Piston Slap: Bolt-on, practical Hemi power?

Jon writes:

I’m wondering how to get the most out of my stock 5.7L Hemi (in a 2007 Chrysler 300C), but without it being so expensive that it becomes impractical.

Sajeev answers:

Interesting question, mostly because impracticality is a relative term. I assume there are plenty of folks who’ll gladly tear into that Hemi for a cam swap, cylinder head work, etc., and consider it just a good use of a single weekend of work and a modest cut of one’s discretionary income. But I’m just gonna go way out on a limb and assume you’re looking for bolt-on upgrades for your 300C, limited to intake, exhaust, and ECU re-tuning.

While you won’t see much more than 30 horsepower on a chassis dyno when combining the tricks below, they will improve performance at full and part throttle. More to the point, they are mandatory before even considering future upgrades, so perhaps there’s more benefit than we immediately consider. So let’s get to it.

Intake: Contrary to popular belief, you don’t need an aftermarket intake/airbox assembly to get both performance and sound improvement. More to the point, aftermarket kits are expensive and accomplish the same thing you can do at home via removal of snorkels, resonators, and silencers. One is certainly cooler looking (if you like aftermarket parts), but neither will add much more than 3-5 horsepower. And many aftermarket intakes cannot isolate themselves from hot air in the engine bay, and sport material choices that cannot resist heat soak like factory parts do, which makes them truly inferior to the work you can do in your own garage.

So instead, open up the intake stream yourself via air silencer removal (here’s my tutorial from 2005) and consider installing a high flow, drop-in air filter (your call if they are worth the trouble). This ensures you get that magical 3-5-hp increase of an aftermarket system, with similar levels of increased induction noise for extra fun around town.

Exhaust: As far as bolt-on performance for this application goes, one look at the restrictions on the factory log manifold is all most folks need to take the plunge. Odds are the rest of the exhaust’s piping can handle the extra power, as the factory 2.5-inch exhaust is big enough to support 400+ horsepower. The factory muffler (that reduces noise when kicking into four-cylinder operation) might not be to your liking, but plenty of aftermarket parts can improve the sound. Unless your catalytic convertors are melted/clogged, they will not be a restriction.

Getting catalytic convertors to work with some header designs (i.e. the longer ones, called “long tube” headers) might be a pain, but odds are any competent exhaust shop can do it. Installation of the headers doesn’t look too hard (especially with a lift), and it will likely add a lot more low-end torque to the equation, even before adding the final piece below.

Tune: Some vehicles are seriously under-tuned from the factory, and many turbocharged vehicles can be electronically tweaked to make much more power. Neither applies here, as the general consensus on the internet for your 5.7-liter Hemi suggests you’ll get 10-20 horsepower with a performance tune, 20+ when including the above performance modifications. Not all tuning companies (or the tuners that tweak the software) are created equal, so do your homework and see which one is best for you.

I’d like to be optimistic and suggest that a removed factory intake silencer, drop-in high volume air filter, aftermarket headers/muffler, and a quality tune will get you 30+ horsepower at the wheels. (Wheel horsepower is the only place you can feasibly measure output, and it’s honestly the only place that matters.) While that might not look like much on paper, the performance at lower rpms will likely benefit from a similar increase in torque, while the revised engine tune will perk up the throttle and transmission’s behavior. To wit, this video shows an aftermarket tune giving 500 more rpms to play with … whether that’s a good thing remains to be seen.

While it may be difficult to justify—on a depreciated machine like the original Chrysler 300—the improvement for $1000–$2000 (depending on how lucky you get buying new/used parts), you can do these at any time, in any order.

To be honest, I would be content with just an aftermarket tune ($400-ish) and an air silencer delete (free). What say you, Hagerty Community?

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