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Old 03-22-2007, 12:54 PM   #1
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Air Dam or Belly Pan

I'm the owner of a Pontiac Torrent. I've been able to get upwards of 26mpg on the interstate traveling 70 to 75 mph. Not to bad, but I would like to be able to hit 30mpg at times or once in a blue moon. For those that are unsure of what a Torrent is:



As you can see from the image, the air dam on this thing is HUGE!!! Bordering on cow catcher to me. My question is, would I benefit from removing the air dam and replace it with a full or partial belly pan? Or would a combination of both be better? Or leave it alone?

The Torrent is pretty much the same thing as a Chevrolet Equinox. An 05 Equinox, from the research I have done, has a cd of .42 and frontal area of 29.3 sq ft. Some changes were done in 07 to improve on the mileage on the vehicles (larger spoiler, relocated antenna, and I believe a smaller air dam) By removing the air dam, I would think that I would reduce the frontal area by 2 sq ft at least.

So what do you think? Improvement, bad move, not changing a brick?

For those wondering, I removed the roof rack.
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Old 03-22-2007, 01:55 PM   #2
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I would think that the belly pan would make a larger difference becuase of how much air is being pushed under the car by the air dam.
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Old 03-22-2007, 03:23 PM   #3
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I agree back off on the speed. If the choice is between an air dam and a belly pan go with the belly pan. It's much better bang for the buck. You get faster warmup, because it traps the heat, higher IAT ( for the same reason), and the aero benefit. While your at it throw in a grill block, that quick and easy, and check tire pressures.
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Old 03-22-2007, 05:37 PM   #4
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And if you don't use them, get rid of those awful roof racks.
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Old 03-22-2007, 06:01 PM   #5
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Rented the Torrent

I've rented the Torrent and agree that the higher speeds kill the FE per the ScanGauge.

Toecutter: he already removed the roof racks.

Since the Pontiac variant of this platform is designed for sporty driving, the tire and wheel combo seem to raise the profile and create excess drag.

It's an extreme measure (and would assuredly mess with your speedometer), perhaps a smaller wheel and tire combo would reduce the air moving under the vehicle and reduce the drag -- gearing may be a factor to consider, tho.

GM really needed to put a 5-speed auto in these (which is coming, including a 6-speed).

The best bet would be to look at the Busted and Confirmed Mods and Aero Mods stickies under the General FE Discussion Section. There may be some under-hood tweaks to benefit your FE performance, but driving style may be the biggest.

It'll be tough...

RH77
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Old 03-22-2007, 08:04 PM   #6
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Didn't see that very last sentence for some reason.
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Old 03-22-2007, 08:06 PM   #7
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Thanks for all the replies.

I know its not the best platform to be trying to get high mileage from, but I like improving unlikely candidates and save a penny or two.

The first thing to go was the roof rack, which I had a hard time convincing the wife we didn't need and if we did, it's a snap to put back on. She likes the way it looked!!!

I realize that reducing my highway speed down to 60 or so would help me crack 30mpg or at least get close to it, but I would like to stay, well, real world speed isn't really a good phrase because 60 is real world. Maybe more main stream speed, just the sane type of speed, not the life threating 80 or 85 while darting in and out of traffic driving that I see regularly. If I want to see how high I can get the mileage, then sure, I'll drop down to 60 or so.

The Torrent already has a 5-speed auto built by Aisin which is Japanese, but the GXP version will have a 6-speed in 2008. For 2007, they changed the final drive gear to 2.48 from 2.70 so that has been cover.

Also, the purchase of a ScanGauge and a grill block of some sort will also be in the works.

Thanks again for all the advice.
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Old 03-22-2007, 08:17 PM   #8
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Quote:
Originally Posted by zpiloto View Post
I agree back off on the speed. If the choice is between an air dam and a belly pan go with the belly pan.
So are you saying to keep the factory air dam and add a belly pan, or ditch the factory air dam and add a belly pan?
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Old 03-22-2007, 08:46 PM   #9
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Quote:
Originally Posted by Bill in Houston View Post
So are you saying to keep the factory air dam and add a belly pan, or ditch the factory air dam and add a belly pan?
It depends on what it looks like under there for attaching the belly pan. More than likely just leave it and use it to help anchor the pan. It would be nice to test with and without. On My Madza 626 the air dam, which extended down about 4", actually decrease FE because of the increase in drag. The 626 sits much lower to the ground than the Torrent. Some one like toecutter could help out here but I think that a belly plan replaces the need for a airdam. The lower the car is to the ground the more important the belly pan becomes.
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Old 03-22-2007, 11:00 PM   #10
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Quote:
Some one like toecutter could help out here but I think that a belly plan replaces the need for a airdam.
Sometimes. The way air interacts with a moving road vehicle is very complex. Usuaully, you'd need a wind tunnel to find out.

From what I've read, the bellypan will typically have a larger impact than an air dam(lots of exceptions). while a bellypan most often won't add drag, it is fairly common for an air dam to from the increased frontal area. You really have to consider each unique car, and the only way to find out if you don't have access to such info from the car's manufacturer or some SAE publication, is to try it yourself. Since normal folks don't have wind tunnel testing, A-B-A FE testing with a scan gauge, coast down testing, and tuft testing all have their uses. But their margin or error is large enough that you won't notice any single gain or loss if it is small. But a lot of small gains add up to something large, so it is very hard for a hobbyist to get it right. some cars are easier than others.

Clencher hasn't had much results with his Tempo mods, but Basjoos and Metro MPG have had some very noticable results. Results will vary a lot.

The only way to see what works if someone else hasn't done it before is to try it yourself.

If my parents hand the Sidekick over to me, I will definately aeromod it and post results. I'll be doing that with the GT6 once it's on the road as well.


Don't just take my word for it though. I'm not an aeronautical engineer or aerodynamics expert. I'm not as qualified to answer this as some other members here who have actually seen these changes first hand or who have studied aerodynamics in a university setting. I've mostly dealt with theory so far.
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