Bore and stroke for reliability?

Hi all.

So I’ve kindof started my own imaginary company in 1950 and I’m having trouble getting my V8’s above 42 reliability. So far I have finished one engine with a bore and stroke of 3.543" for a total displacement of 279.4 ci. I’ve heard that under square engines are better for reliability but make less power and have a much lower redline. Also I would love for someone to explain exactly what one reliability unit means, like 1 reliability unit means x number of miles between failures or whatever.


I’m pretty sure oversquare engines (larger bore than stroke) can rev higher for the same reliability. However I think they have less torque (and therefore power) and efficiency vs longer stroke engines.

In old versions of the game, the reliability rating was multiplied by 1000 and called mean time before failure (km), whereas now it is just a number. I personally preferred mbtf, or maybe have the reliability number have more decimal places for more precision.
I think it is difficult to get above 75 without quality sliders.

42 engine reliability in 1950 is a good number. You could increase bottom end and fuel tab quality to achieve better reliability.

As utopian said, oversquare engines tend to be more reliable than undersquare ones. But they are heavier and slightly less efficient.

One way to check if the engine is good or not, is to try and recreate an engine from the era, to get a feel for how it should be.
Also, in the 50s, a 5000cc engine with 130 hp would be an engineering master piece.

Thanks to both of you. Also Leonardo my 279.4ci (4.5L I believe?) makes 159hp with all quality sliders at 0, I guess I actually put together a pretty nice engine after all.

If you switch test modes you can see the stress of different parts of the engine. The parts will start to turn yellow to Orange to red to flashing red than failure. Different parts show different levels of stress. Bottom end wise your piston and rod will show stress both for too much torque and for too high a redline. Where as the crankshaft will only show over torque. Now over revving the bottom end is the most common way to lose reliability, its normally the connecting rods that start to fail first, but sometimes it will show the piston getting yellow, this might also be the fault of the rods. I’m not great at math but the piston’s speed is determined by both engine revolutions and stroke distance, basically the longer your stroke the more distance the piston has to move and the more momentum it has and the more stress is placed on it as you climb higher in the revs. If you start to notice a drop in reliability and the piston is glowing the quickest way to fix it without losing revs is to shorten the stroke. That said, stroke makes the engine more efficient specificly because of that extra piston momentum, a long stroke means that more torque is made per revolution which makes a more usable engine.

45 is pretty good for the 50’s if you’re looking for a higher reliability and shortening your stroke doesn’t gain you any look to your carburetor, or valve train, the more complex the system the less reliable it is, you might lose some power and efficiency by switching from 2 four barrel carbs to just 1 four barrel, or from a four barrel to a two barrel but it will gain you a small reliability bump. Same with the valvetrain, for more info on that see this

Thanks for the info nialloftara. Seeing as how I built the engine in 1950 my bottom end selection was pretty limited. Cast iron crank, cast rods and cast pistons. That being said now that I know what is good for 1950 in terms of reliability, I’m satisfied now with what I have. I may however replace the two single barrel carbs with one two barrel and see if that helps.

I have a recreation of a 1950 Chevrolet 235 engine in my Real-Life Engine Recreations thread, the reliability of that is 42.2, which is pretty average for all the engines of the period I have created.

I am getting pretty good results with square engines. That means a bore/stroke ratio of roughly 1:1. Especially with cam profiles around 68 which I like.
It isn’t surprising when long stroke makes the engine more power per kilogram, short stroke gives higher rpm, that 1:1 is a good compromise.
It’s also noteworthy that (within certain limits) only the stroke determines the reliability and max rpm (once you found the right stroke for a certain rpm you can move the bore up considerably).
So when I go 1:1 the tech year sort of determines the displacement (for the same cam).
If you need bigger displacement you can simply take a good 4 cylinder block and make it a 6 or 8 cylinder, the physics of the cylinders roughly stay the same.

Large bores also create reliability issues because the valves get bigger causing valve float earlier, which is worse than bottom end issues because it also reduces how much power you make. You don’t even need to go that big before problems start to appear. My ATCC 2 I6 engine is only 2L and with the maximum bore to stroke ratio it ends up severely limited by valve float.

The valve float issue can be fixed to some extent by using a more aggressive cam and a higher quality high-end but that’s not a good solution in some cases, especially since agressive cams will reduce smoothness in the next patch.

But yeah, 1:1 is usually a safe choice, although if you want to maximize certain aspects of your engines performance you will have to go slightly under or over square.

As for changing engine type to change displacement, that also works. The main issue is that not everything fits in everything. The I6s in particular tend to be long and therefore not fit in a lot of cars, depending on the engine layout.

