Notice the differences in the rear tire radius through the launch on each example. The Stage II example is keeping the rear tires crushed to the ground over a longer period of time. This results in a lower overall drivetrain ratio for a longer period of time and a better tire contact patch.
Time to go Stage II!
- Thread starter Alky V6
- Start date
The same vehicle specifications were used for both examples except for the engine power curve and the shift points. Same trans and converter, rear gear ratio, tires, traction factor, etc.
The light blue trace line is the rear tire radius dimension.
The green trace line is the engine bhp.
The blue trace line is the engine rpm.
The red trace line is the percentage of vehicle weight on the front end tires.
The light blue trace line is the rear tire radius dimension.
The green trace line is the engine bhp.
The blue trace line is the engine rpm.
The red trace line is the percentage of vehicle weight on the front end tires.
Where do I need to start, Norbs?
Start by putting the car together and take it down the track
Com'on, Norbs. The graphs don't fuel any thirst for knowledge just begging,... pleading to be satisfied?Start by putting the car together and take it down the track
Ask anything. There are no wrong questions. Only right questions.
That's an EXCELLENT question, Norbs.
Three factors come into play. The level of rpm at the beginning of the shift, the torque curve of the engine and what it is doing throughout the shift, and the setup or configuration of the torque converter.
Let's start with the torque curve of the engine. The more torque that is input into a particular torque converter, the more we are able to increase the stall speed. So the torque level of the engine at the start of the shift and the torque level at the end of the shift factor into the amount of rpm drop.
The next is the engine rpm range that the shift is occurring in. For instance, shifting at 6,500 rpm versus 9,000 rpm. This factor has to do with the two types of flow patterns that we have going on inside a torque converter, vortex flow and rotary flow, and at what engine rpms each of those flow pattern types is strongest and in what rpm range one flow pattern type changes from the one type to the other. These rpm ranges in which the flow patterns will change from vortex to rotary is highly dependent on the torque input into the torque converter and the torque converter setup.
Let's look at my Stage II example with the drag sim. We'll pick out two different shift points. One example will use a 9,000 rpm shift point for both shifts. The other will use a 7,250 rpm shift point for both shifts.
Included in these new graphs will be the amount of torque converter multiplication we have throughout the run, a good indicator as to whether we have vortex or rotary flow in the torque converter, and we'll also include the amount of TC slip.
Vortex flow is strongest when the speed difference between the input into the torque converter (engine rpm) and the output from the torque converter (trans input shaft) is greatest. As the difference in speeds come to more closely match, you gradually move from vortex flow to rotary flow. When you have a rotary flow condition, that is when the TC is considered to be coupled.
Vortex flow will give varying amounts of torque multiplication, depending on the speeds of the input and output of the torque converter and the difference between the two. The greatest torque multiplication, and vortex flow occurring when the engine is at the stall speed of the torque converter and the speed of the output of the torque converter, the transmission input shaft, is at zero.
Rotary flow will give you no torque multiplication. The rpm speeds of the input and output of the torque converter are very close to the same when you have rotary flow. Rotary flow is characterized by low TC slip rates.
A TC can be considered to be coupled at slips rates as high as 15% at high engine rpm.
Included in these new graphs will be the amount of torque converter multiplication we have throughout the run, a good indicator as to whether we have vortex or rotary flow in the torque converter, and we'll also include the amount of TC slip.
Vortex flow is strongest when the speed difference between the input into the torque converter (engine rpm) and the output from the torque converter (trans input shaft) is greatest. As the difference in speeds come to more closely match, you gradually move from vortex flow to rotary flow. When you have a rotary flow condition, that is when the TC is considered to be coupled.
Vortex flow will give varying amounts of torque multiplication, depending on the speeds of the input and output of the torque converter and the difference between the two. The greatest torque multiplication, and vortex flow occurring when the engine is at the stall speed of the torque converter and the speed of the output of the torque converter, the transmission input shaft, is at zero.
Rotary flow will give you no torque multiplication. The rpm speeds of the input and output of the torque converter are very close to the same when you have rotary flow. Rotary flow is characterized by low TC slip rates.
A TC can be considered to be coupled at slips rates as high as 15% at high engine rpm.
This first graph is using a 9,000 rpm shift point with the Stage II setup.
Instead of using a TC slip number or percentage, the chart is using a TC speed ratio. It is the speed ratio comparing engine rpm and transmission input shaft rpm. For instance, a speed ratio of .89 would mean a slip percentage of 11%.
