12 Valve Stuff and What it Does

 Stock turbos

There are tons of hybrid parts that can now be installed on a stock charger. Most of which are hx40 parts. The turbine shaft is the same diameter allowing for many different options. Compressor wheels generally ranging from 60mm to 67mm and hx40 turbines in 64 and 67mm, 10 and 12 blade configurations (in most cases). Turbine and bearing housings can be machined to fit these parts.

  • H1c 56/58/16,18 or 21cm bolts together 3 inch outlet (first gen)
  • Wh1c 56/58/12 bolts together 3 (early 2nd gen)
  • Hx35 56/58/12 large snap ring 3 (late 2nd gen)
  • Hy35 54/58/9 large snap ring 3 (vp44 24 valve automatics)
  • He351cw 60/58/9 large snap ring 4.4inch outlet  (early common rails had he341’s)

4th and 5th gens are 60/60’s

1-3rd gen turbos have a t3 foot. The he341 and 351 have un-divided housings

The HX40 was never put on a dodge from the factory. They were put on 8.3L engines

All of these Holset’s have interchangeable parts. All have a stock reliable hp range at around 350hp exception of the 4th and 5th gens. However, all can be made to handle way more.

Hx40 60/64,67/16 the turbine foot can be a t3 or t4 depending on model

S300g 57/65/t3 The G has a restrictive compressor cover and the bearing housing is smaller. So not all standard s300 parts are interchangeable. This is a considerably less expensive turbo compared to a custom built s300. It is a S200/300 factory hybrid.

S300’s all of which parts can be interchanged (SX and SX-E chargers also have many interchangeable parts) but for simplicity I’m going to stick with the tried and true S series frames here. Your typical expensive Cummins s300 turbo is expensive, right? This is because it a couple different turbos put together. The center section or cartridge is a generic model (they come in different configurations). The compressor cover has to fit the compressor wheel you chose, the outlet on the compressor cover has to be machined to accept the factory band clamp the stock charger used. The turbine housings most typically used are off John Deere’s or Cat’s, so those must be bought separately and have the marmon flange machined to fit an hx40 style down pipe and clamp. All of this takes a $700 box stock turbo charger and makes it worth $1500 plus new.

Extended tip verse non extended tip. This refers to the exducer of the compressor blades. The exducer is the last part of the wheel that touches the air it’s moving. In a traditional compressor the blades are equal lengths with the back face of the compressor. With the extended tip models the blades extend past the back of the compressor allowing for more surface area and thus make the wheel capable of moving more air.

Billet vrs cast wheels. Billet wheels cost A LOT! They do have many advantages. In some cases, the are noticeably lighter. This allows them to spool a bit faster. In some cases, they are in 5 and or 6 blade configurations instead of a standard 7. This allows the compressor to take a bigger bite of air and thus move a few more cfms. A billet wheel can also be heavier which can slow spool. They are typically a little bit more robust than a cast wheel, allowing them to hold up to more abuse. That being said, billet wheels are not for everyone nor are they needed to make hp and do it in a timely fashion. A cast wheel will always be more economical to own. While the performance difference you will see from their billet counterparts are there. In most cases they are so small you could find better places to spend your money. Billet is also extremely fashionable, which is known to add HP.

Gated housing verses no gated a gated turbine housing is used to control boost and over speeding a turbo charger. The waste gate actuator opens when its pre-set pressure has been achieved and opens a port internally to vent unwanted exhaust gasses. Typically with a gated housing they are smaller, which allows the charger to build boost quicker. These housing can have the gate ports enlarged to flow much more than original possible. The stainless housings that High Tech offered have much larger ports than a factory John Deere housing. In a non-gated housing they typically come in larger cm3. This is to help with drive pressures due to not having a gate. Non-gated housings will typically spool slightly slower than a gated housing due to their size and are much less common do to their lack of tuning and their poorer street manners. Non-gated housing are typically much cheaper to purchase compared to a gated housing.

