Our senior design team is having a healthy debate on where to place the intake filter. Each conversation returns to the question of air filter placement and effects induced by each location. Concerns include availability of air and if you were to place the intake behind the car would the direction air traveling past the intake cause a significant loss due to having to change directions to enter the intake. One of our professors whom admits to not knowing much about FSAE had the same concern of placing the intake behind the car as opposed to facing toward the direction of travel.

So my question to the forum would be does anyone have any suggestions on how the advantages and disadvantages could be quantified?

I don't have any CFD results that have an air filter on it, but I do have some runs going right now that show the affect of throttle body orientation to the air stream. Send me a PM with your e-mail and I will shoot you some images when I am done.

EDIT: Or once I fix how I am doing it. CFDesign and me didn't communicate very well this time.

Really, it comes down to the issue of packaging.

Everyone agrees that putting it in the stream where you can get a bit of positive pressure will aid your pressure ratio across the restrictor, however slightly at our slow speeds.

The biggest question is "Is it worth it?" and I think that if you're adding weight in ducting, adding weight in a scoop or a filter box or what have you, you're going to lose more than you gain. But if it fits within your constraints, there is some very small benefit to be had. A quick CFD will get you a result (OK), or even a couple pressure transducers in the intake tract(best).

I would evaluate it in terms of potential power gain (or loss) versus system complexity. If you get 97% power with a rear-mounted setup, but reduce your part count and subsequent mass by 30%, it may be worth it to lose the fraction of power. Also consider intake charge temperature, which can be a much larger factor.

I agree with Wesley on everything that he said completely. I find alot on these cars that packaging dictates a good amount. This competition if you look at the points breakdown is more about handling than power, so I am not concerned about what little I am losing. Only reason I have been even running the CFD is because a team member asked me how flow was affected and I didn't have a straight answer. Figure it can't hurt to have a hard number if a design judge asks.

I will agree with Wes on packaging, but I do feel that pulling cooler air away from the motor and exhaust will have a greater effect than any kind of ducting you will see. I know that the f4i engine block gets hot as Hades, and in Michigan I want to be pulling that nice 40 degree air in (If I could only make it dry, hmmm... maybe a dehumidifier?)

Wesley I agree, and maybe an assumption for the design would be that the gain isn't enough if there is significant weight to be added. If there is no change in weight the safer place to put the intake would be where the intake charge temperature would be the least.

Some of the team mates don't seem to think that the temperature of air is going to be much different in those two locations. To me it would seem to be significant in a place like California where the cement or tar would radiate heat. Sounds like it might be time to go log some temperature on a sunny day. Once our weatherman stops talking about snow up here, I'd think he was drunk except we keep seeing slushy rain ever now and then.

Thanks, Rob

Intake air temperatures ranged around 115-125 for us with a rear mounted intake. (just behind motor near diff)in 2008 at California

IAT's I think were much closer to track ambient at 105-110 at California with our sidepod mounted intake. (Zach, do you remember?)

On the topic of air temperatures, I believe it was Wisconsin one year that ran a rear mounted radiator (just behind the engine) and did a study that I read about the ambient temperature through the radiator. It was pretty impressive how much cooling efficiency they lost with that setup, finding that switching to a sidepod moutned radiator made the system sufficient.

quote:

Originally posted by Wesley:
Intake air temperatures ranged around 115-125 for us with a rear mounted intake. (just behind motor near diff)in 2008 at California

IAT's I think were much closer to track ambient at 105-110 at California with our sidepod mounted intake. (Zach, do you remember?)

Hmmm... thought it would have been more than that. I guess that is still up to 3.5% higher air density with a side vs. rear mounted intake. We have an overhead mount, and I would like to see what the change is in this location since the entire plenum itself sits farther away from the motor. I think that this has the largest play on the IAT's. If you have a plenum that bends right down on top of your motor (most rear mounts intakes, especially on the larger i4's), and it has no designed heat reflection or resistance, it's gotta cause higher temps. Of course I have no data to back that up at the moment, but maybe in a couple of weeks when we start logging more in car data.