Why only 3" exhausts
01-01-09, 09:30 AM
#27
hmm, that doesnt really make sense, I would think horsepower would be horsepower regardless of the type of engine. It doesn't mention anything about engine type, or the amount of cylinders having any effect on flow. Anyone want to elaborate how a 300hp rx7 flows more exhaust than a 300hp v6? I guess it is different though
Also if that were true, wouldnt that mean the rotary has to flow like twice as much fuel and air as a regular combsution engine to make the same power?
Also if that were true, wouldnt that mean the rotary has to flow like twice as much fuel and air as a regular combsution engine to make the same power?
01-01-09, 02:22 PM
#29
Original Gangster/Rotary!
iTrader: (213)
As far as noise goes, I have a 4 inch magnaflow resonated mp and a 3.75 inch Apexi GT Spec catback, I also have the option to run the Apexi ATS, which really quiets things down a lot around town, although the car still drones a bit on the highway. I actually like running without the ATS, I think the sound strikes a good balance between being aggressive but not insanely loud, I'm really happy with it
Edit: optimal exhaust diameter for a turbocharged rotary is vastly different (ie larger) than for a normally aspirated piston engine in my opinion. 3 inch is fine for most on stock twins and even for most street-level 400 rwhp singles, I went to 4 inch for the added response and to say 'Mine is bigger than yours!'
Last edited by GoodfellaFD3S; 01-01-09 at 02:28 PM.
01-01-09, 05:33 PM
#30
I have the Racing Beat dual-tip and love it. It has a great sound, but it's definitely not too loud. Sometimes I wish I could hear it better, but I know it would be too loud for everyone else...I don't want to attract too much of the wrong kind of attention.
01-01-09, 05:52 PM
#31
Depends on outside temps as well, but around 3400-3500 rpms in 4th gear. That's cruising at 3000 rpm and punching it. The setup is very responsive, to say the least. I have the 1.06 hot side A/R IIRC. Also, I ceramic coated basically my entire engine bay
As far as noise goes, I have a 4 inch magnaflow resonated mp and a 3.75 inch Apexi GT Spec catback, I also have the option to run the Apexi ATS, which really quiets things down a lot around town, although the car still drones a bit on the highway. I actually like running without the ATS, I think the sound strikes a good balance between being aggressive but not insanely loud, I'm really happy with it
Edit: optimal exhaust diameter for a turbocharged rotary is vastly different (ie larger) than for a normally aspirated piston engine in my opinion. 3 inch is fine for most on stock twins and even for most street-level 400 rwhp singles, I went to 4 inch for the added response and to say 'Mine is bigger than yours!'
As far as noise goes, I have a 4 inch magnaflow resonated mp and a 3.75 inch Apexi GT Spec catback, I also have the option to run the Apexi ATS, which really quiets things down a lot around town, although the car still drones a bit on the highway. I actually like running without the ATS, I think the sound strikes a good balance between being aggressive but not insanely loud, I'm really happy with it
Edit: optimal exhaust diameter for a turbocharged rotary is vastly different (ie larger) than for a normally aspirated piston engine in my opinion. 3 inch is fine for most on stock twins and even for most street-level 400 rwhp singles, I went to 4 inch for the added response and to say 'Mine is bigger than yours!'
thewird
01-01-09, 10:17 PM
#32
The issue is that what is best for maximum hp is not good for a wide power band. The ideal exhaust would change diameter from smaller to larger as rpm increased in order to maintain optimal velocity of gas flow, which is what makes the power. At lower rpm, there is less volume of gas flow at the port, so you want a smaller diameter pipe to achieve maximum velocity. At highest rpm, there the highest volume of gas flow and you need a bigger diameter pipe for the same velocity. So, any diameter is a compromise and the different sizes move the peak power around and increase or decrease the width of the power band.
Smaller pipe makes more power sooner and less ultimate power. Larger diameter pipe makes more ultimate power, but makes it later. Sooner and later being lower versus higher rpm.
Gordon
Smaller pipe makes more power sooner and less ultimate power. Larger diameter pipe makes more ultimate power, but makes it later. Sooner and later being lower versus higher rpm.