Drive pressure is the speed and force the exhaust gasses are pushing on the turbine. This is the back pressure created between the exhaust valves in the head to the turbine inside the turbo. You need pressure to spin the turbo however to much can damage an engine or a turbo charger. If the drive pressures raise to high the engine is choking and cant expel its exhaust efficiently. It takes proper hard parts and tuning to get drive pressures in the sweet spot where one makes the most power in the most efficient way.

External Wastegates are used to limit drive pressures on a turbo. When a turbo is being ran well off its map, possibly spraying drugs into the engine, it is very beneficial to the longevity of the turbo to install an external gate. They allow for a greater amount of tuning and a more efficient exhaust system. In a compound system the benefits are the same plus the owner has more ability to tune the turbos and thus maximizing power.

Spring wastegates are aftermarket pieces. They use a stiff spring to hold the pucks shut until drive pressure overcomes the springs tension.

Canister wastegates also have a spring but use a diaphragm that is then moved by manifold pressure. As boost raises the pressure overcomes the spring and opens the gates pucks. These are the most common form of wastegate controls found factory. Wastegates are tuning devices and it is very unwise to block them off.

Pressure ratios in most cases a turbos optimal pressure ratio is around 3.0. This is a measure of the work a turbo is doing in a specific range of its best efficiency. All turbos will vary on the ratio that is best suited for it. This is called a pressure map. Many single turbo set-ups run pressure ratios well over optimal ratios. This doesn’t mean that the charger isn’t moving more air or making more HP at a higher map reading (off the map) it means its not moving air as efficiently as it does within its map. So hotter less dense air is being moved with a turbo that is spinning quite a lot faster than it was designed for. Pressure ratio equation is (14.7+boost)14.7= your pressure ratio

Compound turbos are used when big HP or TQ is desired and you have reached the efficiency of a single or desire a more user friendly street truck vrs a large, laggy single turbo. You can use a smaller frame turbo to get the truck moving that fills the time gap (lag) needed to get the big atmospheric charger spinning. By compounding turbos you drastically decrease the pressure ratios of each turbo. Now both can run within their maps and make the most reliable power they were designed for. A single turbo will typically make more HP than the same turbo in a compound system. This is because the smaller turbo is taking some of the hot exhaust energy and cooling it down as well as disturbing the flow of the gasses. This typically increases drive pressure at the secondary (chokes) it while the rest of the pressure is gated to the larger turbo. In short is restricts flow through the exhaust and slows the process down. So some peak HP is lost with the huge benefits of having a high HP truck you can use and drive similar to stock. Pressure ratios for the secondary turbo is figured using this equation
overall PR/primary PR= secondary PR

Injectors, I’ve found and It’s my opinion that injectors should be classified in cross section area to determine proper fitment not the HP ratings the internet gives out. It has always been in my experience that the overall area of the holes gets you very close to what you want. Then all the other decisions can be made. Custom build injectors should always be considered for the best end results. Such as style of injector SAC, VCO, Micro Blind, modified passages, removal of edge filters, pintle lift, ect. SAC style nozzles seem to be the favorite within the Cummins world. 12 valves came from the factory with VCO style nozzles.

times the number of holes

  • 5×9 = 0.0003181 = 40 HP       6×09 = 0.0003817 = 100Hp     7×8.5 = 0.0003106 = 100 HP
  • 5×11 = 0.0004752 = 70 HP     6×11 = 0.0005702 = 125 HP   7×9.5 = 0.0004264 = 125 HP
  • 5×12 = 0.0005655 = 90 HP     6×12 = 0.0006786 = 150 HP   7×10 = 0.0005498 = 150 HP
  • 5×13 = 0.0006637 = 110 HP   6×13 = 0.0007964 = 200 HP   7×11 = 0.0006652 = 175 HP
  • 5×14 = 0.0007697 = 145 HP   6×14 = 0.0009236 = 225 HP   7×12 = 0.0007917 = 200 HP
  • 5×16 = 0.0010053 = 200 HP   6×15 = 0.0010603 = 240 HP   7×14 = 0.0010776 = 240 HP
  • 5×18 = 0.0012723 = 250 HP   6×16 = 0.0012064 = 250 HP   7×15 = 0.0012370 = 250 HP
  • 5×20 = 0.0015708 = lots         6×18 = 0.0015268 = 300 HP   7×16 = 0.0014074 = 275 HP

