Safe to run stage 1a chip with CAT?

[andyrt]

I’m just getting my S14 back on the road after a few years off & having done a lot of body work.

My tester friend says the new MOT is a lot stricter so it’s much better if you’re actually testing the correct car at the test these days. In years gone by I put the CAT back in anyway, but I can’t remember if that was when I was just running the stage 1 chip (actually I can’t quite remember if there was a stage 1 chip, I just remember I swapped it to a slightly updated version at some point). So I’m hoping it’s going to pass with the stage 1a chip & CAT in, and at the same time that the CAT isn’t going to get damaged.

I used to sometimes leave the CAT in for a little while before I had time to put the de-cat back & I have to say I didn’t notice a massive difference in performance. I’m only running a 2.5” exhaust & the standard CAT fits up to the 2.5” pipe perfectly.

So I’m just wondering if the AFR of the stage 1a chip is likely to damage the CAT if I left it in over a long time. I think richer mixtures can damage them.

[sideways14a]

Just put it in for the test and remove it for the rest of the year.

[andyrt]

Just put it in for the test and remove it for the rest of the year.

Yeah that’s what I usually do, but I’m getting old & boring & quite like it being a little bit quieter with the cat in. I was looking at making a decat pipe with a little straight through silencer in it. It’s just free & easier to leave the CAT in!

[bigjoe]

Buy a silenced de cat, tones it down just enough

[arry]

I wouldn't say you're any more at risk of damaging the cat with the chip than without.

[green_rs13]

just pay your mot guy an hours labour to remove and refit the cat.

[andyrt]

I decided make my own silenced decat:



I need to invest in a TIG! But it’s functional. For some reason my exhaust likes the CAT section to be a bit longer than the standard CAT length, it will pull back to fit the standard CAT in ok but just sits better with a slightly longer section in there. Its a 2.5” straight through silencer with the flanges welded on. I think it’s actually a little louder at idle with that in than it was with the CAT but there’s not much in it.

More interestingly it over boosted like mad on the first test run, I forget where I fixed the preset boost level on my bost contoler but I had to drop it back down a level in to stop the over boosting.

I have a 2.5” exhaust system (inc down pipe) but the only decat I could find years ago was a 3” one. I always thought it was probably a bit silly as it was likely disrupting the exhaust flow. It must have been as I had found a level on the controller that got me 16psi with both the 3” decat & CAT in.

I can’t test it too much till my new wheels come & I have some decent tyres on, can’t wait!

[drc]

Looks good enough for the job I would say. Smooth flow in an exhaust is like flow in a hose pipe go from small to big to small again and you will cause a bottleneck, keeping the same size throughout or gradually going bigger from front to back is fine.

You should find the spool is also better when first putting your foot down. Enjoy it!

[andyrt]

Yes I’m looking forward to testing the spool time

I just remembered as I finished putting my new silenced decat in that years ago I was planning on swapping to a 3” down pipe to go on to the 3” decat then onto the rest of the 2.5” system. I think people were recommending that on here. Still I’ll be sticking with 2.5” right though now. I had gone to a bit of trouble smothering out the transition from the 3” into the 2.5”. So I used a bit of cut off silencer to make a short sleeve to keep it all 2.5” & locate the new decat in the correct place.