The basic Paxton kit works very well with the stock engine if tuned properly. We have done over 50 of these "stock" installs with very few issues. The key is in the tuning. Calibrating the production PCM and lowering intake air temperatures can improve power without sacrificing reliability.
At higher boost levels the production engine is just not suited. You can get away with this on some of the earlier "forged motors" as they can be detonated without immediate piston failure. The piston used in the SRT's have the ring high up on the piston for emissions and are cast. A poor tune or bad gas will break the ring lands and make a mess of your motor if boost levels are increased. With better pistons you can run more boost, but over time the production rods and bearings suffer under the load. More so if you track the car. With a production Paxton kit and some minor changes, you can safely track the car for 30 minute sessions.
The 650rwhp range seems to work well on the production engine. If you want the power to be more consistent and linear, we add colder plugs, a custom controller calibration, 170 thermostat, billet crankcase valve, bigger heat exchanger and recirculation pump.
When you add this much power you need to upgrade other parts of the car. This will make it safer and more reliable. At what we call level 1 (stock Paxton kit) we suggest adding our weld in roll bar. This stiffens the chassis and makes the car safer in a roll-over. Next we suggest a torque sensing gear driven posi unit in the rear end. These cars want to go sideways when on power; an upgraded differential will allow the car to go straight. The driveline wants to twist with added power and can be hard to shift; an improved shifter and higher durometer transmission mount are suggested at this power level.
For those who want to go to the next power level (about 800whp, with reliability) a SC specific engine, some fuel system changes and additional chassis and suspension upgrades are needed.
At this point the engine needs to come out. We rebuild the engine complete with a nitrated crankshaft, I beam rods, blower pistons, coated bearings, blueprinted oil pump, blower cam, adjustable timing gear and low bleed lifters. The block is studded and the heads are given a good valve job, better spring and retainers. The balancer and pulleys are changed. The fuel injectors are changed and the fuel pump gets a booster. A new clutch and flywheel is added. We upgrade the CV cages on the half shafts and change the shock absorbers (they tend to be too over sprung and under dampened for this power level.) Tires must be changed to a softer compound to be safe.
The next level (level 3) is more complicated, less reliable and will not pass emissions (900 plus rwhp). Billet main caps, new head castings and a complete new fuel system (tank to engine is required). A complete stand alone engine management system is needed, custom exhaust (headers are needed) and traction control are discussed. The transmission should be upgraded as well. These builds are very vehicle specific and have many variables. They run awesome, but are more prone to failure at this power level (price of admission).
We try to use a complete vehicle approach when it comes to upgrades. Customer expectations and vehicle use play a major role in the final build.
This is just my opinion and experience, others may have different suggestions.
Ofcourse I know it depends on lots of things, hiw I drive the car and so on... But has anyone any good info I am glad to hear it!
is my guess unless you use less boot,or lower compression, or significantly upgraded internals (rods, crank, etc.)