Most of the time 12 valve injectors are classified by hole size and count. The number of holes and size of holes has a direct effect on atomization of the fuel. Typically, the less number of holes with a larger hole size, tend to be dirty. Think denser fuel spray at a lower pressure (less holes but bigger) vrs finer fuel spray at higher pressure (more holes but smaller). Therefore 5 hole injectors are dirty than 6 hole and 7 hole injectors dirtier than 6. The more holes and smaller holes atomizes the fuel better for a given size of injector. This will cut down on smoke while driving and under WOT. ALL depending on application. 12 valves came with 5 hole injectors. 24 valves came with 7 hole. Many believe more power is attainable with a 5 hole as the fuel is denser and can penetrate into the combustion chamber better at high rpms. Also leading one to believe that a 7 hole injector might drive better on the street due to better atomization of the fuel.

Injector spray patterns are important when you consider replacements. The wider the pattern the better the fuel can be atomized. From the factory all 5.9L automotive engines from 1994-1998 have 145* piston bowls. Earlier had 155’s. there are several different nozzle angle to choose from. 145,155,158. All nozzles can be extrude honed to a desired angle. Miss matching injector patterns vrs bowl design isn’t the end of the world, it’s just inefficient. Marine injectors are 155* and many people have ran them for years in their trucks with no problems. 370’s are 5×12’s and 435’s are 5×14’s. originally these were the performance upgrades. Times have changed and there are tons of better options available.

POP Pressure is the pressure that the pintle lifts from its seat inside the nozzle to deliver fuel. Stock 12 valves POP pressure was 240 or 260 BAR depending on the model. POP Pressure has an effect on timing, smoke and atomization. Higher POP Pressures allow the fuel to penetrate the pressurized air better at higher boost levels. Every 10 Bars = 1 degree of timing. 1 Bar = 14.7 psi (1 Atmosphere) and 10 Bars = 147 psi. 10 Bars of added pressure REDUCES the timing by 1 degree and lowering the pressure by 10 Bars ADDS 1 degree. Lowering the pop pressure also has an effect on smoke, there will be more. Rule of thumb is higher POP Pressures help with street driven trucks. It lowers smoke, enhances throttle response, while lowering egt’s. It is also worth noting that it is harder on your injection pump as the pump must work harder to overcome the spring in the injector. Too much of a good thing can be a bad thing. There is nothing wrong with running stock pop pressures in a stock to mild built engine.

Timing is generally set from the factory at 12-14*. This allows for quick starting and a low power curve in the RPM’s. Adding timing has a drastic effect on the power curve of the engine. The more timing the higher in the RPM range the engine will make peak power. But by advancing the timing you also take away from the bottom end power. Spool up is slightly slower, so daily driving or towing with a lot of timing can be a chore. Timing also effects cylinder pressure. Too much of it and the head gasket won’t last. Depending on your truck 16-22 is about the range for a street truck. Because the injection process is starting earlier the fires heat is absorbed more into the cylinder walls which increases operating temperatures. Once in the 20’s clamping force of the head to the block should be an owners concern. Boost numbers can fall with added timing. This is due to how efficiently the engine is running at a higher rpm. Also, it is good to note that additional timing cleans up larger injectors bottom end smoke output as the fuel charge has a longer burn period.

