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Premium Member
14,274 Posts
Discussion Starter #1 (Edited)
Welcome to the comprehensive guide to upgrading and modifying your SRT-4. There are many guides and upgrade paths available on this site but this is the most current version available. It's an evolving document that will have points added, removed and modified as new parts come on the market and extensive testing by the community reveals new or better ways of doing things. The purpose of this guide is to provide you with clear paths to reach your goals with the car and answer all the common questions we see posted each day. Posting is not permitted in this thread. If you have any questions, don't understand something, need to know what comes next or have suggestions to improve this document please feel free to post them here (please don't PM me):

You may link directly to this thread, the URL won't change.

The best advice I can give you before ever picking up a tool is to have a goal and stick to that goal religiously. Doing so will avoid buying parts that will be left over later (money wasted) or making changes to your car which are not reversible (should you need to in the future). Most write ups will tell you that if you buy X mod you'll gain Y wheel horsepower. For the most part it simply isn't true; it's marketing. There are far too many factors that will determine what sort of gains you get like the condition of the car, the octane of fuel used, the ambient air temperture, moisture content in the air, how the car is tuned, the elevation above sea level, mods already on the car and so on. Also, every brand of dyno is different, every dyno is different and every operator is different. Some read high like Dynojets, some read low like Mustangs. I suggest that you always go to the same dyno so you're always comparing apples to apples when you make a change and not worry so much about what other people with the same mods or less mods then you are scoring on their local dyno. All too often we see people posting that they got 300whp with basic mods on 91 or 93 octane pump gas. Guess what? They may think that they did and will have a sheet to prove it but trust me, if they ran on YOUR local dyno their numbers would be closer to your numbers.

Table of contents:
Section 1: Preventive Maintenance
Section 2: First Mods (Universal To All WHP Levels)
Section 3: Stock Turbo Performance Mods (225-325WHP)

Premium Member
14,274 Posts
Discussion Starter #2 (Edited)
First mods

Preventive maintenance:
This is a list of things that should be done regularly or if you just bought the car and don't know the condition of these parts and systems.

1.) Engine oil change
2.) Coolant flush
3.) Gear oil change
4.) Spark plug change
5.) Confirm vacuum line routing
6.) Seal the system
7.) Boost leak test
8.) Compression test
9.) Fuel injector cleaner\dry gas

1.) 5.0qts of any quality, fully synthetic motor oil like Mobile 1 (5w30 in the winter, 10w30 in the summer) and the oil filter of your choice. I change mine every 3K miles.

2.) 6.5qts total of a 50/50 mix of Mopar Engine Coolant or Zerex G-05 Coolant and Distilled Water. I change mine every 20K miles. (NOTE: Don't use any other kind of engine coolant than those listed above; they're HOAT certified. Use of anything else will corrode aluminum parts.)

3.) 2.4-2.6qts of any quality ATF+4 Transmission Fluid and *Mopar Limited Slip Additive (P/N 04318060AB) (*Add 4oz ONLY if you hear excessive chatter, otherwise don't use it.) I change mine every 15K miles.

4.) NGK 4306 Copper Spark Plugs (0.050-0.040 for stock boost levels, 0.040-0.032 for 18+ psi). They're the OEM plugs for S3 kits and high boost applications and almost 1 step colder than the stock plugs. You want to run the largest gap that you can without getting spark blow out. I change mine every 6K miles but you can run them as long as 12-15K miles. Note, Iridiums are not needed on a stock turbo car and many big turbo applications. The electrode fouls long before it reaches it's end of life making the copper plugs significantly more cost effective to run.

5.) Trace each of the vacuum lines to confirm they are all routed correctly for your mods. Many problems we encounter are simply the result of the lines being run incorrectly, especially the Black and Green lines on the Wastegate Solenoid being reversed. Diagrams can be found here: Vacuum Line Setups

6.) Seal up all the existing holes and potential leaks in your vacuum lines and charge pipes. Use zipties where ever a rubber\plastic vacuum hose meets a connector. For larger lines like the PCV hose on the throttle body nipple and brake booster hose located under the throttle body (VERY IMPORTANT to clamp!! If this line pops off you lose your power brakes!) use small stainless worm style hose clamps. For the charge pipes use T-Bolt style hose clamps. The Worm style clamps that came from the factory don't tighten down well enough to completely seal the system. (Parts: 3x 2.5" for both sides of the intercooler and the throttle Body. 1x 2.75" for connecting the hard pipe from the turbo outlet to the hot side intercooler soft pipe. 1x 2.25" for the turbo outlet. More info: T-Bolt Style Hose Clamps )

