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Old 09-07-2006, 08:29 PM   #61
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Quote:
Originally Posted by LordWorm
sucking it in? sucking it out you mean =)
No, sucking the new charge into the cylinder.
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Old 10-07-2006, 06:42 PM   #62
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If you want some science behind my comments then start with Newton's first law of motion.
Quote:
Originally Posted by Isaac Newton
An object at rest tends to stay at rest and an object in motion tends to stay in motion with the same speed and in the same direction unless acted upon by an unbalanced force.
This would make any bend, turn or change in size of an exhaust into a restriction as exhaust gas has a mass.
From those humble beginnings you can move to Bernoulli's principle where;
Quote:
Originally Posted by Daniel Bernoulli
as the speed of a moving fluid (liquid or gas) increases, the pressure within the fluid decreases.
Which in physics terms equates to? As a fluid moves from a wider pipe into a narrower pipe or a constriction, a corresponding volume must move a greater distance forward in the narrower pipe and thus have a greater speed. At the same time, the work done by corresponding volumes in the wider and narrower pipes will be expressed by the product of the pressure and the volume. Since the speed is greater in the narrower pipe, the kinetic energy of that volume is greater. Then, by the law of conservation of energy, this increase in kinetic energy must be balanced by a decrease in the pressure-volume product, or, since the volumes are equal, by a decrease in pressure.
In this case the gas in a larger exhaust will tend to sit and wait to be forced out by exhaust being produced by the engine. If the pipe narrows then the gas will accelerate and thus be drawn from the system through the increase in velocity.
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Old 10-07-2006, 07:57 PM   #63
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Quote:
Originally Posted by Cosmo Dude
If you want some science behind my comments then start with Newton's first law of motion.

This would make any bend, turn or change in size of an exhaust into a restriction as exhaust gas has a mass.
From those humble beginnings you can move to Bernoulli's principle where;

Which in physics terms equates to? As a fluid moves from a wider pipe into a narrower pipe or a constriction, a corresponding volume must move a greater distance forward in the narrower pipe and thus have a greater speed. At the same time, the work done by corresponding volumes in the wider and narrower pipes will be expressed by the product of the pressure and the volume. Since the speed is greater in the narrower pipe, the kinetic energy of that volume is greater. Then, by the law of conservation of energy, this increase in kinetic energy must be balanced by a decrease in the pressure-volume product, or, since the volumes are equal, by a decrease in pressure.
In this case the gas in a larger exhaust will tend to sit and wait to be forced out by exhaust being produced by the engine. If the pipe narrows then the gas will accelerate and thus be drawn from the system through the increase in velocity.
Thats right! you are talking about velocity there! - not backpressure.

Velocity increases as the pipe size decreases - HOWEVER - there comes a point where even with increased velocity the capacity of the pipe becomes a restriction - the gas is unable to move in pipe because pulses that were carried before hand have yet to clear the system. As revs increase, these pulses get closer and closer together, thus start backing up against each other. As the gas travels towards the end of the pipe, it cools, and thus contracts, and loses speed. Faster gas behind it then pushes it through - but there comes a point where this stress becomes too much and thus the next pulse of gas is forced backwards into the combustion chamber...thats backpressure.

If it wasnt the case, we'd all have exhaust pipes that were 1mm in diameter, because you could get stupendous amounts of velocity. Its a trade off, between maintaining velocity, but allowing a larger volume of gas to be expelled through the pipe.

There are other ways to increase velocity. Scavanging in teh collector of the header behaves sort of like a pump. The vacuum that trails the hot gas as it is expelled can be leveraged to "suck" the next exhaust pulse out of the combustion chamber. At a specific tuned RPM (dictated by the speed at which the gas is leaving the exhaust system at a specific engine speed, measured in metres per second), this suction will be applied to the next pulse the instant the exhaust valve opens, thus accellerating the gas in the next pulse forward. This is known as the "scavanging wave".

