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DIY velocity stack DE airbox

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Old 10-07-2018, 10:58 PM
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DeusExMaxima
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Default DIY velocity stack DE airbox

It's fairly common knowledge that the DE Rev Up engine air box has a large velocity stack built in, instead of the tiny lip that is in all the other air boxes. I'm not sure it has ever been conclusively proven but that are box is fairly desirable for its theoretical better air flow.

I thought the Rev Up airbox fit into my desire to keep my car engine essentially stock but improving it in small subtle ways. I seriously considered different intakes but I had my heart set on the rev up air box. The problem I was Finding was that it was hard to justify the $100 plus that people were asking for these boxes when the only difference between the rev up and my box is this velocity stack.

I located one locally and the seller wanted the usual hundred dollars for the airbox. Before I departed with a C note, I wanted to see if there were other and perhaps better options. I believe I found another better option. Here's what I did:

I removed my airbox and peeked inside and saw the little metal lip that is on the backside of the airbox just before the mass airflow sensor. I saw that there was quite a bit of room in there to put a velocity stack or air horn. Velocity Stacks are known by different names. I've heard them called air horns, trumpets, bugles, Etc. No matter what they are called, they all perform the same function which is to scoop air from the mouth of the Velocity stack and have it flow in the tube in a smoother way.

first I looked online to see if I could buy something but I didn't find anything that grabbed my attention. I was going to the local Pick-A-Part for some parts and I decided to have a peek inside the are boxes of different cars to see if I could find other car manufacturers that made are boxes that contained air horns or velocity stacks. All the Nissan's that I saw had the small lip which was the same as mine. I looked through a variety of Japanese cars and even some American cars but I didn't find anything that look like it would work. Then I came to the European car section.

not that Japanese cars don't focus on engineering because Honda was founded by an engineer. But I find that European cars are really really well engineered. They have certain details that other cars don't seem to have. I noticed that BMW and Volvo seem to have air horns and almost all of their air boxes. I saw Audi had some also and so did Mercedes.

I knew the opening to the mass airflow sensor was around 71 mm. The airbox output is also about 71 mm. I look through a variety of these European cars and pulled out some of the air horns.


I took the air horns over to a Nissan Maxima which had the same air box in the car with the little lip on it. I eliminated one of the air horns and purchased the remaining three. Of the three I chose the one on the right. Even though the bottom part was too large I noticed that it was tapered to the top in kind of a reverse funnel. I figured if I cut it about an inch down it would be about the exact diameter of the output of the air box. It turns out I was right.


I cracked open the airbox and drilled the 2 rivets holding the air lip in place.

here is a comparison of the OEM are lip and my air horn:


The OEM lip is 83 mm wide at the mouth. The new horn is 101 mm or almost 1 inch wider at the mouth. The lip is 6.6 mm tall whereas the new horn is 31mm tall, or about 1 inch taller than the lip.



I ground down the lip on my bench grinder and finished it with a file. Thrn I used 2 part epoxy to bind the horn to the lip base. I did this in 2 stsges. The first stage was to put a thin layer of epoxy on the base of the horn and attach it to the lip base. Remember the lip has been ground down so the base is now flat. I waited some time for it to cure and then I mixed up some more two-part epoxy and liberally applied it around the outer joint of the air horn and the base. I let that cure for sometime as well. While it was curing I went to Lowe's and bought some for millimeter bolts and some washers and nuts to attach the air horn and base to the airbox. Once the airhorn was attached, I used a grinder to grind the edge of the airbox output hole to make sure it was flush with the air horn. Basically I ported the air horn and air box opening to make sure that the air would not catch any edges.

now I needed to seal the box back up. Before I attached both halves of the airbox, I scraped off all the residual glue and cleaned it off. I decided to use Shoe Goo as a binding agent for the air box. I wanted to be able to take the airbox apart again in case I needed to.

I applied Shoe Goo to the edge of the airbox and mated it together with the other side. I then applied more Shoe Goo to the outside mating surfaces . I put a 25 pound weight on top of it to press it in place and went to dinner for a couple of hours.






The picture above shows the completed hair box with the new air horn.

I installed the air box and went for a drive. The engine had a throatier sound and it was more responsive. The throttle seemed much more sensitive. The power also seemed a lot smoother. I know but dynos don't seem to mean much, but I believe I gained a few horsepower at least.

total cost was around $10 for the air horn and the Shoe Goo and the nuts and bolts. It was a bit of work but I believe worth it. Also I think the engine needs to adapt to the modification so that usually takes a few days or so. Let me know your thoughts
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Old 10-08-2018, 12:53 AM
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Here is a close up of the BMW airhorn I used:


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Old 10-08-2018, 10:15 PM
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Heres a picture taken through the opening left after taking the air filter out:



I have had a bit of time to drive the car with the large velocity stack. In all fairness, I replaced my y-pipe with the HR pipe a few days ago but I had a chance to evaluate that before I put the velocity stack on. The HR pipe clearly added power and added a nice Rumble to the exhaust. The velocity stack added even more power and gave the engine a throaty sound, particularly on wide open throttle.

in reviewing the comments on people that have performed the 2006 air box swap, it seemed a little bit divided as to whether or not there were any gains. My velocity stack is quite a bit larger than the 2006 velocity stack and I believe it is more effective based on the comments that I've seen and my own impression of the result.

I believe these two mods work nicely in combination with each other. Keep in mind that I do have the 2007 to 2008 OEM Nismo Muffler which is probably a bit more free-flowing than the non Nismo Muffler.
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