We wanted this testing to be performed on the road to obtain real world data, as opposed to on a dyno. This method would allow the air dam to obtain actual flow to be received from moving at realistic speeds on the street. The conditions were less than ideal for tire grip (28 degrees F), so tests with tire spin were immediately thrown out and retested. However, since we’re measuring differential pressure the high density of the air due to the low temperatures has no effect on the overall pressure reading.
The test was performed the same each time, on the same stretch of road. The road was uphill, which is beneficial to increase the time of each pull in order to have a better chance of obtaining accurate sample data to combat the low sample rate of the manometer’s datalogging capabilities. We started off in first gear, rolling into the pedal to wide open throttle to avoid wheel spin, shifting at 7300rpm into second gear, straight into wide open throttle, shifting again at 7300rpm, and immediately into wide open throttle through all of third gear. Each run took approximately 14 seconds to complete. We performed this test 3 times for each configuration, measuring pressure drop from:
- Snorkel inlet to airbox inlet
- Front of airbox to rear of airbox (filter)
- Rear of airbox to entry of intake elbow (MAF housing)
- Entry of intake elbow to throttle body
- Snorkel inlet to throttle body
These runs were performed back to back on the same day, stopping each time briefly (less than 5 minutes) to save the datalog file to the computer, and/or to change pressure test locations on the intake tract.
This graph shows what happens across first through third gear, which is clearly shown by the fact that all five components have three clear humps, each with longer durations. These occur during wide open throttle, and the dips show the pressure approaching 0 between shifts. This graph also shows why having such a low sample rate makes for poor data, but we’ve made up for it by increasing the amount of trials. The fact that the graph maxes out for the overall system at about 9.5in of H2O in all three gears shows that that value is most likely correct for the overall system. Same goes for each of the individual components of the system; in each gear they seem to have the same maximum value. The graph also shows that restriction increases as RPMs increase, because as RPMs increase so does the required flow rate. The short duration of first gear shows the weakness of the sample rate, as the peak numbers of the individual components do not exactly match the peak numbers of each component in second and third gear. For this reason, the graph is most accurate for the third gear section (approximately 9 through 14 seconds), and shows a nice curve instead of a quick peak. However, for illustration purposes, showing all three gears shows that the pressure drop is RPM dependent and not speed dependent as would be initially expected. One would expect more air in the front air dam from the increase in speed to change the results in each gear, but clearly it does not.
This graph also does a good job of “double checking our data.” Remember that the orange line (Snorkel to Throttle Body) is the overall restriction of the system, and that it is the sum of the individual components. The graph of this curve is real world data, and is not simply the overall curves added together in Excel. However, if one were to measure the peaks of each gear for each individual component, and add them up, they would find that they total up to about 9.5in of H2O, which is what is shown to be the peaks of the overall system.
The effect the snorkel had on the system was very interesting. The snorkel showed a consistent pressure gain of about 3in H2O. The fact that the inlet is smaller than the outlet lends that the decrease in velocity of the air as it passes through should increase the pressure. However, the fact that this number is nearly high enough to cancel out any one other component’s restriction shows that in stock for the intake is very well designed. Each other component seems to have a restriction of about 4in H2O (air filter, MAF housing, intake elbow).
This answers a lot about the perceived weakness and the performance of the stock intake. It also goes to show that since the pressure drop doesn’t seem to be dependent on vehicle speed that all of this testing could have been performed stationary while strapped to a dyno. Removing the snorkel should yield no performance gain, but leaving it in could be compared to removing the air filter, or the MAF housing, or having a lossless intake elbow. However, all of these perceived restrictions really are not that bad. Each component having a restriction of 4in of H2O is really only equivalent to about 0.144psi, with the total intake’s restriction being equivalent to about 0.342psi. If I were to perform some completely fake equivalency math, and say that this car makes about 165whp in stock form, and at one atmosphere (14.7psi), a restriction of this size would be equivalent to about 3.84whp. So we would expect to see a gain of only about 3.84whp if we were to create a completely lossless intake system that acted at the exact same air to fuel ratio. However, luckily that math is completely fake, and just for illustrative purposes as there have proven to be larger gains than that achieved without creating a theoretical “lossless intake.” This is true because there are so many more contributing factors than just reducing pressure drop on an intake that is already well designed.
Chase – Engineering