Possibly a dumb question... I'm currently tuned for a catless downpipe. If I switch to a different catless downpipe can I get away with not having it retuned? Current downpipe is a TurboXS 4" taper down to 3". It's a two piece downpipe so you can swap either a catted pipe or catless pipe onto the end of it. Looking to get a "normal" 3" downpipe. My Invidia catback came in today and it's like 6" too long because of the goofy downpipe that's on this car
It could be fine but if the second cat is significantly less restrictive than the first it could cause troubles. You should at least log it to see if you overboost or have any fueling problems.
I figured it wouldn't make a difference. To clarify, the top half of the downpipe is catless. Then for the rear section of the DP you have the option to run a catted pipe or catless pipe. I've been running and tuned on the catless pipe. I just wasn't sure if going from a 4" top section of DP to a "normal" full 3" pipe would make a difference tuning-wise
This is just my opinion and nothing more. You get tuned to run a catless downpipe because the airflow is so much greater/back pressure less that it's easier to overboost. In my head it'd seem like the 4" opening might flow a little more than the 3". Therefore, your worst case scenario is that it'll actually flow just a little less?
Right. That's what posed the question lol I mean the opening is the same as a "standard" downpipe (bellmouth downpipe), but it immediately goes into a 4" pipe (thing is huge) until it gets to the flange on the other end where it tapers to 3". I'm just not going to worry about and keep and eye on it with the data logger like Nhibbs said.
