2002 Chrysler Sebring Convertible GTC
Performance Projects

As you know, I am interested in performance modifications. Since there are practically no companies out there (including Ma Mopar) that will support 2.7L V-6 performance, I've decided to go ahead with my own projects.

Here is a list of projects I'm working on:

• Valve Timing Sprocket Modification
• Bored-Out Throttle Body
• 6061-T6 Underdrive Crank Pulley
• Better Spark Plugs
• Walbro 255 L/hr Fuel Pump Installation
• 68HC11 (68HC12?) Based Fuel Controller
• Auxiliary Fuel Injector Bank
• 68HC11 (68HC12?) Based Ignition Timing Controller
• Garrett VNT-25/T-28 Hybrid Turbocharger
• A-Pillar Gauge Pod
• Indiglo Instrument Cluster Gauges
• True Head-Up Display

Valve Timing Sprocket Modification

The Chrysler Crossfire concept car had a 2.7L V-6 engine that developed 225 HP. There was also a one-off Chrysler Sebring Convertible JX Pace Car that had a 2.7L V-6, also developing 225 HP. While the Crossfire concept car had a radically different intake manifold, the Pace Car intake manifold had only minor changes from the production 2.7L engine found in my car. The stock 2.7L is rated at 200 HP at 5800 RPM.

I strongly suspect that the increase in power is due to differences in valve timing between the stock 2.7L engine and the engines mentioned in the above paragraph. I think this because the 2002 Factory Service Manual for my car lists intake/exhaust valve overlap to be a whopping 2 degrees. While fine for emissions, low-end torque, and smooth idling, this overlap does little for performance. The 2.4L I-4 engine has (I think) about 19 degrees of overlap.

Overlap is important for power. Think of the intake manifold for a second. At low RPMs, the airflow in that manifold has a fairly low average speed. The airflow will not have a decent inertia, and will not scavenge out the exhaust gases formed as a product of combustion. At higher speeds, airflow speeds increase to match the increased demand for air by the engine. This means that the air develops more inertia, and is more likely to push out exhaust gases.

With a low overlap, this scavenging effect doesn't do a whole lot for high-end power. Low-end torque is enhanced by low overlap due to the fact that exhaust gases will not backflow into the intake manifold. A large overlap, on the other hand, will drop low-end torque. A large overlap will also be more beneficial to scavenging effects mentioned above, and will mean that the engine will be capable of breathing better at higher RPMs.

There is a danger that too much overlap may cause valves to violently kiss piston crowns, but at the mild amount of overlap I propose (about 17 degrees), this should not be a problem. I think that a slight loss in low-end torque on my car is worth an extra 25 HP of top-end, with improvements possibly being seen at mid-RPMs as well.

6061-T6 Underdrive Pulley

I propose to have a crankshaft pulley made out of lightweight 6061-T6 aluminum alloy. This will cause the rotating mass of the pulley to become lighter, which will cause the engine to not work as hard to spin up this pulley. Doing some spreadsheet "what-if" calculations using knowledge of physics as it relates to rotating masses, I estimate that I might be able to free up as much as 10 HP, from reducing the weight of the pulley from 7.5 lbf to 1.9 lbf.

In addition, I propose to size the pulley such that it underdrives the power steering pump by about 24%. I do not intend to undersize the alternator/air conditioning pulley for the simple matter that both the alternator and the A/C are not constant loads, but are regulated by the PCM to provide a given output regardless of engine loading. The power steering pump, on the other hand, has no such regulation. In addition, the loads represented by each of these accessories is comparatively small. I estimate that the power steering pump uses about 5 HP at 6000 RPM for pumping. Undersizing the crankshaft power steering pulley as described will probably free up about 2 HP. Most of that will be due to the actual reduction in power transfer to the power steering pump, and the rest (a small fraction) would be due to the smaller moment of inertia for a smaller pulley wheel.

Update - 12 May 2003 - There appear to be no machines shops in the Groton, CT area that are capable of machining a couple of aluminum wheels with grooves in them. This is particularly sad, since Groton is home to a major US submarine base. One would think that shipfitting requirements would produce the equipment (like a CNC lathe) to make a couple of lousy wheel pulleys, but one would be wrong.

Better Spark Plugs

I think that the Champion plugs I currently have are junk. This is due to the bad experiences I've had with Champion plugs on a 1981 Dodge Aries, a 1987 Chrysler LeBaron, a 1993 Chrysler LeBaron, a 1997 Dodge Stratus, and a 2000 Chrysler Sebring Convertible.

With that in mind, I'm trying to find better plugs. Results have not been promising to date. So far, I have tested the AutoLite APP5364 Double Platinum spark plug, the AutoLite AP5364 Single Platinum spark plug, and the Denso Iridium ITV20 spark plug. All three plugs are shorter than the stock Champion spark plug. Compared to the Champion plug, the metal hex center rides lower on the three tested plugs. This required machining a spark plug socket to be narrower at the socket end, from 21 mm to 19 mm, in order to properly tighten the three tested spark plugs in the engine. Otherwise, as the spark plug threads into the cylinder head, the hex pattern would disengage the socket, and the socket would just uselessly rub against the cylinder head without tightening the spark plug. You can see the modified spark plug socket in the picture below.

