Still undecided regarding my exhaust and whether to change it.
Replies to my other thread related to the screemer pipe suggest I may not need to pipe it in to the exhaust to pass a track noise test.
So I have a different exhaust related question;
If I increase my full exhaust size from 75mm diameter to 90mm diameter can I expect an increase in bhp ?
I currently run a full 75mm diameter system from the single turbo to a cat by pass, to a rear silencer, (no middle silencer).
Thanks
Chris
Its all down to the quality of the back box then. When we Db tested mine with 75mm straight through was 112db with a plumbed in screamer pipe.
I can\'t see any way you could pass a sound test on track with a screamer pipe. Possibly at Oulton park because they only test once and don\'t have any on track measurements. But you would still be pushing it.
I don\'t know if swapping to say 2 x 70mm diameter will reduce the volume level with maybe a crossover pipe in the middle ??
Shaun
i think if you increase the size of the exhaust you ll lose bhp less back presure
Thats only with a NA engine where there is resonance issue with the amount of back pressure.
A turbo engine wants the least path of resistance, although there is a limit. Thats why we see drag cars running stumpy 5in exhaust systems.
I think there is a good balance point though.
Shaun
yeah the more back pressure you have on a turbo car the less power you make as the turbo has a lot to push against.
Plus this engine is probably one of the most volumetric engines going! It passes more air than a herd of cows eating vindaloo\'s
4" is a good size, although finding someone to bend that big a pipe reduces the choice some what.
Hi Chris, please remember that if you do this you really need to check the map as a more free flowing exhaust could alter the map your currantly using.
Quote from: batman;573248i think if you increase the size of the exhaust you ll lose bhp less back presure
Not with turbo cars, only NA, the less back pressure (hence bigger exhaust from the Turbo back) will result in more power on a turbo car. you get pressure build up in the exhaust manifold of a good few psi ,the exhaust turbine wheel causing the build up as it is the restriction.
Therefore putting a bigger exhaust on the otherside of the wheel helps to relieve the pressure. (Im sure a physics person can explain this bit)
This is why rear AR sizing of a turbo changes the characteristics of the power delivery, too small an AR will cause the engine to choke and limit top end power but spool is better, to big and lag is introduced.
For ultimate power you will see drag cars with only a short fat pipe coming off the turbo exiting the wing.
So the answer to the question will increasing exhaust size increase power , Yes :D
but it will be noiser unless you have good 4 inch silencers with good baffles
Does anyone know where I could get a 4" exhaust for the FD3 from ?
I\'m running a single Garret GT40, so I would need the down pipe, (no cat), middle silencer and rear silencer ?
Thanks
Chris
Quote from: BlitzBoy;573828Not with turbo cars, only NA, the less back pressure (hence bigger exhaust from the Turbo back) will result in more power on a turbo car. you get pressure build up in the exhaust manifold of a good few psi ,the exhaust turbine wheel causing the build up as it is the restriction.
Therefore putting a bigger exhaust on the otherside of the wheel helps to relieve the pressure. (Im sure a physics person can explain this bit)
This is why rear AR sizing of a turbo changes the characteristics of the power delivery, too small an AR will cause the engine to choke and limit top end power but spool is better, to big and lag is introduced.
For ultimate power you will see drag cars with only a short fat pipe coming off the turbo exiting the wing.
So the answer to the question will increasing exhaust size increase power , Yes :D
but it will be noiser unless you have good 4 inch silencers with good baffles
Deal with this problem at work all the time (chemical engineer).
Backpressure occurs as a result of trying to flow too much fluid (gas or liquid) down a pipe with too small a cross sectional area. As you try and flow more down this area the fluid velocity increases (Velocity = Volmetric flow / CSA). As a result of the increase in velocity, the friction acting on the fluid increases (pressure drop down a pipeline equation - google it!) As a result of this, the pipe becomes a restriction to fluid flow which sort of \'backs-up\' in the pipe causing backpressure. (Think of emptying a juice bottle through two different size holes - which would empty first?)
If you think of a NA car, the backpressure helps close the exhaust valves. If you increase the exhaust diameter and thus the cross sectional area, you reduce the restriction and cause less pressure \'back-up\'. This loss can lead to intake charge passing through the exhaust valves as they might not fully seal and thus a loss of power.
In an FI engine a smaller exhaust (bigger restriction to flow) will increase the backpressure. This increase will be more for the turbo to push against and thus strangle flow through it and cause a loss of power. Increasing the exhaust size again removes the restriction and allows the turbo to more easily throw exhaust gases out.
Hope that makes some sort of sense!!
