TMIC ducting / engine bay pressure

[Voltwings]

So i'm not sure exactly where this goes, but i feel here may be as good a spot as any.

I recently picked up a magnehelic gauge for measuring pressure zones when i start ducting my track miata.
Series 2000 | Magnehelic® Differential Pressure Gage | Dwyer Instruments

What this basically does is allows you to measure the pressure differential between either two points, or a point and atmosphere. Since i am still a few months away from really getting serious with the miata, i decided to play around with the (gen2) stock TMIC ducting.
I know for a long time its been stated that you need a shroud because it helps with cooling, and if you don't have it you will bleed tons of pressure into the engine bay and all that, so i figured why not put that theory to the test.

I will admit that my results are not as strictly scientific as possible, but i feel they are close enough to not matter. Basically i got a Gen2 with the stock TMIC and shroud and rigged up the gauge a few inches inside the hood scoop to get a pressure reading on top of the core.
Units of measure are Inches of water: Definition: https://en.wikipedia.org/wiki/Inch_of_water roughly 27.5" of water = 1 psi. Thanks @Tomas; for setting me straight on the units there.

Part 1: TMIC testing with shroud, measured on top of core in the scoop.

40 mph - .5" of water
50 mph - .75" of water
70 mph - 1.25" of water
80 mph - 1.5" of water


There were slight swells as the driver accelerated, but i was trying to just measure steady state since i felt that was a more controlled environment, i'll try seeing if we actually get some "ram air pressure" when WOT at a later time.

The next step was taking my ETS equipped car with no shroud (like i said, not apples to apples) and doing the same test on the same stretch of road.

Part 2: TMIC testing without shroud, measured on top of core in the scoop

50 mph - .5" of water
60 mph - .75" of water

80 mph - 1.5" again
It would appear that the shroud does provide some purpose at lower speeds, but at higher speeds the affect seems to become less apparent. This leads me to believe one of two things is happening: Either the pressure does a shockingly good job of staying on the core, or the engine bay itself is becoming pressurized, which i somewhat doubt.

The next step in this test will be measuring engine bay pressures on either side of the radiator with FMIC and TMIC cars. A radiator wants the highest pressure in front of, and lowest pressure behind of, it as possible. With a FMIC you're basically lowering the pressure in front, and since the TMIC ducting is open to the engine bay, raising the pressure behind the radiator. I'd like to see what that data says.

Part 2: TMIC car / under tray installed / weather stripping in the cowl installed

Pre radiator:
55 mph - .35" of water
60 mph - 1.15" of water
70+ mph ~1.5" of water

Post radiator:
50 mph - .1" of water
55 mph - .2" of water
60 mph - .3" of water

80 mph - ~.5" of water

Cowl with weather stripping installed:
40 mph - .5" of water
50 mph - .7" of water
60 mph - 1.2" of water

80 mph - 1.6" of water

Part 3: TMIC car / Under tray removed / Weather stripping on cowl installed

30 mph - .1" of water
40 mph - .2" of water
50 mph - .3" of water
60 mph - .4" of water

60 mph was as fast as i was able to get, but clearly the under tray serves an important purpose.

If anyone can think of ways to make these tests more accurate, or tests they would like done as well, please let me know. I figured there may be a better way to go about this, which is why i went ahead and created the thread before i had all my data.

[Spec]

Test with and without the under trey on the same car when you do the radiator test.

[Voltwings]

Yes, that would be a really good one, thanks Ray.

[Easter Bunny]

You can also test with and without the rubber gasket along the rear of the hood.

[Vansquish]

I'd be very curious to see what the results were with a hood-scoop extension like Corksport's too.

[Voltwings]

Originally Posted by Easter Bunny You can also test with and without the rubber gasket along the rear of the hood.

Yes, i know a lot of people remove that, i did my first time around. I'll probably just measure the pressure (positive or negative) in the cowl with it attached, and compare it to engine bay pressure from the above tests. May make things easier?

Basically if i measure say .5" in the engine bay and .6" in the cowl, i can assume the cowl will be putting air into the engine bay instead of removing it, correct? Whereas if i measure .5" in the engine bay, and ... really anything less than that, especially negative pressure, we can assume it will pull pressure from the engine bay?

[Easter Bunny]

Originally Posted by Voltwings Yes, i know a lot of people remove that, i did my first time around. I'll probably just measure the pressure (positive or negative) in the cowl with it attached, and compare it to engine bay pressure from the above tests. May make things easier? Basically if i measure say .5" in the engine bay and .6" in the cowl, i can assume the cowl will be putting air into the engine bay instead of removing it, correct? Whereas if i measure .5" in the engine bay, and ... really anything less than that, especially negative pressure, we can assume it will pull pressure from the engine bay?

Yes. Though if the numbers are very close the removal of the strip may cha he the airflow pattern in that area.

[Spec]

Originally Posted by Voltwings Yes, that would be a really good one, thanks Ray.

