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I'm trying to upgrade my lower downpipes, but it seems there are a lot of different sizes...I'm guessing at the entry and exit. What are the stock dimensions?
 

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2018 Q50 AWD Red Sport
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Most all LDP's are fine. Catted full Downpipes are a bit better but VERY expensive, much harder to install, and a bit louder. LDP's are an excellent value and upgrade with a supporting CBE.
The Fast Intentions "system" being the best power gains, but expensive and a long wait. The wait speaks for itself.

The bigest restriction are the secondary cats which the LDP eliminates.
 

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Discussion Starter #3
Most all LDP's are fine. Catted full Downpipes are a bit better but VERY expensive, much harder to install, and a bit louder. LDP's are an excellent value and upgrade with a supporting CBE.
The Fast Intentions "system" being the best power gains, but expensive and a long wait. The wait speaks for itself.

The bigest restriction are the secondary cats which the LDP eliminates.

Can you make a recommendation for one that won't be loud in the cabin? This is my first experience with DP's and I don't know what to expect. My coworker put a full Stillen exhaust on his Q50 Red Sport with lower down pipes and it's so loud in his car that I can't ride with him.
 

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Can you make a recommendation for one that won't be loud in the cabin? This is my first experience with DP's and I don't know what to expect. My coworker put a full Stillen exhaust on his Q50 Red Sport with lower down pipes and it's so loud in his car that I can't ride with him.
If stock cat-back, go with Megan's 2.5''. The variance from the OEM mid to 2.5'' will cut down on the chances of leak. AMS includes an adaptor place for their 3'' but it's not the best way to do it.
 

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Yea or the FI LDP. It is ALSO 2.5" not 3.0" The 3 inch LDP might cause some flow issue with the stock axle back. I have the FI LDP and in the car there is no sound difference none. On a cold start outside it is a little louder but sounds great and after a few seconds goes back to stock sounding. At idle outside when you are at your trunk it has a little tiny bit more mean sound to it. That is it. LDP on stock axle back sounds stock in the car. I am a 47 year old guy with wife and kids in the car everyday and they have not even noticed at all. I dont know how much power it is worth but it does pull harder and runs better. Removing that cat is a good thing.

I will say this. Just LDP and JB4 on map 7 I am way faster than any Q with LDP and any CBE. And almost stock quiet. Get a JB4 that is half the price of any CBE, and if your buddy does not get a tune you will smoke his car and be able to have a conversation in your car while doing it.
 

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A 2.5" LDP will not make much noise.

OEM secondary cats are ONLY 1.5" diameter. The biggest choke point in the OEM exhaust system. LDPs should always be part of your exhaust upgrade system plan.
 

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Here is a picture of my LDP, the sound is noticeably, because I have 16" resonators instead of the stock muffler.
 

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Here is my 3" AMS lower downpipes bolted to stock Y pipe. I don't have the stock exhaust anymore but here is just a visual for comparison.
This is why a 2.5" or even a 3" with a 2.5" exit works so well. Less turbulence. Well unless you have a 3" X-Pipe, or CBE which are loud, to loud for me. Not all that much difference in performance. But some people like that. Each to their own. Diversity is a good thing.

The more options we have in aftermarket parts the better!
 

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Yes you are right. A 3" can be a little loud. Mine is a 3" X that gradually reduces to 2.75" and then 2.5" out the Sport Mufflers. The X pipe was given to me so I built the rest around it. It has resonators to help keep the sound from being obnoxious. It was basically free because i had all the materials from my job. If not for the 3" X I would have gone with 2.5" piping.

I am curious to see if the dyno agrees with a larger diameter pipe. For turbo you can't really go wrong with larger....just louder.
 

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Good snag! Can't beat almost free.
2.5" vs 3" dynos would be nice. If the 5HP is worth the noise perfect. Some folks like the sound and would go 5HP less for the sound. Ahhh who knows. Regardless nice piping!
 

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I have AMS 3" LDP dropping into the OEM exhaust system. No change in sound inside or out of the car. Here's a video I made for evidence.


