"Hmmm ......"

Jin was thinking about what Marcia and Rodrigo had asked him about.

There are several ways to increase RPM and torque.

First of all, if the material is made from Horaijima, it can be improved more than 10 times.

However, this is not common.

"And then..."

In an actual , that is, a system that converts the reciprocating motion of the piston into rotational motion, the parameters of bore and stroke come into play.

The bore is the diameter of the piston and the stroke is the range over which the piston moves back and forth.

The ratio of bore to stroke is called the bore-stroke ratio, and it is one of the guidelines for engine characteristics, but Jin does not know that much about it.

However, he understood that if the stroke was smaller, the rpm could be higher, but the torque would be lower, and if the stroke was larger, the rpm would be lower, but the torque would be higher.

I also understood that to increase torque, the number of cylinders should be increased.

V8 and V12 engines are typical examples of such engines.

"Star shaped engine ......"

This type of engine is often used in aircraft.

But I still think in-line or V-type engines are the way to go.

Jin recalls now that he has built a Golem engine for automobiles.

"But if it's an in-line type, it would be too long. ......

"Um, Jin?"

"I heard that horizontally opposed engines cancel each other out, right?"

......

"8-cylinder, horizontally opposed, not ......, 8-cylinder..."

"Hello?"

"...... Marcia, if Jin's brother has that look on his face, it would be wise to leave him alone for a while."

Erza seemed to be getting to know Jin pretty well.

"Okay, it's decided. ...... Marcia, I think you can do it."

Jin turns to Marcia as if nothing has happened and states matter-of-factly.

"Oh, yeah, I see. I'm glad to hear that.

"Well then, let's get started.

But then the wait comes.

"Brother Jin, it's almost noon."

It was just after eleven o'clock.

Father, you must not skip lunch.

The time difference between Horai Island and Potrock is about 2 hours and 40 minutes.

Considering the time difference, Jin and the others had breakfast at 9:00 a.m. on Horai Island, but 11:00 a.m. on Potrock was 1:04 p.m. on Horai Island. However, 11:00 a.m. in Potrock is 1:04 p.m. in Penglai. They were very hungry.

Marcia and Rodrigo were also aware of the time difference,

"Yes, Jin. Let's have lunch once.

They left the workshop and headed for the store to get ready for lunch.

Jin had built an addition to the kitchen, which could easily accommodate up to ten people, and he could prepare food for Bacchus and Jeremy in the store at the same time.

"It's only lunch, so it's going to be something simple.

Fifteen minutes later, Marcia served the usual: bread, soup, salad, and fruit juice.

"This salad is delicious.

This salad is delicious," she said.

"Really?

"Is that the aroma of kryptona?"

Elsa, who had also eaten a salad, said so, and Jin nodded his head as if he had just noticed.

"Oh, yes. This is the flavor of honeydew!"

Cryptona is a type of mitsuba known to Jin. It is a common wild plant in the village of Kaina, and is eaten boiled.

"Sure, it's delicious in salads, isn't it?

The Jinzas had never put it in salads, although they had often put it in soups.

"Let's try it at our house sometime.

"Hmmm..."

Jin and Erza exchanged such comments.

After lunch, which was a little late for Jin and Erza and a little early for Marcia and the others, it was time to start engine building.

"I'd rather make it out of iron than bronze.

We wanted to use a stronger material because it would give us more power.

"Yes, I've already bought it. I'm using it for the parts that need strength."

The demand for such materials was increasing since the improved and strengthened Arrow could use more engineering magic than the average magecraftsman.

"Let's see, iron ...... hmm, carbon steel ...... has 0.4 percent carbon content. It just so happens to have a little manganese in it as well. That's plenty."

Nickel and chromium are added to make an alloy steel called SNC steel.

This alloy steel is often used for structural materials.

Jin is the sole supplier up to that point, but after that, Elsa and Arrow help him out.

Especially, Arrow will be in charge of the maintenance from now on.

"We'll use gunmetal bearings. ...... Arrow, don't forget to do the maintenance here.

"Yes, sir."

If they are worn out, they will rattle and lose efficiency, so they are a high priority for maintenance.

Jin made the crankshaft and the golem arm part, Erza made the chassis, and Reiko made the muscle part.

The project was completed in about 30 minutes. Between you and me, it probably would have taken less than 10 minutes if it was just Jin.

"Okay, the prototype is done. Let's get it running."

The prototype engine was about 50 cm long, 25 cm tall, and 50 cm wide. It weighed less than 30 kilograms.

The energy source is a mana tank. The reason is that the latitude of Potrock is low and the concentration of free magical element (ether) is rather low, so it is difficult to operate it efficiently except for Jin.

"Start."

The engine has started to turn over.

The engine is a horizontally opposed type, so there is little vibration and it is quiet.

"Yes, the stroke has been shortened, so the rpm has been increased.

Reiko counted the speed of the marked shafts, and it was about 1000 to 1300 rpm. The torque seems to be reasonable.

The torque seems to be reasonable, so we can call it a success first.

"Jin, I think I can use this. Thank you!

"Jin-dono, then I would like to make a new contract with you.

This engine will be added to one of the engines that we are selling wholesale from Horai Island to the Marcia Workshop.

Since we can't offer them free of charge, we will have to take into consideration the cost of materials and technology, and we will make five of the same size as the prototype at 20,000 Tolls (approx. 200,000 yen) per month, The contract was for five units per month at 20,000 Tolls (about 200,000 yen) each, for a total of 100,000 Tolls.

On the Horai Island side, the artisan (Smith) Golem would be in charge of production under the leadership of the old man.

Thank you, Jin.

No, thank you very much for your help.

At 3:00 p.m. Potlock time, Jin, Erza, and Reiko returned to Horai Island.

"You've been helpful in many ways. ......"

The old man will report back to you as soon as possible.

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"Okay, I understand. As for me, I'll think about the relay station and the ...... recreation room."

I'll think about the relay station and the recreation room, because such interior issues can be easily added later, but the design issues should be taken care of as soon as possible.

"Brother Jin, I'll discuss the meal menu with Mother."

"Oh, yes. I'm counting on you.

Yes.

I want to make one meal a day like we eat on the ground, so we need to think about the selection of ingredients, how to store them, and even how to cook them.

Leaving this to Erza and the others, Jin decided to think about new equipment, including a repeater for communication.