Is the engine cover necessary?

I took mine off 2 weeks after I bought the car in late June 2004, never put it back on.

I'd rather see the engine when I open the hood.

I see your new here, read and learn about things you need to do to keep the car running well.

I guarantee you if you had a cool pre/post core air temp setup you would notice that it recovers quicker from heat soak and cools more efficiently at speed.

But considering the boost and power levels the stock top mount is actually efficient for, it's probably not too noticeable. I keep my cover on to keep the salt/water from soaking my engine bay.

It’s my opinion that the engineers had a purpose for it, and it should be left on. You won’t get power or lose power from it, but looking at it, it’s way more than cosmetic. The hood scoop fits perfectly into the cover which fits perfectly into the stock TMIC, and directs airflow and cooling. But, it also protects the engine, turbo, alternator, rubber and electrical components from liquids, dirt, snow, salt, oil or whatever makes its way into your engine bay. You may think “so what?” But, stuff does get into the hood scoop onto the engine, and can also hit hot or delicate components.

Also, when my radiator sprung a leak, i was sure glad I had it on. The cover was soaked in coolant and the engine and alternator were glowing hot, yet completely dry.

Also, it shields the turbo and exhaust bits from liquids as well, and a hot turbo and any liquids probably aren’t the best combinations. Not to mention that little area off to the corner right above the turbo that locks into the hood scoop. Ever open up the hood after it’s been raining? Droplets do get in there. If you think it’s purley cosmetic, you don’t understand engineering and design. Just look at it next time and picture it locked into it with the hood closed. I really don’t think the engineers cared if you could see the engine or not.

The engine cover don't do squat for dirt protection. It's partly cosmetic, partly a sound absorbent item.

And don't underestimate the power of the design department today when it comes to vehicles - sometimes they come up with the strangest ideas about what's good. (I work in the vehicle industry at the moment and have to do sub-standard solutions in order to compensate for the ideas the design department comes up with.)

The engine cover don't do squat for dirt protection. It's partly cosmetic, partly a sound absorbent item.

 

 

And don't underestimate the power of the design department today when it comes to vehicles - sometimes they come up with the strangest ideas about what's good. (I work in the vehicle industry at the moment and have to do sub-standard solutions in order to compensate for the ideas the design department comes up with.)

I'm not so sure about that. I went to school for mechanical engineering and it definitely looks like it serves as protection for dirt and liquid. Why would it fit so snugly into the hood scoop, and cover all the critical components? Why would it have foam on either side of the bottom of the hood scoop? Also, have you ever seen an engine bay without one, where the owner doesn't clean the engine on a regular basis? It's a filthy mess.

I would have agreed with you on a normally aspirated engine where the hood scoop is purely cosmetic and the engine bay is sealed, but the airflow goes right over the car's hood and directly into the engine bay. Sure, the airflow goes directly on top of the TMIC, but without that engine cover sealing it, it leaks all around the engine bay.

That isn't just air either, it's a mix of dirt, salt, gasoline, oil, coolant and whatever else is on the ground being kicked up, based on your environment or time of year.

These cars are super low to the ground, and just follow a huge truck for a while and see how much you use your windshield wipers. Well, all that stuff is not only going on your windshield, but right into your engine bay.

If you want to run it without the cover, that's your choice, but I wouldn't go saying it doesn't serve any useful purpose.

I mean, why would this aftermarket AVO TMIC have engine cover holes on it, if it really doesn't serve a purpose? They obviously fit it into the engineer's design for a reason. Everything about the hood scoop, ducting, and engine cover screams Bernoulli's Principal. Which also follows thermal dynamics of heat transfer and CFD, along with engine design and engine bay dead space.

Engine covers are put on for a specific reason by the OE manufacturer. When the EPA does it's initial testing, any sensor, solenoid, check valve, injector, etc. that's not out in the open, is ignored.

They will not remove the engine cover to individually test any of these components, so the manufacturers have made it almost to the point that all you see is a large plastic engine cover when you open the hood.

When the EPA sees this, they basically just plug into the OBDII port to make sure everything is working correctly, and check emissions at the tailpipe and if it all passes, they allow the car to be built for production.

