Turbo heat control
 

I've been mulling this idea over for quite a while and want to get some input and opinions on it.

I made a quick template for the upper portion to show what I'm thinking.
Basically, the heat that is radiating off the turbo is the enemy. I've melted brake reservoirs, speedometer and throttle cables, etc. etc. etc.

I've already moved everything I can away from this - rerouted my speed and throttle cables in the cabin, eliminated all coolant lines on the hot side, etc. but there still remain plenty of bits that I want to minimize heat on.

Now, it's possible to shield each individual item - sleeves on each wire/cable/hose, and larger shield for things like the brake reservoir. But, there is still the matter of a very high ambient air temp in the engine bay, and you can't protect everything perfectly. And adding to that is my more unique situation of not having much if any air circulation in the engine bay because all of my heat exchangers have ducted exits - whereas a more oem car has a lot of airflow under the hood, which helps to reduce that ambient temp.

So moving on to my idea of a solution:
I want to build a heat shield for the turbo, but very different from most that you see. The first element would be a shield that surrounds the turbo. Reflective material would be used on the inside surface facing it. The top of this 'box' would seal with the hood, and there would be a scoop/duct that would bring outside air into this box. Then, the bottom of this box would direct the air down into the transmission tunnel, where it could travel down the tunnel and exit over the rear diffuser.

In simplest terms, I'm suggesting taking cool air from the top of the hood and ducting it down in a controlled, enclosed duct to the transmission tunnel. The hot side of the turbo would just happen to sit inside the duct.

My thoughts here are that just boxing in the turbo wouldn't work well - with no air circulation, despite reflective material you'd end up just radiating heat through the shield into the rest of the engine bay. But, flowing air through this system keeps the shield itself from overheating, and I'd bet the air on the outer side of the shield would stay fairly low in temp.

Here are pics of the portion that would sit around the turbo. There would be a bottom portion that directed the air to the tunnel, and a duct supplying air into this box.

https://www.miataturbo.net/attachmen...ine=1400713513

My first thought is that, from what I've read and seen, the center-rear area of the hood is a (slight) low pressure zone. I don't know crap about aerodynamics, but it seems that the area over the turbo might be a better place to exhaust heat than to try to introduce ambient air or positive flow from the outside. I don't know what this potential extra flow out of the hood at that location would do for downforce/lift.

The cowl area appears to be high pressure, could you channel air in from that location into the box around the turbo?

Source:
https://www.miataturbo.net/race-prep...12/#post971580
https://www.miataturbo.net/attachmen...ine=1400733989

I was going to say, the sealing box idea isn't bad but I think it would probably work better to try to suck heat out the top rather than direct it down under. Maybe some sort of reverse naca duct? Interesting idea nonetheless. I'm not sure I'd want it for a car that sees weather since it would essentially direct water on to the turbo area but for a track car it might be a great solution for underhood temps.

Have you looked at the heat shield FM sells?

https://www.miataturbo.net/attachmen...ine=1400741713

It protects the cables, fluid reservoirs, etc. Not quite as all-encompassing as your proposal, but if you're melting stuff on the front or engine side of the turbo then you've got bigger problems. :)

--Ian

For the air source I was considering either a NACA further forward on the hood with a ducted path to the box, or an inlet at the cowl where the pressure is higher. But, the pressure really doesn't build up until the air is at the glass, below that is neutral or low pressure.

Venting upwards through the hood could be done, I do like how that evacuates the air vs. the air needing to pass all the way down the transmission tunnel, and it would allow the system to work properly even if I don't run the flat bottom. For that though, I would need to figure out a good air source low down in a decently high pressure area, if I'm doing this I want a fairly substantial amount of flow through the system.

The bigger area I wanted to bring up for discussion though is the concept of protecting nearby engine components and lowering engine bay temperatures by trapping and evacuating the turbo's heat. The air source I can figure out one way or another.

-Ryan

Yes but every off the shelf heat shield offered for miata turbo systems are... how to put this lightly... not worth their weight.

It's surprising what can be affected after a solid 30 minutes of sustained red-hot temps. Couplers melt and/or get brittle, dip stick handles melt, hoses blister, it gets ugly. With sleeves and reflective shields I've gotten it to the point where it survives sessions reliably.
But I want to design a system that can deal with the heat for two hours, not 30 minutes. That's where the airflow through the shielded box comes in in my mind.

