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Old 05-13-2014, 11:14 AM   #1 (permalink)
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Cobalt Coupe Aero Mods

I know this has been discussed and that the best way for me to learn is to just do it, however I do like to listen to others thoughts and experiences prior to diving in.

So, the cage is a 2009 coupe FWD w/5sp. I've done no modifications as yet, but first up will be an upper grill block leaving the lower open ( 'cause I'm in OK and it'll be summer soon).
Since I'm leaving the lower grill open to the radiator, I want to maximize the air flow through it by forming a ram scoop/duct from the front bumper grill to and around the front of the radiator. My thinking is that it should provide MORE than adequate cooling during my commute ( 100mi/day all interstate) and possibly better flow with less turbulence.
While under the car I should also make an engine bay belly pan from the bumper to the cab. This should also function to keep the engine bay warmer and help my WAI without having to duct to the exhaust minifold.

Any thoughts or suggestions are welcome and appreciated!

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Old 05-14-2014, 01:19 PM   #2 (permalink)
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I haven't done anything to change mine yet, one of these days I'll do the upper block, I wouldn't worry about trying to get any extra air until I see water temp go up, since we have a digital water temp display I'd just watch that.

I've though of extending the existing air dam down a few more inches but haven't yet, I'd have to take it off in the winter. And it's so far back I'm not sure it would help much.

The engine bay from below is wide open so a belly plan might help.

I wouldn't mind lowering it, but don't want to loose any snow clearance. Maybe that's an option for you. Doubt it would save enough to cover parts and alignment.
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Old 05-14-2014, 03:53 PM   #3 (permalink)
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With your partial bellypan, hold the front edge in some sort of slot so that it can't droop down and turn into an air scoop. That's a failure mode.
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Old 05-14-2014, 04:18 PM   #4 (permalink)
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I saw this diagram while browsing. My idea for a belly pan is a hardware cloth reinforced fiberglass piece tucked in behind the front bumper lip and secured. I'm not so sure about the sides or rear just yet.
As far as that diagram, I dont think I will be able to get the proportions just right (the lower space bumper<->radiator), but how much will that really matter for my purposes?
Also, since the layout of my engine is with the TB intake at the FRONT of the car and exhaust at REAR...(ie the right way IMO), I would like to shorten my intake tube and have it in the airflow behind the radiator. Too bad the bend(s) would be too sharp and too many vs stock.

For material; ABS, fiberglass, or Corrugated Plastic? cost, durability, ease of manipulation...ect.
Thanks!
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Old 05-15-2014, 05:44 PM   #5 (permalink)
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how much will .................

Quote:
Originally Posted by OKXXFE View Post
I saw this diagram while browsing. My idea for a belly pan is a hardware cloth reinforced fiberglass piece tucked in behind the front bumper lip and secured. I'm not so sure about the sides or rear just yet.
As far as that diagram, I dont think I will be able to get the proportions just right (the lower space bumper<->radiator), but how much will that really matter for my purposes?
Also, since the layout of my engine is with the TB intake at the FRONT of the car and exhaust at REAR...(ie the right way IMO), I would like to shorten my intake tube and have it in the airflow behind the radiator. Too bad the bend(s) would be too sharp and too many vs stock.

For material; ABS, fiberglass, or Corrugated Plastic? cost, durability, ease of manipulation...ect.
Thanks!
It's unlikely that you'll ever operate your engine at full load,so you'll never require your cooling system to deal with the maximum heat flux.A less than optimum inlet duct will probably be just fine.Just watch your temps as we head into summer.
As to the combustion air inlet behind the radiator,I'd recommend against that.
With the inlet ahead of the radiator bulkhead you have the most favorable pressure gradient for filling the combustion chambers.So your volumetric efficiency is already optimized.The restriction through the heat exchanger would aggravate pumping losses a little.And you'd have no control over charge density with that pre-heated air.Something perhaps not anticipated by closed feedback loop look-up tables.Don't know.
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Old 05-16-2014, 12:45 PM   #6 (permalink)
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Quote:
Originally Posted by aerohead View Post
As to the combustion air inlet behind the radiator,I'd recommend against that.
With the inlet ahead of the radiator bulkhead you have the most favorable pressure gradient for filling the combustion chambers.So your volumetric efficiency is already optimized.The restriction through the heat exchanger would aggravate pumping losses a little.And you'd have no control over charge density with that pre-heated air.Something perhaps not anticipated by closed feedback loop look-up tables.Don't know.
If I am reading this correctly;
? are you suggesting that my intake inlet be in fresh-higher pressure air rather than in the engine bay/warm air? I understand that for power performance, higher density and cooler charge is preferable for cylinder filling. But the interpretation I have from reading these forums is that warm air with low density is preferable for FE by necessitating that the TB plate open more to compensate for an otherwise richer fuel charge.

