Taking out the rain guard does drop intake temps about 20 degrees, and closer to 30 on a hot day. Water is going to get in the engine bay no matter what. If the car is stopped it goes right through the rain guard, and if you have no undertray(who does anymore ) water comes up the other direction. It will hurt nothing, but help you make power. I really could care less about the looks aspect, it just makes sense to do it for the drop in temps

 

Alright this is the deal with pulling that cover off....

It is a good idea, and a free mod that we can all do to our Evo's. It drops the engine bay temperature by over 20 degrees, and it is not difficult to pull off. However, I would not suggest leaving it off or getting the exhaust manifold wet from rain or whatever. That cover is there to protect the manifold from rain due to the damage that getting your manifold wet. Take it off on nice clear days, and put it back on when you think it will rain. That is just my suggestion.

 

I think that is good advice. I am not attacking you just have a question for you/ anyone else. If water hitting the manifold/ manifold cover was such a big deal why is the vent right there to begin with? Water is going to fall onto the manifold if the rain guard is in or out.

 

So do i keep mine on or take mine off? Im so confused!!! lol

 

Well, I guess it would depend on where the water actually lands on the manifold. The louver can provide some sort of coverage/blockage for direct rain access to the exhaust manifold, but obviously not all of it. I work the the HVAC industry, and huge louvers are put on the sides of all commercial buildings that get 0 pulled thru. Keep in mind they're horizontal, not vertical like the one on the hood of the Evo. The vent is also an 'outlet' for heat and air pressure. It's there to keep a positive pressure from being built up under the car, not necessarily for 100% heat relief. So, what that should mean is there's a constant updraft while the vehicle is moving coming out of the vent keeping the run off from falling into the engine. Obviously when the car's cold, rain on the manifold isn't going to do anything, but when the engine is hot, as with any extremely hot surface, cracking and warping can take place when cold water comes in contact. I don't know the engineering that goes into the factory manifold, they'd obviously have to take some account for cold water directly hitting exhaust manifold, but I could guarantee you that a large amount of water could damage headers or even the stocker manifold. That louver will help displace direct contact against the manifold.

My .02

 

well, I have had my CF hood for two years now without the vent, everything seems to be normal. It does however dirty your engine compartment on rainly day. It does keep your engine bay a lot cooler, but I took mine out for looks... its just so much sexier with out the vent cover...

Oh! and I still have my under tray... hahaha

 

Ok lets say for the sake of a discussion (not what i believe) that leaving the rain guard off will ruin a manifold after 2 years. A new manifold will cost you between $50-$100. But the lower underhood temps help you to run a more aggressive tune. Then at that point it becomes just another basic maintenance item.

 

getting rid of that extra 20 degrees is good for a degree of timing, very well worth it in my opinion.

 

seriously?......thats cheap

 

Take it off, its not like you can pop the hood from the vent and steal parts....or can you??? FWIW, I put mine back on after i completed that experiment in my driveway with a slim jim. Oh crap now that i think about it you can do it from underneath or the front, well I ruined a perfectly good wire mesh! We are all screwed! Locktite your engine mounts!

 

done

 

Roflmao!

 

 

I have a stock manifold that i will let go for cheap, so you all ready would have a back up, hell i will even throw in some locktite so no one steals your motor