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Carbs don't have (usually) rev limiters, add it as option?


#1

Hello.
Something that’s bugged me in Automation for a long time, is how Carbs also have rev limiters in the game. The ignition timing was a great change for carbs, but if we’re following that logic, why not go slightly further?

For those who do not know, most (and i really mean most) of carburetted cars don’t have a rev limiter. Instead, the engine simply loses power via valve float and won’t rev any further. There were different ways to actually make a rev limiter back then, but those were really rare and only used on specific times, like making the distributor “lag” behind.

As such, my suggestion is rather simple, have the option to have, or not, a limiter with carbs.
Picture this: I’m making a not-Renault 5 GTR. It has a 1.3L I4 with pushrods. The internals won’t reach their limit before the valve float happens, as such, i wouldn’t bother with a rev limiter as that would be additional engineering time + money.

But now, imagine i’m making a really high performance car, that actually has a good valvetrain which means that valve float will only appear at, say, 6000 rpm. However the internals will begin the screw up at 5500, and the power peak is at 5000 anyway. In this instance, considering all of this, it would be logical to have a limiter. As such i’d spend the additional money to actually have it as it would be highly beneficial.

Maybe it’s a bit of nitpicking, but considering that this implementation wouldn’t be very hard to do, and would just require a “remove limiter” button with added bonuses/costs, i think it’d be a worthwhile addition. Especially considering it’d add quite a bit of realism and immersion


#2

That’s where you put a section in the owners manual that advises against running the engine above a certain RPM.


#3

I think the way calculations work in automation, it takes into account where you set the rev limit to calculate reliability and gearing I believe.


#4

Interesting suggestion, but in the grand scheme of things it would probably not be added for quite a long time as it really isnt that important.


#5

@USDMFTW but why? It’s a straightforward addition that would add, at most, a day to make and balance.

@Sillyworld yes, and i guess that would be the hardest thing to balance. However just assume the limiter is where the valve float gets critical. It just doesn’t make sense realistically

@BobLoblaw Yeah but that’s not a rev limiter like with what you have in the game.


#6

Is this not effectively the same as just raising the rev limit to 12000 and having it go bang before it gets there because your top end can’t keep up and the pistons have tonked your valves or something?

I get what you’re saying but not sure it adds much to the game or would be quite as simple as a day’s job. It wasn’t when I wrote a similar feature into another game engine a few years ago that at the time just implemented the spark cut style of limiter, and that didn’t need the previously mentioned tweaks to reliability calculations and balancing.


#7

@adamd yes and no. Because if you set it to 12000 the game counts the reliability as 0, as effectively it’s saying that the car will be able to rev there. By not having a limit, the game could count where the valve float reaches something like 10hp or something like that and that would be the “limit”


#8

Many other factors are using the “rev limit”, including the shift point for the test track, performance factor and reliability. The way its done isn’t the most realistic, but it gives the devs an easier time doing other calculations that are important to the game without having to put in a bunch of work to do so.


#9

lets pretend the limit in the engine designer is the one your company sets as the official limit and that all employees adhere to that for testing purposes. The test driver knows this limit and sticks to it on track and the publicity departments put it in the brochures and manuals
we can also pretend that customers can and some do ignore the limit causing their engines to go POP, but as that was user error there would be no material difference to the company, except sales of spares parts which is not in scope of the game.

The only place removing the limit would make a difference is in Beam NG and only if the required mechanics are implemented in the exports to support automation engines going pop.


#10

Automation engines do indeed go POP when you rev them past their limits in BeamNG. Just go find a steep hill, leave your car in first gear and watch the destruction.

It’s because of this that for now, I think a good adhoc fix — since let’s be real this mostly applies to the realism of the car in BeamNG — is just to push the limit to 12000 and let valve float do its thing.

I must admit though I have found it strange that unmanaged engines still have rev limiters. So I would add my support for optional rev limiters as an Eventually :tm: thing but right now I have far bigger complaints about the engine and car designer. Like forced induction :stuck_out_tongue: Lets get those taken care of first.

Just as a side note, it’s not necessarily carbureted engines that don’t have rev limiters. It’s just carbureted engines often don’t have rev limiters because they also often use points ignitions systems. Compact discharge ignition systems and EFI allow for easy rev limiting because they are electronically controlled and thus can easily assess when to cut spark, fuel, or both. It’s not per say impossible to speed govern an engine without these but it’s more sophisticated and less reliable.


#11

ooh good to know, where’s my popcorn :stuck_out_tongue:


#12

I just remembered about spark advance on a distributor. Usually using vacuum, it would advance the ignition timing as RPMs increase. That would have a limit, therefore you could rev it too high and lose spark where it’s needed thus cutting off power.


#13

Most engines will overrev just fine even with a fairly retarded spark timing if they are not working against high loads… the vacuum spark advance helps power and economy without any real downside bar the complexity, but it didn’t really rev limit. That said, some carbutated engines did have a governor that either acted as a second throttle, or simply prevented the spark in some manner… it was just often not considered for motor vehicles of the time where the driver was in charge of engine management, and the point of damage was not close to normal operation speeds.

Regarding BeamNG engines overrev, thats currently based on the redline, not actual RPM stress limits calculated by automation. You can blow up a trim of an engine that will normally rev to 6000rpm at 4000rpm, if you just set the automation limiter to 3000rpm… conversely you don’t get damage overreving if you set the automation limit well into the valve float or bottom end stress, power just continues to follow the displayed curve and engine runs happily… which lets you get away with some insane combinations if you so desire.


#14

Depending on how strong an engine was most older engines would quite happily wreck themselves if you just opened the throttle with no load if they had no limiter. The one Rev limiter I do remember seeing was located in the destributor dizzy and was a weight on a spring. Once the dizzy was spinning fast enough the gyroscopic force would pull the weight away from the electrical contact it was bridging. One of the know problems with this was that over time the spring would weaken and so your rev limit would also drop, sometimes quite dramatically.