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Old 07-05-2015, 03:05 PM   #1
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Default Rear Undertray Extractor Design Question

I'm installing an intercooler in the bottom portion of the front bumper, between the inlet of the bumper and bottom of the radiator. It's occupying some of the space of the factory undertray now, thus I have to build a new one. It's like an upside-down v-mount, sort of. Sav did it a long time ago, I dunno how well it worked for him though.

Here's a drawing of what it looks like, and my guess at what the undertray should look like.

I'm not the best at predicting how airflow works, so I wanted to get the expert opinions here on if this extracotr/undertray will work, or what I can change to make it work better? I basically found some pics of how some race cars do hood extractors, and used that design but upside down since it's on the bottom of the car. I labeled some of the points and pieces to make discussion easier.

Thoughts? Do I even need Sheet Metal 3 if the splitter is there? Or would it worthless? Would moving point "D" further down improve airflow through the intercooler?

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Old 07-05-2015, 05:04 PM   #2
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I thought he had done something like this, to provide two separate airflow passages

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Old 07-05-2015, 05:19 PM   #3
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He may have done that, I dunno. I may do that too, but I'm gonna try it without that piece first to see which works better.
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Old 07-05-2015, 05:51 PM   #4
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IIRC the reason they did it was if it is not there, the air just takes the path of least resistance, and then one of the heat extractors does not work to potential

will have to wait till they chime in.
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Old 07-05-2015, 11:07 PM   #5
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Out of curiosity, why are you doing this?
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Old 07-06-2015, 12:15 AM   #6
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Originally Posted by Ted75zcar View Post
Out of curiosity, why are you doing this?
Well I figured having a duct of some type on the bottom was better than nothing. Right? Like when people do hood vents vs just cutting a hole in the hood, the use an actual vent/scoop depending if it's an inlet or outlet.

But I've never made a vent thus this thread!
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Old 07-06-2015, 12:26 AM   #7
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No, the intercooler placement in general. Are you following through with the compound, and need 2 ICs?

I think you will need the diverter BTW. The frontal area of the lower IC will be essentially zero. You will be relying solely on the pressure differnce between the area in front of the radiator and under the car to induce flow. The diverter on the other hand allows you to use the vehicle forward velocity times the apeture area with an efficiency factor for you core flow. According to Corky, you will want ~2:1 ratio or better core flow to charge flow.

Anyway, if you are compounding, sweet. So am I. I think you move a little more quickly than I do though.
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Old 07-06-2015, 12:35 AM   #8
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Originally Posted by Ted75zcar View Post
No, the intercooler placement in general. Are you following through with the compound, and need 2 ICs?

I think you will need the diverter BTW. The frontal area of the lower IC will be essentially zero. You will be relying solely on the pressure differnce between the area in front of the radiator and under the car to induce flow. The diverter on the other hand allows you to use the vehicle forward velocity times the apeture area with an efficiency factor for you core flow. According to Corky, you will want ~2:1 ratio or better core flow to charge flow.

Anyway, if you are compounding, sweet. So am I. I think you move a little more quickly than I do though.
Not compounding it right now. Just doing some testing on different intercooler placement. I couldn't do a traditional V-mount without hacking the entire front end of the car out, but I can do this so I wanted to give it a shot. Still waiting on some parts I ordered to hook up the new IC pipes.

As for the piece you're talking about, I'll test it with and without that, making that piece will be easy. You're probably right, but that piece also steals air from the radiator too hence why I'm gonna try it without that piece first.
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Old 07-06-2015, 01:16 AM   #9
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Sav did it a long time ago, I dunno how well it worked for him though.
Very poorly
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Old 07-06-2015, 01:17 AM   #10
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Very poorly
Would you elaborate please? Do you have any pics of the finished setup? Last I saw was cardboard mockup and no update on how it worked.

Did you have a vent on the bottom like I drew?
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Old 07-06-2015, 01:20 AM   #11
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Why wouldn't a traditional high flowing ic core and a good crossflow not be able to do the job like it does on countless track cars?
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Old 07-06-2015, 01:25 AM   #12
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Why wouldn't a traditional high flowing ic core and a good crossflow not be able to do the job like it does on countless track cars?

What's a traditional high flowing IC core? Mine is an ebay 20x12x3 bar/plate intercooler. I ran this same type with the GT3271 at 28 PSI and it was fine, so I thought it would work with the SC. But AITs are way worse with the blower than they ever were with a turbo.

I've seen track cars run V-mounts and say that works well, but I don't want to cut the front end up to do that.

I'm here, tell me what works. I want my AITs 30-40 above ambient at 30 PSI after ~11 seconds of WOT.

EDIT: Also I believe most track cars don't race on pump gas. This is a street car and it runs on 93 Octane, so I can't accept high AITs and not worry about it because I have E85, or any other high-octane race fuel.
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Old 07-06-2015, 01:30 AM   #13
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step #1 is replacing the egay mediocrity with something proper. I think it was Jason that did a test a long time ago and figured out that a tube/fin (I believe he tested one from TDR) and also I think brain messed with one of those ebay delta-fins and both reported WAY more airflow to the radiator using that vs your typical bar/plate.