With relation to the gas moving around corners - it is true that this will create "restriction" but not backpressure in itself. Also have a look at how fluid dynamics works. Assuming no obstruction (i.e, mandrel over crush bent pipe), the gas will actually accellerate around the corner. It has been a long long time since I did anything with fluid dynamics - perhaps one of our resident physicists can explain better than I, and save me a trip the old text books. It has to do with the gas at the boundary layer on the inside of the pipe being allowed to move at a faster speed (as it has a shorter path to cover the same distance), which alters the pressure of the gas in the corner. This wont work for a crush bent pipe, as the sharp edges, loss in cross sectional area and the like will create turbulence in the gas and slow it down. There would, I assume, be a point where a mandrel bend's radius is too tight in order to take advantage of this. For bends more than 90degrees, one would be looking to use a bend whos radius is 2 or 3 times the diameter of the pipe.

Backpressure only occurs when the a volume of gas int he pipe begins moving in the wrong direction, and starts to "choke" up the engine. Already burnt gas is allowed to remain in the combustion chamber, limiting the efficiency of the next explosion (less room for air and fuel to get in). Due to the expansion of gas in the explosion, as a rough rule of thumb for your "average" engine, 1L of air/fuel mixture will create hot gas that takes up 13L of space. Imagine a 2L engine. Each cylinder is 0.5L in volume, and can generate 7.5L of exhaust gas...wouldnt take much "backpressure" for the cylinder to remain completely full of burnt, hot gas.

So...summing up. In essence, what you are talking about is velocity. And you are 100% absolutely positivly without a shadow a doubt correct. All exhaust systems require velocity in order to work correctly.....but they do not require backpressure...and the use of the term backpressure should be avoided like the plague, as in litterly terms, it refers to gas travelling in the wrong direction in the exhaust pipe.



Edit: as a velocity vs volume experiment, try pouring 1L of water through a 3cm wide piece of pcv, and then a drinking straw each of the same length. The water will move at higher velocity/pressure in teh straw, however the straw will not be able to move the same volume of water as quickly as the PCV pipe. The same principle is at work in exhaust systems........because you cannot input the water at the same rate in the smaller tube...

edit again: sorry, the gas accellerates around the corners because the mass of air at the outside of the pipe has to travel further to get to the same place, thus needs to move faster around the corner... sort of like rotational velocity i think - I'm not 100% on this point, and am open to clarification/correction on it....
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Old 10-07-2006, 08:43 PM   #64
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I don't agree.
My view of your arguement is that opening the exhaust out to the max will give you maximum power. My arguement is that controlling the flow of the exhust will give maximum useable power where you want it.
I will review my old 2-stroke notes and see you again soon.
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Old 10-07-2006, 08:47 PM   #65
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Originally Posted by Cosmo Dude
I don't agree.
My view of your arguement is that opening the exhaust out to the max will give you maximum power. My arguement is that controlling the flow of the exhust will give maximum useable power where you want it.
I will review my old 2-stroke notes and see you again soon.
i have never once said, that a 80 inch wide exhaust pipe, will give you the best possible power. It defeats velocity.

What I am getting at, is you go for the largest pipe possible that maintains exhaust velocity WITHOUT restricting fllow. Why else do exhaust mods? why are we not all running around with 1cm diameter exhausts? could it be that you simply cannot push the waste exhaust through the system at any usable RPM with such a pipe? Maybe....

Yes a 1in exhaust pipe will have higher exhaust velocity than a 2.5. But the 2.5 will move a larger volume of air in the same amount of time.

Another experiment, take 2 buckets. Drill a 1 cm hole in one, and a 3cm hole in the other. Fill both with water. which one squirts the longest? the 1cm - higher velocity. Which one empties first? the bigger hole, higher rate of flow.

