That’s just 500 rpm of difference. And it’s normal, not high. If it wasn’t clear - for me “not very revvy” = normal. What’s your point then?
And as I’ve shown you reaching Audi engine’s figures is not possible in Automation without going for crazy quality spam or poor reliability - so Automation can’t be compared to real world cars 1:1. I’m writing about Automation here, not the real world.
An Audi, much less a B7 RS4 isn’t exactly the paragon of reliability.
How much reliability is enough reliability? IRL cars don’t spend even 10% of their driving time near redline.
3 of these engines are high stroke designs with very high redlines and they all achieve acceptable reliability values for me. Especially since the V8 was on race intakes.
And all 3 use lightweight forged pistons and I-Beam Titanium conrods.
Something being do-able doesn’t make it the optimal choice.
Well excuse me for using forged internals in a high revving performance motors.
I did say the main reason I use undersquare is to cut down on engine weight when building faster cars…
(On the subject of: Small bore, long stroke)
with the correct bore and stroke you can make a reliable high revving engine while still using cast iron internals
And here we differ, because for me none of these engines has an acceptable reliability* (for a modern one, that is). As @TrackpadUser writes, it’s doable, but I wouldn’t call it optimal - heck, even my supercar engines are more reliable. I wanted to write it before, but forgot - I see comments here mostly from people like you, specialised in making extreme performance cars and I’m a minority and a counterweight here, trying to balance everything. Unlike what the content of this forum might suggest, most cars aren’t sports ones, and I think that there might be some people like me here, who like to make also normal cars.
@lordvader1 Exactly what I wrote, applied to a specific condition of not having forged internals.
######*But I think that might be more of an interface problem, than the problem with the engines themselves. We don’t really know what would a yellow glowing part in Automation mean in the real world - maybe some issues nearly at the redline are perfectly fine, maybe not.
Why do people keep thinking I only build supercars? I am not Gryphon Gear. Just because I don’t make minivans and superminis alot and doesn’t mean I don’t build economy cars.
Anything above 50 reliability is OK in my book especially since these cars will not be driven at their limits where the engine starts taking damage.
You don’t only build supercars (or even not only sports cars) but I feel like you focus way more on them. For example weight reduction over reliability gain… in a normal compact 
In a sports car, sure, that might make a lot of sense. In a compact, not really, fancier interior will add way more weight than this underquare engine will save. And it will make nearly no differene.
I had to. The car’s engine bay is cramped as shit with DW and transverse layout.
DW? But anyway, if I wanted to rev that high I’d rather use forged internals, as they are not really expensive.
Double wishbone. I changed the parts around to show it isn’t impossible to get half decent reliability with a high stroke. The actual car uses low friction casts and a much lower stroke for 1.8 liters.
Ok, someone might find this example useful. But for me it’s still unreasonable 
I know that I’d build a completely different engine.
The thing is, the weight advantage is fairly minor compared to the reliability penality. For a 2L inline 4 there is a difference of 10kg between the undersquare and overquare extremes. In the 2000s that’s pretty much never more than 1% of the total weight of the car.
And while you might consider 50 reliability to be good enough, in 2015 that’s 5 points of competitiveness that you loose in demographics like commuter and family compared to a car with 75 engine reliability considering everything else to be equal.
As for my mention of forged internals, it was more to point out how the only way to get decent reliability at high-ish rev ranges when it comes to heavily undersquare engines is to spend loads of money on better internals. It might work for high-end sports cars, but when it comes to making cheap cars that’s not really a solution.
When building engines I do a quick build with the compression as low as you can go, just to get the motor running then figure out where you want your power band, is this a low end economy engine, a balanced mid range performer or a top end screamer. Set the cam so the curve is roughly where you want it then set the rpms about 6-700 above the peak power. Go back to the block and stroke it out until just before you lose reliability, then adjust the bore to get the desired displacement you want, go back down and adjust the ignition to smooth out the torque curve, there will be a point where more advance just hurts the engine, stop before then. If you’ve narrowed your bore and added timing advance you’ve probably moved your peak power up the Rev range a bit, as long as it has a few hundred rpms between peak and cutoff you’re good, now you can play with compression and fuel mix based on how much performance you want the engine to have. Finally you’re on to exhaust, low and mid range engines will want a exhaust size 1 tick smaller than max power, high end can be free flowing.
These simple steps should give you a nicely serviceable engine that’s light and smooth without much fuss and are how I start off every engine build. My most important tip is leaving the stroke shorter than you have to with a larger bore can lead to heavier engines that suffer from poor low end torque, always stroke the engine as much as your internals can take.
I updated the guide adding @nialloftara @TrackpadUser @szafirowy01 @FrankNSTein
I haven’t added all that has been said because many thing are redundant or a bit out of the purpouse of the guide (but still helpful for the discussion).
We don’t build ‘supercars’ either, according to the Automation metric 
I want a separate metric for my own class of cars, the megacars…
Whenever I design an engine for a particular car, I factor in the size of that car’s engine bay and the intended application(s) for that engine. Generally I prefer to use undersquare engines for when economy, small physical size and light weight are required; oversquare engines, on the other hand, are more useful in high-performance applications, especially if they have more advanced valvetrains.
As for quality sliders… On the bottom end they really can make a difference at times, since they allow the internals to withstand more revs. Increasing the valvetrain quality reduces valve float, if that worries you more than the durability of the bottom end. For the fuel system, adding quality will significantly improve reliability and efficiency while also reducing the octane rating. However, quality sliders for turbochargers and exhaust systems provide minimal improvements by comparison.
Oversquare does help performance, but excessive oversquare only adds weight and can lead to valve float as valve size, and therefore weight are linked to bore size. A heavy valve takes more effort to close quickly so if you wanted a 3 liter inline six that redlined at 8000rpms I’d leave the base bore and stroke alone untill I’d set my redline and gotten the engine running, then I’d pick the internals I wanted then gone back and stroked the motor until just before reliability was affected then set the bore to reach 3 liters. that’s why I didn’t use under or over square in my description, I don’t think about that when building, only that your stroke should be as long as possible given your desired max rpm.
For the valve sizes going nuts with big bores, does the game get more realistic with 4V/5V heads? It would be nice if the game handled oversquare engines the way they are in real life (Durable, high-revving, but absolutely no torque). Sport bike engines tend to be massively oversquare, and they rev to the moon.
If not, more precise valvetrain control would be amazing… Dare to dream!
Big bore short stroke does tend to lack torque, but not by a huge amount. The game is hard limited to 12000 rpms due to the way engine sound is made, but that’s already well beyond all but a handful of road legal car engines. Valve trains won’t get more complex than VVL, though we’ll get a intake slider with the new engine designer to allow for runner length and the ability to add an active manifold similar to how VVL is done with two sliders.