Graeme
Not completely accurate on the N/A exhaust dynamics there, I think...in an N/A engine thats been properly designed, the headers will be of a tuned length so as to employ resonance frequency return pulses to scavenge gas away from the exhaust valves and speed up the removal of gas along the exhaust. Short version; valve belches out a pulse of exhaust gas that wafts along the pipe until it hits a restriction, then returns along the pipe, just like a bum-gas ripple in yer bath when it hits the edge :Giggle.
This creates a high-pressure/low-pressure cycle at the valve area, high as the pulse returns, low as it recedes, just like waves on the beach (ahh, the poetry:)). If you tune the exhaust length, ie put the first restriction that causes the wave return in the exact spot you want it, it can time the low-pressure wave with the valve opening at a certain rpm, and thus scavenge the gasses away faster.
This is one of the major problems with N/A tuning, because along with cam profile efficiency, this effect is narrowing the rev range at which the engine is at its most efficient. Especially noticeable on bikes that rev to ridiculous cielings but are only efficient really for a couple of thousand rpm out of what can be a 17,000 rpm scale....
None of which really bothers turbo\'d engines, which push the exhaust gas out pretty much regardless of what restrictions may be in the way...up to a point. Obviously, the less restriction, the easier it is for the turbo to pump gas past it, which is why the less backpressure, the better.
None of this is especially interesting, but it is true :Giggle
Excellant info Graeme and Nik
Quote from: C J R;573236If I increase my full exhaust size from 75mm diameter to 90mm diameter can I expect an increase in bhp ?
yes. :D :D
Quote from: Archbish;574368If I increase my full pipe size from 2 inches length to 6 inches length can I expect an increase in flange?
Yes Bish
hahahahah :rollin
Quote from: Archbish;574368yes. :D :D
:rollin :rollin
Agreed nik, I was looking at it from a fairly narrow angle admitedly!
Also something to bear in mind is that the same theory applies to removing cats from exhausts - these are essentially a restriction in the \'pipe\'. Its also why tuning NA is made slightly harder if you don\'t know whether this restriction was accounted for in the design of the system - you can actually do more harm than good for the reasons myself and Nik outlined above. :Thumbs-up
I\'ve never understood why car design is so far behind bikes in exhaust tech...the manufacturers seem happy just to bung on a length of tube with a cat in the middle and hope it works. Yamaha patented an "EXUP" (EXhaust Ultimate Powervalve) back in the late eighties which was basically a barrel valve in the exhaust that opened and closed the aperture of the pipe at different revs. This meant they could tune the exhaust harmonics for a far wider range of rpm than just having a straight-through pipe. Just about every spotsbike has something similar now, and has for years, but there\'s no sign of the most rudimentary version on anything short of a supercar. Just lazy penny-pinching from car manufacturers, I suppose
Was that 2 stoke or 4 stroke ? The 2 stock needs a very good designed exhaust to make any power at all !
I\'ve got a copy of :
http://www.bookfinder.com/dir/i/Scientific_Design_of_Exhaust_and_Intake_Systems/0837603099/
Shows stuff from the 20\'s in how they desgined stuff. Not very relevent to a rotor though !
Shaun
Wow, that book looks a bit intense for my puny brain, Shaun! The Exup-style valves are a four-stroke thing, but you\'re right, wave scavenging effect is even more vital in two-strokes, which is why you used to see such gorgeous bits of engineering as hand-welded titanium expansion chambers on GP two-strokes.
Funnily enough, most of the understanding of two-stroke \'spannies came from an engineer working for MZ of all people (sort of the Lada of the bike world for many years) when they were at Zschopau (sp) behind the Iron Curtain in East Germany. Walter Kaaden, his name was IIRC, and he\'d developed the idea of pulse scavenging on the MZ gp racers, which from then on were unbeatable. In a proper spy thriller stylee, he defected to the West, specifically Suzuki I think, with a whole load of diagrams and tech drawings, at a neutral GP whilst his wife and kids were smuggled out of East Germany to meet up with him. MZ couldn\'t compete with the spending and developement power of the Japanese, and the two-stroke era of GPs was a Jap playground from then on in.
You\'re right, nothing much to do with rotaries, but it makes a good story. I always kinda thought of rotaries as a lot like a two stroke, but it goes roundy-roundy rather than uppy-downy, anyway :Giggle Helps me understand stuff in my feeble brain!
The Rotary Development book on the same webpage as the manuals explains it in serious depth. That really does mess with your head.
I bought the book for the intake information for the FB but wasn\'t a lot of help.