Gordon
thewird
01-02-09, 12:08 AM
#34
Thank you
thewird
N/A cars: As most of you know, the design of turbo exhaust systems runs counter to exhaust design for n/a vehicles. N/A cars utilize exhaust velocity (not backpressure) in the collector to aid in scavenging other cylinders during the blowdown process. It just so happens that to get the appropriate velocity, you have to squeeze down the diameter of the discharge of the collector (aka the exhaust), which also induces backpressure. The backpressure is an undesirable byproduct of the desire to have a certain degree of exhaust velocity. Go too big, and you lose velocity and its associated beneficial scavenging effect. Too small and the backpressure skyrockets, more than offsetting any gain made by scavenging. There is a happy medium here.
For turbo cars, you throw all that out the window. You want the exhaust velocity to be high upstream of the turbine (i.e. in the header). You'll notice that primaries of turbo headers are smaller diameter than those of an n/a car of two-thirds the horsepower. The idea is to get the exhaust velocity up quickly, to get the turbo spooling as early as possible. Here, getting the boost up early is a much more effective way to torque than playing with tuned primary lengths and scavenging. The scavenging effects are small compared to what you'd get if you just got boost sooner instead. You have a turbo; you want boost. Just don't go so small on the header's primary diameter that you choke off the high end.
Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure.
For turbo cars, you throw all that out the window. You want the exhaust velocity to be high upstream of the turbine (i.e. in the header). You'll notice that primaries of turbo headers are smaller diameter than those of an n/a car of two-thirds the horsepower. The idea is to get the exhaust velocity up quickly, to get the turbo spooling as early as possible. Here, getting the boost up early is a much more effective way to torque than playing with tuned primary lengths and scavenging. The scavenging effects are small compared to what you'd get if you just got boost sooner instead. You have a turbo; you want boost. Just don't go so small on the header's primary diameter that you choke off the high end.
Downstream of the turbine (aka the turboback exhaust), you want the least backpressure possible. No ifs, ands, or buts. Stick a Hoover on the tailpipe if you can. The general rule of "larger is better" (to the point of diminishing returns) of turboback exhausts is valid. Here, the idea is to minimize the pressure downstream of the turbine in order to make the most effective use of the pressure that is being generated upstream of the turbine. Remember, a turbine operates via a pressure ratio. For a given turbine inlet pressure, you will get the highest pressure ratio across the turbine when you have the lowest possible discharge pressure. This means the turbine is able to do the most amount of work possible (i.e. drive the compressor and make boost) with the available inlet pressure.
01-02-09, 03:38 PM
#38
hmm, that doesnt really make sense, I would think horsepower would be horsepower regardless of the type of engine. It doesn't mention anything about engine type, or the amount of cylinders having any effect on flow. Anyone want to elaborate how a 300hp rx7 flows more exhaust than a 300hp v6? I guess it is different though
Also if that were true, wouldnt that mean the rotary has to flow like twice as much fuel and air as a regular combsution engine to make the same power?
Also if that were true, wouldnt that mean the rotary has to flow like twice as much fuel and air as a regular combsution engine to make the same power?
Horsepower is horsepower... But HOW it is generated is the key to your question. Like what was mentioned above first key you need to look into is understanding NA vs. turbo/supercharged setups. In a NA setup, what you are reading would be correct b/c there is a certain amount of backpressure NEEDED.. While in a forced induction setup backpressure is more of an enemy for reasons listed above that have to do with turbo efficiency and spool.
The rotary moves more exhaust than a normal piston engine and yes it does use more fuel per firing (how many cars from the factory do you know that use 550/850cc injectors??). It has 2 exhaust ports out of the motor (1 per rotor) and must vent exhaust from 3 separate firings out of each port. So yes, volume is a bit more than out of one bank of a V6.
I have never seen any manufacturer go overboard with a stock exhaust system, infact it is mostly the opposite. As mentioned above the stock FD is equipped with a 3" exhaust. It is just restricted with a precat, cat and then the muffler.
As Goodfella said he runs a full 4", he is over the 400whp mark BUT the exhaust has helped with his spool. Personally on my 500r setup I am right over the 400whp mark and use a full 3" (with high flow cat) and see spool about as fast. But I even ran this setup with the stock twins and was only pushing around 330whp.
To answer one of your original questions, I do not think I have ever seen anything smaller than 3" exhaust components for the FD. And even if I had I would not reccomend them b/c of the detrimental effect it would have on the life of your turbos. If you are concerned with noise get a dp, keep the stock cat, and use the above catback mentioned. It really is not that loud.
edit**thewird... I am not sure what is different between our setups but with my full 3" system I see 15 psi by about 3600-3800 depending on outside temps. 1.06 hotside with longrunner mani.