Yea, whatever dog.

[torquemaniac]

Testing the pressure over a gen1 TMIC could be nice also...front of the car usualy has higher pressure reading, so the gen1 could see more pressure over the TMIC since its feed from the front of the car (upper grill area)

[Voltwings]

I now realize this is going to be a very large amount of data, so I cleaned up the OP to hopefully make it easier to read, and added the following data from tonight:

Part 2: TMIC car / under tray installed / weather stripping in the cowl installed

Pre radiator:
55 mph - .35" of water
60 mph - 1.15" of water
70+ mph ~1.5" of water

Post radiator:
50 mph - .1" of water
55 mph - .2" of water
60 mph - .3" of water

80 mph - ~.5" of water

Cowl with weather stripping installed:
40 mph - .5" of water
50 mph - .7" of water
60 mph - 1.2" of water

80 mph - 1.6" of water

[torquemaniac]

Originally Posted by Voltwings Cowl with weather stripping installed: 40 mph - .5" of water 50 mph - .7" of water 60 mph - 1.2" of water 80 mph - 1.6" of water

Did you mean ''cowl with weather stripping unistalled''?

[Voltwings]

Originally Posted by torquemaniac Did you mean ''cowl with weather stripping unistalled''?

Nope, installed, as it comes from the factory. So if im looking at this right, the cowl at the base of the windshield is basically a high pressure zone, and compared to the post-radiator readings, removing that weather stripping would be pumping air into the engine bay.

[SuckSqueezBangBlow]

I have taken that weather striping on and off so many times, I wonder if I should take it off again.... I am having a hard time interpreting the date (and nice job on the testing!)

I guess I will wait and see if it is beneficial or not.

[Voltwings]

Originally Posted by SuckSqueezBangBlow I have taken that weather striping on and off so many times, I wonder if I should take it off again.... I am having a hard time interpreting the date (and nice job on the testing!) I guess I will wait and see if it is beneficial or not.

In my mind, the number on the cowl is higher than the number in the engine bay. Pressure moves from high to low, which leads me to believe it would flow into the engine bay.

[DaUberSchwebel]

I'd really like to see some results with the under tray removed as well. I noticed my BAT's really dropped after I removed mine. However, I removed my EGR and TB coolant lines at the same time. I'm sure that was the main reason they dropped, but would like to know if there is any benefit to not having an under tray.

[Voltwings]

Originally Posted by DaUberSchwebel I'd really like to see some results with the under tray removed as well. I noticed my BAT's really dropped after I removed mine. However, I removed my EGR and TB coolant lines at the same time. I'm sure that was the main reason they dropped, but would like to know if there is any benefit to not having an under tray.

Im getting there lol one thing at a time. The car needs an oil change this friday, and since im off work i may just see about doing it then. I'll still need to find a FMIC car with the time to replicate all these tests as well on.

[Dano]

Originally Posted by Voltwings Nope, installed, as it comes from the factory. So if im looking at this right, the cowl at the base of the windshield is basically a high pressure zone, and compared to the post-radiator readings, removing that weather stripping would be pumping air into the engine bay.

even if that is the case, the air at the base of the windshield is cooler than in the bay. so the net effect of removing the strip is positive. or am I missing something?

the positive effect may be minimal (i.e. unmeasurable) lol

[Voltwings]

Originally Posted by Dano even if that is the case, the air at the base of the windshield is cooler than in the bay. so the net effect of removing the strip is positive. or am I missing something? the positive effect may be minimal (i.e. unmeasurable) lol

While that is true, i guess my underlying thought is that it would raise the pressure on the backside on the radiator and reduce its efficiency. So, that makes a few assumptions:

1. We're swapping water cooling effectiveness for air cooling effectiveness in that case.
2. We're assuming its already at a point where the stock radiator cant keep up and we will see a negative impact in cooling by raising the pressure on the backside of the radiator.
3. while there is a rather large amount of pressure on the base of the windshield, i suppose without more testing its hard to quantify how much actually makes its way into the engine bay.


Im just trying to collect the data, someone smarter than me can decide what to do with it

[Dano]

Yes, too many variables and you'd need to define what your goal is.

1) reducing engine bay temps
2) reducing ECT

the two may be necessarily mutually exclusive in some scenarios like the strip removal.

I think something like the scoop deletes the scoobie guys install is great for letting heat out AND should (just a guess) decrease the pressure in the engine bay so also would aid in lowering ECT.

Who's up for cutting a giant hole in the back of their hood?

[Voltwings]

@Code Monkey; Dont talk about it, be about it.

[Code Monkey]

A giant hole? My peen would get all banged up against the walls.

[Tyhackman15]

You want the vents to be in LOW pressure zones, not high pressure zones. Ramming air (even if it's ambient temp) into the back of your engine bay is a bad thing. Reduces the air moving through the radiator by increasing the pressure behind the radiator.