7.) Buy or build a boost leak tester and use it to boost leak test the system ( more info: MPx 2.5" Boost Leak Tester ). Test with the key on, engine off to a couple psi over what you intend to run. Note, if you have the vacuum ejector --> intake line correctly installed (some call it the 'factory boost leak'), plug it with a bolt during testing and please don't disconnect it. It's purpose is to purge fuel from the evap canister. Track down and seal all the leaks you find until you can't hear any air escaping. Next, spray soapy water around the throttle body mating surfaces, fuel injector o-rings, MAP sensor and intake manifold to check for vacuum leaks. The system should hold the pressure for at least a couple seconds before it starts to go down.

8.) Cylinder compression testing your engine before modding will confirm that the cylinders are capable of holding pressure. This is a very important step to avoid costly repairs in the future and insure that your engine can handle increased power without failures. Turn on the engine and get it up to operating temp, once reached turn the engine off. Make sure the battery is fully charged. Remove the spark plugs, the Auto Shutdown (ASD) relay and make sure the throttle body blade is fully open during testing. Insert the compression gauge into spark plug hole #1 (you may need Special Tool 8116 or the equivalent to reach it). Crank the engine until maximum pressure is reached on the gauge, write down the number. Repeat testing of cylinders 2, 3 and 4 writing down each result. Dodge's specification is that no cylinder is less then 100psi and all cylinders are within 25% of each other. The consensus of opinion is that these numbers are far too low for a car that's going to be modded. I recommend that none be lower than 130psi and all are within 10% of each other. If you find a cylinder that's not in spec it could be the head gasket, piston rings or valves\valve seats. Find out what the problem is and repair it before continuing.

9.) Fuel injector cleaner is an additive that desolves deposits on your fuel injectors. These deposits can clog injectors or alter their spray pattern. Dry gas\gas line anti-freeze is a compound that bonds to any water that may be in your fuel tank which converts the water into a compound that can be burned by the engine. Water in the fuel tank can rust metal parts in the fuel pump and injectors. I recommend running a bottle of cleaner through your gas tank every 6 months and a bottle of dry gas every fall (before it gets cold out).

Premium Member
14,274 Posts
Discussion Starter #3 (Edited)
First mods:
This is a list of recommended mods to correct some known issues with these cars as well as prepare the car for future performance modifications.

1.) Spark plug wires
2.) Ignition coil
3.) Fuel pressure regulator\fuel filter
4.) PCV Line oil catch can
5.) PCV line check valve
6.) Lower control arm (LCA) bushings
7.) Booger shifter bushings
8.) Solid motor mounts, motor mount inserts or filled stock mounts
9.) Drop in K&N air filters and cold air intakes

1.) Spark plugs wires are the 2nd leading cause of spark blow out behind spark plugs. Everyone has their own preference as to which are best to them. Personally, I prefer Magnecor KV85 wires but I've had success with Mopar Performance wires and MSD wires. Many people like Granatelli wires but I generally don't recommend solid core wires on these cars due to the interference they can generate. (NOTE: Always use dielectric grease on both ends of the plugs wires. This compound seals electrical connections to repel water and helps prevent the spark from arcing to the valve cover.)

2.) The ignition coil is the 3rd leading cause of spark blow out. If you've already changed the plugs and wires and still have an ignition issue this is the next thing to look at. (*NOTE: Many people incorrectly refer to a condition called 'fuel cut' when they're actually describing ignition problems. Presumably they learned about this from other platforms. These cars DO NOT have any type of fuel cut, ignition cut or boost cut. The PCM will allow you to run as much boost as you choose to but if you feel it hitting a wall and cutting out at a certain boost level, chances are it's a problem with the plugs, wires or coil. More rare, but possible is an issue with the fuel pump, clogged injectors or the fuel pressure regulator\filter). The stock dodge OEM coil has proven itself to be the best performing coil available for these cars though many people have had success with Granatelli coils. I DO NOT recommend using an MSD coil in these cars, they have a very high failure rate and don't cope with the heat generated by the turbo very well.