It would be wonderful if a higher pressure/cooler air charge could provide me with more power AND a better FE, because that is a much more budget friendly mod than the exhaust header I need to save for. I could do a CAI for just a few 10$
---although, looking at my past week avg compared to the same drive last week, I don't think that a cooler charge is better for my consumption as the weather was in the 90's last week and only ~70 this week for the afternoons.

For a little info about my engine set up;
2.2L I-4 , DOHC VVT , MPFI with electrically operated TB...really nothing fancy for these days.

Last edited by OKXXFE; 05-16-2014 at 12:57 PM..
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Old 05-16-2014, 04:03 PM   #7 (permalink)
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Quote:
For material; ABS, fiberglass, or Corrugated Plastic? cost, durability, ease of manipulation...ect.
They really would be all about the same, maybe coroplast is not as durable as ABS or fiberglass. Consider Polymetal; the strength of 5/8" plywood at 1/10th the weight.

I don't know about the air intake, but what I hear is pretty much CAI for power, WAI for economy. If you want to go down that path, I'd look to Autospeed:

Ballistic Bellmouths

Making your own Bellmouths

Building and Testing an Airbox
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Old 05-16-2014, 06:25 PM   #8 (permalink)
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suggesting

Quote:
Originally Posted by OKXXFE View Post
If I am reading this correctly;
? are you suggesting that my intake inlet be in fresh-higher pressure air rather than in the engine bay/warm air? I understand that for power performance, higher density and cooler charge is preferable for cylinder filling. But the interpretation I have from reading these forums is that warm air with low density is preferable for FE by necessitating that the TB plate open more to compensate for an otherwise richer fuel charge.

It would be wonderful if a higher pressure/cooler air charge could provide me with more power AND a better FE, because that is a much more budget friendly mod than the exhaust header I need to save for. I could do a CAI for just a few 10$
---although, looking at my past week avg compared to the same drive last week, I don't think that a cooler charge is better for my consumption as the weather was in the 90's last week and only ~70 this week for the afternoons.

For a little info about my engine set up;
2.2L I-4 , DOHC VVT , MPFI with electrically operated TB...really nothing fancy for these days.
I'm not an engine expert.
My carbureted Honda uses a heat-riser and mixing valve to attempt to maintain about 110-F intake air into the carb.
With electronic fuel injection,your BSFC should already be figured for the production intake/exhaust configuration.
Metering is extremely precise with EFI,I'm not sure the warm air mod will pay dividends.And I don't mean to disrespect those who advocate it.
If your present inlet is ahead of the radiator core,from a volumetric efficiency standpoint,I believe that you ought to maintain that.It is providing a minimum pressure drop while filling the combustion chambers.
You'll need so much mass of air per a given power setting,that doesn't change.
Your Mass Airflow Sensor already 'knows' how much air is coming in,and is providing a calibrated signal to the CPU to provide the fuel injection with the correct pulse width in order to provide the proper mixture.
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Old 05-17-2014, 07:10 AM   #9 (permalink)
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You folks really are very helpful. Thanks!
I have my first set of experimental data! While enduring a slow day at work I decided to grab the packing tape gun and attack my car. I sealed off the upper grill partition just to see what it might do.
Now, I understand that this on it's own is rather weak since the only non-variable was the road and speed traveled. I pretty much change everything else for my return home.

The Route: 50mi interstate highway; mostly concrete pavment
Ambient Temperature: 86*F winds SW@ 6-12mph (tailwind)

Traffic was a bit heavier than usual for Friday, and they didnt appreciate my doing 60-65mph on a 75mph road. I used my Hazard lights when a truck would come within 50m, it seemed to work as I dont think anyone ACTUALLY flipped me a "howdy". So keeping an eye on my coolant temps and speed I reset my AVG mpg as I got on the freeway, hard to do as I had several thousand miles on that average and had JUST got it to 37. Anyway, I definitely have some ducting to do as my coolant temps were flirting with 200*F after about 20mi. I didnt want to pull off and scrap the block but also didnt want to overheat, AAA or no AAA. Instead I adjusted the hvac vents and cranked on the heater to vent out the passenger window. It really works!
So, once I got home, I checked the avg...44.5mpg! my previous two tanks at this speed came in at 37-38mpg avg. I know this is just one run with too many variables so it doesnt mean much, but I havent seen this ever, and I drive the same route every day for the last year.
I am going to keep it in place and do some pre-fab to see about helping the cooling but first result looks promising!
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Old 05-17-2014, 03:31 PM   #10 (permalink)
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My cacklator says 18.6%! As you think ahead to the partial bellypan, remember that diagram has a control flap at the outlet. There's a lot of ways you could do that—sliding, rotating or hinging it.

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