I plan to upgrade the Y pipe and possibly the midpipe and hoping that the sound will remain muted
 

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Adding a Y pipe wont change sound much. Changing the stock midpipe will. The stock resonators do a better job than anything aftermarket at keeping things quiet. I talked for a while to another member MoonSport on here. He did the same thing. Replaced LDP, used a Megan Y and either a Tanabe or a Megan midpipe and it was just to much for the stock muffler. The LDP and Y pipe the stock muffler was ok but remove the stock resonators with some larger piping and aftermarket resonators and it rasped through the stock muffler. He bought a HKS axle back to get it right. That axle back alone is $1,100 dollars. So just my advice if you are keeping the stock muffler leave the stock midpipe or get the FI resonated CBE.

Here is a link to the thread. Look at the 5th post down....

https://www.infinitiq50.org/forum/q50-general-discussion-forum/126881-anybody-running-lower-dps-stock-exhaust.html

Serstylz2 are you running map 7 on you JB4 or are you running higher than 7psi in a custom map.I am just curious if 7psi over stock will get you 16.8psi total. That is where I would like to be at. Below 18 but real close or at 17.... Thanks....
 

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Adding a Y pipe wont change sound much. Changing the stock midpipe will. The stock resonators do a better job than anything aftermarket at keeping things quiet. I talked for a while to another member MoonSport on here. He did the same thing. Replaced LDP, used a Megan Y and either a Tanabe or a Megan midpipe and it was just to much for the stock muffler. The LDP and Y pipe the stock muffler was ok but remove the stock resonators with some larger piping and aftermarket resonators and it rasped through the stock muffler. He bought a HKS axle back to get it right. That axle back alone is $1,100 dollars. So just my advice if you are keeping the stock muffler leave the stock midpipe or get the FI resonated CBE.

Here is a link to the thread. Look at the 5th post down....

https://www.infinitiq50.org/forum/q50-general-discussion-forum/126881-anybody-running-lower-dps-stock-exhaust.html

Serstylz2 are you running map 7 on you JB4 or are you running higher than 7psi in a custom map.I am just curious if 7psi over stock will get you 16.8psi total. That is where I would like to be at. Below 18 but real close or at 17.... Thanks....
Interesting that he had that experience, because @Ddnspider has CATLESS full downpipes, megan Y and tanabe mid and his car is smooth.


My Map 6 was peaking at +7 PSI to reach 16.8 PSI on my dyno run, but keep in mind I was running e30 at the time, which I no longer run on stoc fuel pumps. There was also a quick spike to 17.2 psi during that dyno run on the logs.
 

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Thanks that is exactly what I wanted to know....;)
 

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Who makes Y-Pipes for Red Sports besides Tanabe?
Megan.

Tanabe makes mid pipes as well.

Note that if you use a Megan Y pipe and stick with the stock mid pipe it most likely will leak as the y pipe outlet is much larger than the stock mid pipe inlet.
 

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I have a Megan racing LDP, Megan racing Y, Tanabe Mid and Infiniti axle back, I started with the axle back, then go the Y, that was a huge difference in sound alone, MUCH louder. I then got the Mid pipe and that did not make too much of a difference. What made the biggest difference in sound was the LDP, that made it noticeably louder than before. Exhaust is always the best place to start, especially if you are running a JB4, let your car get rid of all those fumes before you expect it to take more in, the larger the diameter, the more it gets rid of! In my opinion I’d say to do the whole exhaust at once, otherwise its going to bottle neck and wont do much good. **Spend a bit more for quality products, they also help sound, I made the mistake of just doing an axle back and then I had to piece everything together because I wanted more, as a result I found the cheapest parts I could, comparing my sound to my buddies AMS 3” LDP and exhaust is night and day.
 
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I have AMS 3" LDP dropping into the OEM exhaust system. No change in sound inside or out of the car. Here's a video I made for evidence.


I plan to upgrade the Y pipe and possibly the midpipe and hoping that the sound will remain muted
Im thinking of the same setup but going Megan LDP, and Rev9 mid/y pipe non resonated to add a touch of sound. The stock muffler should keep it nice and quiet.
 
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