3.) In the SRT-4 the fuel filter is integrated into the fuel pressure regulator located on the exterior of the fuel canister (which mounts inside the fuel tank). The regulator maintains 58psi (+/-5psi) of fuel pressure to the fuel rail at all times (even when the car is off). Over time deposits will become trapped in the fuel filter (which is a non-serviceable item) so it needs to be replaced periodically. I recommend every 60K miles. (NOTE: Stage 3 cars do not use the stock fuel pressure reg\filter, it's a special unit specific to S3 fuel canisters.) (NOTE2: Those that have decided on a goal greater than 425whp can skip this step, you'll likely be running a return line with an in-line, aftermarket fuel filter.) You don't have the drop the fuel tank to access it, the procedure to change it can be found in the factory service manual located here: SRT-4\Neon Factory Service Manuals

4.) The PCV line from the passenger valve cover to the throttle body serves two functions. For purposes of this document we'll just cover the fact that oil vapor is pulled through this line from the valve cover to be burned in the engine as part of the emissions control system. (NOTE: Altering your PCV line may cause you to fail visual inspection in some states like California.) The purpose of adding a catch can is to simply catch and trap this oil for later disposal with each oil change. Oil has a very low octane rating, when it's pulled into the engine to be burned it can cause knock (pre-detonation) which can potentially damage an engine. There are many different kinds of catch cans on the market to choose from. I generally prefer products that are designed for function over form as sight glasses, drain holes and the like are potential leak points. I run and recommend BWoody Performance products, they're a very simple design and can be placed just about anywhere in the engine bay. Diagrams showing how to hook one up are located here: Vacuum Line Setups

5.) The stock PCV valve, even new, will always leak a little bit of boost pressure which can rob you of some power. By installing a one-way check valve between the throttle body and oil catch can you can prevent all boost pressure from escaping the throttle body and possibly pressurizing your valve cover (very messy). It's important to choose a check valve that's within spec; 3/8's inch with 0.25psi cracking pressure and remember to have the arrow facing towards the throttle body so engine vacuum can pull oil into the catch can properly while blocking boost pressure from escaping. I recommend products from Boomba Racing and BWoody Performance. Diagrams showing where to place it are located here: Vacuum Line Setups

6.) The factory lower control arm bushings are made of rubber with flex slots built into them. Over time they deform and tear which causes your front tires to toe-out ( \ / ) under acceleration causing 'wheel hop'. Wheel hop causes a lack of traction, inability to launch straight and can snap axles. To correct this problem and eliminate wheel hop swap the stock parts for solid LCA bushings from Prothane or Energy Suspension so the tires remain straight (| |). Uncommon's complete guide to changing them can be found here:

7.) The stock bushings on the shifter side and transmission side are made of soft rubber with holes drilled around the perimeter that allow flex. To remove the slack and give you a more 'connected' feel to the transmission I recommend replacing all 4 with Booger shifter bushings. They also make gear changes more precise which will make it easier to get in and out of gears without missing shifts. Many of our supporting vendors carry these and they're very easy to change.

8.) The stock motor mounts are metal brackets containing rubber inserts which have holes in them designed to dampen engine vibration from transferring to the frame of the car. While this does improve ride comfort they have the unfortunate side effect of allowing the engine to move around and flex in the engine bay. When it moves during shifts it may relocate the transmission for a moment making it hard to get into the next gear and it can cause the axles to snap under acceleration. To correct this problem you can remove the stock mounts and fill them with Urethane. It's inexpensive and very effective. Some vendors sell hard plastic inserts that get placed into the holes of the upper and lower motor mounts to fill the voids thus preventing flex, these will still dampen some engine vibrations. My preferred method is replacing the upper and lower engine mounts and transmission mount with solid mounts available from a number of vendors. These mounts will increase the vibrations in the passenger cabin but they make you feel much more connected to the engine and keep the engine perfectly square in the engine bay. I recommend kits from AGP Turbo and BWoody Performance.

9.) The stock SRT-4 air box is VERY well designed. There is absolutely no performance difference between using a drop-in K&N air filter and an aftermarket cold air intake so on a budget the drop in filter is the way to go. Many people choose to install aftermarket cold air intakes (myself included) because they look much nicer in the engine bay and clear up a lot of space for mounting other mods like oil catch cans. They all function the same (it's just a metal tube) so I really have no preference but I urge you to choose one that has nipples\ports for the factory valve cover to intake line, intake air temp sensor and emissions line from the vacuum ejector. I do not recommend older style K&N CAIs, the elbow by the turbo is thin rubber and tends to collapse under boost starving the engine of air which will make it bog down.

