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I would think this value must have an impact on throttle transitions and throttle stabs. When we change to a FAST intake or worse yet a positive displacement supercharger I would think this value should be modified for the anticipated airflow that the engine is about to receive.
Has anyone tried experiementing with this value?
Howard
I thought it had a bit more to do with transients, as well as air flow response.
I haven't played a lot as I'm still messing with Impact factor and evaporation rates, but I have looked at it.
My thoughts were that a larger manifold volume would act as a "dampener" to the throttle air flow. For example, when you snap the throttle open, you need to fill the manifold plenum before the higher pressure reaches individual runners and inlet ports. Then on throttle close, it takes some time to build vacuum in the manifold. This can be seen in the difference between MAP calculated airflow and MAF measured air flow. The MAP airflow lags the MAF air flow..... Obviously then, the bigger the area of the manifold, the worse the lag gets.
The thing is though, that the "lag" is a factor of the manifold volume, not the tune setting. Run an 8-TB setup and you have blistering response, because the throttle blade is within 4" of the back of the inlet valve. There is a big chance that people that have installed these manifolds have not even bothered to change the manifold volume setting. same goes for the FI guys, I don't think any one has tried changing this setting.
I guess if you had the specs of the FAST, it wouldn't hurt changing this setting to suit but I'm not sure about changing it for FI. It may have something to do with MAP readings (SD tune), so in theory changing the MAP settings for FI also corrects the manifold volume for FI.
Simon
On a possibly remotely related topic, what the heck is "drive pressure". Someone mentioned it to me yesterday and I've never heard of it. It's supposed to be the pressure between the compressor wheel and the intake or something like that? Like the difference of the pressures in the manifold... or something. A little confused, need another cup of coffee :(