Spark Plug Comparison (Left to Right) of Stock Champion, Autolite AP5364, Autolite APP5364, and Denso Iridium ITV20

With all three plugs, the testing procedures began the same. As each set of plugs were installed, the battery was disconnected to allow the PCM to reset. A test run of at least 10 miles was then attempted. Pending successful (no detonation or loss of power) testing here, a dynomometer test would have then been performed.

With the APP5364's installed, the car had moderate misfire on all cylinders, both at idle and under load. Due to this misfire, I only ran the APP5364's for about 20 miles. Pulling and inspecting these plugs revealed that not one of these plugs developed a light tan coating on their insulator. This is indicative of a plug that was running slightly hotter than normal. The misfire suggests that the plugs expected a richer mixture than was provided, even after resetting the PCM by disconnecting the battery.

The AP5364's produced the same results as the APP5364's. Again, after only 20 miles, these plugs were removed.

The engine ran much better with the ITV20s, compared to the APP5364's. However, there was a slight drop in power as compared to the stock Champions. I also noticed detonation at throttle tip-in with the clutch disengaged, and a noticable loss in response at tip-in with the clutch engaged. I suspected a plug that was also too hot for the engine. After pulling these plugs out after 170 miles of operation, only one (cylinder #1) showed the light tan color indicative of a spark plug of correct heat range. The other plugs were bone-white. The plugs for #4 and #6 cylinders also had a couple of black flecks on their insulators. The bone-white insulator and the flecks are indicative of plugs that are one heat range too hot.

As of this time, there appears to be no viable replacement to the stock Champions. This is bad, since if there is no equivalent plug that is one actual heat range colder, trying to run this engine with any meaningful (5 or more psig) boost, or anything above a 50 shot of nitrous oxide, is flirting with engine disaster.

Walbro 255 L/hr Fuel Pump

I think this pump should fit. It fits the Neons and the 1G Stratus platforms with minimum effort, and there's no reason why Chrysler would choose to radically change the fuel pump/sender assembly from 2000 to 2002. These assemblies look very similar, from looking at the 2000 Sebring Convertible Factory Service Manual and the 2002 Sebring Convertible Factory Service Manual.

If it works, this pump will give me more fuel capacity over stock.

Update - 12 May 2003 While talking with another member over at 2GSS.org about a possible nitrous oxide kit for the 2.7L engine, the idea of using a fuel pump out of a 2nd generation 3.5L Dodge Intrepid was tossed around. That car's engine is rated for about 250 HP, and with mild boost or a 50 shot of nitrous, ought to be capable of 300 HP with no fuel system modifications. If this is so, and the 3.5L Intrepid fuel pump assembly will fit my gas tank, then this would be a better option. The Intrepid fuel pump itself ought to be able to support fuel requirements for 300 HP. The Intrepid integral fuel pressure regulator will be also able to handle the increased fuel output needed to support 300 HP.

Update - 24 January 2004 I now have a spare fuel pump assembly for a second generation Dodge Stratus. I have ordered a Walbro high-pressure 255 LPH fuel pump for a Dodge Neon, as well as consumables (fuel pump regulator, sock filter, sending unit, and o-ring sealer) for the Dodge fuel pump assembly. With luck, I should have the spare fuel pump assembly rebuilt with the Walbro in place. It will then be installed in my car. Regardless of how much fuel the stock pump assembly can actually put out at the specified stock fuel pressure of 58 psig, the Walbro pump should be more than adequate for boosting the 2.7L engine to as much as 7 psig.

Disassembly of JR Dodge Stratus Sedan Fuel Pump Module

Update - 03 February 2004 The pump does fit into the fuel pump assembly. It's the same shape as the stock pump. Based on this, and on examination of the stock pump, I conclude that the stock pump is a Walbro 190 LPH pump. This is the lowest capacity pump that Walbro manufactures. Based on this, and aided by certain calculations, I conclude that the stock pump can flow enough fuel to boost the 2.7L engine to 24 psig. The weak area for supporting boost is obviously the fuel injectors.

Comparison of Walbro 255 LPH (Left) and Stock (Right) Fuel Pumps

68HC11 (68HC12?) Based Fuel Controller

This, along with the auxiliary fuel injector bank described below, will enable my engine to support up to 10 lbf of boost.

I haven't yet decided whether or not to use a 68HC11 or a newer 68HC12 as the brains. From reading about the 68HC12 capabilities, it does sound very impressive, but I already have about 8 68HC11's laying around.

Update - 24 January 2004 This project has placed on hold for now, due to recent research into alternate ways of adding more fuel under boost.

Auxiliary Fuel Injector Bank

This will allow more fuel to be delivered to the engine, thus allowing up to 10 lbf of boost.

Update - 24 January 2004 This project has been terminated, due to recent research into alternate ways of adding more fuel under boost.