Premium Member
14,274 Posts
Discussion Starter #4 (Edited)
Stock turbo performance mods, part 1:

The following is the first set of mods for those wishing to add power to a basically stock car (stock - 275WHP) or those wishing to progress towards maxing out the stock turbo (300+ WHP).

1.) Wideband O2 gauge
2.) Handheld flash programmer
3.) Performance exhaust
4.) Direct fit, front mounted intercooler

1.) A wideband O2 gauge is a monitoring device that will show you the exact ratio of fuel to oxygen. Maintaining the correct ratios are critical in a forced induction engine to both make good power and prevent serious engine or turbo damage. The SRT-4 is equipped with a pair of narrowband sensors, one in the O2 housing (upstream sensor) and one in the catalytic converter (downstream sensor). These narrowband sensors are only capable of detecting if the 'mix' is richer or leaner than ~14.7AFR (Air\Fuel Ratio). Richer means more gasoline is present while leaner means more oxygen is present. Richer or leaner isn't specific to one single point, it's more an indication of direction towards 10 or towards 20 you're going (the range of 10:1 - 20:1 is typically what a wideband can sense). The narrowband sensors aren't capable of telling if you're at 10 or 12 or 13, they just know that it's richer than 14.7AFR. While the car is at idle or cruising at partial throttle the PCM (powertrain control module) in the car makes changes to the mix, on it's own, based on input from the upstream O2 sensor to try and maintain the ratio at 14.7 (the downstream sensor is only used to measure the efficiency of the catalytic converter). This is known as the 'stoich point', or ideal air:fuel ratio for an internal combustion engine. When the O2 sensor sends a signal that the mix is richer than 14.7AFR the PCM reduces fuel injector pulsewidth (how much fuel is being sprayed) until the O2 sensor sends another signal that the mix is leaner than 14.7AFR where it increases fuel injector pulsewidth. It see-saws back and forth like this constantly. When you go into boost and begin forcing more oxygen into the engine the PCM stops monitoring the O2 sensor and runs a pre-programmed amount of fuel which is calculates based on air temp, PSI, RPM and vehicle speed. Most Mopar PCM calibrations (stock, Stage 1, Stage 2, etc) run rich from the factory for safety reasons. They typically run an AFR of 10-11AFR. The reason for this is because gasoline has a cooling effect on the engine which is needed to prevent the melting of internal components and the turbo by super heated exhaust gasses. This is where the wideband O2 gauge comes into play. Since the car only has narrow band sensors it's up to you to monitor the ratio to make sure it's not too lean and causing damage or knock (pre-detonation of the mix before the spark plug fires). To make good power the ratio should be richer than 11.5AFR for 91octane, 11.8AFR for 93octane and 12AFR for 100octane race fuel. Other types of fuels and octane ratings of gasoline will make good power at different ratios by that's beyond the scope of this document. A wideband gauge can also be used as a diagnostic device to ensure that your fuel pump, fuel filter, fuel pressure reg and injectors are working properly since the PCM has no built in ability to do this for you. Lastly, when you go into deceleration the PCM has a function called fuel cut decel. This is designed to shut off the fuel injectors to save gas. Widebands will typically show this as 20+AFR or ---. To summarize, the normal numbers for idle and cruising should be 14.4-15.1AFR, wide open throttle should be 10-12 (depending on fuel used) and deceleration should be 20 or ---. When you're looking at the gauge these are the numbers you want to see, if you don't something is going wrong. As for recommendations, your best bet is to buy a wideband gauge that is capable of datalogging (the data can be captured to be analyzed later). I suggest products from Innovate Motorsports like this: Innovate MTX-L Wideband Gauge though AEM wideband gauges like this: AEM UEGO Wideband Gauge are very popular. I run an AEM UEGO myself but it doesn't have a built in ability to datalog so I use an Innovate SSI-4 to capture the signals from the AEM UEGO which adds to the total cost of ownership and increases the complexity of the install. If the MTX-L was out when I was shopping for a wideband that's what I would have gotten. (NOTE: for a wideband to read properly the sensor needs to be placed BEFORE the catalytic converter. Here's an install guide that's specific to the AEM UEGO but the same locations for power\ground and placement of the sensor are the same for all widebands: How-To: Install AEM UEGO Wideband)