Its a balancing act. I've never denied that. I would never in my right mind recommend a 3in system for a 2L NA motor. however, By the same token I also wouldnt recommend a 1in pipe for the same car. It is velocity yes, that determines where the power is....however if you do not get velocity at the collector on the header, the damage is done, because at this point you have maximum velocity with unimpeeded flow. . No amount of increasing velocity passed that point will improve power, because to increase the amount of velocity beyond that point, you need to restrict the AMOUNT of gas that can flow into the narrower pipe. The only thing you can do after the collector is reduce it. Beyond the collector, all that matters is getting the gas out of hte pipe in teh most efficient means possible - velocity has already been achieved at the collector, all you need do is ensure you don't lose it (either through restrictions, or by too big a pipe that allows gas to slow down)


The location of power in an exhaust system, is dictated by header primary lengths and nothing more. You cannot bolt on a muffler that moves the power around, or put a giant knot in the pipe to increase power. It is simple, rudimentary exhaust design. What would you rather, "usable" power at 3000rpm on an engine that is only capable of reving as far as 4000rpm before it cannot rev anymore, or USABLE power starting at 3000rpm with a maximum RPM of 8000rpm before the exhaust size even begins to become a bother.

You can disagree until your heart is content, it wont change the facts. Go and put a pea shooter on your car, i'll slap the 2.5 on, and we'll see who gets to the 404m mark first.

Ta.

P.S. you are now talking about velocity...not backpressure...can you please tell me how much backpressure I need? i'm still dying to know. Or at least be man enough to admit that you may have had the wrong end of the stick - as you have changed your tune from being a backpressure proponant to a velocity proponant in the space of half a dozen threads... Sorry mate, these 2 things are NOT the same thing (quite the opposite, infact)
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Last edited by LordWorm; 10-07-2006 at 09:16 PM.
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Old 11-07-2006, 03:29 PM   #66
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Wow... who knew that such a simple post could create such controversy!

I've found everybit of literature i can find on he topic and...

Cosmo dude... your post 2 posts ago concerning bernoulli and newton were saying exactly the same as Lord Worm... all the right theory... i nearly fainted when i read it... but for some reason you still disagree... so here are my thoughts in my words which might be a bit clearer for you to understand.


When you modify a car for more performance, the engine will produce more exhaust and will expell it faster. For example... you have a high flow air filter... more air in = more air out, if you have a new ecu or bigger injectors... more fuel in = more burnt fuel out... and all this gas wants to go faster through the exhaust.

Exhaust is expelled in small pulses each time a spark plug fires to burn the air and fuel. These gases are then removed by the extractors (hence the name) and sent down the exhaust. BUT between each piston firing comes a lapse in the velocity of the exhaust.

Lets pretend this is a stock engine with a 4 inch mandrel straight through exhaust system. Because the exhaust system is so freakin massive in comparison to the amount of expelled exhaust from the engine, there will be too much room for the exhaust to move around in there and due to the engine's vacuum effect (which is supposed to suck in air and fuel) already expelled exhaust will be vacuumed back into the engine reducing the amount of injected fuel that can be burnt. It's pure physics and chemistry.

for maximum efficiency: C8H18 + 25/2O2 => 8CO2 + 9H2O

that is (ideally)... 1mole of ocane needs 12.5moles of oxygen to completely combust into carbon dioxide and water. But petrol isn't 100% octane and air is only 21% oxygen... so don't start thinking you need 2 parts fuel to 25 parts air... that is wrong.

That was a bit off the track... but hope you found it interesting.

Anyways... lets pretend this massive exhaust system is an 8 lane californian highway, the engine is darwin producing very little traffic and the lapse in velocity is a grandma travelling at 35km/h (and slowing) in the middle lane. She needs a push a long to get to the other end of the highway... because there is only a small amount of traffic on such a large highway it is very unlikely that someone will run up the back of her before she starts going backwards. However, if the same highway happened to be only 2 lanes she would have to go faster.

The path for your exhaust must be small enough for the exhaust to flow through with high velocity but large enough so that exhaust does not build up back into the engine. Crush bends will increase the risk of exhaust build up, particularly if you are using high-end revs which will expell more exhaust (more piston firings = more fuel = more air = more exhaust) this is why bigger exhausts are better for higher end power (to a point).

notice i didn't say back pressure once.