The Injection pump has the most to do with the HP you are planning on making. The more fuel the pump can move efficiently, the more power it can efficiently make. This has an effect on properly selecting injectors. A 13mm pump moving 800cc of fuel doesn’t need 5×16 injectors to make 500 HP like maybe a half worn out stock 12mm moving only 350cc’s does. The larger pump can atomize fuel much better by forcing it through a smaller injector with much more gusto. The more fuel you can move to the injectors the more you can tune your engine. There are 3 models of p7100 injection pumps that were on 2nd gen trucks. 160’s, 180’s and 215’s the 160 have a problem up high in the rpms because they have a much lazier camshaft. The fill rate for the barrel is much shorter making overall HP harder to make once you really start modifying the truck. That does not mean a 160 pump can’t do big things. It means it just a little harder. Added transfer pump fuel pressure is a huge plus to the smaller pumps as maximizing available fuel during the short fill time is crucial. The 180 pumps seem to be the most desirable, visible identical to the other 2 they have the desired camshaft is stock form. The 215 pump moves more fuel than both the others in stock form however has a notch that retards timing 3 degrees up top making it a lesser choice to the 180 for big HP in stock form. There are many internal pump upgrades such as quick rate camshafts, Heavy duty springs and lifters. All pumps can be heavily modified.

Delivery valves are fuel injection event stops, located under the holders the injection lines attach too. They are easy to change. There is a collar on each valve. This collar in stock form is very thick, by installing aftermarket valves or machining the stock valves, a longer injection period is attained. This drastically effects power due to the extra fuel, the injector sprays longer. This also makes for a sloppier injection process as the pressure falls off. Also because of the extra fuel smoke and exhaust temperatures can grow exponentially. Delivery valves are awesome upgrades but the size of the valve again will be determined by its application. A lazer cut valve

Plungers and barrels are the pistons and cylinders of the p7100 pump. Think of the injection pump as another little engine hanging off your bigger engine. These parts can be upgraded with larger parts therefore moving tons more fuel. Stock are 12mm. To bench a pump on a stand a technician can adjust fuel amounts by turning the barrels of the pump (balancing). The backyard mechanic can loosen these barrels on the top of the pump and tap them all the way towards the firewall to max fuel delivery. Note that this does not insure the pump is anywhere close to balanced. It only insures that each plunger assembly is giving 100% of what it can deliver. 100% can be different between assemblies.

Over Flow Valve is mounted on the front of the injection pump. It is a special fitting that limits unused fuel inside the pump so there is constant flow internally. The stock valves are prone to becoming weak and lowering fuel pressure. They have a spring and a BB in them that cover an orifice. Tork Tek make nice replacements in various sizes depending on your needs and applications. These replacements are typically one piece fittings with a single orifice, no moving parts.

AFC or air fuel control is an extremely important part to the injection pump. This is how the fuel curve is tuned. There are three main tuning parts to the afc. The pre-boost setting on the back of the housing is first. This adjustment puts a pre-load on the afc spring allowing for X amount of rack travel under no boost situations. This is an important initial set-up for smoke control and getting the charger to light quickly. Secondly is the star wheel adjustment. This wheel adjusts the tension on a spring inside the housing. This tension is the determining factor on how much manifold pressure is needed to start the fuel enrichment process. Too much tension and fueling is delayed. Too little tension and you get way too much fuel way too soon. There are aftermarket springs you can install behind the star wheel to get different spring rates. A good base setting will be close to stock from zero boost to initial movement and close to stock psi at the halfway point of foot movement. Max travel should happen in the 20’s on stock engines and notably higher in modified engines. Lastly is the foot. This foot moves on a rod inside the housing. This foot is moved on its rod by the movement of the afc diagram (AFC spring on one side, manifold pressure on the other). Depending on the position of this foot inside the injection pump determines how much rack travel is possible at that given time. The goal of the afc is to progress the fuel delivery smoothly for street driven trucks. Without it you have idle fuel and un metered fuel. (track stuff) or in many opinions un tunable. Never (Gut) an afc on a street driven truck. By doing so you take away all tuning capabilities.

