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Old 07-08-2011, 02:10 PM   #1
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Default Vented Hood Data

I apologize in advance if this has been covered for real before - I can't find it buried in existing threads.

Does anybody have any before/after temp differential on adding a vented hood alone? Same track, same ambient, same everything?

I'm kind of stuck on my existing rad & oil cooler setup (FM/PWR Twincooler) because it fits & works with my setup. Problem is I'm limited to 15 min. track sessions when ambient gets up around 90F (250 water/260 oil, bail out early). All ducting/sealing/bellypan stuff is in place, nowhere to go there. I just need to decide between a vented hood or a new rad/oil cooler/intercooler setup with supporting fab work. I'll lean toward the hood if there's any supporting data for ~15-20 degree coolant temp drops.

Thanks in advance.

Tim
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Old 07-08-2011, 02:22 PM   #2
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There's probably a reason they don't make that "twin cooler" anymore. How thick is the radiator you're trying to use?

If you have the radiator ducted and sealed, with a belly pan behind it and the car is still overheating in mild, 90*f temps, something else is wrong. The vented hood will help, but I was able to track my car in 100*f heat without the vented hood.

Sell that twin cooler and get the TSE radiator, leave the intercooler where it is, and run a Carbontrix hood vent.
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Old 07-08-2011, 03:09 PM   #3
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Vented hood helped my highway w/AC overheating. Engine still ran hot because I had other issues, but before vented hood I was boiling coolant. After replacing with a vented hood (no other changes) I was simply running hot.
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Old 07-09-2011, 03:48 AM   #4
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Welp, coupled with proper ducting, which you supposedly have, I went from 250 pre radiator (and pulled off early as you are) to 160 post radiator. Moved the sensor along with adding the scoop and ducting.
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Old 07-09-2011, 04:13 AM   #5
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What kind of sensor are you running? Is it possibly heat soaking?
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Old 07-09-2011, 04:54 AM   #6
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A vented hood is not going to correct a major issue like that. It will help, but it's not going to knock 40*F off the CLTs. If you don't have another underlying problem (like you overheat on the street too or something), if you drop our radiator in you should see a ~40-50*F CLT drop.
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Old 07-09-2011, 09:38 AM   #7
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I'm guessing he doesn't have a reroute, his ducting isn't as good as he claims, or he's not running the proper mixture of water. Or all three. Tied with an absence of an extractor scoop, that'll make a 50* difference.
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Old 07-09-2011, 09:55 AM   #8
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In any case, the PWR is smaller than a Koyo 55, which barely does the job in a Spec Miata on a hot day. Even with a reroute, fast turbo cars need more.
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Old 07-09-2011, 01:42 PM   #9
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Quote:
Originally Posted by curly View Post
I'm guessing he doesn't have a reroute, his ducting isn't as good as he claims, or he's not running the proper mixture of water. Or all three. Tied with an absence of an extractor scoop, that'll make a 50* difference.
I have a reroute (PIA - negligible gain), full bellypan with a fence section blocking radiator underfow, and side skirts extending up to the rails. Along with the usual foam stuffing on the sides and sealed top. Roughly 85% water, bottle water wetter & leftover 50/50 mix for the balance.

I've been running the car like this for 3 1/2 seasons with no problems or boilovers on an 18 Lb. cap. The only time I top 250F is afternoon open track or late session when track temps are way up (for here in the northeast anyway). Previous owner ran it for a couple of seasons at VIR too.

My only issue with a new rad is whether the stock fans remount (run parallel, right side cools the oil cooler) and what to do for an effective oil cooler/ducting. There's only so much area available there. Also, my intercooler is a top/bottom tank unit that blocks only the rad, the oil cooler is fully exposed to airflow. This is the upgraded FMII package circa '04 that I bought the car with.

What I'm trying to weigh here is the effectiveness of a good vented hood vs. redoing the whole rad/oil cooler/bellypan setup. Sounds like you're saying I need the whole shebang plus a vented hood?
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Old 07-09-2011, 01:48 PM   #10
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Quote:
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Welp, coupled with proper ducting, which you supposedly have, I went from 250 pre radiator (and pulled off early as you are) to 160 post radiator. Moved the sensor along with adding the scoop and ducting.
I see from your pic that you also cut the bumper for more inflow. Combined with the vent I can certainly see that helping. Did you do all the mods and new rad at once, or piecemeal?

I still drive mine on the street (looks stock besides the rollbar) and would prefer not to cut it up too much.
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Old 07-09-2011, 01:54 PM   #11
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A vented hood is not going to correct a major issue like that. It will help, but it's not going to knock 40*F off the CLTs. If you don't have another underlying problem (like you overheat on the street too or something), if you drop our radiator in you should see a ~40-50*F CLT drop.
Thanks, I'll certainly consider it. Do you have a recommended oil cooler & mounting location to go with it? (I just ordered some new hoses for the TC dammit).

I have no underlying problems & never overheat anywhere, but could if I didn't pay attention on a hot day.

I'll give you a call at the shop next week to discuss.

Thanks,

Tim
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Old 07-09-2011, 02:19 PM   #12
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Quote:
Originally Posted by TimM View Post
I apologize in advance if this has been covered for real before - I can't find it buried in existing threads.

Does anybody have any before/after temp differential on adding a vented hood alone? Same track, same ambient, same everything?

