If the Dodge SRT-4 needs anything, it's a limited-slip differential, not more power. For 2004, it's getting both. In addition to a factory-installed Quaife differential, the new SRT-4 is getting a ratings boost from 215 hp to 230. As anyone with a right foot already knows, the "215 hp" SRT-4 was already underrated, making 223 hp at the wheels on our Dynojet. So is the new power real, or just a ratings adjustment? That depends on the weather.
We dyno test with a decent fan and a monkey spraying water on the intercooler. This, we've found, is a reasonable simulation of the 80-mph breeze that should actually be blowing across the intercooler at the top of third gear. DaimlerChrysler tests with a relatively hot intercooler, so it gets less power. The SRT-4's engine management actually adjusts for hot weather by increasing boost until it's making the same power it would in cold weather, so there should still be no difference. Problem is, the 2003 model had injectors that weren't quite big enough to allow full compensation under DaimlerChrysler's test conditions.
For 2004, injector flow rate has been bumped up 10 percent, leaving the headroom for better altitude and temperature compensation. Because DaimlerChrysler measures injector flow differently than the aftermarket, getting a useful flow rating is difficult. In DC world, the new injectors are 577 cc/min. In our world, with lower fuel pressure (43 psi is the older standard; DC uses 58.) and different test fluid density, we think they may be considered 378cc/min. We'll bench test some when we get our project car.
With the new calibration, we've been told to expect about 5 hp more under our test conditions, and about 15 in more severe heat.
But power isn't enough to satisfy some of you. Since our first test of the car, we've received approximately 6,000 letters saying exactly the same thing: "Sure the SRT-4 is fast, but it's still a Neon. It'll break down before the end of the quarter mile, blah blah blah..." We really wanted to shoot back some knowledgeable defense of the poor Neon, but ignorance held our tongues. Sure, the 70,000-mile powertrain warranty suggests some level of engine strength, but we'd never actually seen inside one.
To close this glaring knowledge gap, we went to Michigan with a camera and a list of geeky questions about rod bolt diameters, valve angles and combustion dynamics.
What we found is a ridiculously strong-looking engine that should survive many a quarter mile. You can thank the PT Cruiser for the SRT-4's powerplant, as it was a desperate need for a horsepower-based PT sales boost that justified turbocharging the 2.4-liter engine and gave the development team the signal to go overboard.
With a short deadline on engine development, there was no time to prove the durability of low-cost, marginal-strength parts. Where typical engine development teams would spend time whittling away pennies finding the least expensive design that could meet durability targets, the turbo 2.4 team just threw in stronger parts and more expensive materials, cost be damned.
Along with its beefiness comes heft, however. The SRT-4 engine weighs 339 pounds (with the alternator, but without the A/C compressor, power steering pump, or any oil in the pan). That's enough words, look at the pictures. n
|Engine block |
|Block construction : ||Cast iron, closed deck, split crankcase|
|Bore x stroke :|| 87.5mm x 101.0mm|
|Displacement :|| 2,429cc |
|Compression ratio :|| 8.1:1 |
|Bore spacing :|| 96mm |
|Deck height :|| 238.14mm |
|Connecting rod design :|| Forged, cracked caps, threaded-in 9mm rod bolts|
|Connecting rod length :|| 151mm |
|Rod/stroke ratio :|| 1.50:1 |
|Crank design :|| Cast high-hardness steel|
|Main bearing diameter :|| 60mm |
|Rod bearing diameter :|| 50mm|
|Head construction :|| Cast aluminum |
|Combustion chamber design :|| 48-degree pent-roof with partial cloverleaf between intake valves|
|Valvetrain :|| Hydraulically adjusted rocker arm with roller cam followers|
|Intake valve size :|| 34.80mm|
|Exhaust valve size :|| 28.45mm|
|Intake valve angle :|| 24.46 degrees|
|Exhaust valve angle :|| 23.5 degrees|
The cast-iron block looks extremely stout, with a closed deck on top and a very strong spl
The crank is cast, but the use of higher-hardness steel and careful attention to detail ma
The connecting rods are forged in one solid piece, machined, and then broken in half. That
The rod bolts are the same 9mm in diameter as the naturally aspirated 2.4, but use a sligh
The extra heat of turbocharged combustion makes for some hot pistons. That heat is carried
Of course, those low oil flow situations will be rare, since the SRT-4 oil pump uses a hig
The balance shaft assembly hangs under the front three cylinders. While it could be remove
The structural cast-aluminum oil pan hides some interesting details. The gasket, for insta
The turbo pistons, cast by Mahle from a eutectic aluminum alloy, have a shorter pin height
The shorter piston never reaches the top of the bore; this is actually top dead center. Th
The combustion chamber is classic pent-roof, with the spark plug in the middle where it be
The valvetrain uses rocker arms, which increase valvetrain mass compared to a cam-on-bucke
Here's an important detail when you're trying to cool 223 hp. Water pumps are made up of s
Things start getting strange here. Tight packaging in the PT Cruiser forced some creative
Things get stranger. The turbine discharge is also part of the manifold/turbine housing ca
A few more interesting things about the turbo: Packaging constraints dictated a reverse-ro
OK, engine management geeks, that's a 32-tooth crank trigger wheel (34-2). The engine mana