iv been offered one of these, never heard or seen one until now, both pipes have a 54mm diameter going into a single 68mm exit.. has anyone try or tested one of these? they really do look the dogs dangly bits :D
(http://i49.photobucket.com/albums/f279/ooomoo/frpipe1.jpg)
looks nice
That could be more restrictive than a Feed 80mm downpipe.
Feed x-section - 5027.2mm squared
This - Downpipes - 4581mm squared
Pickup - 3632mm squared
Bet it does make the sound completely different though using smaller bore pipe.
Does look very nice but it does disappear under a lot of stuff !
i thought it might have been better, being it flows 54x2, but suppose the exit size will restrict it..
I think this kind of setup helps your torque.....bit like a 4-2-1 manifold would on a piston engine...
well the guy u has it says its the best downpipe for street driving :S dunno whats meant by that but he was running 280rwhp on a standard car only with this fitted.. but dont quote me on this as its only what i was told, he did say it really improved the response tho
that will be the torque!!!!
hang on, i thought both rotor housing fed into a common manifold to the turbos before exiting via the downpipe? as such it wont be acting like a 4-2-1 manifold as in our case it goes 2-1 before it reaches the downpipe. splitting into 2 again isn\'t going to matter surely? Also along with what shawn said regarding the difference in area, also consider the increase in perimeter, and as fluid velocity reduces close to walls, the net velocity and hence flow will be reduced further still. oh and with the increased velocity will also come increased heat transfer, and so i would think it would be a prime candidate for exhaust wrapping!
(sorry if this sounds like i am raining on your parade, i don\'t mean to, just thought i should point out a couple of things. sure looks pretty though!!)
Marco
Never even thought about the surface area ! There is an increase of 32.3% of surface area on the dual pipe over a 80mm feed pipe. Plus if this is the case it would also mean that this would be a heavier part if made out of the same gauge.
Shaun
so overall, would the duel downpipe give more power than the feed one? your all getting to technical for me lol..
unless it was really cheap and you fancied having a play to see the differences i would give it a miss. unless there are some flow issues in the feed downpipe that this one overcomes (which i doubt) then it is probably not going to give you any benefit. or put it another way, do you think your downpipe is the choke point at the moment? if it aint broke......
nah was just curious to be honest bud, just never seen 1 before :)
I think Rich (20b boy) has seen some of these and I\'m sure he would know how they perform.
Fish
It could make for a quieter system. Technically the Feed one should be better but that doesn\'t always mean that it actually is.
Shaun
i am finding that exhaust wrap makes the exhaust quieter, well in car anyhow!
I will let you know in the next few weeks what this type of system is like as i\'ve got a knightsports full twin pipe system to go on mine i\'ll do befor and after dyno runs and let you know
Ooooo nice.. is this the system martin was selling?
yes although it might be sold again by the time i get round to testing it:Nono!
Knightsports makes their downpipe dual so I don\'t think it\'s all talk.
(http://www.knightsports.co.jp/blog/images/fd3s-dualfronttube-001-thumb.jpg)
double post
it\'s for sale on rhdjapan.com
it does make sense in a way because hot exhaust gasses need lots of romm to expand and to get out of the system so having a lot of space directly after the turbo\'s makes absolute sense.
Reducing diameter towards the rear of the car will keep the speed in the exhaust system toget them out as the gasses cool and need less room.
Ever though why group A rally cars just have a 70mm throughout exhaust system?
Quote from: SpeedworksEver though why group A rally cars just have a 70mm throughout exhaust system?
because they are restricted on the engine capacity and have an inlet restrictor that limits mass flow to a set figure. No point going any larger than the bare minimum required.
Quote from: Speedworksit does make sense in a way because hot exhaust gasses need lots of romm to expand and to get out of the system so having a lot of space directly after the turbo\'s makes absolute sense.
i agree, but i think what shawn and i are trying to say is that the cross sectional area of the two pipe is still less than that of a big single (using the feed one as an example) and it may also have other, negative effects such as increased pressure drop and increased heat transfer due to the larger surface area of the pipe work. the only way i can see this being negated is if the header arrangement at the top of the downpipe is more efficient, if using two pipe means that this part can be optimized then it may be worth the bother!
sure that\'s why, I have an 80mm Trust downpipe and will have dual 60mm runners from DP to catback with middle and rear muffler (dual 60mm).
It has more capaictiy than a single 70mm pipe and due to smaller diameters a lower resonance band, keeping the exhaust tone deep and low.
I may be being really dim here, but I thought that within certain limits a narrower bore which then widens further along means the gas flows faster? Which would surely be what you want, to clear the most restrictive part of the system as quickly as possible. That\'s why two-stroke expansion chambers start really narrow, and then ballon further along to utilise wave-pulse scavenging effects.
