the fuel injectors. The factory fuel injectors are rated 19 pounds per hour and have a limit of about 330 horsepower assuming stock fuel pressure, a very fuel efficient engine (bfse = 0.46), and a 100 percent duty cycle. A 100 percent duty cycle will not hurt them for a run down the drag strip, but they will not hold up for long if you subject them to that routinely, such as for an extended high speed run (or road racing). Under those circumstances the factory injectors are only good for about 265 horsepower. Raising the fuel pressure will make the fuel injectors act like bigger size fuel injectors which is another option (but your factory computer is not set up for that so expect some problems). Injectors are commonly available in 24, 30, and 36 pound per hour sizes. Other larger sizes are also available. For most cars the 24 pound injectors will work fine. The larger size injectors will have trouble idling at low rpm's. Injectors start at about $200 for a set and aren't as bad as you may think to install. You have to remove the upper intake manifold and the fuel rails to install them. Make sure you put a little bit of oil on each injector o-ring before you install them. The penalty for not changing the injectors if you truly need them is the same as for the fuel pump, melted (and broken) engine parts.

          Now it's time for a K&N air filter. You can do this earlier, but on a reasonably stock engine, this modification is only worth about 1 horsepower. At this stage, it is worth about 4 horsepower. This mod is cheap (about $35) and very easy to do, so you may want to do it earlier. Don't forget to oil the filter properly. Without the proper oil, the filter will not filter out the contaminants which will result in damage your engine.

          Somewhere in here you also need to install a larger throttle body. The factory throttle body is 58mm in 86 and 60mm otherwise. They are available in 65mm, 70mm, and 75mm among other larger sizes. In this case bigger is not better, especially for a street car. For most cars the 65mm unit will provide the best results. If you make around 400 horsepower, then move upscale some more. A 65mm throttle body flows 17 percent air more than a 60mm unit.

          To make really serious horsepower requires changes to the electronics, but up to about 400 horsepower, the factory electronics are fine. I would not recommend most of the various chips available for your engine. The factory ignition system is good up to about 350 horsepower unless you have added a supercharger. If you add a supercharger, or exceed 350 horsepower, then add one of the various available ignition systems.

          Camshafts can make a big difference in the way your car runs, but require a lot of work to install one. They are best done during an engine rebuild. Installing a camshaft with more lift will probably require new (longer) pushrods because the cam will have a smaller base circle. Most people will be happier if the err on the side of being too conservative with a camshaft, particularly if they have an automatic transmission. Radical camshafts will kill your gas mileage and your bottom end performance which is so important on the street. I still remember a friend's car (72 Maverick with a 302) which was awesome from 35-90 miles per hour, maybe the quickest I've been in for that range, but the car was a total dog from 0-30 miles per hour. A pinto would beat him (easily) in that range. That Maverick also got 6 miles per gallon, definitely not desirable for an everyday street car. Also keep in mind that factory roller lifters, which allow so many wonderful things to happen for street car performance, will limit your upper rpm to about 6250 because they are heavy in comparison to other styles of lifters. You should definitely talk to several sources before picking a camshaft, and include the camshaft manufacturer in that list. Make sure you check for piston to valve clearance and valve spring bind before you buy a cam, and before you start the engine. I talked to the cylinder head manufacturer before I bought my cam. If you don't check, you can destroy all kinds of valuable engine parts upon initial engine start up (very, very bad, and expensive).

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©Copyright 1998 Ron Lee


© 1998 Michael Lee
© 2004 Michael Lee