A vent on the low pressure portion of the hood will reduce underhood pressure, allowing hot air to be pulled out, and allowing more air to pass through the radiator.


Example: http://i.ytimg.com/vi/wjjOgX_C5g0/maxresdefault.jpg

The air should be flowing out of the vents (as seen), not into them

[sheston]

I took the cowling (the plastic that has the windshield wiper squirters in it) out of my car and when I sit in traffic I can see the heat waves coming out in front of my windshield. Doesn't seem to hurt the normal operation of my IAT or BATs

[Tyhackman15]

Originally Posted by sheston I took the cowling (the plastic that has the windshield wiper squirters in it) out of my car and when I sit in traffic I can see the heat waves coming out in front of my windshield. Doesn't seem to hurt the normal operation of my IAT or BATs

When you aren't moving, of course heat will naturally rise. The larger concern is when you are WOT for extended periods of time, taxing your cooling system (for most people).

Of course all this is application specific talk.

[Easter Bunny]

I think that removing the weatherstripping on the back of the hood would only be beneficial for drag racing

[JgamB]

Originally Posted by Easter Bunny I think that removing the weatherstripping on the back of the hood would only be beneficial for drag racing

That is all I needed to hear. I knew I clicked the "subscribe to thread" for a reason.

[torquemaniac]

IMO, removing the weather strip will only improve heat removal when sitting in traffic

Im 100% with @Tyhackman15;

[MSP611]

hmm well it looks like ducting in the rad on the sides and on top is the way to go... then duct ur intercooler in.

[kidlifecrisis]

I'm going to try and experiment with a duct between my fmic and the radiator as that should be fairly simple to mock up and fit with the bumper off. I haven't yet decided whether I should just duct the top and sides and allow some air to go under the IC, or go all the way around.

After that would be figuring out ductwork from the bumper cover to direct more air into the core and subsequently through to the rad.

In these temps (80s/90s) unless I'm just cruising my ECT is living between 205 and 214 constantly

[MSP611]

Mazdaspeed6 for road racing

this thread on the last couple pages have great info on ducting even tho its a ms6

[Dano]

You need fan controller mod. I only ever see 195

From pablos group. Sp36 whatever.

Tappin

[MSP611]

I need to get one of those when I order my block... another thing to add to the list.

[Dano]

my post was in response to @kidlifecrisis; but yeah that is a must have mod once you up the HP to say beyond 350-400WHP IMO.

edit: but generally a good mod at any HP level. cooler is always better if you aren't concerned with emissions.

[kidlifecrisis]

True, but with that kit my fan would basically just be on 100% of the time. Step 1 is to try and redirect the air that's currently going around everything, then depending on my results I can make the call on the fan controller

[Voltwings]

Updated OP with the following information after removing the under tray

30 mph - .1" of water
40 mph - .2" of water
50 mph - .3" of water
60 mph - .4" of water

60 mph was as fast as i was able to get, but clearly the under tray serves an important purpose.

[DaUberSchwebel]

Thanks for the results. My under tray is going back on today.

[Yanahdi]

As far as air flow one way I've seen people test it is to just tape a bunch of paper strips at multiple points on the car. PITA and looks goofy as shit but it does work. Obviously no quantifiable data but it can serve as a way to confirm data from pressure testing.

Best results would need another car with a camera man to drive alongside.


Sent from my iPhone using Tapatalk

[Easter Bunny]

Originally Posted by Voltwings Updated OP with the following information after removing the under tray 30 mph - .1" of water 40 mph - .2" of water 50 mph - .3" of water 60 mph - .4" of water 60 mph was as fast as i was able to get, but clearly the under tray serves an important purpose.

where was this measurement taken?

[Voltwings]

Originally Posted by Easter Bunny where was this measurement taken?

about 1/2" behind one of the little flappers on the passenger side to allow it a chance to open. I didnt want to put it behind the fan because i wasnt sure if that would skew the readings.

[Voltwings]

Ok, so I got a FMIC from a local that I installed today and will be doing more testing. I'll try to lay this out as orderly as I can, but I think what all I am going to test is:

1. Under tray attached. All cowl ducting in place. All stock TMIC ducting in place. FMIC installed.

- Pressure in front of the FMIC core.
- Pressure behind FMIC core (in front of condenser)
- Pressure behind radiator (in engine bay)

2. Under tray removed. All cowl ducting in place. All stock TMIC ducting in place. FMIC installed.

- same tests as part 1.


3. Under tray attached. Cowl weather stripping removed. All stock TMIC ducting in place. FMIC installed.

-pressure behind radiator (in engine bay)
-Pressure in cowl area (at base of windshield)


4. Install @JSmith;s hood scoop ducting. Cowl weather stripping attached, under tray attached, FMIC installed.
- Same tests as part 1.

5. Install Jsmiths hood scoop ducting, remove cowl weather stripping, under tray attached, FMIC installed.

-pressure in cowl area (base of windshield).