-Ryan

I used to be melting wires and stuffs in the engine bay. But the problem was easily solved with a FM shield. Got even better with some vents on the bonnet.
I am running GTX2863 with about 290whp and I track the car.

I fully agree that you should vent through your hood. As a general principle heat rises. So trying to force it low is already an uphill battle, but it could be done. Doing the vent through the hood can work. Using the airflow over your hood as suction for your box.

As far as plumbing air through the box have you considered what some people do for their ram air intakes? Now bear with me because I am coming at this from the Subie world... but some of our larger HP builds we would plumb air to the intake via Headlight mods or foglight mods. Not making it a direct source, but instead an additional source of air.

https://www.miataturbo.net/attachmen...ine=1400787997

or

Fog light example

Maybe find a way to plumb some of your bottom air source from the front bumper/front of the car?

I've got the one that FM sells on mine. It's a nice piece, works well. No brake booster melting issues or anything else like that.

Okay to all the people telling him to buy the FM shield just stop. This is ThePass, the same guy who won the miata challenge super modified. That's at minimum 10 wheel to wheel races at full bore in a year. Much different than a HPDE in terms of heat, thus the statement that off the shelf stuff doesn't work.

My :2cents: use the relatively high pressure zone on the hood to push air past the turbo and into the diffuser where it has a natural low pressure zone. But what do I know Im a :noob:

Something tells me blowing cold air at a hotside or sucking a ton of air past it is going to take out quite a bit of its efficiency and possibly introduce some other weird issues.

I've never seen this done before though so I'm just guessing.

It's a sound approach. Take a look at the Evo X and R35 GT-R for some OEM perspective on this. There's strategic heat shielding nearby the turbo(s) and NACA duct(s) in the hood of both them that direct air over the turbo(s).

I can't picture what the downstream side of this arrangement looks like on those cars, but as I recall it's not very elaborate at this end, basically dumping into the underfloor region.

Another side benefit is, when parked, the air in the box reverses direction, acting like a chimney to let heated air escape.

The GTR ducts are directly over the turbo manifolds, and the airflow is over the factory heatshield and turbine housing. There is no ducting below the turbos to draw air off and underneath. However, there are NACA ducts in the flat undertrays to help move air out the back, so it may conceivably pass fully through the bay and down the driveline.

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wow that's pretty cool.

1st time for everything I guess.

Do it OP :D

There is a company called "Subtle Solutions" that builds a Chimney Duct w/ Heatshield for the WRX/STI that does exactly what you are looking to do.

https://www.miataturbo.net/attachmen...ine=1400797641

I don't necessarily like the design as it steals air from the TMIC on the Subaru, but then you don't have a TMIC ;)

Actually, it appears I spoke too soon. It looks like the stock shroud has some sort of mesh in there anyway and this just ducts it directly to the turbo

http://i.ebayimg.com/00/s/MTA2NlgxNj...TXEr5/$_57.JPG

I agree with 18psi, go for it.

I vote NACA duct on the undertray ducted up through the heat shield and out a louvered vent in the hood. It doesn't seem like you need super high velocity air in there so I would think that could get the job done.

With a NACA duct on the undertray, you might be able to get away with just sucking ambient under hood air from around the turbo. Its not going to help you at idle or in slow traffic but then you won't have to cut a hole in the hood.

Now we're getting somewhere! :)

I know a guy running a lemons car with a turbo that sticks up out of the hood. Besides the janky lemons-grade build quality of the whole thing, the exhaust pointing at the driver, and the turbo blocking the driver's view a bit, he said it works pretty darn well. I don't think he's had any issues with the air over-cooling the turbo.

To be honest, I don't think the air will do much of anything to the turbo, I think it's too hot to care. The idea behind the airflow is to move the heat coming off the turbo instead of letting it just sit stagnant and heatsoak everything around it. It's to keep the heat shield cool, not so much the turbo.

This is really encouraging. I didn't realize that was what those NACA ducts did on the GTR. I'm liking this idea more and more.