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Old 11-07-2006, 04:16 PM   #67
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Originally Posted by FLiP
Wow... who knew that such a simple post could create such controversy!

I've found everybit of literature i can find on he topic and...

Cosmo dude... your post 2 posts ago concerning bernoulli and newton were saying exactly the same as Lord Worm... all the right theory... i nearly fainted when i read it... but for some reason you still disagree... so here are my thoughts in my words which might be a bit clearer for you to understand.


When you modify a car for more performance, the engine will produce more exhaust and will expell it faster. For example... you have a high flow air filter... more air in = more air out, if you have a new ecu or bigger injectors... more fuel in = more burnt fuel out... and all this gas wants to go faster through the exhaust.

Exhaust is expelled in small pulses each time a spark plug fires to burn the air and fuel. These gases are then removed by the extractors (hence the name) and sent down the exhaust. BUT between each piston firing comes a lapse in the velocity of the exhaust.

Lets pretend this is a stock engine with a 4 inch mandrel straight through exhaust system. Because the exhaust system is so freakin massive in comparison to the amount of expelled exhaust from the engine, there will be too much room for the exhaust to move around in there and due to the engine's vacuum effect (which is supposed to suck in air and fuel) already expelled exhaust will be vacuumed back into the engine reducing the amount of injected fuel that can be burnt. It's pure physics and chemistry.

for maximum efficiency: C8H18 + 25/2O2 => 8CO2 + 9H2O

that is (ideally)... 1mole of ocane needs 12.5moles of oxygen to completely combust into carbon dioxide and water. But petrol isn't 100% octane and air is only 21% oxygen... so don't start thinking you need 2 parts fuel to 25 parts air... that is wrong.

That was a bit off the track... but hope you found it interesting.

Anyways... lets pretend this massive exhaust system is an 8 lane californian highway, the engine is darwin producing very little traffic and the lapse in velocity is a grandma travelling at 35km/h (and slowing) in the middle lane. She needs a push a long to get to the other end of the highway... because there is only a small amount of traffic on such a large highway it is very unlikely that someone will run up the back of her before she starts going backwards. However, if the same highway happened to be only 2 lanes she would have to go faster.

The path for your exhaust must be small enough for the exhaust to flow through with high velocity but large enough so that exhaust does not build up back into the engine. Crush bends will increase the risk of exhaust build up, particularly if you are using high-end revs which will expell more exhaust (more piston firings = more fuel = more air = more exhaust) this is why bigger exhausts are better for higher end power (to a point).

notice i didn't say back pressure once.
Someones been reading

It'll always cause controversy, because of the whole backpressure mythology, perpetuated by V8 bogans with nothing better to do with their time then to come up with crap to explain why things are so...(also, super efficient engines with high octane fuels in the dark old days WOULD cause valve burn and the likes...a little backpressure to leave residual gas in the cylinder and reduce the efficieny of hte burn seems to be the only hard evidence I can find that makes it useful (yeh...real useful hey!) hardened valve seats with the coming of unleaded petrol have cured this I believe.

There are also many things that can be MISTAKEN for backpressure... velocity is one. The reflection of negative pressure which makes scavanging possible is another.

I realise I wont convert everyone. The idea is so far ingrained in motorsport mythology that to do so would be impossible... but I'll continue to put the info out there. Those that chose to listen can bask in more power...those that dont can continue to clog their engines with burnt exhaust gas and starve their cars of outright power =)

So, whens the 2.25in mandrel system going on?
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Old 11-07-2006, 06:37 PM   #68
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system is coming when tax retun is paid

so 10 days or so
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Old 15-07-2006, 04:15 PM   #69
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Oh come on for **** sake. exhausts on your car isnt going to make that much of a difference apart from noise.
i have a crush bent exhaust and having a look at the bends id have to say i might have lost like maybe half a cm from the bend of the pipe. WOW thats right. why pay like double the price. a lot of normal steel pipes are now coated and turn black when the car heats up. it protects it from rusting.
if your going to spend $500 on your car i would seriously look at other options.
just remember... no matter what anyone says. when thye mean MORE POWER from your exhaust.. you might get 2kw more . if you keep your car clean n take out **** from the boot it might be acheaper option hehe
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Old 15-07-2006, 04:30 PM   #70
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I won't post, I won't post, I won't post...

