Intake modifications are the #1 way to increase engine output. Airflow into the combustion chamber is restricted by the air filter, throttle body, intake plenum, lower intake manifold, valve lift, and cylinder heads. If you don't want to do your own porting, you should still make sure you know a little bit about extrude-hone porting.

Purchase a K&N cone filter for a Mustang 5.0. Go to PepBoys and look at the two Mustang V8 K&N cone filters. One is the 302's (5.0L), and the other is for 289 (4.6L). You want the 5.0's. Another way to tell is one will look like it is too big for the car, and the other one will look like it is WAY TO BIG for the car. You want the smaller one for now.

Disconnect and remove the battery, so you have access to the computer. Go ahead and unbolt the computer that was revealed by removing the battery (it is the large black box that connects near the end of the flexible black tubing). Now remove the cover to the computer (fear not, the computer's internals are sealed with about an inch of silicone). This should allow you to remove the entire flexible tubing leading to the airbox.

Now remove the crankcase vent and vacuum tubing from the airbox. You will need to put a filter on the crankcase vent tubing (don't plug it up). Unbolt the entire airbox assembly, and remove it. Take a look at the thick rubber tubing leading to the throttle body that was connected to the airbox. You can go ahead and plug the filter on and drive forever like that - it will not fall if you push it back into the groves. Don't bother running a large tube all the way to the front of the car and locating the filter there - the loss in engine bay room does not justify the possible 1/2 horsepower gain this would provide.

Now bolt the computer back in, with the cover removed so that it has some air circulation, and put the battery back (obviously). Start the car and drive it around a little and note the somewhat tinny whine of the engine at high RPMs has been replaced with a gutteral roar instead. This is good.

The stock 3.0L SOHC V6 engines have a 46mm Holley throttle body. Although entirely adequate for stock aspiration, much larger throttle bodies are on the larger (3.3L and 3.8L) V6 engines available from Chrysler/Mitsubishi.

You have two options regarding obtaining a larger throttle body - either contact Forward Motion and purchase one for about $210, or head on over to the junk yard and get one yourself for $35.

If you opt for the junkyard, keep in mind that the throttle body is usually not going to be damaged, but it will be very dirty. You are going to have to get at least a full bottle of WD-40 to clean one out, and a Dremel tool will help alot as well. The engines you are looking for are generally in the large Chrysler cars, you will almost always find at least one per trip. If the throttle body looks like the one on your car (ignore the vacum connections on the top), and it is a Holley, then it will probably fit. Make sure the sensors are intact (not essential), the throttle plate spring is taut (should feel like it's going to take your hand off), and there is no visible damage to the unit. Disconnect the sensor harnesses and vacuum lines, and remove the throttle and kick-down cables. To remove the cables, hold the lever that moves with the throttle plate so that the plate is completely open, and slide the cables out, one at a time. Unbolt the two nuts holding the throttle body on and keep them just in case you drop one.

Installation will be much easier if you spend the time to pull intake tubing from other cars that fit the throttle body and your K&N filter (you better have one if you're considering a throttle body upgrade).

You need to clean the throttle body before you install it on your car. Unscrew the sensors and flush the entire unit with WD-40 until the WD-40 runs out clean. Use a Dremel with a steel brush tip to clean out the entire inside of the unit where the air will pass through. Rinse the unit with WD-40 again. Be sure and clean the throttle plate, too. Screw the sensors back on.

Reinstall the stock throttle body gasket (note the cutout for the airflow is big enough for the larger throttle body), and slide the new throttle body onto the bolts. Tighten down the nuts (don't He-Man them), and reconnect the sensor harnesses. Its going to take some effort to get the stock air hose on this new throttle body if you didn't get new hose, but you should be able to. Now plug those two vacuum ports on the top with something besides Bondo or RTV sealant.

Start the car. If the car seems to be idling or running very funny, or you get a check engine light, you probably need to replace the sensors on the throttle body you installed with the ones on your original unit. Also check that you remembered to plug the vacuum ports and reconnect the sensors.

You should notice a definite improvement in high-end response, and a little more pull at the lower and middle end. Depending on the modifications you've done to the motor, replacing the stock 46mm unit with a 52mm unit will gain anywhere from 4-15 horsepower with a naturally aspirated motor, and about 10-25 with a forced-induction (other than ram-air) setup.

The stock intake plenums are actually well manufactured, but the way they are designed is not the greatest at facilitating airflow. The two most common internal designs seem to consist of the plenums that exist on the older cars, and the plenums on the newer cars, especially the ones on the P-body cars. The older, larger one is designed such that it sends the air down a runner to the back of the plenum, where the MAP sensor would be located, then distributes it back up the plenum to the cylinder ports on each side. This is stupid, but helps increase torque by lengthening the airflow's path. This plenum is forged, and a very time consuming piece to port by hand. It weighs about five or six pounds.

The newer design is open inside; there is nothing preventing the air from flowing straight to each port. This plenum is made from an alloy and is much lighter than the forged iron ones. It usually has extra fittings for an EGR transducer & idle air control motor above the EGR port.

As far as porting is concerned, the first area of possible improvement exists at the curved surfaces before the ports, on the bottom section of the plenum. By grinding them down you eliminate the small restriction they impose to the airflow, improving the high-end response of the motor slightly. You can also enlarge the entire opening before the port, to help channel more air down it. If you port the lower intake using extrude hone porting, you should match the plenum's ports with that of the lower, to take advantage of its increased size.

The second area is the mouth of the plenum. If you aquire a throttle body larger than 52mm, you will have to port the opening of the plenum to take advantage of it.

If you have extra time, you can grind down the round ridges up in the top of the plenum, this also helps reduce airflow restrictions.