I'm kind of stuck on my existing rad & oil cooler setup (FM/PWR Twincooler) because it fits & works with my setup. Problem is I'm limited to 15 min. track sessions when ambient gets up around 90F (250 water/260 oil, bail out early). All ducting/sealing/bellypan stuff is in place, nowhere to go there. I just need to decide between a vented hood or a new rad/oil cooler/intercooler setup with supporting fab work. I'll lean toward the hood if there's any supporting data for ~15-20 degree coolant temp drops.

Thanks in advance.

Tim
You mean that you have the stock ducting in place right?
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Old 07-09-2011, 03:54 PM   #13
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IMO the big effect of the reroute is idling in traffic.

I measured temps with the stock routing, of coolant exiting the back of the head, and the front of the head (feeding the radiator). The differential between back and front was greatest at idle.
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Old 07-09-2011, 04:21 PM   #14
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Quote:
Originally Posted by TimM View Post
Thanks, I'll certainly consider it. Do you have a recommended oil cooler & mounting location to go with it? (I just ordered some new hoses for the TC dammit).

I have no underlying problems & never overheat anywhere, but could if I didn't pay attention on a hot day.

I'll give you a call at the shop next week to discuss.

Thanks,

Tim
If it doesn't overheat anywhere except on the track, it sounds like an inadequate radiator. Pretty common to be honest. Increasing the mouth area isn't the way to go - radiators work best if you feed them with an area about 1/3 the size of the surface area.

We've been tucking FC Rx7 oil coolers into the nose in place of the stock crash beams - even with no airflow they are big enough to do the job.

Call me late next week, or email and I can get back to you more quickly.
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Old 07-09-2011, 05:54 PM   #15
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Sav, did you cut out the cross member that the crash beam bolts to? Or is there enough space with just removing the crash beam? Does the bumper seem to sag at all without the beam there?
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Old 07-09-2011, 05:57 PM   #16
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Quote:
Originally Posted by TimM View Post
I see from your pic that you also cut the bumper for more inflow. Combined with the vent I can certainly see that helping. Did you do all the mods and new rad at once, or piecemeal?

I still drive mine on the street (looks stock besides the rollbar) and would prefer not to cut it up too much.
What Sav said, don't cut a hole in the bumper like me. I have ducting from the stock "mouth" to the lower half of the radiator. The hole I cut feeds the oil cooler, which then goes up past the panel in front of the radiator.

I took my car off the track for a summer to get my over heating issues resolved. From my second to last track day to my most recent, I added 460 injectors, MS, ducting, proper oil cooler, proper reroute, water wetter, and extractor scoop all at once.

I moved my coolant gauge sensor from the top radiator hose to the bottom radiator hose, and went from 250*+ temps in ~15 minutes, to rock steady 160* for the full ~23 minute session. I pushed like mad and got it up to 165* once.

Couple BIG things to keep in mind is it was 20* cooler ambient than what you're talking, 70*. And as I said it was my first time back in almost 2 years. And I'm on all seasons, so I'm not pushing as hard. And you're probably making more power, I'm most likely barely at 200hp.

If you're marginally happy with your current track days, I say you install an extractor hood or add one to your stock hood. Might not look stock, but I think you'll need/want it no matter what you do. Then post good detailed shots of your ducting for us to analyze/critque. Then see where that takes you. If you want to not risk anything and never have any overheating issues, get the RX-7 FC oil cooler Sav is talking about, and purchase his radiator. Your twin cooler should still fetch good 2nd hand money.
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Old 07-09-2011, 06:00 PM   #17
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Quote:
Originally Posted by TimM View Post
I see from your pic that you also cut the bumper for more inflow. Combined with the vent I can certainly see that helping. Did you do all the mods and new rad at once, or piecemeal?

I still drive mine on the street (looks stock besides the rollbar) and would prefer not to cut it up too much.
Quote:
Originally Posted by falcon View Post
Sav, did you cut out the cross member that the crash beam bolts to? Or is there enough space with just removing the crash beam? Does the bumper seem to sag at all without the beam there?
Crash beam is still there, the little nubs that are conveniently bolted in are gone though, they normally cover the two grey areas on either side of the oil cooler shown below.

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Taken from this very helpful thread:
https://www.miataturbo.net/general-miata-chat-9/ducting-airflow-37262/
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Old 07-09-2011, 07:10 PM   #18
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Quote:
Originally Posted by curly View Post
I moved my coolant gauge sensor from the top radiator hose to the bottom radiator hose, and went from 250*+ temps in ~15 minutes, to rock steady 160* for the full ~23 minute session. I pushed like mad and got it up to 165* once.
??? that don't make any sense at all.
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Old 07-09-2011, 09:35 PM   #19
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Wouldn't relocating the sensor give you inaccurate water temps? The lower hose should be cooler anyway, yes?
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Old 07-10-2011, 04:18 AM   #20
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I used to have the PWR twincooler so I can relate to your problem. First, the oil cooler side uses round tubes. These have a low cooling surface area to oil volume so even with direct ambient and mechanical airflow (via the fans), it's really not enough to keep the temps in check when you are near/over 200 whp on track. Get a nice Mocal, Setrab or Earls stacked unit. Next, the PWR is 37mm, but it is a single row core. This means has an OE level of surface area to coolant volume. In actuality, since the OE radiator row inside the core is thinner than the twincoolers, it probably does a bit better job with convection. Fins per inch are a bit more dense with the PWR unit though so it's probably a wash.

With new problems comes new ideas and with new ideas comes innovation. The latest group of Miata radiators have left the vertical flow design in favor of the cross flow design. The units from TS, FM and BEGi employ this design and some have additional features that you may or may not need depending on your application. All of them have proven themselves better than the best vertical flow radiator made for the Miata.

Give each of them a call to determine which one is right for you.
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