Second: while the MSM rad you're using is better than the stocker, it is nowhere near something like TSE's crossflow. Those two things alone should get you what you need. The last would be good ducting. If it holds up on a turbo track car on a 110* track, it should hold up for you.

Third: if airflow to the rad is not as important for you, get a precision or something else with a proper core. Those are about as efficient as it gets for heat exchange

Traditional as in normal, what all of us use, intercooler in front of radiator. Nothing weird

PS: you're not gonna see 30* over amb on a blower at 30psi for 11sec of wot. period (without spraying down the house with w/m/etc). one can only dream.
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Old 07-06-2015, 01:34 AM   #14
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Quote:
Originally Posted by 18psi View Post
step #1 is replacing the egay mediocrity with something proper. I think it was Jason that did a test a long time ago and figured out that a tube/fin (I believe he tested one from TDR) and also I think brain messed with one of those ebay delta-fins and both reported WAY more airflow to the radiator using that vs your typical bar/plate.

Second: while the MSM rad you're using is better than the stocker, it is nowhere near something like TSE's crossflow. Those two things alone should get you what you need. The last would be good ducting. If it holds up on a turbo track car on a 110* track, it should hold up for you.

Traditional as in normal, what all of us use, intercooler in front of radiator. Nothing weird

PS: you're not gonna see 30* over amb on a blower at 30psi for 11sec of wot. period. one can only dream
Coolant temps are rock solid, I don't think I need a better radiator.

AITs are what I want lower. What intercooler brands or types do these awesome proven track guys run? I've seen a ton of people run ebay bar/plate intercoolers, but hey if there's something A LOT better I'm in. What is it? What do you run?

Hell, what AITs are these proven track setups seeing? And at what power level?
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Old 07-06-2015, 01:37 AM   #15
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my bad, I thought at first you were concerned with flow to the rad.

in that case, anything with a garrett core. Precision is my personal favorite. heck, even bell intercoolers are pretty legit
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Old 07-06-2015, 01:39 AM   #16
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here's the most recent discussion I participated in
https://www.miataturbo.net/build-thr...5/#post1211634
check out those few pages

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Originally Posted by 18psi View Post
treadstone is not looking bad at all.



vs precision


vs egay tube fin failaidz
[IMG][/IMG]

vs mishiFAILgay
[IMG][/IMG]

vs godspeed type-Mediocre
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Hell, what AITs are these proven track setups seeing? And at what power level?
I'm not a track guy, but having messed with a ton of heat exchangers I've never seen one stay within 30* of ambient at 30psi for an 11 second pull, and that was on a turbo, I'm guessing a blower is way worse.
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Old 07-06-2015, 02:12 AM   #17
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Quote:
Originally Posted by patsmx5 View Post
Would you elaborate please? Do you have any pics of the finished setup? Last I saw was cardboard mockup and no update on how it worked.

Did you have a vent on the bottom like I drew?
It vented under the radiator. Airflow was inadequate, IATs were extremely high. I ended up using the same principles, but flipped, so that the IC sat further back and airflow was ducted above it to the top of the radiator.
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Old 07-06-2015, 02:20 AM   #18
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It vented under the radiator. Airflow was inadequate, IATs were extremely high. I ended up using the same principles, but flipped, so that the IC sat further back and airflow was ducted above it to the top of the radiator.
Thanks for the info. I'm not picturing how you changed it though. Where was the new location of the IC?
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Old 07-06-2015, 02:27 AM   #19
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Quote:
Originally Posted by 18psi View Post
here's the most recent discussion I participated in
https://www.miataturbo.net/build-thr...5/#post1211634
check out those few pages





I'm not a track guy, but having messed with a ton of heat exchangers I've never seen one stay within 30* of ambient at 30psi for an 11 second pull, and that was on a turbo, I'm guessing a blower is way worse.
Thanks for the info and pics! I typed up a reply but lost it...

Ok I have a tube/fin IC and the inside of it looks like the one in your last pic (godspeed) regarding fin density. It's not as bad as the ebay tube/fin you have in your pic but it's certainly not like the precision or Treadstone. Hmm.

And yeah it looks like getting a very-effective intercooler with high boost isn't really that easy. I'm emailed a few different track guys and more than one told me they didn't even CARE what their air temps were because of E85.... It just wasn't a problem.

Still I want to get them as low as possible. Looks like I need to do some reading on IC cores and figure out who has or can make one the size I need with a better core.

Still, anybody that actually has a 300+whp car and tracks it, what are your AITs?
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Old 07-06-2015, 02:30 AM   #20
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on a sustained pull like you're describing, i've seen 170-180 repeatedly with like 80-90 ambient
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