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