Shaun
Found the below link on google and it should answer most of your questions on exhasut theory both N/A and turbo. Basically the turbine (the hot bit in the exhaust flow) within the turbo requires a pressure drop across it to work - high pressure upstream (from engine exhaust) and low pressure downstream (in the exhaust pipe), the less back pressure downstream the better. That why bigger down pipes and de-cats make more responsive (less lag), as the turbo will accelerate quicker and make boost sooner.
As with all things there can be a down side, the less back pressure downstream, the quicker the turbine will spool up and you can then end up with over boost - either open loop system (no feed as per original Mazda system) does see the extra boost, so does not control or with an after market closed loop system you need to add more gain to slow the boost rate increase, or the next thing is the original waste gate runs out of capacity. So before going for a huge exhaust, no cat and a free flow silencer, ensure you have a fast acting/robust boost control system with enough capacity to control overboost.
http://www.tercelreference.com/tercel_info/turbo_exhaust_theory/turbo_exhaust_theory.html
Quote from: Nik da Greek;574614Funnily enough, most of the understanding of two-stroke \'spannies came from an engineer working for MZ of all people (sort of the Lada of the bike world for many years) when they were at Zschopau (sp) behind the Iron Curtain in East Germany. Walter Kaaden, his name was IIRC, and he\'d developed the idea of pulse scavenging on the MZ gp racers, which from then on were unbeatable. In a proper spy thriller stylee, he defected to the West, specifically Suzuki I think, with a whole load of diagrams and tech drawings, at a neutral GP whilst his wife and kids were smuggled out of East Germany to meet up with him. MZ couldn\'t compete with the spending and developement power of the Japanese, and the two-stroke era of GPs was a Jap playground from then on in.
Always thought this was a fascinating story, and your right this rider and the drawings of the exhaust system he smuggled away tucked in his his leathers was the single biggest step forward that one of the Japanese bike manufactures ever made (I thought it was Yam)
Story I read said that this guy could have been champ that year but instead started a GP and litteraly drove around the back of the circuit never to be seen again!
Back to Rotary,
I have been told that Knight Sports always trained for free guys for Mazda\'s race division however they were always taught on N/A rotarys because you need to be good to get the porting, carburation and exhaust working together properly to obtain power and that Turbo\'s were viewed as "easy power" where as you have to work at it to get power from N/A.
Wow, heaps of valuable information all originating from my simple question.
Thanks Guys.
Based on the above link "Turbo Exhaust Theory" it seems I\'m contemplating the right course of action to increase the size of exhaust from 75mm to 90mm, as the car is already producing between 450 to 500bhp through the 75mm pipe.
The turbo starts to operate at about 3,500 rpm, so I may see an improvement to say 3000rpm with a 90mm exhaust.
What\'s also interesting is to avoid bringing the wastegate pipe in further away from the turbo, the above document suggests 12-18" to avoid disrupting the main turbo flow.
All I need to do now is find a decent exhaust builder AND I will ensure the car is remapped before use (thanks Clive).
Chris
Interesting stuff. Biggest question would be how loud you want to go. Would need some interesting silencer arrangements !
Shaun
Hi Shaun,
I hope to be around 95 - 100db if possible. Not sure if a mid and a rear silencer would achieve that db ?
Chris
Good Question. Probably best off talking to somebody that races the FD to spec a good setup.
Shaun
Would it be worthwhile making this a stickie somewhere?
Some fairly useful info that peeps might make use of?
I\'m new to Rotaries having just bought an FD3 so I can\'t really comment on how the engine responds best to exhaust design and power resulting from it. Does the engine need a bit of turbulence at low rpm to get it going off boost? That\'s got to be a consideration for the chaps on here running a big single...
If you are going to track day the car then you should aim for 95 db on a static noise test. There is nothing worse than being pulled in and told to limit it to 5,000 rpm. Most tracks have a 98 db noise limit.
I very much doubt you would be able to make 95 db using a four inch pipe and definately not with a screamer pipe....:mmmm
Quote from: suba;584902Does the engine need a bit of turbulence at low rpm to get it going off boost? That\'s got to be a consideration for the chaps on here running a big single...
No ,you dont need turbulant air coming out of the exhaust ports to drive the turbine wheel of a turbo, you need fast Hot gasses is what spools up a turbo, so its down to the porting and tuning to help spool
I should be able to advise the results of this modification shortly.
The car is in having the Trust 4" exhaust fitted this week and the screemer pipe plumbed in.
The design we are aiming for is to have the screemer pipe lengthened so it enters the main exhaust tubing just before the mid silencer.
