What can influence Air Load.

Hi all,

I'm curious as to what could influence the air load to fall and then climb again between 4000 rpm and 5200rpm. The file attached is a 4th gear run on the street and have found the same effect in all gears. The vehicle is a 2005 Toyota Hilux, 4x4 fitted with the 1GR-FE 4.0lt v6 which I have supercharged. The engine mods being a bigger crank pulley, long tube headers, bigger exhaust and reflashing using HPtuners. In this rpm range I see no reflection in TPS, MAF g/s,volt, Inj dc or spark which I thought would be an indication. Any ideas. Appreciate your assistance.

I can't read the file, and more actual information would be useful, but one possible answer is if the engine's mechanical spec' has peak torque airflow around 4k where it falls off before the supercharger's boost starts taking affect - this is going to show up most with a centrifugal type supercharger.

That said, I would have expected it to show up in the air-mass entering the engine?

If it was a N/A engine it could be a mis-match in the upgrades and/or cam' timing. If you know you have the clearances, you could try altering the camshafts' timing a little one way or the other to see if that fills the hole?

Hi, I've attached the file again as a screen shot so hopefully you can see it this time and as you mention cam timing, I've included the cam file. VVT is only on the intake cams. If I have the information that you require, happy to assist. The supercharger is a Magnuson/Eaton Model MP90. Thanks.

Sorry, I mean I don't have the s/ware, not that the file was corrupt.

That's a bit clearer, and in context I take it that "air load" refers to what might be considered "boost"?

If so, and I may be wrong, what you need to bear in mind is that "boost" is best thought of as a resistance to the airflow from the supercharger. If the air being pumped into the engine isn't 'bled off' by passing intot he cylinder(s), it will increase - it's like blowing into a straw with the end open compared to the end closed - you need to increase the pressure of your blowing to move the air through it.

In this case, I would say the camshaft timing is such that there is more resistance - from the opening period compared to the residual "back pressure" from residual exhaust gases and/or earlier closing - to the air passing into the cylinder at rpm below the dip, then the intake cam moves to a position where the air passes into the cylinder more easily, due to less resistance, which bleeds of the pressure a little, before the overall breathing of the engine starts to increase resistance again.

Playing with the cam' timing should help fill the dip.

This is also an excellent illustration of why I HATE this whole idea of using "VE" for tuning - the more accurate term would be "Mass Efficiency". "Volumetric Efficiency" should reflect the internal breathing - the relative volume of air in the cylinder Vs the actual volume.

If using the "tuners" definition of "VE", there is little, if any, difference, but the engine's actual ability to use the airflow is markedly different.

Gord, I totally get and respect what you're saying.

I look at it as there's the VE of the engine, and it is different from what we tune, but actual engine VE is something we never use. We never run the engine with no manifolds, no throttle, etc. so it's a theoretical thing we never get to experience.

What we are actually running and tuning is a complete engine assembly. Once I accepted that, a supercharger or turbo is just one more part of the engine assembly that gets incorporated into the total VE of the whole system.

Hi, thanks for your reply and I totally understand what you are saying. I'll have a play with the VVT and see if I can smooth out the dip. Cheers.

Sounds good Phil. Just remember some of what you're dealing with is the nature of the airflow of the engine, and you can't always force it to do what you like, but you can find the best of what it has to offer.