If this is true, wouldn\'t two narrow downpipes clear the turbo outlet of backpressure faster than one big one thats the same diameter all the way along? I\'ve probably got this entirely a!se-backwards, feel free to shoot me down in flames now! :)
the difference is with a 2 stroke you want to get scavenging, and at certain revs use the exhaust pressure to slightly increase the charge in the cylinder. the difference here is that there is a turbocharger, and we want that to work as optimally as we can. the amount of work that the turbo can extract from the exhaust if a function of the pressure difference across it- the greater the pressure difference, the greater the mass flow through it. so ideally we want the lowest possible pressure just after the turbo, which for us it atmospheric. so in an ideal world we would want no exhaust at all, but that wouldn\'t be really practical (or popular with the neighbors) so we need the minimize the pressure losses aft of the turbo. now for a given mass flow, you are correct in that the flow velocity will be greater in a smaller diameter tube, but that is because it has to flow faster to get the stuff through it (to maintain the mas flow) however pushing air/exhaust/water/whatever through a small pipe fat is less efficient than through a big pipe slow. think straws, you can breath through one thin small straw, but it takes less effort if you have a big fat straw. the extra effort is the same thing as the back pressure on the exhaust. so by reducing it we can theoretically gain a little from the turbo.
however there will come a point where increasing the diameter of the pipe (either exhaust or straw) will have negligible effects, as the back pressure is so low. the thing i am starting to wonder is just how close our exhaust systems are to this point!
marco
bloody hell these exhausts are complecated things lol.. i thought it was just a bit of pipe :yes
mainly, most US and Japan exhaust use oversized bores. Even that big that exhaust gasses have so much space that the speed inside the tubing is reduced.
This means you get back pressure as well. Exhaust gasses jus float arround in the pipe
What you need is a venturi effect, lots of room when gasses exit the manifold/turbo to let expand the hot gasses , a narrow section and then free air.
I had a 76mm HKS DP on my previous FD, OEM cat and 70mm catback and exhaust gas speed was higher then ever meaning you have great flow so less backpressure on the turbo. no big end tip, just a 70mm straight pipe. Deep sound and a lot better response on the gas pedal
sorry i am not following you with the narrow section- why would that help with flow? i grant you the speed would increase, but thats because you need to maintain mass flow through the system- i cant see how it would scavenge the exhaust in anyway.
i am not trying to be argumentative btw, it is just that the idea doesn\'t \'click\' in my head, and wondered if you could explain it a bit more.:Thumbs-up
I bought this a while back.
http://www.amazon.co.uk/Scientific-Exhaust-Systems-Engineering-Performance/dp/0837603099/ref=sr_11_1?ie=UTF8&qid=1203962092&sr=11-1
Interesting read, but more piston based. Bought it while I was researching the intake on the FB.
Shaun
No problem Marco, me neither. The 7 community is small but we shpould help eachother.
I work in automotive accessories industry on a european level and I\'m quite familiar with high tech developments as we base our developments on those discoveries.
Just very simple...Hot air is dense so when it exits the exhaust manifold itw ill need to pas throught the exhaust pipe. Which is, due to its size, a restriction.
Exhaust gas speed is high because the hot air wants to escape and the engine is pushing it out. restriction will slow it down.
if you change the midpipe and catback with a 90 or 110mm catback you wil create so much space in the tubing that the gasses will lose speed and start floating around.
Just start your car with an OEM catback. You\'ll see fumes coming out with speedhold your hand at the tip and you\'ll feel pressure. Do this with a 110mm catback and you\'ll feel just a little wind passing.
When gasses stand still at the back of the car, they will slow down gasses more to the engine and create back pressure as well.
so to keep optimal speed you should do something like 80mm downpipe going to a 70mm midpipe and catback. preferably with a 70 mm tip as well
this will keep speed in the exhaust gasses and stil create a little backpressure to let the engine breath in some exhaust gasses for recirculation (like valve overlap with high performance piston engines).
Even more important is the pulse of the engine that it is putting out. The rotary has more pulses (combustions) per rotation, so exhaust gas speed is even more important. A pulse works best if you put it in a continious environment . So for the pulse you should take a 70mm pipe front to back.
Putting in the 80mm front pipe is a little compensation for the hot gasses to expand, but the rest must be a continious environment to ensure optimal flow.
So exhaust gasses are pulse driven by the engine. by using different diameters (76mm DP, 70mm midpipe and 100mm catback) you create an unstable pulse and variabnle exhaust speed which will make the gasses do odd things you could never imagine (ever seen a 3D simulation of that?)
Gasses being sucked in again and such...
for a oem turbo\'s or a small single I would recommend a 76 or 80 mm DP and a a full 70mm midpipe and catback. Free air after the exhaust tip should the creat your venturi effect.