1.00 - .89 = .11
Notice with the red trace line in first gear, near around 7,500 rpm the TC speed ratio takes a quick turn towards better coupling. The power level from the engine has increased to a level where the engine attempts to cause more slip rate in the TC, but rising engine rpm is countering the rising bhp level and forces the TC to move quicker towards coupling. It would probably be better to show the tq curve rather than the hp level for this type of comparison. The power curve in this example peaks at around 8,200 rpm and begins to level off.
The rpm level plays a strong part in how strongly the TC moves to rotary flow. The higher the rpm, the stronger the TC wants to be in rotary flow. This is due mainly to the centrifugal forces on the fluid inside the TC.
Instead of using a TC slip number or percentage, the chart is using a TC speed ratio. It is the speed ratio comparing engine rpm and transmission input shaft rpm. For instance, a speed ratio of .89 would mean a slip percentage of 11%.
1.00 - .89 = .11
Notice with the red trace line in first gear, near around 7,500 rpm the TC speed ratio takes a quick turn towards better coupling. The power level from the engine has increased to a level where the engine attempts to cause more slip rate in the TC, but rising engine rpm is countering the rising bhp level and forces the TC to move quicker towards coupling. It would probably be better to show the tq curve rather than the hp level for this type of comparison. The power curve in this example peaks at around 8,200 rpm and begins to level off.
The rpm level plays a strong part in how strongly the TC moves to rotary flow. The higher the rpm, the stronger the TC wants to be in rotary flow. This is due mainly to the centrifugal forces on the fluid inside the TC.
Now, this one is interesting. The only difference is using a 7,250 rpm shift point on both shifts with the Stage II setup.
The shifts in this example are occurring at a rpm range where there is still a high TC speed ratio happening, and the TC stays in torque multiplication for the vast majority of the run.
The TC is also not coupling very well in this example due to the lower rpm operating range. In this example it's clear to see that the engine rpm operating range plays a large part in how well this particular TC setup couples at this horsepower level.
In this example, a spragless torque converter would be quite adequate, especially on an 1/8 mile track, since the stator remains in torque multiplication mode and only finds the need to overrun at the very end of this 1/4 mile run.
The shifts in this example are occurring at a rpm range where there is still a high TC speed ratio happening, and the TC stays in torque multiplication for the vast majority of the run.
The TC is also not coupling very well in this example due to the lower rpm operating range. In this example it's clear to see that the engine rpm operating range plays a large part in how well this particular TC setup couples at this horsepower level.
In this example, a spragless torque converter would be quite adequate, especially on an 1/8 mile track, since the stator remains in torque multiplication mode and only finds the need to overrun at the very end of this 1/4 mile run.
A few interesting things about the Stage I graph. The TC torque and speed ratio trace lines look much like the Stage II graph with the 9,000 rpm shift point, even though the shift point of the Stage I setup was only around 7,700 rpm. The difference between the two being not just the shift points, but also the engine torque curves.
The simple answer to Norb's question is, the interaction that the different engine torque curves and the different engine rpm operating ranges have on the particular characteristics of the same torque converter result in the different rpm drops through the shifts.
Sorry I couldn't make the answer any simpler, Norbs. Any answer that involves torque converters is going to be a very complex and abstract answer. I hope what I layed out allowed you to form some visualizations in your mind of what's going on.
Very few people have the ability to visualize such a technical and abstract topic in their mind. That's what makes trying to convey the finer points of how a torque converter operates, especially in a racing situation, so difficult. I'm sure I lost a lot of people with this long explanation. Oh well, no one can say I didn't make a fair attempt. This is probably the most involved attempt in trying to explain such a subject anywhere.
If anyone has any questions, don't hesitate to ask. Have a grrreat day.
Very few people have the ability to visualize such a technical and abstract topic in their mind. That's what makes trying to convey the finer points of how a torque converter operates, especially in a racing situation, so difficult. I'm sure I lost a lot of people with this long explanation. Oh well, no one can say I didn't make a fair attempt. This is probably the most involved attempt in trying to explain such a subject anywhere.
If anyone has any questions, don't hesitate to ask. Have a grrreat day.
If it turns out that I might need as much as 15 psi boost to obtain the proper amount of power for the launch at around 5,500-6,400 rpm with the Stage II setup, that should allow power to come in quicker as the car leaves the line and rpm increases. The boost level will be at a fair level and have a good head start to begin with as the VE of the engine comes in. Pull motor pull.
