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Originally Posted by CaryTheLabelGuy
I didn't see this post until now and I never addressed it when it was posted. So here goes:
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Originally Posted by Boss330
As regards the throttle valve, have you checked out if it is opening in relation to accelerator pedal position during regular driving?
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Being that this is a Valvetronic engine, the throttle plate has some strange behaviors as it attempts to regulate boost in concert with the EWGs. The throttle plate does open in relation to pedal input at partial throttle and light loads. However, once you enter medium to high loads and the engine starts to build significant amounts of boost, the throttle plate will open and close as it sees fit to help control boost entering the engine, past the throttle plate itself. So while you might see a spike in boost as measured before the plenum, the engine itself isn't necessarily consuming that much boost. You can be at full boost, WOT and the throttle plate might start closing up as much as 50% or so.
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Originally Posted by Boss330
Reason I'm asking is that on valvetronic engines it's usually intake valve lift that regulates air flow, the throttle valve is there just as a back up if valvetronic should fail. As I am sure you know, valvetronic varies intake valve lift, acting like a throttle valve. Lift can be varied from between 0,300mm at idle, and on the overrun, to full lift of 2,5-3mm (which I guess varies between engine types). And some direct fuel injected engines also run under what is called a stratified charge. Stratified charge is a condition where there is a surplus of air compared to fuel, the throttle valve is usually completely open under these conditions. In effect the engine operates like a diesel engine with excess air and open throttle. It's the amount of injected fuel that regulates the power output.
As we all know, fuel and air needs to be at a stochiometric ratio to ignite, so how can a direct injection engine run with a air/fuel ratio of 20:1 and higher? This is the beauty of direct injection, when fuel is injected directly in the combustion chamber. They manage to create a pocket of air/fuel where there is a stochiometric mixture.
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Your description of DI and Stratified Charge are correct. However, Air/Fuel mixtures can ignite leaner than Stochiometric (14.7:1 for pump gas and most race fuels) even in non-Direct Injection engines at idle and very light throttle, without any damage, especially on a modern non-DI engine. I routinely tuned Mitsubishi Evolution's (4G63) as lean as 18 to 20:1 at idle and light throttle as well as the K-Series Honda engines without any issue or misfires and most of those engines are still running on my tunes today without any issues or damage, including my personal Evo VIII. The 2JZ Supras I tuned didn't tolerate such lean mixtures at idle and light loads, but could easily tolerate 16.0:1, especially at idle. Tuning at such lean mixtures does increase NOx emissions, however.
As for the S55 and N55, they run normal 14.7:1 AFRs (stochiometric). I've never once observed my S55, for instance, run leaner than 14.7 once AFR stabilized at light and medium loads as well as idle. Some DI engines do utilize stratified charge like the Mitsubishi GDI, for instance. Stratified Charge is mostly used in N/A engines, however.
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Originally Posted by Boss330
point is that a open throttle on a direct fuel injected engine, and especially on a valvetronic engine, doesn't necessarily mean that much...
Could you possibly check if the throttle valve isn't open at all times?
And even with a fully open throttle valve on the S55, it doesn't mean there is airflow through the engine. Valvetronic could be at minimum valve lift on the intake valves and thereby cutting airflow...
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This is true. The throttle valve is never 100% closed (even at idle, where Valvetronic is used heavily to stabilize idle RPM), but it does open significantly on throttle (pedal) lift-off while in significant boost. There is also usually a boost spike as measured in the plenum just after lift-off followed by a very gradual decrease in boost, which leads me to believe that the engine, through Valvetronic and an open throttle valve, is blowing the boost charge through the engine using either cold or hot blowing (at least in Sport+ I believe fuel is injected, thus making it hot blowing ALS). This explains the burps or "farts" we all hear on lift-off. |
Thanks for taking the time to log the "odd" behaviour of the throttle plate. Interesting stuff indeed!