Oh, I don't mind cutting a hole in the hood :)

To everyone suggesting venting out the hood, I am leaning towards going with this flow direction as well the more I consider my car's specific aero situation:

Here's the position of the turbo under the hood, it's far enough forward still that the area above it on top of the hood is still low(ish) pressure:

https://www.miataturbo.net/attachmen...ine=1400824833

A vent directly above the turbo should work well to pull air out in that location, given that I find an inlet position for the air source that is higher in pressure than that zone above the hood.
To pull air in from above would require a duct that reached to at least the base of the windshield, and that would require cutting the firewall. I'd prefer to cut the hood rather than the firewall.

Furthermore, I have a rather massive and fully ducted hood vent. This affects the airflow and pressure above the hood. Here's the C6R:

https://www.miataturbo.net/attachmen...ine=1400824833

It's a different car, but that sure looks to me like the air venting out of the hood vent reduces the pressure at the base of the windshield - the pressure is there on the sides, beyond the width of the vent, but is much more diminished in the center where the hood vent is affecting airflow over the hood.
This makes me think that venting out of the hood would work well, but venting in is not going to work in this situation.

Time attack, not wheel to wheel ;)

Yeah i was thinking about your thread on my drive home last night. The theory of using the areo of the car to help pull heat off the turbo seems like you are heading down the right path. Maybe get some fans and colored smoke to start testing out your theory?

lol at the off the shelf suggestions.

I'd make the box around the turbo exactly as you've pictured, with a brake duct riveted to the side. Add another to the cowl, and suck air from the high pressure cowl into the box, and out the top of the hood. Just put the duct right in the corner.

Only aluminum:
https://www.miataturbo.net/attachmen...ine=1400864594

<- Should have realized was in Race Prep section.

:inout:

So maybe I'm missing something ... why pull air from the cowl?

Given: all of your current heat exchangers are ducted out of the engine bay, therefore airflow through them is unaffected by air pressure of the engine bay itself.

Therefore: run one opening from the high pressure bumper area into the engine bay. Run hose pointing at turbo, if you want. Put reverse naca duct or louvers above turbo for exit.

Profit?

I'm with you Mobius. Pressure doesn't build into anything significantly positive until you get to the windshield glass itself. Fine for an intake, but I'm trying to force air through the duct.

Venting directly up and out looks like the best exit. So the higher pressure at the inlet the more effective this will be. Logical place to look for that is the front of the car.

The only concern is introducing drag with a forward facing duct. But unlike a duct going to a heat exchanger which is a large flow impediment, this actually shouldn't have much obstruction, so I'm thinking drag increase would be minimal.

If I'm ducting from the front, I'm thinking one 3" diameter hose should do the trick... Does anyone know where to find flow data for different hose diameters?

I have an inlet on the right side of the air dam for the oil cooler, so I could kill two birds with one stone and satisfy my OCD for symmetry by matching that inlet with one on the left for this.

-Ryan

Great thread,

I like the idea of a duct from the front or from the undertray. How do you intend to run the hose, which way through the bay, also what kind of hose?

Dann

Probably the same stuff used for brake ducting, high temp. Need to figure out the routing...

Do you necessarily?

If you provide a bumper opening for a source of air, provide the low-pressure exit through the hood, and put some radiant heat shields around the turbo that will also act to reinforce the chimney effect, aren't you 90% there?

Edit: taking you above template, but leaving the front open, is what I'm thinking. It will create its own airflow. Sealing it and ducting the source opening directly to it would probably be more effective, but will be more fiddly.

It would probably be effective to some degree, but I'd like to make it more

Building a bit on that though, what do you guys think about heat differentials; the heat radiating off the turbo has to be what, several hundred degrees? That temp quickly falls off as you get further from the turbo, but my hood has been 600* after a session, so 600+* around the turbo safe to say...

Comparing to that, what's the air temp coming out the back side of the radiator? 200-ish or less?

Since the desired effect is to simply move the super hot air around the turbo out the hood, not to actually cool the turbo itself, I'm thinking 180* air will be just as effective at this as 95* air (ambient in the summer).

