Originally Posted by oab_au
Deciphering Dyno charts for some is like me, looking at Phil’s source code. It looks very good, but tells me nothing. To Phil it has a whole lot of clues in plain sight.
Reading a torque chart tells me every thing about the performance of the engine and transmission. Everybody looks at the Numbers, how much power does it make?
I look at the shape of the curve, is it flat or peaky, are there any dips or peaks. What happened in the breathing to cause that dip or was it the exhaust?
The charts that Tina posted, shows the torque delivered to the wheels through the 1st-2nd gear change that we can read, to see the effects of the change on wheel power. To understand this we have to know that the ratio change does to the flow. When we do the ratio change from first gears ratio of 2.785:1 to second gears 1.515:1 we will be changing the speed of the engine by 2800 rpm. At full throttle the auto box will change at 6500 rpm, so the engine speed has to slow to 3700 rpm.
In the before chart we see the torque line rising fast at the start and slowly decrease as the speed rises. At about 34.5 MPH/6500RPM the fuel injection pulse to every second injector is turned off. At the first green line the band is applied and the box is in second gear. The rise in the torque line between the two green lines is the Torque converter slowing the engine down the necessary 2800 rpms. This is helped by the 50% torque cut that is on, but the torque still increases as the 2800 rpm difference brings the converters torque multiplication factor up to 1.9 times. As the engine slows and the speed difference reduces so does the torque factor. The peak of this is reached at about 36 MPH and the engine has come down to speed at about 37 MPH, the injection is brought back on gradually to conform to the “no change felt policy”, and the engine is restored to full power at about 38 MPH. All the time between the two red lines is the lag that we feel, about 4.5 MPHs worth.
In the after chart a better view shows the three changes into 2,3,4. In this chart we see by the flat Air/Fuel curve that there is no cut made. The change takes place at the first of the green lines at about 33-34 MPH/6500 RPM. When the band is applied and the box is in second gear, the torque converter starts to slow the engine, but because the engine is still at full power the multiplication factor of about 1.9, results in a much higher torque output, peaking on the red line, at about 36 MPH. By about 38-39 MPH the engine has slowed to the new ratio speed of 3700. This is fortunate as this puts us right in the middle of the Inlets Inertia torque curve, where it is putting out 90 odd % of the total torque, this then multiplying by the factor of 1.9 produces an increase torque flow of about 227 ft lbs.
The other things to be noticed is that when the band is applied at the first green line, there is no shock recorded in the torque, as it would have shown up as a sharp increase. over a very short period. The following torque peak is due to the converter multiplying the torque over a longer period that is felt as a surg, and as the hydraulic engagement pressure is increased in this time, the band can easily hold this increase.
Comparing the 3 changes, it can be seen that the amplitude of the torque peaks reduces as the gearing is increased, the 3-4 change has a lower torque peak that the 1-2 change. You should note that Tina’s car is fitted with 4.44:1 diffs so the lower ratio produces torque peaks in her car, that will be higher, and over a shorter period, than a car with the STD 3.45:1 diff ratio.
Harvey.
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06-02-2008, 11:55 AM
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