Discussion and questions related to the course Road Tuning
I have watched the webinars around tuning cam timing and noticed that Andre mentioned that when adjusting cam timing if the AFR gets richer the engine has dropped/lost VE.
My question is, if tuning steady state on the road and AFR goes richer would it be safe to say that lowering the cam timing just before AFR goes rich(like retarding timing when torque doesn't increase) will be the optimum cam timing?
Did you have a more specific scenario in mind? What engine, what ECU, what's been done to it?
Just generalising with a theory. Was wondering if the above method would save dyno time. I know every engine will want different configurations and I suppose my theory of thinking was around the same way ignition gets tuned on the road. If knock is present, reduce timing by 2* and leave it(assuming you advance by 2* increments). I was thinking that maybe cam timing could be done the same way. Advance cam timing and when VE drops(AFR goes richer) reduce cam timing.
Suppose a better way to pose the question would be, If tuning cam advance on a dyno do you see peak torque just before VE drops?
Does the engine have intake and exhaust variable valve timing, intake only, dual equal VVT (like the big 3 have used over the years) 2 step lift (VTEC), is it turbo, is it direct injected, what fuel is it, what temperature is the engine? For example tuning exhaust VVT can be a lot different from intake side VVT.
Do you want to use it for fuel economy as well as power? Nevermind emissions as most contexts here it doesn't apply.
You're right in the sense that you keep trying different combinations of VVT to get to some final result like torque or VE or whatever, but the more you narrow down the details the better the advice will get. Like if you advance the intake cam you get better VE but you could also knock more and make less power but it depends on the fuel and the compression ratio.
For my engine its intake only, FI and e85.
My question is generic, not engine specific. I'm just thinking about a theory to save dyno time. For road tuning ignition the theory goes that you get the most power just before knock, based on this tuners will adjust ignition just as knock starts then retard ignition by a safe amount saying this is optimum. My question is, "in theory" can we do the same for cam timing.
Yes, I know that every engine setup will produce different results, that isn't my question. In theory, do you see the most power/torque from cam timing just before you lose VE.
Need to be careful with the road tuning technique of increasing timing till you reach knock, then retarding it, as this will only result in the best possible tune if the engine is knock limited (encounters detonation before peak torque). Its possible you can far over advance the ignition timing at points, and actually lose torque, without encountering knock. This is the main limitation of road tuning.
VE and torque are intrinsically linked. If your VE is higher, more charge air will end up in your cylinder for a given pressure and temperature in the inlet manifold. You need to inject the right amount of fuel to go with this air to hit your desired AFR. If you adjust the cam timing, your VE will change, but the pressure and temperature in the inlet manifold (and thus the quantity of fuel injected) wont change, so your AFR will move. If it gets leaner, your VE has increased (more air to the same quantity of fuel), and thus so has your torque, if your AFR gets richer, your VE has decreased, and so has your torque.
As you move the cam timing, and the VE picks up, you need to make the corresponding change to your fueling table to get your AFR back to your target.
Where this starts to get tricky is that, for example if you're boosted, more overlap can lead to more scavenging, especially at lower rpm. That can lead to more boost, which leads to higher temperatures and more knock.
While the theory would suggest that yes, you could monitor AFR and use this to help predict the optimal cam timing, the reality is that the magnitude of changes are just too small, and you need to maintain exact operating conditions while making your tuning changes which makes this all but impossible to do accurately on the road. I know several tuners who have tried to do this on the road before they had a dyno to use and found that they weren't even in the ball park.
If you don't have a dyno then you're probably going best to just use a generic trend for the inlet cam timing and accept it isn't perfect. Typically I'd expect zero degrees advance at idle. You'll then typically see the cam timing advance to around 30-35 degrees around peak torque (2500-3500 rpm for example), before retarding back to zero a little before the rev limit. You'll also find that at lower load (cruise for example) you'll want much less advance then you will under full throttle so you need to smooth and interpolate the map with this in mind.
Yes, I understand this is generic and isn't going to be perfect for every application, but my point is that you'll probably be as close as you will get by trying to monitor AFR in steady state on the road.