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.
http://www.srtforums.com/forums/f75/how-rewire-fuel-pump-lower-gauge-wire-421929/
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.
