Hey guys I was just wondering what size flex pipe i need to order from summit. this is for my inline kit. I was looking at a 3"x4" flex, but the flex joint dia is 3.5" will that be a problem? Is the length right too? Also I will be welding it on a 70mm test pipe will that pose a probem. thanks for the help.

 

For the flex pipe I see two problems. First a 4" flex pipe is too short. I ordered a 6" one to begin with and they sent me a 4" on accident. I realized this and contacted the company I ordered it from and they never got back to me on why it was the wrong size. I emailed a few times but never got a response, and the only reason I didn't pursue it was b/c I got another one for free when I got my exhaust installed (I ordered it originally b/c no one seemed to carry 3" diameter but when I got it put on they had one in stock). Anyway all that to say that when I went to get it installed I asked if 4" was too short and was told by the fabricator that it was way too short if you're only running one flex pipe seeing as how 4" doesn't have enough play. 8" length (of flex pipe, overall length may be 10"-12") is the minimum that you want to run. I ran a 12" section of flex pipe and it fit just fine. I also ran a resonator, but no cat, so you'll have room. Just make sure you install it as close as possible to the downpipe, but leave enough room for the Lambda sensor bung (if you're using AEM EMS with wideband or some other form of wideband) as you will want the sensor as close to the manifold as possible. Also leave room for any other o2 sensors that you need to install.
The other problem I see, and this may not be a problem, is that you are using 70mm exhaust, which is 2.75" so I don't know if they can stretch it that much to accommodate the 3" flex pipe...but I am no expert on that so don't quote me. It just seems like it could be an issue. Are you running a 3" downpipe? Or 2.5"? It is best to keep the same diameter from the downpipe back. I am running a 3" single exhaust as it flows better than 2.5" for turbo (depending on your power goals). Also I do not know your exhaust setup, if you are having to get a flex pipe welded on why are you having to attach it to a test pipe? Did you buy a cat back system? If you haven't purchased the system or the test pipe yet just buy a universal muffler and take it to an exhaust shop. It'll be maybe $150 to get it fabbed up from the downpipe back, they may charge extra for a flex pipe and resonator (which I would recommend since you're not running a cat). My 75mm(2.9") HKS muffler ran $350 and install was $150 so $500 total was cheaper than most cat back systems, and that was with the titanium muffler and all, you could get a decent muffler for less than I paid. I just like HKS.
But long story short, get 8" or longer flex pipe, and make sure it's the right diameter to mate up to your test pipe if that's the route you chose to go. The actual flex pipe outside diameter doesn't matter. I have 3" and had plenty of clearance. Sorry for the book!

 

thanks for the info, as for my set up I have a 3" dp to a 70mm test pipe and to a greddy ti-c. The installer of the kit ha welded the dp to the test pipe hence why I will just weld the pieces togeather.