Fuel plates are throttle stops. They are the last part of the equation when you talk about AFC tuning. The foot at full movement moves past the fuel plate so that it can then meter upper rpm fuel. A fuel plate limits WOT rack travel and there for top end fueling. Plates can be custom ground to tailor to a trucks specific needs. EGT’s should be a consideration point when modifying a plate.

Mack rack plug is a replacement rack stop that simply threads into the front of the injection pump. The factory plug allows for 19mm of total rack travel, while the Mack version allows for 21mm. this effects WOT fueling only. 215hp pumps do not benefit from this plug due to the fact that rack travel is already at or near 21mm.

Delivery valve holders are the fittings on top of the pump that the injection lines attach to. They make aftermarket holders with larger orifices. Which obviously can flow more fuel. If one were to install larger lines or larger holders it wouldn’t be a bad idea to replace them at the same time to keep the system balanced. Again, holders are not a cost effective way for the majority of people to make usable HP and tend to be for competition purposes.

Governor springs should be the first thing anyone does to their 12 valve. 1st or 2nd gen. the governor springs purpose it to limit fueling at a desired RPM range. Stock is around 2200 rpms. The springs are attached to weights and this assembly spins. When the centrifugal force becomes greater than the spring tension the weights begin to open and limit fueling. The stiffer the springs the harder and longer the governor can fuel. 3k and 4k springs work wonders on these trucks. They make 5k and custom springs but these get extremely hard to run on the street, especially with an automatic transmission.

Fuel volume or lift pump pressure is a very important part to these systems. The diesel fuel lubricates the plungers and high volumes of fuel is needed to feed them. P7100 pumps cannot draw their own fuel. Stock lift pumps put out around 30psi of fuel that fluctuates due to it being a lever style pump driven off the camshaft. The factory lift pump works well but begins to fade quickly when the injection pump is flowing much more fuel itself. There are many different kinds of aftermarket fuel systems available. Most of which flow considerable amounts more fuel per hour than stock at much higher pressures. The better the fuel flow to the injection pump the higher the HP potential goes. Modified 12 valves like fuel pressure and can be ran above 50psi of pressure. At some point internal seal failure can become a problem.

Injection lines stock size are .084 aftermarket versions are available in .093 and .120 mild steel and stainless steel. Stainless lines are much harder which gives them the tendency to crack. Oversized injection lines can have an effect on timing due to the larger amount of fuel working through the lines for a specific push of fuel from the pump. In almost every street driven truck there is no need for larger lines. Idle quality can be effected causing a lope or lack there of idle. Unless all out HP is you goal and the lines are the restrictive part of your system this upgrade isn’t necessary.

Camshafts in a diesels engine has the same effect that they do in a gasoline engine. The effects are not nearly as noticeable however because your still driving around turbos, and turbos = lag in one form or another. A camshaft changes efficiencies. It allows air in and spent air out easier. By allowing an engine to breathe you always open up the possibilities for more HP. Manifold pressure will drop with a camshaft as the restriction at the valves is now slightly less typically due to the overlap time in the exhaust and intake ramps being longer. This doesn’t mean your not making the same or more power it just shows that you are making it easier.

Pistons and their bowls. The injector squirts its fuel directly into the cylinder on top of the piston (Direct Injection). That fuel is delivered into a large bowl. Older non intercooled engines had 155* injectors as well as marine engines. Everything else has 145* injectors. A 155* piston has a larger bowl. A wider spray angle helps with having a complete fuel burn as the spray is spread out inside the cylinder more. If one were to rebuild an engine or play in the performance world the larger bowl pistons are worth considering.

Head studs and or Bolts are a very important part of any engine. Whether it be stock or modified. Holding the head onto the cylinder is a big deal. The stock bolts have a tensile strength of something like 150,000psi while aftermarket versions range from that to well over 200k. There are a few different manufactures of high quality head studs out on the market. These replacements can increase clamping force by a staggering amount. Which allows for more power to be made while having the assurance the head gasket should stay in place. Stock head bolts are 11.2MM most people opt for 12mm replacement hardware. There are also 14mm studs that require tapping the block for installation. Replacement head bolts are also available to install that significantly increase clamping force. These bolts can be bought online or places like Fastenal. They are grade 12.9 allen head bolts. A head stud will most likely provide more clamping force with less failure rates in high HP engines but know that the allen bolts are a very good alternative to stock.