2. Long ago before we had control over the PCM and the ability to change just about every setting in it we were forced to use devices like aftermarket WGAs (waste gate actuators), manual boost controllers and electronic boost controllers to set and control our boost levels and devices like SAFCs (stand-alone fuel computers) and Map Clamps to set and control our fuel trims. Those days are gone and all of those parts have become obsolete on this platform (i.e. DON'T WASTE YOUR MONEY ON THEM!!!). Today we use handheld flash programmers to flash a modified 'tune' on to our PCMs to make the PCM do whatever we want like increasing boost levels, changing when the cooling fans turn on\off, changing the redline, changing fuel settings to tune our desired AFR and changing ignition timing settings. By far the most popular of these devices are made by Diablosport. As of now you have three choices the Diablosport Predator (DSP), Diablosport Trinity (DST) and the new Diablosport InTune (DSI). All of these devices work the same way and use the same tunes but the DST has a full color screen and can be permanently mounted in the car to display additional gauges that the car didn't come with from the factory like intake air temp, knock\retard, very accurate PSI readings and so on. The DST also has the ability to datalog external devices which makes it ideal to hook up things like oil pressure sensors, wideband sensors and so on. Personally I run a DSP and that's usually what most people choose to do because the cost is more than half that of the DST. Either of these units come pre-loaded with a custom tune called the 93tune (it's poorly named because it can be used on 91octane fuel too). I know I wasn't going to quote you numbers but on the average most people will see a gain of 25hp and 40ft/lbs of torque just buy installing the tune. It's one of the greatest bang for the buck mods available for the SRT-4. Either device also has the abilty to datalog every parameter of the PCM which you can then use for diagnostic and tuning purposes later as well as show and clear CELs (check engine lights) with the DST having more storage space to save much larger logs. I could seriously go on for a hundred pages about how to use these devices and what they can do but that's beyond the scope of this document. A weath of information can be found here: SRTForums Dsport Workgroup and information on the DSP\DST can be found here: Diablosport Predator and here: Diablosport Trinity

3. An engine is little more than a big air pump. Air goes in, air goes out. With the addition of a drop-in air filter or aftermarket intake you've increase the engines ability to get air in and now it's time to increase it's ability to get air out. The more air you can get through it and the faster you can do it the more power you can make. Remember that the best exhaust on a turbocharged car is no exhaust, unlike a naturally aspirated engine the turbo generates it's own backpressure. You have so many choices when it comes to exhaust that it's just impossible to cover them all so I'll just explain the three main strategies. The first is the 3" TBE (turbo back exhaust) system. This is a full system available from many of or vendors that replaces everything from the O2 housing to the tips with 3" pipe. These systems flow very well and, in most cases, will alter the tone of the exhaust significantly. This is your best option to keep noise levels down and maintain a stock appearance. Next is the 3" SEE (side-exit exhaust). These systems typically replace the downpipe from the O2 housing then add a specially bent section with custom hangers to have the exhaust tip protrude out just before the rear wheel on the driver's side. These types of systems flow a little better than 3" TBEs but they're typically louder and produce more drone at highway speeds. Last is the 3" cutout. This is basically a replacement downpipe that can be hooked up to the stock rear section or a full 3" rear section that includes a Y which can be opened up to dump the exhaust directly to the pavement under the driver. These types of systems are VERY loud but flow better than anything previously listed because the exhaust gasses have a very short path from the engine to the atmosphere. Most are available with either a manual or electric opener so you can run the car with the exhaust open at the track or on the dyno then close it for normal driving which diverts the exhaust flow out to the rear of the car. For 3" TBEs many people prefer systems from MPx or Thermal R&D. For 3" cutouts the hands down winner is Needswings. The choice of running a catalytic converter is up to you but keep in mind that even high-flow ones are a restriction and you probably won't pass visual inspection if you live in a state that cares about such things. If you have a stock PCM and go catless you'll likely throw no-cat CELs, this is a very easy fix by doing this mod: How-To: Non-Fouler Mod. Personally, I run a 3" Needswings catless cutout with a McCord power plate electric opener and the non-fouler mod hooked up to the stock rear section. When I have to go in for state inspection it's only 4 bolts and a clamp to put my stock downpipe /w cat back in. Remember to use a new gasket on the O2 housing to downpipe connection to ensure you have no leaks, these are available from the dealer for about $6/ea.

