Well I think I am in the correct area to post this. Anways some background car is a 2g eclipse, srs(ebay exhaust), with megan racing downpipe, s16g. My question is I am going crazy to figure out if my exhaust is a full 3 inch now, I unfortunately didn't install the exhaust system because I was too busy hanging with my gf and family over the holidays banghead. The guy I had do the install said it was an easy install they lined right up, and I know megan racing has a couple different downpipes with different ID. There anyway to tell if its full 3inch? Also running stock 2g o2 housing if I replaced or ported it would the car get any louder?

Can you not measure outside diameter of the pipe? That will give you a close enough approximation of the inside diameter.

91-GS said:

Can you not measure outside diameter of the pipe? That will give you a close enough approximation of the inside diameter.

Click to expand...

Ya I could measure the outside circumference.

Divide that circumference by 3.14 to get the diameter. Unless it's oval, there needs to be much more math done for an oval pipe.

Use calipers is always my solution to a problem like this. Harbor Freight has them for $15 and its useful to have one on hand for future projects.
http://www.harborfreight.com/6-inch-digital-caliper-47257.html

okay thanks for the input, one other question I am on the stock o2 housing. If I change to either a evo 3 housing or megan racing will it make the car louder?

No, it'll just reduce some backpressure post-turbo from the bend.
Just remember that the Evo3 housing outlet is angled differently than others as it was designed to be used in conjunction with Evo3 downpipe. This will likely present an issue with DP rotation, especially with a Megan downpipe (I have one and can attest it's designed for stock angled O2 housings).

ALSO bear in mind that the Megan o2 housing may NOT be welded properly on inside seams. Be very careful in examination; I've had to send 'er back because there was a hole in the weld for the bypass -- right in that tight radius spot. Of course, my replacement had a warped flange out of the box, but I made that work at least.