EDIT: What I mean above is for most all vehicles, but there are exceptions as in our LGT engine cover with a directional design to enhance TMIC performance. You can look at a lot of newer cars (Audi, Lexus, VW, Cadillac, etc.) and when you open the hood, you can't see anything other than black plastic covers. The EPA then just does as I explain above.

^ That actually makes sense.

Sealing could be done without a huge piece of plastic, just a rim around the intercooler.

It won't do squat for dirt since it would come in through the radiator and come out on the underside of the intercooler anyway.

My understanding is the lower engine cover has a greater purpose specifically with regard to proper airflow for the TMIC, and obviously keeping the engine bay clean.

The lower cover and the saggy butt syndrome Subaru imposes are intentional for keeping the intake charge cool.

"Saggy butt"?

The lower rear ride height common on turbo Subaru's. I read an article that explained Subaru designed their turbo models to be a little lower in rear ride height to allow better airflow characteristics over the hood and under the motor, to allow more air into the hood scoop.

I'm not so sure about that. I went to school for mechanical engineering and it definitely looks like it serves as protection for dirt and liquid. Why would it fit so snugly into the hood scoop, and cover all the critical components? Why would it have foam on either side of the bottom of the hood scoop? Also, have you ever seen an engine bay without one, where the owner doesn't clean the engine on a regular basis? It's a filthy mess.

I would have agreed with you on a normally aspirated engine where the hood scoop is purely cosmetic and the engine bay is sealed, but the airflow goes right over the car's hood and directly into the engine bay. Sure, the airflow goes directly on top of the TMIC, but without that engine cover sealing it, it leaks all around the engine bay.

That isn't just air either, it's a mix of dirt, salt, gasoline, oil, coolant and whatever else is on the ground being kicked up, based on your environment or time of year.

These cars are super low to the ground, and just follow a huge truck for a while and see how much you use your windshield wipers. Well, all that stuff is not only going on your windshield, but right into your engine bay.

If you want to run it without the cover, that's your choice, but I wouldn't go saying it doesn't serve any useful purpose.

I mean, why would this aftermarket AVO TMIC have engine cover holes on it, if it really doesn't serve a purpose? They obviously fit it into the engineer's design for a reason. Everything about the hood scoop, ducting, and engine cover screams Bernoulli's Principal. Which also follows thermal dynamics of heat transfer and CFD, along with engine design and engine bay dead space.

Eh.... yes and no. Air really doesn't like to be pushed, especially turbulent air around a sharp 80 degree bend and through a porous media. The TMIC's on these cars benefit way more from the venturi effect than bernoulli's principle. Look at the underbody of any fancy german or itallian car, there's a reason why there's so much plastic. The seal that the engine cover provides probably improves the flow by providing a slightly higher positive pressure zone above the intercooler, but that's only going to be marginal at best. Keep in mind, the hood scope on these cars are incredibly small and is optimized more for a better drag coefficient. This was one of the first cars in which subaru really focused on the drag coefficient and have since dramatically increased the size of their hood scopes since then. If you really want to increase the airflow then you should consider adding a front splitter, a better under-engine cover, or even add a fan behind the intercooler.

Engines are engines, and engines get dirty. Putting a cover on top just helps hide the dirt from the average joe and makes it look fancy. Honestly, my engine cover would just pile leaves and maple copters on top of my intercooler, which obviously blocks airflow.

Also, I'm pretty sure the main reason why the perrin/avo/mitsimoto intercoolers have it is to keep poeple like you who prefer to keep their engine cover happy.

My understanding is the lower engine cover has a greater purpose specifically with regard to proper airflow for the TMIC, and obviously keeping the engine bay clean.

 

The lower cover and the saggy butt syndrome Subaru imposes are intentional for keeping the intake charge cool.

Pretty sure the saggy butt only hurts airflow? Ideally you want a low pressure zone underneath to suck air through the radiator and tmic. Basically the same logic as a rear diffuser.

The lower rear ride height common on turbo Subaru's. I read an article that explained Subaru designed their turbo models to be a little lower in rear ride height to allow better airflow characteristics over the hood and under the motor, to allow more air into the hood scoop.

Is it really saggy or is it just in your eyes?

You'd need to check the free height under the car front and rear.