4. The last modification for this section is an intercooler upgrade. When the turbo compresses the charge heat is generated as an undesirable side effect. To cool the charge back down the SRT-4 comes equipped with an air-to-air intercooler that looks like a radiator. As the car is in motion (or being blown on by a fan at the dyno), outside air passes through the intercooler and takes with it some of the heat of the charge inside of it. The factory unit is extremely well designed and good to at least 350hp however due to it's small size it develops 'heat soak' after a couple of pulls. Heat soak is a condition where the intercooler is simply too hot for the outside air rushing past it to have much of cooling effect on the charge. To correct this I recommend upgradeing to a thicker 'direct fit' unit such as the AGP Direct Fit Intercooler. These units have cast end tanks like the stock unit which doesn't generate turbulance allowing the charge to flow freely through it. They have a thicker core which combats heatsoak, don't require any cutting or removal of your front crash bar (not safe), cool the charge better than the stock unit (remember for every 10F you lower the charge temp you get ~1% hp) and will support around 400hp. I DO NOT recommend BFMIC (big front mount intercoolers) on stock, Stage 3 or entry level big turbos. Most don't flow very well so you get drops in pressure accross them, take much longer to pressurize so throttle response gets slow and the motion of the car combined with their weight has a tendency to either tear them open or damage the mounting points on the car.

Stock turbo performance mods, part 2:

This section is for those that wish to max out the stock turbo to the 300+ WHP range.
(We're not going to discuss race gas here as an option because it's far too expensive to use every day. If you have that kind of money, you're not going to be driving an SRT-4.)

1a. Alternative fuel - E85
1b. Supplemental fuel - Methanol injection
1c. Supplement to fuel - Nitrous Oxide (N2O)

2. 3BAR MAP and TIP sensors

3. Fuel pump upgrade

4. Custom tunes

1a. E85 is an abbreviation for 'flex fuel' meaning a mixture of up to 85% denatured fuel ethanol and gasoline or other hydrocarbon by volume. If you have E85 in your area this is a better choice than Methanol injection. To see if you have a station in your area, check here: E85 Filling Stations. E85 produces 10-15% more power in an internal combustion engine than gasoline does. This is because it has a higher octane rating [94-96 (R+M)/2] and burns cooler than gasoline which allows you to run higher boost levels, leaner AFR (12-12.5AFR) and more timing advnace. The only drawback is that your range on a full tank of gas will decrease by ~30% because you have to burn more of it than gasoline. There are three required mods to run E85 on a stock turbo and they are fuel injectors that are at least 30% larger, an upgraded fuel pump and a custom tune. For the fuel pump choose the very popular Walbro 255lph (liters per hour) fuel pump, many of our vendors carry this pump with an install kit for around $100. It's an upgrade to your stock pump which is a Walbro 170lph. For the injectors, 750cc/min or larger injectors from one of our many supporting vendors will do. Lastly you'll need a custom tune. There aren't many people doing them right now but no one does a better tune on this platform than Tru Dyno Sports. Send a private message to "Turbo666" of TDS for information on email tunes for E85. (NOTE: You CAN NOT run E85 without a custom tune.)

1b. Water\meth injection sprays a fine mist of fluid into your cold-side pipe or intake manifold to increase the octane rating of gasoline and provides a cooling effect that significantly lowers charge temps and exhaust gas temps. If you don't have E85 in your area this is a great option that will produce almost as much power. The higher octane and cooling effect allows you to run higher boost levels, leaner AFR (12-12.5AFR) and more timing advance. You can choose to run any concentration of water to meth but the most common is 50/50 mixed by weight. The more meth in the mix the higher the octane, the more water in the mix the better the cooling effect. On a stock turbo I highly recommend placing the nozzle in the cold side pipe before the IAT (intake air temp) sensor which will prompt the PCM to advance timing in response to senseing the colder air temps. A good video can be found here: Benefits of water methanol injection for gas engines a great write up can be found here: Methanol injection explained. I run and recommend meth kits from Coolingmist as for meth itself you can source it from local chemical supply houses and many local drag strips sell M1 meth. You'd then just have to mix it with distilled water (by weight) to get your desired concentration.

