Exhaust sizing question
11-05-07, 11:55 PM
#1
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Exhaust sizing question
Hey guys,
I havent posted in a real long time, but I have a questions. I am looking to change up my exhaust. I am going to get rid of my single side 3" RSR GT2 exhaust, and I am looking for a more subtle dual exhaust. I was thinking of dual apexi world sport 2, but the sizing only comes in 60mm (2.25") or 80mm (just over 3") inlets. I am not sure which size inlet to get. I dont know what size to get for my application, is dual 3" bad even with ok hp numbers? I have a NA-T with a GTE bottom, and around 500whp.
If you guys have any ideas. I would even consider a similar looking exhaust to the apexi world sport 2 but a full dual exhaust. I want to keep it clean, like a muffler and tip look, not so much a can guy anymore. Something kinda quiet at start up and idle too. I geuss Im getting older and my tastes are refining. I already searched a lot and came up with nothing. I trust my peers at CL to not do me wrong.
Kevin
I havent posted in a real long time, but I have a questions. I am looking to change up my exhaust. I am going to get rid of my single side 3" RSR GT2 exhaust, and I am looking for a more subtle dual exhaust. I was thinking of dual apexi world sport 2, but the sizing only comes in 60mm (2.25") or 80mm (just over 3") inlets. I am not sure which size inlet to get. I dont know what size to get for my application, is dual 3" bad even with ok hp numbers? I have a NA-T with a GTE bottom, and around 500whp.
If you guys have any ideas. I would even consider a similar looking exhaust to the apexi world sport 2 but a full dual exhaust. I want to keep it clean, like a muffler and tip look, not so much a can guy anymore. Something kinda quiet at start up and idle too. I geuss Im getting older and my tastes are refining. I already searched a lot and came up with nothing. I trust my peers at CL to not do me wrong.
Kevin
11-06-07, 07:07 AM
#2
Diameter of Pipe(s)
There are two rules of thumb here. First, air can flow at ~115CFM per square inch of pipe cross-sectional area. Second, 2.2CFM of flow is required for each horse that your engine is making at the crank.
Assuming .040" thick pipe, the following CFM flow rates and HP capacities can be extrapolated using A=(pi)*(r)^2 and the above rules:
1.75" pipe = 252 CFM = 115hp
2" pipe = 333 CFM = 151hp
2.25" pipe = 425 CFM = 193hp
2.5" pipe = 529 CFM = 240hp
3" pipe = 770 CFM = 350hp
4" pipe = 1387 CFM = 631hp
These numbers above are of the theoretical maximum horsepower allowed with no backpressure for a given pipe diameter. This does not mean that a race-ready Supra Turbo could not make significantly more than 350hp on a 3" single exhaust. It simply means that on a 3" single exhaust, any power over 350hp is being made in spite of (and at the expense of) exhaust backpressure.
These numbers also assume that pipe diameter is consistent throughout (ie. mandrel bent). Most exhaust shops do not use such methods. With traditional crush bent pipe, the bends will present regions of decrased cross-sectional area and -thus- decreased flow.
For a dual exhaust, you can simply double the numbers above to receive appropriate flow and horsepower capacity values.
A slightly undersized system will provide better boost response and a more fulfilling low end. A slightly oversized system will provide more pull at the top end.
-------------------
If you are currently on a 3" exhaust (770 CFM), a dual 2.25" set up (425CFM*2) would supply you with more flow than your 3" single. If you are looking for subtlety, also consider noise. Larger pipes make significantly more noise. A 3" dual set up would wake the dead.
There are two rules of thumb here. First, air can flow at ~115CFM per square inch of pipe cross-sectional area. Second, 2.2CFM of flow is required for each horse that your engine is making at the crank.
Assuming .040" thick pipe, the following CFM flow rates and HP capacities can be extrapolated using A=(pi)*(r)^2 and the above rules:
1.75" pipe = 252 CFM = 115hp
2" pipe = 333 CFM = 151hp
2.25" pipe = 425 CFM = 193hp
2.5" pipe = 529 CFM = 240hp
3" pipe = 770 CFM = 350hp
4" pipe = 1387 CFM = 631hp
These numbers above are of the theoretical maximum horsepower allowed with no backpressure for a given pipe diameter. This does not mean that a race-ready Supra Turbo could not make significantly more than 350hp on a 3" single exhaust. It simply means that on a 3" single exhaust, any power over 350hp is being made in spite of (and at the expense of) exhaust backpressure.
These numbers also assume that pipe diameter is consistent throughout (ie. mandrel bent). Most exhaust shops do not use such methods. With traditional crush bent pipe, the bends will present regions of decrased cross-sectional area and -thus- decreased flow.
For a dual exhaust, you can simply double the numbers above to receive appropriate flow and horsepower capacity values.
A slightly undersized system will provide better boost response and a more fulfilling low end. A slightly oversized system will provide more pull at the top end.
-------------------
If you are currently on a 3" exhaust (770 CFM), a dual 2.25" set up (425CFM*2) would supply you with more flow than your 3" single. If you are looking for subtlety, also consider noise. Larger pipes make significantly more noise. A 3" dual set up would wake the dead.
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