Hi guys and girls. I've been running a 2001 GD1 Honda fit for almost a year now. I've done afew things to it. Hks super power pod filter and hi power axel-back exhaust. I spent around $1200 nzd on these to get them from Japan (yep I'm a idiot) but after I installed then found I got a boost in kmpl from 13 to 14.5-15.5 which is cool.

I just recently picked up a Megan exhaust header from a guy in Holland. And yes, I knew there could have been some problems but not quite as many as I was expecting. I'm writing this thread as no one else that I have seen has experienced these issue and I hope this will give some people Abit info in how to solve them if they come about them in the future.
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Now I​​​​I have no idea if mine is a test one or a full production one but my five day nightmare started when I tried to take off the stock header. I spent an whole day trying to get the stock header off. Mostly coz I didn't have the right tools. Once I got it off and started to fit the new one the bolts didn't quite line up from the header to the block. Comparing the gaskets (stock and aftermarket one) to the header bolt holes I found that two of the bolt holes were slightly off where they should be meaning the bolts couldn't go in straight. On the far bottom whole I just cut it out with a saw and the bottom middle hole was only very slightly off so used a dremal to grind it out. I thought I'd finished everything so I stuck it all back together and started her up. Very load and check engine light. Rats.

Took it all apart again to realise that I had forgotten the gasket between the header and the cat. Opps. The header never came with a new gasket but I heard the one it would come with was too big anyway. So I headed down to repco to see if they could fix it. Nope, nothing like the gasket required. So in the end I spent an hour drilling out the stock one to fit (stock one was too small) as I knew it would fit in the pipe. By the time it was large enough to fit it was so thin it was starting to break. I chucked it on anyway. I plastered a good amount of crc gasket glue stuff down there and put it back together. Started her up and still check engine light. This time it was because I was stupid and put some crc gasket stuff on the gasket between the header and block and it was uneven as hell. Took it apart again and cleaned all that off, wreaking the gasket in the process. cleaned up the stock gasket and put it to good use. But the other problem was that the structural attachment for the header was off. This meant I took that off and drilled that out with a dremal too. Altogether this took 5 days to do instead of the usual afternoon.

Review of the header though. It definitely has more torque at higher rpm and revs faster. Very loud at low rpm but once you get over 3.5k it is quiter (same with the hks axel-back). I have a cvt model currently but it goes to 4.5k real fast in sport. Faster than before and lot better with multiple people on the car.

Anyway hope this maybe be helpful and if you got to the end well done.

Cheers guys and girls