You shouldn't need a 3.5 inch coupler. The 90 should have be flared out on one end and regular 3 inch on the other end. Use the flared side for the 4 inch air filter then the regular side should be 3 inch. It kinda looks like both sides of your pipe are flared out which I have never seen. If that's the case then just cut the flare off of one side.

 

The pipe that i have i 3 inch inside diameter and the outside diameter is 3.5. So i took a 3 inch coupler, cut it, then taped around it to make it be 3.5 inches. its not the best but it works for now

 

I believe they do sell that pipe in 2 versions, one with a flare at both ends, and one with a flare only on one end. In the version with one flare, the 3" fernco fits perfectly over the tb and non-flared end of the pipe, and a 4" clamp on k&n filter fits perfectly over the flared end. This would lead me to believe that maybe a 4" fernco would fit over the second flared end, but i don't have a pipe like that, so I don't know for sure. You could head back to the hardware store and grab a pipe like you've got and find the fernco that will fit it. They do make fernco's that would go from 4" to 3" http://www.homedepot.com/h_d1/N-25ec...1#.URJaiKX5Ouk

so if that is the case, i would suggest picking up one of those instead of hacking off the end of your pipe, it will be a little cleaner.

 

anyone try this on the 3.7? was thinking of building one for mine

 

dont know much about that engine, space may be an issue. You could always buy the pipe and hold it in there to see if it will fit. Then you could return it if it doesn't fit.

 

Just installed mine and it sounds glorious.

 

nice! it does make quite a difference. Pics?

 

Pics tomorrow. I can totally hear it over the exhaust.

 

wonderful isnt it? I couldn't believe the difference, sucks air like nobodies business. Did you get a k&n, spectre or something else?

 

K&N that I had before I bought this. I cut off the expanded part of the pipe so the filter isn't so close to the radiator.