Stage2 with stock catalytic converters

[CeglA]

Is it safe to use ots Stage2 ( not maxed out ) with stock catalytic converters?

For example Mhd says that downpipes are recommended with Stage2 and requied with Stage2+.

I flashed Stage2 in a stock M4. Everything run somooth, logs looks good (no significant timming corrections, egt is fine etc...).

I read that s55 has great oem cats, very little restrictive.

What are your experiences?

[b_w.]

Stock cats flow well. Should be good to go but any tune carries some risk even though tons of guys, including myself do it.

[CeglA]

I am aware of the risk. My car has been tuned for 5 years and during that time I had a catless downpipe installed. Recently, however, it cracked and I installed catalytic converters, because I planned to quiet the car down a bit anyway. However, I would like to keep the mhd stage2 map, where a downpipe is only recommended

[M 4 FUN]

Yes, it works perfect with the stock cats. I had it myself for four years without a correction in the logs or any fault code. We also did dyno comparisons with and without the catted downpipes so there is no problems with restriction.

[CeglA]

Originally Posted by M 4 FUN

Yes, it works perfect with the stock cats. I had it myself for four years without a correction in the logs or any fault code. We also did dyno comparisons with and without the catted downpipes so there is no problems with restriction.

Thanks for info!

Out of curiosity, what was the difference in power?

[aka Hootie]

I run a Stage 3 custom tune with stock down pipes with no issues. Its tracked tuned so putting down 577 whp. I do have Mosselman turbos and supporting mods. No issues.

[mike@x-ph.com]

i would not do it, there is a reason tuning companies recommend you upgrade your downpipes for stage 2

[M4SSAD]

Originally Posted by mike@x-ph.com

i would not do it, there is a reason tuning companies recommend you upgrade your downpipes for stage 2

Whats the reason? I want a stage 2 OTS map while keeping stock cats to keep M performance sound the same.

[HotRodM4]

Been on bm3 stage 2 93 oct ots with stock cats for 2 years now. No problem.

[mike@x-ph.com]

Originally Posted by M4SSAD

Whats the reason? I want a stage 2 OTS map while keeping stock cats to keep M performance sound the same.

High-flow pipes reduce backpressure on the turbo, allowing for a faster spool and making it easier for the turbos to maintain maximum power at high RPM. Staying stock means less air for the turbo and less breathing room to work with.

Tuning companies offer maps for stock downpipes with stock airflow,that's Stage 1. They also have maps for upgraded downpipes with more airflow, known as Stage 2.

If Stage 1 and Stage 2 could safely run with the same hardware, tuning companies wouldn't differentiate between them, and they would have them under the same stage.

[theweebabySeamus]

I do use the stage 2 91 map with stock cats, but it is worth noting that BM3 changes high flow downpipes from 'Recommended' to 'Required' on this 93 map, so it's not for nothing.