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Valve Float!


Is there a way to deal with valve float besides making the bore x stroke ratio smaller and put 5 valves per cylinder?


Yes, a more aggressive cam profile and more Top End quality will help.


In the real world, shouldnt stiffer valve springs help with floating too?


Yes, sure. Basically this happens in the game when you change the cam profile, more quality makes the valves lighter. But you can’t set the spring stiffness independently (and no, this will not be added to the game at this point because we would be starting from the beginning then :wink:). Stiffer springs would also mean that the engine has to work harder to open the valves and thus that it’s less efficient. That’s a part of the cam profile calculations already.


I can’t get a good power curve anymore, the rev limit need to be right on the peak power to stop valve float effecting the performance.
the lower the cam profile the worse the valve float gets.


That’s a misunderstanding, Bloozed. Valve floating affecting performance is fine, valve float affecting performance AND reducing MTBF is not fine. It’s working as intended.



Is there a way to stop the power dropping off so rapidly. I had an engine with a high profile cam making power with no valve float @6800 rpm, limiter set @ 7000.
I wanted the engine to not be so peaky, maybe still producing 95% or so of its max power up to maybe 500-1000 rpm past its peak, before dropping off. so I reduced the cam profile thinking it would smooth out the power peak. but as I reduced the cam profile the power came down the revs but so did the valve float. it didn’t take much for the engine to fail due to the valve float. it seams to only go about 200-300rpm before the power drops sharply.
I don’t think that the valve float would be a very big problem when you have a low cam profile (less than 40), I would have thought the limiting factor would be air flow.

I used to have a mini that hit valve bounce at 7200 rpm, the engine would just stop revving completely when it got there, It made a good rev limiter :wink: .



The valve floating point is heavily connected to the head type you are using, so if you want to continue revving you should choose DOHC stuff or add lots of top end quality.


Just so I’m understanding correctly, it’s normal for it to warn me about valve float with the following setup?

N/A 2.0 i4 DOHC 16-valve
Cam/VVL: 40/70
Everything FULL quality
Max power at 8500 rpm
Rev limiter at 8500 rpm

Yes, I know rev limiters aren’t typically set at peak power, but this was just a valve float test because I can’t build any high-revving engine without getting the valve float warning. Perhaps I’m just misunderstanding because I’m used to the post-test warnings meaning I need to change something, not warning me that something is normal. :neutral_face:

EDIT: I was able to stop it by tweaking the bore:stroke to be 1:1, which changed the peak power to 8800 rpm. It is now fine if the rev limiter is set to 8800 rpm, but warning me about valve float at 8900 rpm.


There are two different valve float warnings: The one which is just informative is the one which says something “valve float is reducing engine performance”. This is no big deal and you don’t have to worry about it too much. This just gives you the power drop near the RPM limit. The more severe one says that valve float reduces MTBF. In this case, lower the RPM limit, reduce bore (you already figured that out :slight_smile:), use better head types/more valves or increase top end quality.

Seeing that you got peak power at maximum RPM lets me guess that you got the first warning. You may even want to increase the RPM llimit to have a wider high power range, even if power drops off a bit. The bottom end of course has to able to cope with the extra stress.

Valve float also depends a lot on in which year you build your engine, so a pretty modern one should be able to rev higher than an old one.


Okay I understand now. However, this leads me to another question.

If valve float (just reduced performance valve float) is occurring at an RPM greater than the peak power output, is considered normal and working as intended, and is unavoidable, is it necessary to give a warning for it? From a user-friendliness point of view, an unavoidable warning for something that is normal, displayed in the same manner that ‘bad’ warnings are, might lead to some confusion.

Perhaps the warning should only be shown if it is affecting the peak power output or the lifespan?


It almost always affects peak power, as that usually is the breakpoint. At peak power you already have a tiny bit of valve float for these engines and you would have significantly higher power at even higher RPM without it.

This being an important thing, what message would not have confused you?


Well I wouldn’t say it’s important. I’m not trying to blow it out of proportion or anything. If it’s normal for valve float to occur at peak power in high revving engines like you say, then I guess it’s not an issue at all. I don’t know much about it, which is why I was confused. See, I originally saw it as something I had to fix, but when I couldn’t and saw someone say it was normal, I started questioning the purpose of the message.

However, if valve float is normally the ‘bottleneck’ of high revving engines, then I now understand the purpose of the message. :slight_smile: If that’s the case, I think it’s all cleared up now.


That’s exactly the point, the massage can be misunderstood and probably misleading. We need comments like yours to make the game more approachable for those with less knowledge about engines and the game itself. But I don’t know how the hint can be improved.


I can’t think of a way to improve it, to be honest. It may cause some initial confusion for some such as me, but I do see that it’s necessary to know what your bottleneck is. It doesn’t seem like too many people are finding it confusing, so it might not be something to worry about. Just a lack of knowledge on my part is what it came down to.


I also found it confusing, and tried to fix the problem to get rid if the warning also.

If if is something that is normal and unavoidable, there shouldn’t be the warning.
It only effects what happens after peak power, so does it matter?

I think they should remove that warning, there isn’t a warning for when other restriction are reducing performance like when the intake or exhaust are too small.


The thing is it does matter, because if you didn’t have some sort of warning you’d have no idea that getting rid of valve float would improve it, or that it’s starting to happen at all. It’s fairly easy to discover exhaust and intake limitations, but there are so many things that influence valve float that you’d never guess it was happening.

I think we might just need to re-word to warning to make it really super clear what it means


I think we might just need to re-word to warning to make it really super clear what it means[/quote]

I think that would be a good idea. First I also thought that this message is something that needs to be get rid of. Normally you get some warning after the testing you still need to fix something. Fex. engine running too rich, engine knocking etc.

But if the text would be better (I have no idea what could be better) it wouldn’t be that confusing.


Why not get rid of the warning (unless it is reducing lifespan), and make the valve float indicator in the manual test mode more sensitive? Currently, valve float can occur and it stays green. Perhaps it could be adjusted to the point where yellow is an indication it’s reducing power and red is an indication that it is reducing the lifespan. I figure that might be an alternative worth discussing that avoids confusion.

Plus, it follows the trend of the previous warnings and indicators: warning messages mean something needs to be changed, while colored indicators in the manual test mode show you what parts are bottle-necking the engine.


The valves manual test mode should turn yellow if there’s a problem. As I see it, if there’s a warning message, there should be a colour-coded warning to correspond with it.