Pistons are one of those parts everybody installs but not everybody actually understands. Todd, Will, and Myer break down piston design from top to bottom, and if you have ever wondered why there are so many options or which one belongs in your build, this is the episode you need.
They start with piston bowl design and why it matters more than most guys think. Narrow bowl versus wide bowl, reentrant versus non-reentrant, and how each design affects the way fuel and air mix inside a diesel cylinder. Because diesels fire fuel directly into that bowl at the very end of the compression stroke, bowl geometry has a direct impact on combustion quality, smoke, and power output in a way gasoline engines never have to deal with. Swirl numbers get covered too, and why that circular mixing motion plays a bigger role in emissions and haze than it does in outright peak power.
The conversation moves through piston options platform by platform. Common rail, 24 valve, VP44, and 12 valve all get their own breakdown. The guys talk about why they almost always steer people toward a narrow bowl for over-the-road use, but also when a wide bowl makes sense, like sled pulling and nitrous-limited classes where you are chasing every last horsepower.
Cast versus forged is a big chunk of this episode and the guys do not sugarcoat it. Forged pistons are stronger and handle RPM abuse better, but the increased wall clearance required, the wear characteristics, and the oil ring differences make them a poor choice for anything that sees regular street miles. They even mention their factory 6.7 cast pistons surviving a truck that averages 2200 horsepower down the track, and what that says about how capable a properly built cast piston really is.
The 12 valve guys get their section too. Stock pistons, the early first gen wider bowl swap, and why the shop has largely moved away from recommending low compression pistons now that six seven blocks are the go-to platform for high-output Cummins builds.
Piston coatings and cylinder honing round out the episode. The guys cover their coating experiments on Myer's race truck, what coatings can and cannot protect against, and why proper piston wall clearance is still the thing that determines whether any of it survives.
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0:00 Intro and episode overview
1:00 Why piston bowl design matters in diesel combustion
3:30 Fuel injection timing and mixing action explained
5:45 Reentrant vs non-reentrant common rail pistons
8:30 Injection split explained and how bowl width affects it
10:30 Narrow bowl vs wide bowl for varying RPM vs constant RPM applications
11:30 Why they always recommend narrow bowl for street builds
12:00 Factory 6.7 cast pistons at 2200 horsepower
15:15 Every Cummins piston is 1000 hp capable
15:45 Recommendations by use case including sled pull and nitrous classes
18:20 Forged pistons in diesel builds
19:10 Why forged pistons are not ideal for street miles
20:20 Forged piston wall clearance and why race engines feel loose
21:45 OEM oil ring design vs forged piston ring packs
24:25 Steel pistons for 5.9 common rail
26:45 VP44 piston options
27:20 Compression height and low compression piston options
28:00 12 valve piston breakdown including the first gen wider bowl swap
29:00 Why they moved away from low compression pistons for most builds
37:00 Piston coatings and current experiments
38:55 Why proper piston wall clearance matters more than any coating
41:00 Keeping heat in pressure and out of the piston
41:50 Cylinder honing and proper surface finish for ring seal
43:30 Plateau honing and what it looks like on a profilometer
45:45 Wrap-up
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