Today I was bored and decided to mod the stock airbox. I bought a maf adapter and a large velocity stack sold at pepboys ( I'm so impressed that out of all the crap pepboys sells, they actually sell a very nice velocity stack that measures about 6" IIRC ).

The velocity stack was way too big to fit so I cut it down to 4.75" and I ripped out the oem velocity stack and inserted the maf adapter. In the end the velocity stack came out so big that the air filter wont fit but honestly I don't care much because dust is not a big issue here in Puerto Rico, it rains WAY too ofter for dust to be a problem and airfilters can last 4 times their normal life expectancy. If I ever do decide to put the air filter on I just have to make the V-stack smaller...maybe 3.5" or simply glue it directly on the airbox and not use the maf adapter ( which is what I'm leaning it ).

Here are some pics:

 

cool mod

 

wow

 

I would put some sort of mesh or something that resembles a filter on there you dont want a rock to get sucked up that giant trombone there and cause hell on your MAF or throttle body

 

That's also a good idea...maybe I'll try that. I had a Pontiac Grand Prix ( I've actually had two ) that ran without a filter for over 150K miles with no issue..lol.

 

I tried running an open 3" velocity stack and lost a few whp.......it seemed like the turbulence that is created without a filter has a negative effect on the maf sensor itself. Just fyi. Back to Back runs the car made 4whp more with a filter.

 

Nice! I was going to try this but could never find a v-stack the right size. BTW. It looks like you could cut down the maf adaptor down further to get the stack back enough to fit the filter back in?

You have a brand or p/n on that pep boys stack?

 

I thought of that but it wouldn't be enough. I could just epoxy it to the airbox and problem solved. I can't remember the brand of the V-stack ( threw the packaging away ) but it's in the rice section of pepboys..lol. It's next to the conical airfilters and modular chrome intake piping with maf adapters.

 

Not sure if that's really going to help. The stock airbox was not just slapped together, there's definite engineering in it. The velocity stack sorta throws all that out the window.

 

The airboxes inbetween years are bascily the same. ie.. I took a Z v-stack and put it into my 03 airbox

 

velocity stack sizing is used to tune the optimum rpm range using helmholtz resonance theory. Unless there is an inferior design in the stock velocity stack, going larger will not net any gains, and will only result in shifting the optimum rpm range

 

Well, nissan just slapped a larger stack on the same box for the HR's so I guess it isn't rocket science. I've done this before on other cars and it's always helped ( it's never given large gains but never decreases in power ).

 

Alright, don't take my word for it......all I did was run back to back tests with results (within 5 minutes) and it showed a decrease. Oh and the open velocity stack was the 1st pull. Perhaps your butt dyno is crappy?

 

I never said otherwise, but I'm still going to try it out for myself. Your setup was not identical to mine, or was it ( you said it was an open V-stack while mine is still inside the box )? Are you sure the reason why your car lost power isn't because you didn't give it time to adapt?

 

Interesting. Have a pic of the dual HR v-stack??