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Discussion Starter · #1 ·
While looking at Fast Intentions down pipes, I noticed that they have lowered and full down pipes. I tried looking online but can't find a clear answer as to what the difference is? I'm assuming it's a significant difference if the price for full down pipes is 4x what lowered down pipes run you.
 

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Simple answer, lower downpipes replace just the secondary cat. Full downpipes replace the primary and the secondary cat.
 

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Simple answer, lower downpipes replace just the secondary cat. Full downpipes replace the primary and the secondary cat.
isn’t full down pipes then basically like straight piping a car? couldn’t i just get LDP and then do a cat delete for a lot less than FDP? what are the benefits of getting FDP if people say that the HP increase is negligible?
 

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isn’t full down pipes then basically like straight piping a car? couldn’t i just get LDP and then do a cat delete for a lot less than FDP? what are the benefits of getting FDP if people say that the HP increase is negligible?
Most full down pipes will come with cats, lower downpipes don't. That's why they are so much more expensive. If you get catless full downpipes you will throw CEL's. If you're just looking to get a little extra power from your daily, LDP's are great. If you're looking to build a full on track/race car then you'd obviously want to go all in on catless full downpipes. If you are somewhere in the middle and are chasing the most power you can get with cats, then FDP's with cats is the way to go.
 
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Here's why you run 3" DPs. Getting the most performance out of a turbo is contingent on having the least backpressure over the rev range. The 3" diameter presents a large area for the outlet vs the stock primary converter. Although everyone wants big hp #'s for bragging rights, I'm more interested in getting more torque for daily driving my Q. Out of the box, when FI installed the 3" Catted DPs, I could instantly tell the motor was more torquey at the bottom end than with the OEM primary cat in the loop. The 3" diameter also helps reduce turbo lag, because less flow resistance enables the impeller to "spin-up" quicker, too.

If you don't have the funds to buy a good 3" catted DP, then the 2.5" LDP is a good compromise, as it removes the secondary cat as a restriction, and frees up exhaust flow for lower backpressure. Why not a 3" LDP, you ask? Because as explained above, the 3" area of the pipe is there, but because it is moved downstream with the OEM primary cat "in-the way", the 3" LDP is not really offering that much relief in backpressure at that point. To keep the flow dynamics argument simple, having the 2.5" after the cat is better for maintaining exhaust flow velocity as the exhaust is making its way through the rest of the exhaust plumbing.

Once you have the 3" DPs, shouldn't you have a 3" CBE, too? Not necessary unless you've gone bigger turbo, like Pure Turbos Stage 2, because the 2.5" diameter again helps maintain flow velocity and scavenging. With a 3" all the way back, unless you have bigger turbos and higher exit pressures, you'll likely experience pipe resonance (i.e., drone, rasp) with the bigger 3" CBE and stock turbos.
 
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Discussion Starter · #6 ·
Here's why you run 3" DPs. Getting the most performance out of a turbo is contingent on having the least backpressure over the rev range. The 3" diameter presents a large area for the outlet vs the stock primary converter. Although everyone wants big hp #'s for bragging rights, I'm more interested in getting more torque for daily driving my Q. Out of the box, when FI installed the 3" Catted DPs, I could instantly tell the motor was more torquey at the bottom end than with the OEM primary cat in the loop. The 3" diameter also helps reduce turbo lag, because less flow resistance enables the impeller to "spin-up" quicker, too.

If you don't have the funds to buy a good 3" catted DP, then the 2.5" LDP is a good compromise, as it removes the secondary cat as a restriction, and frees up exhaust flow for lower backpressure. Why not a 3" LDP, you ask? Because as explained above, the 3" area of the pipe is there, but because it is moved downstream with the OEM primary cat "in-the way", the 3" LDP is not really offering that much relief in backpressure at that point. To keep the flow dynamics argument simple, having the 2.5" after the cat is better for maintaining exhaust flow velocity as the exhaust is making its way through the rest of the exhaust plumbing.

Once you have the 3" DPs, shouldn't you have a 3" CBE, too? Not necessary unless you've gone bigger turbo, like Pure Turbos Stage 2, because the 2.5" diameter again helps maintain flow velocity and scavenging. With a 3" all the way back, unless you have bigger turbos and higher exit pressures, you'll likely experience pipe resonance (i.e., drone, rasp) with the bigger 3" CBE and stock turbos.
So if i’m running a 2.5” exhaust. i should get a 2.5” dow pipe? rather than a 3”?
 

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Here's why you run 3" DPs. Getting the most performance out of a turbo is contingent on having the least backpressure over the rev range. The 3" diameter presents a large area for the outlet vs the stock primary converter. Although everyone wants big hp #'s for bragging rights, I'm more interested in getting more torque for daily driving my Q. Out of the box, when FI installed the 3" Catted DPs, I could instantly tell the motor was more torquey at the bottom end than with the OEM primary cat in the loop. The 3" diameter also helps reduce turbo lag, because less flow resistance enables the impeller to "spin-up" quicker, too.

If you don't have the funds to buy a good 3" catted DP, then the 2.5" LDP is a good compromise, as it removes the secondary cat as a restriction, and frees up exhaust flow for lower backpressure. Why not a 3" LDP, you ask? Because as explained above, the 3" area of the pipe is there, but because it is moved downstream with the OEM primary cat "in-the way", the 3" LDP is not really offering that much relief in backpressure at that point. To keep the flow dynamics argument simple, having the 2.5" after the cat is better for maintaining exhaust flow velocity as the exhaust is making its way through the rest of the exhaust plumbing.

Once you have the 3" DPs, shouldn't you have a 3" CBE, too? Not necessary unless you've gone bigger turbo, like Pure Turbos Stage 2, because the 2.5" diameter again helps maintain flow velocity and scavenging. With a 3" all the way back, unless you have bigger turbos and higher exit pressures, you'll likely experience pipe resonance (i.e., drone, rasp) with the bigger 3" CBE and stock turbos.
Iridium

Placing my order for FI exhaust and am confused on the resonated or non resonated exhaust. I am going with FULL downpipe with high flow cats.
 

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Placing my order for FI exhaust and am confused on the resonated or non resonated exhaust. I am going with FULL downpipe with high flow cats.
The FI Cat-back Exhaust (CBE) has the option for resonators just aft of the X-pipe. Resonators reduce drone that naturally occurs from the exhaust pulses in straight piping. The resonators basically allow the sound waves to dampen as they make their down the pipe without affecting (restricting) the exhaust flow.

Looking at the picture below (from bottom of the pic to the top), the mid-pipe, and then X-pipe (which includes the two resonators shown). The Lt. & Rt. mufflers, which are part of the CBE, are not shown.

24754


The full downpipes are connected at one end just aft of the turbos and the other end connects to the mid-pipe of the CBE (circled in red above).

Hope this helps clear things up.
 

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The FI Cat-back Exhaust (CBE) has the option for resonators just aft of the X-pipe. Resonators reduce drone that naturally occurs from the exhaust pulses in straight piping. The resonators basically allow the sound waves to dampen as they make their down the pipe without affecting (restricting) the exhaust flow.

Looking at the picture below (from bottom of the pic to the top), the mid-pipe, and then X-pipe (which includes the two resonators shown). The Lt. & Rt. mufflers, which are part of the CBE, are not shown.

View attachment 24754

The full downpipes are connected at one end just aft of the turbos and the other end connects to the mid-pipe of the CBE (circled in red above).

Hope this helps clear things up.
You have resonated ones as well. I just placed my order. Thanks you are awesome.
 
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