Interesting observations...
10-04-2004, 06:56 AM
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Interesting observations...
Yesterday afternoon, as the initial stage of my project to install an RS4 IC in my '99.5 A4, I started plotting air pressure at a dozen points inside the engine compartment and around the front end of the car in 5mph increments from 20-80mph.
I'll need another few hours to finish recording all the readings, but I've noticed two interesting things so far:
1) The pressure differential between the front and back sides of IC is reduced by 40% -- Yes, 40%! -- when I was within ~50' of a car in front and didn't return to the free air reading until I dropped back to 100' or so. I haven't determined if/how this affects air flow through the IC -- that's next weekend's project! -- but my hunch is that it falls off correspondingly.
2) The wheelwells are at positive pressure, but at less pressure than in front of the IC, hence the reason why the vents in the S4 liners work. Because the pressure ahead of the IC increases more quickly with speed than it does inside the wheelwell, the pressure differential across the IC likewise increases with speed and (presumably) improves airflow as well. In other words, the faster you go, the better the ICs work ... duh!
However, while the vented S4 liners clearly offer an improvement over the non-vented A4 liners (I'm seeing ~15% greater pressure differential below 40mph, which is as fast as I've tested them so far), the best solution is no liner whatsover, as the pressure differential between the front and back of the IC increases a further 30%! If not for the risk of damage to the IC and upper fender area from stones being thrown off the tires, I'd seriously consider running "naked" and leave the liners at home in the garage. However, as a compromise between performance and protection, I'm going to investigate making some replacement liners from a heavy-duty 1/4" stainless-steel mesh. I figure this should be small enough to keep the big stones out, but large enough not to restrict airflow too much. Stay tuned...
I'll need another few hours to finish recording all the readings, but I've noticed two interesting things so far:
1) The pressure differential between the front and back sides of IC is reduced by 40% -- Yes, 40%! -- when I was within ~50' of a car in front and didn't return to the free air reading until I dropped back to 100' or so. I haven't determined if/how this affects air flow through the IC -- that's next weekend's project! -- but my hunch is that it falls off correspondingly.
2) The wheelwells are at positive pressure, but at less pressure than in front of the IC, hence the reason why the vents in the S4 liners work. Because the pressure ahead of the IC increases more quickly with speed than it does inside the wheelwell, the pressure differential across the IC likewise increases with speed and (presumably) improves airflow as well. In other words, the faster you go, the better the ICs work ... duh!
However, while the vented S4 liners clearly offer an improvement over the non-vented A4 liners (I'm seeing ~15% greater pressure differential below 40mph, which is as fast as I've tested them so far), the best solution is no liner whatsover, as the pressure differential between the front and back of the IC increases a further 30%! If not for the risk of damage to the IC and upper fender area from stones being thrown off the tires, I'd seriously consider running "naked" and leave the liners at home in the garage. However, as a compromise between performance and protection, I'm going to investigate making some replacement liners from a heavy-duty 1/4" stainless-steel mesh. I figure this should be small enough to keep the big stones out, but large enough not to restrict airflow too much. Stay tuned...
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