More powerful engines are less reliable. Motorcycle makers get twice the specific power out of their engines compared to cars, but the engines won't last 100k miles or even 50k and they require frequent major maintenance. Car buyers are no longer willing to ever have their car in the shop so most mainstream cars are very detuned. High-strung engines that need maintenance are a niche market.

Almost all production motorcycle engines that aren't being raced and are getting regular oil changes will last 100k easily. The leading cause of motorcycle end of life is crashes, not engine failure.

As you go more esoteric, you need to rebuild the engine, replace piston rings, etc. But those bikes are either built for it (off road two strokes) or have the budget for it (racing). Still don't need to scrap the whole engine.

Perhaps oil changes counts as high maintenance. It can be a bit messy, but it's quick and cheap on most bikes. More time is spent oiling chains overall though.

Taiwan has drive through automated oil change machines that suck the oil out and fill up via a tube into the filler. Makes sense especially for <125cc scooters which do not normally have oil filters.

Motorcycle engines are largely not scaled down car engines tuned for performance at the expense of reliability. They are designs built from scratch under different constraints. A mid-level motorcycle engine from a Japanese manufacturer should last longer than a mid-level car from a Japanese manufacturer, all else being equal.

There are motorcycles that you buy facing the near certainty that it will most likely outlive you, like KLR 650, or you can get a Ducati with a Desmosedici Stradale in it, where you have to get valves adjusted (major service) every 2500 miles. But given timely service, no motorcycle will last less than 50k miles, and most will last above 100 before an engine block rebuild.

Comparing cars to cars, or motorcycles to motorcycles, the logic holds though.

Mid-level Japanese car engines can go waaay longer than 100k before an engine block rebuild. I had a Mazda 3 over 200k with no major service (A/C died...I left it dead)

In Australia it's not uncommon for Toyota 22R engines to run for 400Kkm before needing a rebuild.

> I don't understand why they decided to make two models out of the same engine.

Increasing performance puts greater stress on the engine, increasing maintenance cost and/or failure rate. If engine breaks down before end of warranty, it's producer's cost.

The IS350 used to share the same engine as a Toyota Sienna minivan https://en.wikipedia.org/wiki/Toyota_GR_engine#2GR-FKS

Nothing new, tons of cars share engines. The same engine in the Sienna also powers the RX350.

No one said cars don’t share engines. OP is asking about why they make two models out of same engine.

This is an extreme example of it.

Have been done for a really long time with car manufacturers.

It does simplify manufacturing.