There is no best choice of course but I want to have reliability close to the maximum possible at the particular year, and quality at 0. Quality improvements should be avoided at all costs because they are kind of a magic bullet that make it impossible compare designs. If I stick to that principle, square gives me the best hp per kilogram. The key seems to be that a square engine can achieve a similar reliability as a short stroke engine, but is much lighter. Of course I would get most hp/kilogram with long stroke but only if I make big compromises in reliability and rpm.

However, take that with a grain of salt. It depends on the year and the type of car. I currently build small sports cars in earlier years, ca 1960-1975. CAM profile is usually 65-70. If you want to build simple, reliable engines with low rpm (<5,000) you should not rule out long stroke engines, even in the early years. And year 2000+ I have no experience, but the better materials should allow to build long stroke engine with larger displacement and higher rpm.

Quality isn’t ‘‘magic’’

It means using better materials and doing more optimisation of your designs that end up costing more.

Ex: Higher top end quality could mean:
-Valve springs made out of more expensive materials.
-Valves made out of titanium instead of steel.
-Manually polished ports and valves to help airflow.
-Better coatings.

For the bottom end it would mean:
-More optimized design with tighter tolerances that causes more rejects/requires more expensive manufacturing processes.
-Better coatings.
-Better bearings and bushings.

I could probably make a similar list for every single quality slider in the game. The quality slider is not magic and it emulates things that are doable IRL.

There’s an associated cost in both money and production units that scales up with both the complexity of a part you’re improving, and with the amount of quality you use. It’s not just giving performance away for free.

Were you to attempt to build to a budget, or for a tournament with restrictions, you’d quickly come to appreciate the way quality scales the costs and production units.

Furthermore, you’ll find that tech pool is going to play a big role in tycoon mode. A hint as to the requirements and penalties can be seen in various scenarios.

You can only use quality so liberally as long as money does not mean anything in the game, but once you run a real company you will quickly convert to the other philosophy.

In the game right now it’s a bit like cosmetic surgery, many people do it but no one wants to admit it :wink:

…or flagrantly and openly abuses it [size=85]like I do… but I’m also upfront about the ridiculous prices of the cars that result, they were never intended to be anything else[/size] :stuck_out_tongue:

You’ll find that a lot of players are really quite scrupulous about using the quality sliders when making their own models, because they’re so mindful and particular about their vision of making a relevant car. That’s the kind of person this game attracts.

When you take part in a tournament from the challenge and competitions sub-forum, you usually end up having to balance performance and costs. And quite frankly in most tournaments, if you use no quality everywhere you will get wrecked.

If you ask me, I don’t see what is fun to put all sliders at +15 all the time, but putting some of them at +5/+6 depending on the situation can wield good results w/o raising the price too much. You just have to think about what would make sense in your situation, and it doesn’t take that much to make a big difference on the performance, notably when it comes to the top end.

So yeah, while having a ton of quality on a cheapo econobox doesn’t make much sense, bringing the sliders up a little on a sportier or luxurier car does make sense. Back when I made econobox engines they rarely had quality, except maybe +1/2 on the top end for the engine made to be used in a hot hatch.

I think game quality will play a role in the game, and in the sandbox, and a small quality boost may not drive the price to astronomical heights. But to me it’s not interesting from a engineering and industrial perspective to produce over-expensive cars. Or on other words, everyone who can design a great, inexpensive car can also make an expensive one, but not vice versa. A car that costs 10 times as much would be much harder to succeed in the market, so in the end the most affordable will win, or those with a special prestige. There are examples but they did not succeed because they invested lots of money, but because they had special skill. For example the Italians around Modena have an antique craftsman tradition that is hard to repdoduce in other parts of the world, especially in the mass produced American market. So it was less a question of money, but of people.

Also, smaller engines are more reliable than larger ones in the early stages. More size means more mass and therefore more strain on engine components. 300ci and larger will suffer more reliability at higher RPM - so adjust the quality scale up to get better results for now.

Smaller engines are generally more reliable overall. In the early game years, the 40s and 50s, you do not have access to many parts, and this is especially noticeable on the bottom end. You have to compensate by A) Decreasing engine size, B) Making the engine massively oversquare, or C) Lowering the RPM limit.

I usually play from 1960 to 1980 and all my engines are currently 1:1 to 1:1.1.
I have a simple technique to find a good right bore / stroke. I usually adjust the stroke until it matches the rpm (the rpm depends on the CAM profile I want to use, usually 70). I just move it to the point where the reiliability starts to decrease. That becomes the rpm limit.
With the bore you have more flexibility, depending on the displacement you want. I adjust it after the stroke so that it matches my rpm range and until I get the best hp/kg.
The later the year, the longer stroke becomes feasible, and more hp/kg.