|
|
| VE vs Exhaust
This article is going to try to help people understand the relationship between VE (Volumetric Efficiency) and the exhaust being used.
First thing is understanding what VE is. Basically,VE is a measure of how full the cylinders are.
The more air fuel charge that you can pack into a cylinder, the more power that the engine will make. This means that an engine setup with a higher VE number will make more power.
There are many modification that can increase VE. This article will concentrate on how the exhaust affects the VE.
The picture below is a screen copy of a Screamin Eagle Race Tuner. There are two screens being shown. One screen is on top of the other (overlapping). First notice the drop down list under "Table Selection" located near the left top of the picture. We are looking at "VE Front Cylinder and VE Rear Cylinder". The two screens will compare the VE of the front and rear cylinders. The area that we will compare will be the 100% columns This particular map is of a setup consisting of: Stock 96" engine with 25deg Injectors P/N 27709-06 E Air Cleaner and Breather Kit P/N 29440-99C and slip on mufflers. The comparison of these these maps is the Stock Exhaust Header.
The object is to have an exhaust that will have very close to the same VE on both the front and rear cylinders. The stock header assembly actually has a very even VE in both cylinders.
If one cylinder has a substantial increase of VE than the other cylinder, the power balance is not only off but the performance modifications will enhance or exaggerate the out of balance problem. Basically one cylinder will keep the other cylinder from it's full potential.
It is a fact that a 2 into 1 exhaust will usually out perform a true dual system or a set of drag pipes. The key is to find a 2 into 1 that will have an even VE on both cylinders. These are few and far between.
 
Notice that the numbers in the cells at 100% throttle are very simular in both front and rear cylinders. This shows that the VE of both cylinders are very close. This is a good thing.
Also notice that the highest VE is around the 3,500 RPM area. This is where the peak TQ will be with this stock cam and stock exhaust. Peak TQ will have the highest VE which will require the most fuel consumption. The results is a higher VE number.
This is why it is it is so important to choose the correct cam timing and exhaust to create optimum power.
Next I will show a couple of examples of the VE comparisons of different well known exhaust through Power Commander VE maps. The reason for using PC maps instead of SERT maps is because the factory SERT maps don't use after-market exhaust on their maps.
I also need to explain the PC system a little so you can understand the numbers in the cells.
PC maps use the base map of the bike. The map will look very simular the the previous map shown. The difference in the PC map is that the map cell numbers are all "0" on there base map.
Example: the cell on the SERT at 3,000 RPM and 100% throttle position is "94". The stock number on the PC at the same position will be "0" on a stock PC map.
The PC adds or subtracts to the "0" to correct the A/F ratio.
Example: +10 will be an increase in fuel (meaning a higher VE). -10 will be decrease in fuel (meaning a lower VE). Basically the higher the numbers are in a cell, the higher the VE will be compared to a stock map.
I will cut and paste the cells instead of posting pictures of the maps.
2500 - 6000 RPM at 100% TP
Rinehart D&D
True Duals Fat Cat
RPM R Cyl FT Cyl R Cyl FT Cyl
2500 27 10 38 40
2750 15 4 36 40
3000 12 9 29 34
3250 14 19 21 26
3500 31 23 18 19
3750 23 23 12 16
4000 25 19 14 17
4250 24 14 16 17
4500 22 11 13 14
4750 20 12 12 14
5000 18 12 12 19
5250 18 17 18 20
5500 21 16 23 24
5750 24 20 24 26
6000 25 17 24 29
From this chart you can see that the D&D Fat Cat has a higher
Cyl. vs Cyl. VE compered to the Rinehart True Duals.
There are areas where the Rinehart rear pipe created a higher VE (from 3500 - 6000)compared to the Fat Cat but, the draw back is that the front pipe has a problem creating a high VE at the same RPM. It's too bad that the front pipe can't perform as well as the rear pipe.
I am not saying that the Rinehart pipe is bad. I'm just showing the results from what I see on this particular chart.
The Fat Cat doesn't seem to scavenge as well as the Rinehart's rear pipe but, the cyl. to cyl VE is more even than the Rinehart.
| |
|