Perrin CAI related thoughts..

[Account Attempt No. 4]

Hey all, I put on my Perrin CAI very late last summer and I'm just about to start driving her again now that the snows melted

Now, I've been thinking about the aerodynamics of actually getting the fresh air TO the cai, and it seems to me that if a Grill is going to be put on (like the Grill Craft one), then its going to somewhat restrict air getting to the cai. Right? Obviously air is still going to get through it, but its going to be lessened.. Which means that most of the air would have to come from under the bumper. Has anybody done this/ seen the effects of this?

Secondly, behind the front bumper is the crash bar, which is -as we've all seen- a massive chunk of Styrofoam. I completely understand the need for this, but it seems to me that if the crash bar wasn't there, you could increase the air getting to the cai. So my thoughts are: Replace the crash bar.

I've come across the Drift Armor Drift Bar, which seems simple enough to install and basically takes out that Styrofoam chunk, (which can be seen in this great picture I stole from Ryan Quinn.. hope you don't mind).

What are your thoughts on this? Am I out to lunch on this or does it make sense?

[gramicci101]

That bar is designed to protect your engine and important bits if you slide into a wall at an event. What happens if you're on the road and you have an accident and that thing tears right through the other car? Especially what happens once both your and their insurance find out that you've modified the OEM impact protection? Or if you hit a pedestrian crossing the road? The OEM crash bar isn't just there for you, it's there for the other guy too.

What about the HKS scoop? It seems like it would draw much more air in than the normal snorkel.

[Account Attempt No. 4]

As I said, I completely understand the need for the crash bar.

My question is how to increase the fresh air to the CAI.

The HKS scoop seems to me would be the exact same as the Perrin CAI, as they sit basically in the same spot, sooo the same amount of air would be accessible to both. (not talking about how much air does or does not enter the CAI, just how to get it TO the cai)

[G-Man]

I don't think a little more cold air is worth the safety hazards or liability if something bad happens, or even the cost/benefit you would get from it. there are plenty of other ways to get more power without the risks this adds.

a vented hood should lower engine pressure and get more air going through everything including the CAI while lowering engine temps. I think the best way to get more air into your engine starts with a T, ends with an URBO

[gramicci101]

That whole area should be under positive pressure when driving at speed.

[Account Attempt No. 4]

Right, I was thinking about the vented hood as well, figured it would make for more of a "free-flowing" area.

And I agree that its under positive pressure, but in that area behind the Suby logo where the CAI sits, my mechanic argued would be one of the warmest parts of the engine, on the left side of the rad where there is a pocket for the air to go, in essence making the CAI not so Cold-air anymore..

Don't get me wrong, I have other performance mods that I use for power. I got the Perrin CAI mostly for looks and that sexy growl it gives. I'm really just curious if it in fact would do anything, given all of these factors.

[PERRIN_Chris]

I wouldn't really recommend modifying things too much as far as getting air to the filter. We actually tried a few things when we were developing the intake, and it really messed with the MAF readings.

[G-Man]

Originally Posted by gramicci101

That whole area should be under positive pressure when driving at speed.

I do not know much about car areo, am I missing a major side effect of a vented hood? or does it take no hood to break that rule?

[gramicci101]

The area behind the bumper is open to the front, so as you drive forward air is forced in, which raises the ambient pressure. Since that's where the intake pulls from, there isn't really a shortage of air. The size of the intake itself may be a restriction, but that's above my pay grade.

A vented hood does a few things. First, it allows the heat in the engine compartment a place to escape. Which is good, because our engine bay is an oven. Second, the direct airflow on the radiator, plus the fans on the radiator, are working to pressurize the engine bay with air. Hot air, because it was just forced through the radiator. You can see this sometimes when you're driving fast, because the hood will lift and shake around a bit, which is disconcerting. Hood vents relieve that pressure and give the heat from the radiator a way out.

@plucas is the aero expert; I'm sure he can correct me on some of these points.

[kuhlka]

Originally Posted by gramicci101

The area behind the bumper is open to the front, so as you drive forward air is forced in, which raises the ambient pressure. Since that's where the intake pulls from, there isn't really a shortage of air. The size of the intake itself may be a restriction, but that's above my pay grade.

A vented hood does a few things. First, it allows the heat in the engine compartment a place to escape. Which is good, because our engine bay is an oven. Second, the direct airflow on the radiator, plus the fans on the radiator, are working to pressurize the engine bay with air. Hot air, because it was just forced through the radiator. You can see this sometimes when you're driving fast, because the hood will lift and shake around a bit, which is disconcerting. Hood vents relieve that pressure and give the heat from the radiator a way out.

@plucas is the aero expert; I'm sure he can correct me on some of these points.

I've done 120ish in my car and I've never noticed the hood having issues.

Unless you're talking about triple digit speeds, ram air tends to be worthless for most vehicles. I recall motorcycle tests showing only a few horsepower gained at like 120+ on a Suzuki Hayabusa...

Ambient air temperature has a much bigger impact on power. A vented hood probably wouldn't hurt, though.

[G-Man]

Thanks that is what I expected, I thought your comment about pressure was meant to be a negative on the idea of a vented hood. I would like to think that because the engine bay has a little less pressure, due to the extra places for air to escape, there would be less resistance for air to get into the engine bay therefore creating more airflow in front/through of the radiator/intake.

Of course we are getting to the splitting of hairs on how much good it will do for the intake, but I would do that over removing the crash bar.

[gramicci101]

I've done 70 and had my hood lift up and shake a bit. People on here have said that having a vented hood or opening up the side vents helps alleviate that.

[Account Attempt No. 4]

I don't plan on removing the crash bar, I was just speculating that it would allow for a bigger pocket of air in front of the radiator.

What i AM however concerned about is that my Grill Craft grill will restrict airflow coming in from the front of the bumper. (see picture)

[Account Attempt No. 4]

...Compared to say.. this