Downpipes & Best Practices

[Bumflik]

Louder for sure hahahah

 

[traska_rz34]

I have gone down the downpipe rabbit hole and have no clue what to get or what I want. I found multiple options:

• Full high flow catted downpipes
  • PLM
• Full non-catted downpipes with catted O2 sensors
  • Boosted6 Auto 4"
• Resonated lower downpipes
  • Boosted6 Auto 3"
  • Mo Powa 2.6"
  • CZP options
• Non-resonated lower downpipes
  • Many options

My main goal is to NOT throw CELs while gaining more sound but not to the point where the cabin is uncomfortable, can't hear music, etc. It's so hard to judge sound on YouTube videos...

 

[FSUZ33]

Not my area of expertise. Haven't fallen into that rabbit hole. ... yet.
Resonated DPs are supposed to be quieter in the cabin while not reducing performance (or very minimal reduction).

 

[KrackaC8]

I have gone down the downpipe rabbit hole and have no clue what to get or what I want. I found multiple options:

• Full high flow catted downpipes
  • PLM
• Full non-catted downpipes with catted O2 sensors
  • Boosted6 Auto 4"
• Resonated lower downpipes
  • Boosted6 Auto 3"
  • Mo Powa 2.6"
  • CZP options
• Non-resonated lower downpipes
  • Many options

My main goal is to NOT throw CELs while gaining more sound but not to the point where the cabin is uncomfortable, can't hear music, etc. It's so hard to judge sound on YouTube videos...

Your "main goal" statement should automatically disqualify the 4" downpipes, there is just no reason to go that big at these power levels/turbo sizes unless your main goal is maximum volume. Stock turbos really don't benefit much from 3.0" vs. 2.5" as dual-2.5" is capable of flowing ~500whp, with dual-3.0" being more than capable of flowing anything you throw at the stock or stockframe turbos.

To minimize turbulence in the exhaust stream, I wanted something that smoothly necked up from the UDP outlet flange to the AWE catback; both the Spool and the new B6A LDPs accomplish this. If you go a different route, I'd rather have 2.5" --> 3.0" than 4.0" --> 3.0" as that's a big steel wall your exhaust gasses are slamming into.

Getting back to your "main goal" statement, I suspect a full downpipe, even catted, is likely going to be louder than you want for a street/wife-friendly car where you can still enjoy the radio, conversations, phone calls, etc. If you do go with a full catted downpipe, AMS makes an excellent option with a true EPA-certified cat core (very similar to the ones I ran on my C8, after a ton of research). Note that not at cat cores are created equally, and many of the generic Chinese cores will still throw a CEL as they are not efficient (or sometimes doing nothing at all, other than acting as a restriction in the pipe). The GESi G-Sport cores that AMS uses are the real deal, while still flowing incredibly well. On my C8, I went with the GESi G-Sport GEN2 400-cell S-Wound cores, which actually out-flow a standard 300-cell HFC, while still being 49-state legal.

 

[KrackaC8]

Not my area of expertise. Haven't fallen into that rabbit hole. ... yet.
Resonated DPs are supposed to be quieter in the cabin while not reducing performance (or very minimal reduction).

Straight-through perforated resonators will not decrease ultimate flow or power gains, assuming they're cleanly welded onto the pipes at either end.

 

[Tranzor Z]

I got the Mo Powa from a veteran on eBay. No cats, but has resonators. I can't judge the sound because I'm almost straight piped.

They fit fine from what I can tell. I paid $290 and the seller is faster than anyone I've ever dealt with! Beautiful welds too!

Pipe is pipe. If it fits, who cares about a name you'll never be able to even see.

 

[KrackaC8]

I got the Mo Powa from a veteran on eBay. No cats, but has resonators. I can't judge the sound because I'm almost straight piped.

They fit fine from what I can tell. I paid $290 and the seller is faster than anyone I've ever dealt with! Beautiful welds too!

Pipe is pipe. If it fits, who cares about a name you'll never be able to even see.

These pipes are nice, and basically what B6A used to sell prior to releasing their new version. For a 2.5" catback, these are absolutely what I'd choose.

 

[traska_rz34]

These pipes are nice, and basically what B6A used to sell prior to releasing their new version. For a 2.5" catback, these are absolutely what I'd choose.

I've got the Stillen competition exhaust, which I believe is a 3" pipe. The main two to decide between are the Boosted6 3" or Mo Powa 2.6" resonated pipes. Shoutout to @Tranzor Z for the lead on the Mo Powa stuff. Dude has a TON of great feedback on eBay and online.

 

[KrackaC8]

I've got the Stillen competition exhaust, which I believe is a 3" pipe. The main two to decide between are the Boosted6 3" or Mo Powa 2.6" resonated pipes. Shoutout to @Tranzor Z for the lead on the Mo Powa stuff. Dude has a TON of great feedback on eBay and online.

...and he can thank me for the link to them!

Stillen Competition is 2.5" and also what he has on his car.

 

[Cujo2811]

Yup, the OEM is two piece, upper & lower downpipe with a Cat on each.

Thanks for the recommendation.
Will go with the Cat-back Exhaust for now and leave the downpipe as stock.
No point spending money on a LDP, when I already have FDP.

Need to know invest in a ECU Tune, probably through EcuTek.

There is a cat on each? I thought both cats were in the uppers?

 

[KrackaC8]

There is a cat on each? I thought both cats were in the uppers?

Uppers have monitored 600-cell cats (primaries).
Lowers have unmonitored 400-cell cats (secondaries).

4 cats in the stock exhaust system.

 

[SavedByFaith_]

There is a cat on each? I thought both cats were in the uppers?

I believe so.
There are 4 in total, one on the upper and one on the lower, so two on each side, making 4 in total.

Do not quote me on it, as I've yet to change my OEM DPs (waiting for warranty to elapse on my NISMO).
I'm sure others who've done work on the DPs can confirm.

 

[KrackaC8]

I believe so.
There are 4 in total, one on the upper and one on the lower, so two on each side, making 4 in total.

Do not quote me on it, as I've yet to change my OEM DPs (waiting for warranty to elapse on my NISMO).
I'm sure others who've done work on the DPs can confirm.

Correct.

 

[Cujo2811]

Just looked it up. OK, so changing the LDP only removes the lower cats, which are couth of the O2 sensor reporting back to the ECU. So should not throw a CEL.

 

[KrackaC8]

Just looked it up. OK, so changing the LDP only removes the lower cats, which are couth of the O2 sensor reporting back to the ECU. So should not throw a CEL.

Correct, no CEL from lowers, the secondary cats are unmonitored.