68HC11 (68HC12?) Based Ignition Timing Controller

This will provide a set amount of timing retard for boost conditions. My preliminary idea will have the controller retard the crankshaft and camshaft position sensor signals by a set number of degrees while under boost. This should fool the PCM into not seeing the ignition controller, while providing the necessary boost ignition retard.

I haven't yet decided whether or not to use a 68HC11 or a newer 68HC12 as the brains. From reading about the 68HC12 capabilities, it does sound very impressive, but I already have about 8 68HC11's laying around.

Update - 24 January 2004 This project has been placed on hold for now. I think that running at 93 octane with a boost of 7 psig ought to prevent detonation from occurring. This, along with finding an engine thermostat that opens at 180 F, ought to reduce the chance of detonation or pre-ignition.

Garrett VNT-25/T-28 Hybrid Turbocharger

This will provide up to 10 lbf of boost. The T-28 compressor wheel is a bit more efficient than the older T-25 wheel that it replaces. I'm using a turbocharger with variable nozzle turbine technology to substantially reduce turbo lag. Also, it's a pretty neat concept.

Intake View of Garrett T-28/VNT-25 Hybrid Turbocharger

Update - 08 May 2003 This project is currently on hold. Currently, I have found no spark plugs that are at least one heat range colder than stock. Running with stock plugs and 10 psig of boost practically begs for preignition, and resultant engine damage. Therefore, the turbo project is on hold until further notice.

Update - 24 January 2004This project is back, in a way. I am torn between installing this turbocharger, and a recent development in supercharging technology of an Eaton M62 supercharger powered by three 24 volt electric motors rated at a total of 18 HP (In other words, an honest-to-goodness electric supercharger, as opposed to el-cheapo eBay bilge fans or that model airplane motor being marketed as the "eRam Electric Supercharger"). As both projects demand that the engine gets fed the proper amount of fuel, fuel delivery research is ongoing.

Side View of Garrett T-28/VNT-25 Hybrid Turbocharger

A-Pillar Gauge Pod

In order to properly support turbocharging, it is necessary to have certain gauges installed in order to monitor the engine. Specifically, a boost gauge is necessary to monitor the turbocharger's boost output, and an oil pressure gauge is necessary to ensure that the turbocharger receives adequate oil pressure to run properly.

I had this as a long-term project, but recent events concerning aluminum flakes inside the engine prompted me to install an oil pressure gauge. An Autometer electric gauge was selected, along with a universal gauge pod from Autozone. I discovered that the oil pressure switch is a 3/8 NPT thread (!), and was packaged right in between the rear exhaust manifold and the engine block. This latter caused me to run a 3/8 inch steel braided hose, and to relocate the oil pressure switch onto a tee at the end of that hose.

The oil pressure gauge now works, and is even wired up to the car's interior lighting circuit. Normal oil pressure, when cold, is about 65 psig at idle, and this will drop to about 7 psig when the engine is idling warm. Maximum oil pressure is about 65 psig.

Oil Pressure Gauge Installation Mounted on A-Pillar

Indiglo Instrument Cluster Gauges

I wanted indiglo instrument cluster gauges, since my old Limited had them, and I thought they were pretty cool. I went ahead and ordered a electroluminescent (EL) sheet from an electronics supplier, and set about the project.

I discovered that, in order for the gauge itself to light up properly with no dim spots, at least 1/2 of one side of the gauge face must receive power from the inverter that actually powers the EL backing. I have not yet installed the gauges into my car, because I am looking into a way to interface the inverter into the car's interior lighting circuit. This is somewhat harder than it sounds, since the interior lighting circuit is actually a pulse-width modulated 80 Hz square wave, with its duty cycle corresponding to the desired light intensity. The inverter, on the other hand, expects a constant DC voltage. Therefore, some sort of low pass filter is necessary to power the inverter from the interior lighting circuit.

Oil Pressure Gauge Installation Mounted on A-Pillar

True Head-Up Display

I wanted a head-up display, such as can be found in both fighter aircraft and in the newer high-end GM cars. To this end, I researched ways into reading the car's internal data network.

I found out that the car uses a standard SAE J1850 VPW network, which has a defined timing protocol and a defined electrical waveform. The standard itself is pretty easy to find at the SAE website. The car uses this network to pass messages between the PCM, BCM, CMTC, factory radio, and instrument cluster in a standard SAE J2178 data format. Again, this is pretty easy to find on the SAE website. ELM Electronics sells a little PIC-based SAE J1850 interface chip, that uses a 20 MHz crystal, and that acts as a bridge between the J1850 network and a standard serial interface. This is what I'm using.

I decided to use a Noritake-Itron 64x128 pixel vacuum fluorescent display (VFD) for the actual HUD display. This unit is kind of tricky to program, but I was able to get it to display some text after figuring out the VFD's quirks.

Homebrew Head-Up Display, with a "Hello, 2GSS!" message

I currently am looking for a decent 5 VDC power supply to power the VFD. A normal linear supply, such as would be made from a 7805 voltage regulator, is not sufficent to provide the approximate 1 A requirement for the VFD, without having to resort to a noisy forced air cooler. Other than that, the unit is almost ready for in-car testing.