And since the secondary goals are:
- need decent pressure at inlet to ensure directional airflow
- ideally don't add another opening to front surface of car which would marginally increase drag
- *bonus goal* be able to vent the turbo heat through this system while stationary in pits

If I duct air off the back of the radiator fan for this vent system, I think I'll achieve every one of those goals, including the bonus of being able to kick the fan on in the pits and push air through it.

The slightly hotter than ambient air is still cool air relative to the turbo, this would be super efficient (recycles "wasted" air), doesn't add another opening to the front, and requires less ducting length and simpler/straighter than needing to go around the intercooler/radiator.

I'm liking this more and more as I go over it in my head...

-Ryan

Good idea, please continue.

:dealwithit: My six year old is watching me type, and he wanted "the glasses falling on the beaver." :)

The most direct way to get rid of the heat would seem to be out of the exhaust. I know that some people ceramic coat the hot side, and others put a heat blanket over the hot snail.

A slightly larger heat shield area could be made as you're suggesting--and it would definitely benefit from internal heat coating. It would basically act like a larger version of the turbo jacket, except that you want the radiant heat to exit a chimney.

Maybe a good test would be to build the shield first and put some heat strips on it to check temperatures. Obviously if stuff is melting then it's too hot:


If the box with heat shield doesn't do enough to stop the heat, then play around with air flow. You may not even need an outlet to make a difference.

Duct / Exhaust Hoses

Bernoulli's equation will give you a very close approximation. You'd need to use CFD to get exact numbers because the geometry likely gets rather complex when factoring the effect of your duct work, turbo, heat shield and hood vent.

See also Lined Silicone Air Duct Hose Pressure and Vacuum Limits

Have you considered adding a thermally insulating turbo blanket instead?

Let me know if you simply want a pre-made K-member...stronger, lighter, and more room for ducting.

The TD04-15G with its external wastegate has a funky shape that is difficult to wrap a turbo blanket around. The only decent looking blanket for a TD04 I've seen (not interested in the china-made ebay stuff) is the PTP blanket, but that's for a Subaru TD04, and from what I can see the shape seems different enough that I'm not sure it would fit my turbo. Don't really want to take the $150 gamble on that.

I'm considering wrapping the downpipe, but possibly would do that even with the duct since the downpipe extends out beyond the shielded area...

-Ryan

I'm sure you know this but I'll say it for posterity; wrapping exhaust headers concentrates the heat to an extent that the metal underneath can become brittle and crack. You may not have any issues, but then again you might.

Yep so I have heard, and why I have not used wrap to keep heat down to date.. but was considering it as a way to, as you said, contain the heat and evacuate it out of the exhaust.

I did some testing with hose and duct placement relative to the radiator fan yesterday and then started construction of the heat shield, but only had a little time to spend on it before going to the dyno so I'm rejoining that project later today after I get some work done.

-Ryan

All exhaust systems suffer from thermal fatigue. But using thermal insulating barriers is generally not an issue provided you're using the right exhaust materials to begin with! Inconel, 304SS, 321SS, galvanized mild steel, cast iron and various proprietary alloys all have their purpose. As we all know, design is a matter of compromise and all exhaust systems are wear and tear items so I would expect a mild steel downpipe to behave differently than an Inconel one. And cost a lot different, too!

If it was me I'd probably call PTP to ask them about how one of their blankets might fit your application. I'd also consider Zirotec or your ceramic flavor of choice. Belts and suspenders approach. Not that this ducted vent idea is bad idea. It's a neat science project and seems very resourceful and economical to achieve. I just rather drive than tinker!

I have a ptp blanket on my td04 and it is rather effective. It is a pretty general shape using stainless wire to tie the ends together so it may fit, though would second giving them a call to find out.

Thanks for the solid info on the ptp blanket fitment.

I've spent some time researching the subject of turbo blankets and decided a blanket is not the appropriate tool for what I want to achieve.

Progress with my heat venting system is ~50%, had to sideline it a bit to prep for a shakedown at an autocross that was today. That went well with just a few small bugs to work out overall, so back to this project in the next day or two.

I'm making it modular so that I can do some back to back testing of a few different configurations and hopefully have some good data at the end of this.

Considering my options for taking heat readings. The alcon brake temp strips and brake temp paint both have less than ideal temp ranges and increments. Not to mention rather $$. I might just use a digital infrared temperature gun.

-Ryan