A stock head gasket, head and bolts are all most everyone will ever need. The key to longevity is a flat head and a flat block with plenty of clamping force. Millions and millions of miles have been logged on factory configurations with no modifications. Much higher than stock cylinder pressures can be safely contained this way. Its when you get into big turbos, advancing timing and lots more HP than stock when you need to consider better hardware.

O-rings are actually stainless wire that is placed perfectly over the stock fire ring installed on the head gasket. A grove must be machined into the head for these to be installed. This provides greater clamping force on the fire ring in the attempt to keep higher cylinder pressures contained inside the cylinder.

Fire rings are steel rings that are placed around the cylinder. They replace the stock fire ring found in a head gasket. So a special head gasket must be used. The head and block need to be machined for these to be installed. Once installed there is little doubt that this is the best way to hold boost in. however heat cycles on daily driven vehicles can cause failures of these rings while cost and time to install them is a big factor.

Compression ratios play a role in a diesel engine that most people don’t think much about. The higher the compression ratio the snappier the engine is off idle and before boost. If batteries and the starter are up to snuff the faster it will start as diesels are compression ignition engines. However the more boost you try to cram into the engine the harder everything has to work to fit it in. The engine internals will also be working extremely hard to try to smash the air. When this occurs slightly lowering the compression starts to look good. This can be achieved in many different ways. Lowering the compression on a 12 valve will make it harder to start. It will have worse street manner and most likely be a pain to drive normally. Changing the way the internals of an engine work are for the big HP guys.

Valve size again helps with air flow. Air in and air out is the recipe on HP the more you move the more you can make. BUT huge valves will lower the velocity of the incoming air as it has less restriction coming in. the slowed charge will not be pleasurable in lower HP engines one may actually loose HP. If you don’t have the available rpms and over all HP to utilize the larger area then chances are you are going to lose performance.

Performance heads can be looked at exactly like bigger valves. Bigger is not always better. The massive flow numbers of a fully ported head or these new custom built ones look awesome but understand these are for engines that make way more than any normal truck is going to drive around with. They would be very ineffective at helping a 500hp truck. With that all being said. Porting the exhaust side of a stock head to match the exhaust manifold is a great idea. This allows the engine to expel its burn cocktail easier and quicker thus getting it to the turbo faster. Exhaust velocity out of the engine will speed up and aid in performance.

Valve springs and valve hardware all this jazz is needed when you start spinning these engines higher in the rpms than what they were designed for. The stock valve springs are quite soft. This allows for valve float. Which is when a valve cannot seat itself back on the head before the cam is pushing it back open. The retainers and keepers that hold the valve in the head can also be looked upon as weak links. The valve can start to pull through the small OE keeper and eventually drop a valve into the engine. The HP gain from replacing these three parts is zero, however the peace of mind is priceless.

Harmonic Dampeners do just what they claim. They reduce internal vibrations that the engine is producing. It’s been claimed that at 4100rpms the 12 valve has a potential destructive vibration. As this may be the case almost all the 12 valves on the road can’t rev that high, modified or not. A new balancer or performance balancer are always good insurance. The fluid style dampeners noticeably smooth the vibrations in a daily driven truck. You don’t need to make 1000hp to benefit from a quality harmonic balancer. The smoother the engine runs the greater the potential for longevity and power output.

