Tips on making small engines(inlines) with high RPM?

[MSgt Peterson]

So I was wondering If any vet could give me a few tips on making smaller engines with high RPM's? With most engine's I've made, I'm never able to get them higher than 6,500 RPM unless there large engines. I've been trying recently to make Inline 4-6 engines with high RPM's like 9,000 - 11,000 with but little luck.

Oh I should mention I'm no car whiz, I'm not stupid, being a kid of a mechanic but I'm no expert either lol

[Clueless]

One thing you can try is to design your engines to be oversquare -- that is, with a slightly larger cylinder bore than stroke. This should let you run higher RPM generally. The type of top-end (SOHC vs DOHC etc) matters too -- the more advanced, the higher it can run essentially.

[MSgt Peterson]

Originally posted by Clueless:

One thing you can try is to design your engines to be oversquare -- that is, with a slightly larger cylinder bore than stroke. This should let you run higher RPM generally. The type of top-end (SOHC vs DOHC etc) matters too -- the more advanced, the higher it can run essentially.

Thanks for the tip, I'll have to keep that mind. I was thinking of running with a I was thinking of using a DOHC this time around.

[Boudewijn]

The main thing you need to do is the bore/stroke small, have good internals(like forged or better), and have good top end(like dohc 4v/cyl)

[MSgt Peterson]

One of you are saying do a stroke and the other saying cylinder lol

I'm essentially trying to create a racing circuit engine

[Boudewijn]

Yeah you need oversquare, but you cant reach 11000rpm with a big bore, you need them both to be kinda small

[Clueless]

Originally posted by Boudewijn:

Yeah you need oversquare, but you cant reach 11000rpm with a big bore, you need them both to be kinda small

Yup. Think of it like this -- smaller cylinders are kind of easier to run (less friction etc) = can run faster. And +1 for forged internals -- many lesser means of production just won't be able to handle it.

[MSgt Peterson]

I've gotten to 9,000 RPM's so far lol

[Admiral Obvious]

I mean, if you really wanted to, you could just crank the bore and stroke to minimum, like a .4L (that's 400cc) I3, you can get them to 12k easy without stress, even if you use low cam profiles. The engine basically won't output any useful power however.

[CBR JGWRR]

1. Short stroke. The reason for this is the longer the stroke, the further the distance the piston, conrod and crankshaft (potentially for this part) have to travel in the same amount of time, and ultimately trying to go too fast wrecks the metal because of the stresses involved in the constant acceleration/deceleration. (imagine how you'd feel if someone forced you to jump up and down 150-200 times per second)

2. lighter materials. Making it lighter massively reduces the forces involved, which means provided strength isn't compromised, you get more rpm. (downside is this is usually more expensive)

3. better manufacturing process. Casting is cheap and quick, but doesn't really give good performance. Forging is an improvement but more expensive and time consuming, while machining from billet is wasteful but the best available in Automation. (there are other methods becoming used, most notably single crystal casting, but typically they are only used in aircraft engineering at the moment; at the lower end you have 3D printing, which could be used to 3D print components, but you wouldn't want them for a high rpm application)

4. Big bore. That is, if you are looking to actually produce power, not just a technical exercise; bigger bore does come with the limitation that it makes the piston heavier, which increases stresses on the whole system, and massively increases the weight of the whole engine because of the larger engine block it requires.

5. Use more cylinders for the same capacity; again, makes the rotating elements of the system lighter (although increases overall weight) and therefore easier to rev. Much more expensive to design and build.

6. Keep in mind Automation is designed to model road cars, touring/GT racing cars at a push. It is not designed to handle motorcycle engines (where there have been production engines with over 20k rpm in the case of 1990's 250cc/400cc machines) or highly strung or race engines; in the real world, even 9k rpm covers almost every car on the market.

7. More valves and better valve operating. One of the limits on internal combustion engines is how quickly you can get the new air/fuel mixture in and the old one out. (or partially recycled back in as is common in trying to get the most energy out of the fuel) While the best method is electronically controlled pneumatic valves that have no cams at all, there are almost no road car manufacturers that uses it due to the higher costs. (been in F1 for decades though)

8. exhaust tuning. Much more relevant at high rpm than low rpm, length of exhaust (which you can't adjust in Automation) and diameter of exhaust (which you can) affect how well you can pulse the exhaust to better optimise gas flow, which improves high rpm torque. This is much less significant for Automation's turbocharged engines however, as you are limited on the types of manifold. (Automation's turbos are equivalent to 80's technology)

[MSgt Peterson]

These are very good tips since I'm not the greatest of engine makers but I've gotten better thanks to all your tips.

Last night, I manged to make a decent I4 at 9,000 RPM's with 200 HP. Right now, still trying to make a I4 with a dochc that will put out something like 250 HP at 10K-11K RPM's. I'm trying to do on a 1980's car. I haven't gotten around to designing a modern car just yet.

[Boudewijn]

Originally posted by MSgt Peterson:

These are very good tips since I'm not the greatest of engine makers but I've gotten better thanks to all your tips.

Last night, I manged to make a decent I4 at 9,000 RPM's with 200 HP. Right now, still trying to make a I4 with a dochc that will put out something like 250 HP at 10K-11K RPM's. I'm trying to do on a 1980's car. I haven't gotten around to designing a modern car just yet.

Its way harder with an older engine

[Admiral Obvious]

Originally posted by Boudewijn:

Originally posted by MSgt Peterson:

These are very good tips since I'm not the greatest of engine makers but I've gotten better thanks to all your tips.

Last night, I manged to make a decent I4 at 9,000 RPM's with 200 HP. Right now, still trying to make a I4 with a dochc that will put out something like 250 HP at 10K-11K RPM's. I'm trying to do on a 1980's car. I haven't gotten around to designing a modern car just yet.

Its way harder with an older engine

This. The valvetrain is usually going to be the limiter in achieving high power at RPM in earlier engines.

[MSgt Peterson]

I don't remember, can you put a newer engine in a older chassis like put a 05 engine in a 85 car? I've always just made new motors when I play in sandbox.

[Boudewijn]

Originally posted by MSgt Peterson:

I don't remember, can you put a newer engine in a older chassis like put a 05 engine in a 85 car? I've always just made new motors when I play in sandbox.

Yes you can do that