1c. Nitrous Oxide is easily the greatest bang for the buck mod available for these cars. With the stock engine being built so well it's safe to spray a 50-75shot all day long (your clutch may not last that long though without being upgraded). Unlike E85 and meth, N2O is a direct power adder. It increases the available oxygen in the mix to generate more power. More fuel will be required so upgrading the fuel pump to a Walbro 255 is highly recommended. There's a wealth of information available on kits, setups, nozzle sizes and tuning here: SRTForums Nitrous/Cryo Injection Discussion and kits can be purchased from many of our vendors. N2O can be used with gasoline, gasoline+meth or E85.

2. (NOTE: Skip this section if you have a Stage 2 kit already installed on the car, it comes with 3BAR sensors.) The stock SRT-4 MAP (manifold absolute pressure) and TIP (throttle inlet pressure) sensors are 2.25BAR. They max out their readings around 18.5psi. While it's possible to run higher boost and tune without 3BAR sensors it's not as easy because you'll be running the same fuel and timing tables at 18.5psi as you do at 22 or 24psi. This will handicap you to some degree on how much power you can put down. 3BAR sensors are capable of reading up to around 29psi which is more than enough for any stock turbo and most big turbos. The 3BAR sensors made for the SRT-4 have been discontinued but the stock Caliber sensors available at any Dodge dealer for ~$25/ea work just fine after a minute or two of modding the tips with a nail file. Here's Duster360's great write up on how to do it: How-To: Mod Caliber 3BAR sensors. If you aren't that handy you can get an adaptor from MPx here: 3BAR sensor with adaptor (you'll still need another sensor from the dealer to use as TIP). You will need a simple rescale tune in order to run these sensors or serious engine damage may result. PM "Turbo666" of Tru Dyno Sports for more information. (NOTE: Again, DO NOT install these sensors if you don't have a rescale tune.)

3. The stock fuel pump works very well (it's a Walbro 170LPH) however, as you increase the hp of your car you're going to start having problems maintaining proper fuel pressure over ~300whp. For this I recommend the Walbro 255LPH fuel pump. It's a direct fit unit that will support upwards of 400whp with easy. Here's a complete kit for under $100 that includes the pump, seals, canister tool, ect: Walbro 255 Kit Here's the How-To for those that want to save the labor and change it themselves (pretty easy to do, scroll through the whole thread for all the info): How-To Walbro fuel pump install

4. Custom tunes are exactly what the name implies, they're made just for your car and your car alone. There's only so much that you can do by making changes to the DSP/T handheld, AFR can only be adjusted in 1K increments for example where a custom tune can adjust in much smaller increments to get you a dead flat AFR while you're in boost. Custom tunes can also be tailor made to account for specific mods that you have to get the most power possible out of them. May local dyno shops have the ChipMaster Revolution software required to make custom tunes but, for the most part, they use the default 93tune templates and just tweak them. To really make some power you need a tune that's truly custom from a tuner that knows the intricacies of these cars. For that reason I only recommend and run custom tunes from Tru Dyno Sports. PM "Turbo666" to discuss your goals and options.

Stock turbo performance mods, part 3:

The following is a list of optional mods that are your choice to do or not. Most of these mods aren't needed by everyone or only for people trying to squeeze every last HP out of the car.

1. Fuel pump rewire mod
2. Ported intake and exhaust manifolds
3. 3" O2 housing
4. Larger throttle body
5. Forward Motion WGA\Mopar Stage 2 WGA

1. I'll write this up later but in a nutshell you can get a little more fuel out of the stock fuel system at higher RPMs by doing the mod.

2. An engine is little more than a big air pump. The faster you can get air in and out the more power you can make. The intake manifold won't help much for peak WHP but there will be some small gains through most of the powerband. The exhaust manifold will help reduce EGT slightly and allow you to take full advantage of your 3" exhaust system.

3. The stock O2 housing isn't very restrictive to begin with for a stock turbo but upgrading to a ported exhaust manifold and 3" exhaust will yield some small gains with a 3" O2 housing.

4. The stock throttle body is already a little oversized for a stock turbo so you won't see any measurable increases in peak WHP but there are some small gains to be had through most of the powerband.

5. The stock WGA works just fine on PCM control for just about everyone casually modding a stock turbo car. For those that want a little more spring pressure to keep the wastegate tightly closed or those that want to rebuilt boost a fraction of a second quicker than a stock WGA the Forward Motion or Mopar Stage 2 WGA is for you.
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