Crossplane V8 vs Flatplane V8 - 90 Degree Even Firing V8 In Engine Simulator

Описание: This is another simple one, with nuance to the depth and description. V8s are some of the most flexible engine layouts when it comes to creating even firing engines. The best way to demonstrate this is the time tested comparison of the main even firing orders. Cross plane crankshaft or a flat plane crankshaft?

If you're looking for a quick summary, Cross planes can run smooth, flat planes generally always run rough but make more power. Cross planes are a no brainer for ho hum vehicles, but the engines share similar severity of compromises when used and optimized for performance.

And the best way to show the difference is by showing how it alternates between banks with a 90 degree angle. And how the forces on an engine work, these ones specifically.
(specific orders may vary, these match the video's examples.)
Crossplanes: R-R-L-R-L-L-R-L (uneven alternation, leads to exhaust problems) 0:00-1:14
Flatplanes: R-L-R-L-R-L-R-L (even alternation, simpler exhaust designs to make more power) 1:15-2:29
Primary Forces: Caused by pistons moving up and down non symmetrically. Causes a rocking couple. (Engine wants to flip over itself, causing frequent vibrations)
Secondary Forces: Caused by the conrods moving in such a way that the distance, velocity, and acceleration of the rotating mass in the cylinder deviates from expected, causing vertical forces in plane. (Very frequent shaking and buzzing)

TL;DR: Crossplane cranks work in V8s because, it's two I4s filling in the gaps in their intervals to create an even firing engine. The I4s would have uneven firing operating exclusively from each other due to having a cross plane crank. They prevent the engine from vibrating a ton, but the cranks are heavier to prevent the engine from literally turning over itself. This leads to slow revs and a reduced redline, but smooth operation across the band. Crossplane I4s suffer the same fate as the V8s.

Crossplane cranks lead to uneven firing Inline 4s, but in a V8, the other bank offset by 90 degrees fills in the gaps of the other bank's four cylinders for an even firing interval of 90 degrees over 2 rotations. The engines primary balance is not ideal (the pistons in the engine move in a way that makes the assembly want to flip the engine over itself), but secondary balance is perfect (the engine doesn't want to shake itself to pieces). In response, the crank has counter weights that slow down the engine.

TL;DR(#:2) Flatplane cranks make a V8 run like two I4s offset by 90 degrees. Most I4s have a flatplane crank. They rev high, rev fast, and make more power. This comes with the caveat that they will shake themselves apart unless you pull engineering wizardry off. This is a fundamental problem with I4s using these cranks too.

Flatplane cranks operate the engine as if it were two even firing inline 4s, where one is offset by 90 degrees. The cranks achieve perfect primary balance (rotation over itself is completely counteracted by the pistons in each bank moving to act against rotation), but they don't achieve secondary balance (the engine violently vibrates). There are ways to reduce the vibration, either with longer rods connecting to the crank compared to the stroke, or with other engineering tricks. But higher revs and redline come with the lighter crank, increasing the power the engine makes.

And shockingly there isn't a simple answer for performance engines. Both have character in their sound. Both have weird trickery with firing orders (fun fact: Crossplane V8s can fire the entirety of their bank in sequence before going to the next bank, with the correct cam timing? ie: LLLLRRRR), (fun fact: Flatplane V8s often vary their order slightly, but the most notable outlier is the Ford Voodoo V8 found in the last gen Mustang GT350? Look it up.)

Either way, both needed to end up in this video, because both are even firing V8s with an ideal angle. Crossplanes are an obvious choice for utility, but the lines blur when you need to perform well.

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