Electric powered accessories such as cooling fans and water pumps can be very useful tools when working with high HP engines. By eliminating the parasitic draw of these it takes to turn these accessories and spinning them with 12V power you free up some HP. The Engine can spin easier faster because it isn’t spinning a big heavy fan. The fans look sweet on these truck but no that they do not cool as well for towing as the OE fan does. They are better suited for play trucks that do not tow regularly or particularly heavy. Electric water pumps become useful when engines are running at a sustained high rpms. A standard belt driven pump continues to create more and more block pressure the faster it spins. This can pop out freeze plugs and cause other gasket failures. An electric water pump will run at the same speed regardless of engine rpms. Eliminating these failure points. On street driven trucks your typical water pump is good insurance. They last forever while an electric should be monitored.

Freeze plugs as stated above can pop out. Especially with higher rpm engines. They make some really nice billet freeze plugs with o-ring seals as well as plugs that bolt on, virtually eliminating a blow out.

Lifters have a crown built in to them. As they wear they can develop flat spots which mess with valve timing. Anytime a new camshaft is installed it is advised to replace the lifters. Aftermarket lifters generally have a larger diameter face on them allowing for a longer contact time with the camshaft which helps with wear. When you get your pocket book out you can look at roller cams and lifters. These again are for very high, very abused engines looking for the last drop of HP.

Pushrods are what the lifter pushes up that then pushes a rocker down to open the valves inside the head. A pushrod is a big metal straw. When higher psi valve springs are used and higher engine rpms are ran, it is advisable to upgrade to a thicker walled pushrod. The pushrod can deflect under a load giving inaccurate valve openings.

Intake manifold is the part that directs the air into the intake plenum of the head. OE versions are quite restrictive. Plenty of HP can be made on a stock intake but in the game of more there is definitely room for improvement here. Banks came out with a twin ram intake years ago, that evenly places incoming air in the head verses having the charge enter closer to the front of the engine. This slightly lowers egt’s and smoke under all boost conditions. There are many less expensive versions of this now. Single ram like stock with much smoother flowing pipes and twin ram intakes. It is advised to keep your grid heater when installing an aftermarket intake if you live anywhere it gets cold.

Intercoolers cool the compressed air before it reaches the engine to be burned. The cooler the air charge the denser it is and the more power the charge will make. Stock intercoolers have their limits and will fail under high levels of boost causing a boost leak and lack of performance. Much larger, stronger aftermarket coolers are available. These are rated to cool a much larger volume of air much more efficiently. Note that the bigger coolers are bigger, therefore you will experience a touch more turbo lag pressurizing the system before the charge air gets to the engine. So, on a stock truck or one close to it a larger intercooler can and most likely will hurt performance. There are also air to water intercoolers. Most often used in performance applications due to mounting problems. These can be installed using an external water pump and an external very cold water charge. This insures the coldest most dense air being ingested into the engine.

Intercooler boots connect the solid charge pipes to the various intake components. At these points you need a flexible rubber or in most cases silicon connecter. Stock boots can fail under high levels of boost as well as expand causing a slight delay in the air charge reaching its destination.

Air filter assemblies come in many shapes and sizes, all designed to get more air and hopefully cooler air into the engine faster. Again the cooler and more efficiently the air coming in the more potential it has to make HP.

Exhaust manifolds in stock form are quite restrictive. It is important to have an engine set-up that breathes well for the HP it is designed for. Stock manifolds do their job but do fall short in the performance category. They all have T-3 turbo flanges which restricts flow needed in performance situations. They also are known to crack under high heat cycles which also ruins performance. Many aftermarket versions are available, ranging from three piece cast iron, stainless steel and cnc steel. These all can be coated in high temperature coatings in the hopes of lowering under hood temperatures and getting hotter exhaust gasses to the turbo in a less restrictive manner to aid in spooling. Flange options are T3,T4 and T6

Turbine diverters are very cool performance pieces to be used with dual volute turbochargers in T4 or T6 configurations. They have a flapper valve on one side of the flange that operates on manifold pressure (boost). In a no boost situation half of the exhaust flow is crammed into one volute of the turbo aiding considerably in spool time. Once a set level of boost is made the valve begins to open and allows the charger to take the full volume of gasses through both sides of the turbine housing. These diverters are expensive but really help when trying to street a large turbo that suffers from lag.