So all those big ass, loud and over the edge catbacks with 110mm tips and 100mm tubing... hell no...Look at RE Amemiya and their dolphin tail tips, no big bores there...
it\'s all about size... but the biggest is not always the best :D:D/D
thanks a lot for the post, it gave me a lot to think about! esp about the pressure pulses, i had always assumed that because of the turbine blades the pressure pulses would be really high frequency (i.e. the speed of the turbine rotation) but on further thought i guess you would get the base pressure variation due to the engine with the effects of the turbo overlaid onto that?!
i am still not with you on the speed issue though, surely this is to do with mass flow? assuming that density remains constant (so ignoring the effects of cooling) and assuming the exhaust gas isnt approaching mach 1, then we can assume that the volumetric flow is proportional to the mass flow. so in simple terms we have a set volume of gas to move each second. as we pass this set volume through different diameter pipes the speed will vary accordingly- if you have a pipe with a cross sectional area of 1m^2, and we need to move 1 cubic meter of gas per second, then the flow velocity is 1m/s, if the cross sectional area is halved then the velocity must be doubled to make up for it. however every time you change the diameter (going smaller to larger or vice versa) unfortunately the energy transfer isn\'t 100% and so you lose energy. if you lose too much energy the flow stagnates and just sits there. obviously in an exhaust this isn\'t going to happen and it will be forced along, but the turbo will see this as greater back pressure. (the turbo sees the work required to move the exhaust gases out as a back pressure). so ideally you want an exhaust with uniform cross section?
similarly if you take into account the viscosity of the exhaust gas, the velocity of the exhaust flow makes an effect- the higher the velocity of the gas the greater the energy loss to skin friction. now i will happily admit that the energy loss due to this is probably small compared to other issues, but still, it points to larger diameter exhausts being the way to go?
thing is, something about what your saying sounds correct, i just cant work out why!
Marco
Quote from: SpeedworksJust very simple...Hot air is dense so when it exits the exhaust manifold itw ill need to pas throught the exhaust pipe. Which is, due to its size, a restriction.
Nice post :Thumbs-up however hot air is not as dense as cold air, just thought that should be corrected :)
looking at it another way
isn\'t it just because of the space restriction, two pipes are flatter than one large pipe, other downpipes are squashed in this area to clear so it could be a simple packaging reason. I doubt most of these products have any great science behind them, it would cost far too much to fully understand what is going on.
I still think that speed of gasflow is of more relevance than just volume, so long as there\'s enough volume to hold all the expelled gas. I take on board what Marco was saying as sound physics, but at the end of the day, there\'s no point in having a massive amount of space in the downpipe if all it does is let the gas float about doing nothing and going nowhere. I think that\'s kinda what Speedworks was getting at, but my puny brain gave up the ghost a bit! I\'ve now fortified it with some gin, and that seems to help!
I admit that most of what I know about performance engines comes from bikes and it doesn\'t necessarily translate, but all the real pro performance bike zorts (Yoshimura, Akrapovic, even Micron) have tapered headers to accelerate the gas, then a fat bit for the capacity to hold enough gas, then a thinner bit where the downpipes meet in a collector for the silencer. I also agree with Mike, in that a lot of manufacturers are doing what looks nice or what the trends dictate without much research into the science of it, and on the road it\'s probably academic, but people like Arrow or Akrapovic sell the same exhausts to trackdayers as they do to World Superbike teams, and believe me, they spend a LOT on R&D. If you\'re charging £700 for the silencer alone in the cutthroat bike market, it\'d better work! If they think you want tapered headers for gas speed, I think they may be right!
Race bikes do have a bigger mid section to create backpressure towards a non turbo engine. It creates more low end power for acceleration.
For those who ever drove Honda Camino 50cc bikes, they should know.
You had differnet brands of exhausts back then.
Proma: very big but short mid section-> lots ow low end power, limited top speed.
Simonini: thiner mid section but long and smooth _> less low end power but high speed
If by having different lengths and diameter\'s of exhaust you can tune an engine, why then do drag cars/bikes use large diameters with virtually no length to them?
Quote from: Ricco_04If by having different lengths and diameter\'s of exhaust you can tune an engine, why then do drag cars/bikes use large diameters with virtually no length to them?
Just a guess but drag cars/bikes have virtually no noise regulations either :Gigglemost exhausts are a compromise. Not forgetting that exhaust manufacturers also "tune" their exhausts to make a nice noise
Yes true, but im on about making the power. Regardless of noise, if they could make more power with a tuned system then surely they would.
As for the downpipes there cant be much peak difference. Personallly I would go for the more normal single pipe, if for nothing more than because there is less metal.
I was always told that it\'s more critical to have a stepped exhaust because, again, I was told that the gas expands more as it journeys to the exit of the exhaust. Hense why Apexi (and others) make stepped exhausts (Ie Apexi GT-Spec)
Oh, im not saying im right by the way, im also trying to understand it by asking questions :)
because they run such big turbo\'s any decent size of tubing will not compensate
Ok well i\'ve finally got mine fitted:cool and it sounds absolutly amazing!:D so quite just taking it easy and when its ticking over its not loud but very basey i suppose is the word!and then when you floor it,-well its just says more more more and its not a hearing killing noise which is exactly what i want:rollin , the car feels a lot more responsive and faster on acceleration to.Will get it on the rollers on sat hopefully and get the power figures and compare them to my last lot a couple of months ago(the exhaust is the only thing changed since then)
Oh and having two pipes running down the length of the car looks great to!:cool