Hi, I'd had a recent event while tuning a vehicle and was wondering if anybody could tell me what this was called (I don't have a name for it but I know it exists)

For this example I will use a naturally aspirated engine (although my event was on a turbo car) for clarity and simplicity,
ex.
I have 6L engine with a map sensor,
I go to wide open throttle while driving and notice my map sensor shows 0psi like it should.
I tune the ignition timing by EGT (lowest egt with minimum timing advance) and by torque output (best torque +/- 5% with minimal timing advance).

Now, I add 2000lbs of weight to the vehicle in the trunk, and do this again.
Suddenly my octane is insufficient, and the timing is too advanced. I expected this of course, but I do not have a name for it. Clearly "Map" tuning is not "load" tuning, since I just increased load significantly (the force opposing the connecting rod is higher) and the LOAD scale still just shows the same old 0PSI.

The reverse is also true, I REMOVED 2000lbs from the vehicle and suddenly the engine could stand quite a bit more timing advance at the same octane. Same 0PSI shows on my map sensor.

Anyone could tell me what this is called, I would be most appreciative... thanks

 

Its called tuning. lol

 

hehe, yeah I suppose. I just thought there was some other name associated with the loading of the engine for different circumstances. I bring this up because a well known tuner seemed shocked when I told him that 0psi on a map sensor was not "full load" on his "eddy current dyno" and that additional load in the form of a dyno brake, or cement bricks in the trunk, could be applied to increase load all the while the map sensor was still showing 0psi, even to the point that the engine was decelerating at WOT.

I went on to explain you could peg the map sensor to 0psi in neutral if you wanted, free-revving the engine, and that each gear afterwards, 1, 2, 3, etc... applied a different form of load to the connecting rod as the engine accelerated more slowly through each gear per unit time. Ultimately what I am getting at is that the force required to turn a dyno roller, for instance a dynojet roller, which is a given weight, could not actually simulate the rolling resistance of the vehicle, and this would alter final timing values, the greater the descrepancy between vehicle rolling resistance and dyno roller turning resistance would result in a "perfect dyno tune" being farther and farther off it's mark once the vehicle hit the road, with the timing of course being too far advanced if a heavy vehicle were dyno'd on a lightweight roller.

So theres no name for it? I suppose we could call it "load based tuning" but that leaves something to be desired. How about "multiple rolling resistance load based tuning" or "actual rolling resistance fine tuning".

I've come to expect this sort of thing, and for the last five or eight years now I have been tuning my cars on the street first, and then taking it to the dyno for 1-10 passes just to make sure everything was peachy. And the cream was, if I knew the vehicle was heavy, like a MKIV supra for example, I also knew it would pick up a significant bit of power with a bit more timing on the dyno, even though the street timing unit I had picked out for it was optimal for the real road.

 

We like to refer to this as WORK, defined by the ability to move a mass over a period of time. When you change mass or time, you change the amount of work done. Your MAP sensor value is only one parameter in determining how much work your engine is doing. Tune what the motor handles under real world conditions, and leave the dyno numbers in the junk bin with the ***** enhancing pills.