Downpipes & Best Practices

[Phorari]

I installed the AMS catless LDP this weekend. The install was fairly easy but time consuming as I did it on jack stands.

I still retained the OEM cat in the UDP not CEL it any issues so far.

The LDP is probably the most restrictive part on the car. It goes from like 2.5 inch down to ~1.5 inch. I measured the UDP at about 2.75 inches going into my 3 inch exhaust.

Car sounds much better. You get abit of a deeper tone, more spoil noise and a VQ rasp.

I paired AMS LDP with Invidia Gemini 70mm CBE, no rasp, slight drone at 1.5k rpm. Any droning issue with your setup?

 

[FatRatZ]

Strange I contacted AMS before I installed mine as I'm not ready to tune my car yet. They advised me that I wouldn't get a CEL and it's been good so far.
The science is sound as the sensor is after the factory cat.

Mine was good with the LDP and the AWE touring. No lights / CEL.
Once I put on the piggyback tuner from Stillen, the light started showing up. It’s seems to stay off untill you get on the power in one of the higher boost modes in the Stillen piggyback app.

 

[FatRatZ]

it should help but no guarantee, it’s an old fashion lawnmower spark plug defouler or o2 sensor extender. This is why ams has the extended o2 bung welded into the pipe for you.

You can also pack the extender with steel wool. The best solution is to have a tuner to disable the o2 check in the ecu.

Never saw this before - thanks. Are they all the same size / thread pitch?
I’ll give it a try.

 

[Phorari]

FYI - I replaced LDP with ISR and installed a Stillen piggyback tuner. AWE Touring exhaust.
It throws a code / CEL. Seems to code mostly in more aggressive maps.
I cleared the codes but these may be permanent write codes - that is, the light is off but a dealer can still see the code when connecting through consult.
I read some people space the second O2 sensor to mount further out/ protrude less into the pipe - is that a thing that works?

I also have a piggyback tune but from Racechip with AMS LDP/CBE going on 6 months, no CEL regardless of map.

 

[thesilverbullet]

Never saw this before - thanks. Are they all the same size / thread pitch?
I’ll give it a try.

Z should be M18 x 1.5mm - a common lawn mower spark plug thread size.

the secondary o2 acts like a temperature probe - if it heats up to fast, it will throw a CEL. So the extender keep it from heating up too fast. The steel wool helps with damping temp rise to prevent spikes on startup.

 

[T3R5Z]

Z should be M18 x 1.5mm - a common lawn mower spark plug thread size.

the secondary o2 acts like a temperature probe - if it heats up to fast, it will throw a CEL. So the extender keep it from heating up too fast. The steel wool helps with damping temp rise to prevent spikes on startup.

Maybe AMS put abit more engineering into the placement to make it act more like OEM

 

[T3R5Z]

Thanks for the info.

Can you confirm the weld joint (from upper cat to the upper’s exit flange) is the same (2.75”) as the flange exit point or is the weld joint smaller as it appears in the picture.

Ok so i can't measure the flange as i'm not taking off the LDP but ive got the gasket which is close enough.

LDP - UDP Gasket is 2.6 inches.
LDP - UDP flange is 2.2 inches.
LDP - Exhaust is 1.75 inches

i measured the UDP - LDP Flange and it was about 2.75 inches, i didn't see a 2 inch restriction. The gasket could be slightly smaller as its joining 2.75 inches to 2.2 inches.

The most optimal path would be getting a 2.5 inch exhaust and LDP but i don't think there would be much restriction on a 3 inch system either. Replacing the UDP is ALOT!!! of work and not worth IMO unless you get to the stage of swapping turbos and then it would be an engine out job anyway.

Whoever designed this needs to go home and look in the mirror.

 

[thesilverbullet]

Ok so i can't measure the flange as i'm not taking off the LDP but ive got the gasket which is close enough.

LDP - UDP Gasket is 2.6 inches.
LDP - UDP flange is 2.2 inches.
LDP - Exhaust is 1.75 inches

i measured the UDP - LDP Flange and it was about 2.75 inches, i didn't see a 2 inch restriction. The gasket could be slightly smaller as its joining 2.75 inches to 2.2 inches.

The most optimal path would be getting a 2.5 inch exhaust and LDP but i don't think there would be much restriction on a 3 inch system either. Replacing the UDP is ALOT!!! of work and not worth IMO unless you get to the stage of swapping turbos and then it would be an engine out job anyway.

Whoever designed this needs to go home and look in the mirror.

Thank you for the info. if the udp exit ID is 2.75”, the upper cat / flange weld joint ID should still be ~2.5 even with weld drop thru & shrinkage. So catless lowers it is.

 

[T3R5Z]

I paired AMS LDP with Invidia Gemini 70mm CBE, no rasp, slight drone at 1.5k rpm. Any droning issue with your setup?

Yeah slight drone but not unbearable. My cars not a daily so it doesn't bother me. If it was I probably would have splashed out for the AWE with it's any drone mufflers.

 

[thesilverbullet]

There is only one sensor per side and its the lower. The Upper will still do its job and wont throw CELs

I went full for both, switch over to catted to prevent 1. bad smell and 2. Rasp. The hi flow cats will perform just as good as catless

Thanks for posting this diagram.

If these dimensions are correct, the ID of the upper‘s neck down weld joint is ~2”?

The upper’s exit flange ID maybe larger but the weld joint‘s ID is smaller and the bottle neck. So if you keep the upper, there is no advantage going with a 4” vs 5” X-pipe?

if you go with full dps, then you would need a 5” X-pipe?

 

[T3R5Z]

Thanks for posting this diagram.

If these dimensions are correct, the ID of the upper‘s neck down weld joint is ~2”?

The upper’s exit flange ID maybe larger but the weld joint‘s ID is smaller and the bottle neck. So if you keep the upper, there is no advantage going with a 4” vs 5” X-pipe?

if you go with full dps, then you would need a 5” X-pipe?

I think the location of the arrow in the diagram is wrong. It should be pointing to the upper neck of the LDP which is measured at 2.2 inches and then would drop to about 2.

There is no way it drops From ~2.75 to 2. That's definitely not what I saw.

 

[thesilverbullet]

I watched a video on removing the uppers - i won’t be doing that - catless lowers only it is…

 

[Bumflik]

I watched a video on removing the uppers - i won’t be doing that - catless lowers only it is…

Aaaaa I went Catless LDP too. Only reason to up grade to FDP is if you are upgrading turbos and going for big big power. Other than that LDP upgrade is adequate with oem turbos up to 480HP to wheels.

 

[ZMidlife]

With about 1 week on the new FBO 93 with FDPs and AWE. I can see this car is definitely much more enjoyable in day to day driving!

 

[Hernandooo]

Thanks for posting this diagram.

If these dimensions are correct, the ID of the upper‘s neck down weld joint is ~2”?

The upper’s exit flange ID maybe larger but the weld joint‘s ID is smaller and the bottle neck. So if you keep the upper, there is no advantage going with a 4” vs 5” X-pipe?

if you go with full dps, then you would need a 5” X-pipe?

5" diameter? That's a bit overkill for fdp

I would just match it all the way through?