Whatever you do, don't interfere with the long runner down the middle. A lot of torque is generated by its design, and you will get funny readings from the sensor because the vacuum around it will change.

Equipment required:

• Dremel tool (don't use a Mini-Mite, dumb-dumb)
• 20-30 Grinding wheels (the gray ones)
• 10-15 Fine grit polishing wheels (gray ones again)
• Several assorted silicone carbide bits of different shapes
• Vacuum cleaner
• Flat-head screwdriver

Keep in mind these directions will almost definitely not apply 100% to every car, so don't panic when small differences arise.

To remove the plenum, start with the air hose leading to the throttle body. Unscrew the hose clamp holding the tube on, twist the tube off, and put it out of the way. Second, unbolt the throttle body, and pull it straight off the bolts. If the throttle body has any vacuum hoses connected to it, just leave them connected. Now unbolt the EGR tube, which is the tube leading from the exhaust manifold to the lower part of the plenum, underneath the throttle body. You only have to unbolt the bolts on the plenum. Disconnect the brake booster vacuum line, which is the largest vacuum host connected to the plenum - it is on the driver's side and connects to that large booster bolted to the firewall. Remove the vacuum line for the EGR transducer controller, which is on the same vacuum tree as the booster line. Now remove the vacuum line coming from underneath the lower intake, that plugs into the side of the plenum. On the passenger's side of the plenum, remove the vacuum hose coming from the fuel pressure regulator - it is the little thing wedged in somewhat underneath the plenum, and remove the hose leading to the map sensor, which is bolted onto a bracket in front of the alternator. If there is a sensor harness on the plenum, remove it as well. Unbolt the eight bolts holding on the plenum, check one more time for any stray hoses/tubes/harnesses you missed, then pull it straight up off the engine. Cover the ports with a piece of cardboard or a rag while you work on the plenum.

To seperate the two halves of the plenum, remove the eight screws using a large phillips-head screw-driver, then drive a flat-head into the seal somewhere around the unit. Use your hand to pound it in, and don't panic when it goes POP! and the two halves part. Don't try and pry it open, if the halves don't fully come clean of each other when you push the screw driver in, just drive it in another location until the two halves come apart.

If you are going to port an alloy plenum, a Dremel tool with an oxide bit will grind the thing to a pulp in no time, but with an iron one, even silicone carbide bits don't last for more than 15 minutes a pop. The best approach with the metal ones is to use the carbides or cutting wheels to gouge out sections of the metal, then shape it out with the grinding wheels.

When the shape is correct, it should be very smooth, but go ahead and polish it with a fine grit wheel spun at high speed. You will go through bits at about the rate of 1 every 10 minutes, but keep in mind Dremel tools were not designed for such extreme applications as porting a solid-iron chunk of metal.

There is not that much to do with the plenum that requires a full blown grinder, so if you have one, I can't really recommend you use it unless you are very skilled with detail work. Use a Dremel.

Porting the plenum and lower intake is not something I would recommend doing until you have tended to the other things such as the exhaust and throttle body. Even then, don't go overboard because you could move the motor's full powerband off it's rev range if you gouge out too much material. Intake porting on naturally aspirated cars is about tradeoffs - you can't really take advantage of increased airflow until the RPMs are high, and at lower speeds you want the air as dense as possible. Removing every restriction to air flow lowers the air density and, subsequently, reduces the engine's volumetric efficiency. Reduction in VE always equates to a reduction in torque, which means you are making less power at that rev range.

If you have ever seen a histogram of a motor's powerband, imagine grabbing it by the top and pulling it up and farther down the rev range - you have increased peak horsepower, but you have reduced the range at which the engine makes enough power to accelerate the car from its current velocity. Obviously, if the engine is being run continuously in the 3000-6000 RPM range, this is a good tradeoff, and definitely helps the car perform better. On the other hand, when you are driving in traffic, the motor sits in the 750-2000 RPM range, and feels sluggish. Then you floor it to keep up and the motor revs up to it's powerband where most cars would start slowing down, and the car all-of-a-sudden takes off.

If you have an automatic, you only have three or four gears, which means you have less control of where the motor revs at. Your best strategy is to keep it simple and just remove obvious restrictions to airflow, and mabye open it up a little more. If you have a 5-speed, you have complete control of what RPM the motor plays at, and you are less concerned with a loss of low-end torque, which allows you to partake in a more aggressive port.

Bottom line: if you modify only the engine's intake ports, big ports yield higher trap speeds, better high-end performance, and work best with downshifts, where as smaller ports yield lower E.T.s, better 0-60ft times, and accelerate better at low engine speeds. In a street race, the engine with larger ports will lose off the line, but if the race continues, will pull ahead and top out at a higher speed.

If you don't want to lose any torque from massive porting, increase the speed at which the air flows into the plenum. This can be done at the intake side via forced induction or ram-air, and at the exhaust side by increasing its scavenging and air flow characteristics.

Extrude-hone porting is a process by which an abrasive substance is pumped through the area to be ported at high speed. This results in a clean port that removes the greatest restrictions without gouging out other areas as well. Extrude-honing is the best way to port a lower intake manifold as it's elaborate twisting shape makes die grinding impossible.

If you are considering a port and polish, start with the heads and have them redone with larger valves. When the heads are complete, port match the manifolds and plenum to the ports on the cylinder head. Have the exhaust manifold flow-matched so that each port has the same flow characteristics, and have the lower intake flow-matched as well. You can also have the newer plenums flow-matched for maximum performance. The combination of these procedures, along with a good, free-flowing exhaust system will easily net you 40-50 horsepower.

Every performance modification done thereafter will have a profound effect on performance, and it's benefits and disadvantages should be considered before installation.