Last edited by oo7arkman; 01-02-09 at 03:46 PM. Reason: addtions.
01-02-09, 05:12 PM
#39
The old 500R spools sooner then the new 500R-SP from what I've seen. I might be able to get it to spool quicker by leaning it and possibly advancing the timing more but I was only able to have it on the street for one day and most of that was break in before the tuning (most of which was done on the dyno). On the dyno it spools by 5000 RPM so its not realistic enough to tune response so I will have to wait until the spring.
thewird
thewird
01-02-09, 07:33 PM
#42
Encyclepedia Boring-tanica
hmm, that doesnt really make sense, I would think horsepower would be horsepower regardless of the type of engine. It doesn't mention anything about engine type, or the amount of cylinders having any effect on flow. Anyone want to elaborate how a 300hp rx7 flows more exhaust than a 300hp v6? I guess it is different though
Also if that were true, wouldnt that mean the rotary has to flow like twice as much fuel and air as a regular combsution engine to make the same power?
Also if that were true, wouldnt that mean the rotary has to flow like twice as much fuel and air as a regular combsution engine to make the same power?
Rotary engines don't flow twice as much, more like over three times as much. The engine is performing all three strokes at once meaning three power cycles for every full rotation of the crank (e- shaft). Because of this it makes an excellent air pump with it's volumeric (sp) efficiency limited by two factors: 1. internal dimensions and geometry (not something easily changed) and 2. Intake and exhaust plumbing. As RPM increases VE goes down, that and the limits of air flow available at atmospheric pressure making the requirements of an N/A very different.
Rotaries by their nature generate exhaust gas temps roughly 1.5x higher than piston driven vehicles and such produce a lot of exhaust energy (thermal load is the main propellant of a turbine blade, not gas flow as often thought, although the two are inter-related concepts.) This super hot exhaust travels at a higher velocity regardless of volume thusly requiring a sufficiently free flowing escape route. The back pressure created by "corking" the exaust is detrimental to overall power and reliability. As boost goes up so does power (in theory usually) and so does fuel consumption and exhaust heat > hence energy. There are however some special considerations for specific goals on HP, torque, purpose of the car, type of turbo, where you want your power, etc. That dictate larger or smaller piping sizes. All these are highly specialized however and have more effect on N/A cars than turbo's.
All in all the rule hold true that 3' is the smallest acceptable piping for FD's and most ported TII FC's.
01-02-09, 08:41 PM
#43
Original Gangster/Rotary!
iTrader: (213)
Not from what I've heard, the HK$ is INSANELY loud and not remotely streetable in my opinion. Has a nasty tone too. Sorry to offend anyone running it, just my opinion
As already stated I am *extremely* happy with my setup, I feel it has basically allowed me to have my cake and eat it too rwt to spool/power production vs noise.
Re: the diff iterations of the 500R I spoke with Sean at length about it and came to the conclusion that I wanted to stick with what I had. the SP offers more power potential but at the cost of spool due to it's larger turbine wheel.
I'm very happy with my setup and Sean's support of the products purchased through him (500R turbo kit and full exhaust). As a matter of fact when I purchased my Apexi catback and shipped it to A Spec to be modified for my flange-less/slip sleeve diesel setup, he performed the mods and shipped it to me in NJ free of charge, can't beat that kind of service
As already stated I am *extremely* happy with my setup, I feel it has basically allowed me to have my cake and eat it too rwt to spool/power production vs noise.
Re: the diff iterations of the 500R I spoke with Sean at length about it and came to the conclusion that I wanted to stick with what I had. the SP offers more power potential but at the cost of spool due to it's larger turbine wheel.
I'm very happy with my setup and Sean's support of the products purchased through him (500R turbo kit and full exhaust). As a matter of fact when I purchased my Apexi catback and shipped it to A Spec to be modified for my flange-less/slip sleeve diesel setup, he performed the mods and shipped it to me in NJ free of charge, can't beat that kind of service
01-02-09, 08:45 PM
#44
Clearly, you need smaller primaries upstream of the turbine to get boost spooled up quickly as a first order priority on a turbo and smaller primaries will increase velocity and therefore spool up. Spooling up the turbo let's say doubles the air going through the system as long as its not constrained by backpressure.