It was interesting to note that the underside of the car showed scorch marks where the wastegate had opened and it appears flames had exited the screemer pipe, (the exhaust throws out flames, so i guess it was obvious the screemer would be doing the same, I just hadn\'t contemplated it).
I need to arrange a remap after the modification and a noise test, but I\'ll post up the results.
Quote from: suba;584902If you are going to track day the car then you should aim for 95 db on a static noise test. There is nothing worse than being pulled in and told to limit it to 5,000 rpm. Most tracks have a 98 db noise limit
lol, With a free flowing 3in system on my single I was 112db at 5500 !! Its all down to the quality of the silencers. I\'m looking for something quieter for track use !
Shaun
Simple question then compared to whats above!
If car was run at 1bar on 3" exhaust, would you see a power increase with 4" exhaust but still run at 1bar?
(Thinking Turbo 13b)
amazing load of info,albeit its all internet sucked :) and heresay :Laugh,nobody on this forum has actually proved anything by putting up dyno graphs on mods they say works and does not :2Rolleyes,nobody here has proved the gain or loss by plumbing in the screamer pipe into the main system,or increasing the the down pipe to 5" and leaving the screamer pipe to vent to atmosphere,its all proven by via the rolling road.all \'facts\' here are heresay and not backed up by physical evidence :),does i ncreasing the size diameter make the system louder or softer ?..........:bandit intersesting to know
Quote from: Ricco_04;585001Simple question then compared to whats above!
If car was run at 1bar on 3" exhaust, would you see a power increase with 4" exhaust but still run at 1bar?
(Thinking Turbo 13b)
if you got good auxillaries and sombody who knows hoe to map the caron a rolling road :Talking1
Bumping this good thread :cheers
3.5" exhaust has been good enough for ~450rwkw 600+rwhp *dynodynamics* (not one hit wonder but repeated many times). SMB mufflers.
I will find an extract from a Garrett Engineer who wrote up a fantastic few paragraphs in relation to turbo cars and what effect down stream turbine pressure has on all up system pressure (when considering turbine expansion ratio). *over anyones head yet?*
In a nut shell the larger turbo/turbine you run the less effected it is to exhaust back pressure (post turbo) as the turbine expansion ratio to flow the said given amount of gas is LESS :Typing So drain pipe "I ran over a dust bind Honda exhaust" is only really needed on a small turbo working its ring hole out! as its at a very high expansion ratio to make the power you need/want to have.
I use a 3.5" diameter system on my own car, with a catalytic convertor, and middle muffler and a big rear muffler and plumbe back exhaust. Turbine outlet pressure is 4psi range at 7500rpm and honest 440bhp output. Exhaust manifold pressure is around 17.5psi and inlet boost pressure is 18psi (better than the fammed 1:1 pressure relationship people strive for), car is whisper quiet too for a Rotary Turbo at this power level. The catalyst imparts over 2.5psi to this post turbine pressure level, without that you could run 700+bhp worth of air flow through the system and still stay at 1:1 pressure with the right sized turbine (housing and wheel).
Exhausts dont need to be as large nor loud as some people think to make good power :3gears-rh
Quote from: RICE RACING;719020Bumping this good thread :cheers
3.5" exhaust has been good enough for ~450rwkw 600+rwhp *dynodynamics* (not one hit wonder but repeated many times). SMB mufflers.
I will find an extract from a Garrett Engineer who wrote up a fantastic few paragraphs in relation to turbo cars and what effect down stream turbine pressure has on all up system pressure (when considering turbine expansion ratio). *over anyones head yet?*
In a nut shell the larger turbo/turbine you run the less effected it is to exhaust back pressure (post turbo) as the turbine expansion ratio to flow the said given amount of gas is LESS :Typing So drain pipe "I ran over a dust bind Honda exhaust" is only really needed on a small turbo working its ring hole out! as its at a very high expansion ratio to make the power you need/want to have.
I use a 3.5" diameter system on my own car, with a catalytic convertor, and middle muffler and a big rear muffler and plumbe back exhaust. Turbine outlet pressure is 4psi range at 7500rpm and honest 440bhp output. Exhaust manifold pressure is around 17.5psi and inlet boost pressure is 18psi (better than the fammed 1:1 pressure relationship people strive for), car is whisper quiet too for a Rotary Turbo at this power level. The catalyst imparts over 2.5psi to this post turbine pressure level, without that you could run 700+bhp worth of air flow through the system and still stay at 1:1 pressure with the right sized turbine (housing and wheel).
Exhausts dont need to be as large nor loud as some people think to make good power :3gears-rh
glad to see proper real world info on here finally :wave
regards
c
they said it\'s gonna generate and give some power, I agree