However, power is made by how much gas and air you can get through the entire system over time. Quickly doubling the amount of air seen at the head of the pipe still leaves you with that air increasing significantly over the remaining rpm range. Going from 4-8,000 rpm you double the air volume.
I think his thinking is a bit weak relative to the exhaust in just saying it needs to be big enough not to create harmful backpressure. The backpressure and scavenging he talks about in NA systems is more beneficial in 2 stroke motors and has to do with tuning the reversion wave. I'd love to see the torque curve of the guy making 550 hp with a 2.5 inch pipe versus someone making the same power with a 4 inch pipe. I'd suggest that the guy with the smaller pipe makes more power lower on the rpm scale than the guy with the 4 inch pipe.
When I ran a full 4 inch system on my turbo car, I made more ultimate power at 7500 rpm than with a 3 inch system, but I had a notably wider power band with the 3 inch system. But, like I said, this isn't something I know a lot about...
Gordon
However, power is made by how much gas and air you can get through the entire system over time. Quickly doubling the amount of air seen at the head of the pipe still leaves you with that air increasing significantly over the remaining rpm range. Going from 4-8,000 rpm you double the air volume.
I think his thinking is a bit weak relative to the exhaust in just saying it needs to be big enough not to create harmful backpressure. The backpressure and scavenging he talks about in NA systems is more beneficial in 2 stroke motors and has to do with tuning the reversion wave. I'd love to see the torque curve of the guy making 550 hp with a 2.5 inch pipe versus someone making the same power with a 4 inch pipe. I'd suggest that the guy with the smaller pipe makes more power lower on the rpm scale than the guy with the 4 inch pipe.
When I ran a full 4 inch system on my turbo car, I made more ultimate power at 7500 rpm than with a 3 inch system, but I had a notably wider power band with the 3 inch system. But, like I said, this isn't something I know a lot about...
Gordon
Gordon,
Did you ever get the SARD "doggie dick" exhaust to work?
01-03-09, 12:08 AM
#45
Thx for all the repsonses guys, one last question:
How loud would it be if I went with a straight through 3" dp, 3" mp and a racing beat dual catback? I actually dont mind a nice sounding exhaust, but Im worried about cops and CHP on the highway
How loud would it be if I went with a straight through 3" dp, 3" mp and a racing beat dual catback? I actually dont mind a nice sounding exhaust, but Im worried about cops and CHP on the highway
01-03-09, 01:40 AM
#46
always modding
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I have a 3" DP 3" MP and an HKS super Drager catback
a) it's SUPER loud.. and droney... on cold starts in the morning.. with the engine idling around 1,400 rpm it shakes the walls and windows of my house..
I wait no more then 10 seconds and drive just to put some load on the engine and quiet it down!
b) it's so raspy and buzzy.. partial throttle acceleration sounds like a gay honda fart can sound... WOT is fine
i'm actually embarrassed of my exhaust system.. the muffler looks great..
the car turns heads.. and then it's all ruined by my exhaust note..
what I don't know is how much of the buzz sound is caused by the muffler (maybe it's blown? i dunno) and how much of it is caused by a lack of resonator...
I was contemplating the Trust 80mm Titanium exhaust as a replacement..
or just putting a 3" Borla XR-1 into my current MP..
i'm just afraid I'll castrate my cars power...
oh and btw.. going non-seq.. makes the car MUCH louder as well..
01-03-09, 09:16 AM
#48
http://www.rx7.com/store/rx7/fdexhaust.html
and then just add a Racing Beat Dual exhaust. Considering your are in CA, that's going to be your best option.
01-03-09, 11:04 AM
#49
Original Gangster/Rotary!
iTrader: (213)
If you are worried about noise, but want some performance; look at getting the Bönez Performance Converter System:
http://www.rx7.com/store/rx7/fdexhaust.html
and then just add a Racing Beat Dual exhaust. Considering your are in CA, that's going to be your best option.
http://www.rx7.com/store/rx7/fdexhaust.html
and then just add a Racing Beat Dual exhaust. Considering your are in CA, that's going to be your best option.
01-03-09, 02:53 PM
#50
With my 3" dp, resonated mp, and apex N1 (not the dual) my car has a nice sound and isn't too drony on the hwy. And at WOT is sounds dang good. My resonated mp is from rx7store.