Ah, damn.

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Old 15-07-2006, 05:14 PM   #71
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Originally Posted by andrewgrazier
Oh come on for **** sake. exhausts on your car isnt going to make that much of a difference apart from noise.
i have a crush bent exhaust and having a look at the bends id have to say i might have lost like maybe half a cm from the bend of the pipe. WOW thats right. why pay like double the price. a lot of normal steel pipes are now coated and turn black when the car heats up. it protects it from rusting.
if your going to spend $500 on your car i would seriously look at other options.
just remember... no matter what anyone says. when thye mean MORE POWER from your exhaust.. you might get 2kw more . if you keep your car clean n take out **** from the boot it might be acheaper option hehe
Wrong.
Wrong.
Wrong.
Wrong wrong wrong wrong wrong.

An exhaust on its own will remove restrictions. Depending on how restrictive your stock pipe is (usually quite), will depend on how much power a sports exhaust "adds". Crushbends are NOT overly that much better than your stock pipe (which is likely crush bent anyway), because they add turbulence which slows the gas escaping the system down. Alot. This reduces power, and gives the potential for the dreaded "backpressure". Half a CM is a stack.. and its not just hte amount of pipe size you are losing, its the severity of the bends that is bad.

Depending on the car - an exhaust could release substantial power. (i say "release" because it all comes back to the manifold/header - an exhaust itself doesnt so much "add" more power, but allows the gas to flow more freely.. its not actually adding anything more on its own)


Headers,if designed correctly can add even more.

Hell, tests have proven that a racing COLLECTOR (the last part in the header, usually overlooked) have added as much as 9kW to a V8 motor ON THEIR OWN.

Mandrel bends are not overly that much more expensive if in mild steel. I've never heard of this magical turning black compound that protects from rusting, usually HPC coating (which is satin black or polished aluminium in appearence, depending on what you ask for, and stays that colour no matter how hot or cold the stuff is as long as it never exceeds its operating temp) is applied to stop mild steel from rusting. Its not necissary to coat stainless in it, but many do because it keeps the heat in the pipe which - er, guess what? adds power. Not much, but a measureable amount at least.

Now, if you are having a chop at my "potential power figures" of course an exhaust wont do that on its own - its common sense. What i said is that a given pipe size will allow the motor to flow to a maximum power dependent on size before the pipe becomes a restriction again. You do, of course, need to do other mods to get it to this point.

To say "exhausts only add noise" only shows you dont really have much of an idea on how things work. A poorly designed crush bent system is going to add alot of noise for very minimal gains, yes. Time for you to do lots of reading about how things work i think....

Oh and, for the record - it is quite possible for a decent set of headers to add upto 20kW to a stock motor - maybe more. Try adding that much power to the car through other mods, and see how far you get with the stock pea shooter exhaust. Not very, i'd imagine.
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Old 15-07-2006, 05:28 PM   #72
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I have dyno proven the stock exhaust to only accommodate a 2.4kW gain from any number of mods (ie: CAI, intake cam, and header more precisely) before a catback was installed netting a 13kW gain.

Funnily enough, reducing the axle-back with a very intricate series of curves on a twinloop muffler gained 9kW before bouncing the rev limiter to an unknown max power. Problem being the bottom end sucks nuts now, however it IS quiet...

My point? The exhaust is critical in it's design. Not only that, the way you muffle it too...

Gav.
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Old 15-07-2006, 05:33 PM   #73
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Originally Posted by chicaboo
I have dyno proven the stock exhaust to only accommodate a 2.4kW gain from any number of mods (ie: CAI, intake cam, and header more precisely) before a catback was installed netting a 13kW gain.

Funnily enough, reducing the axle-back with a very intricate series of curves on a twinloop muffler gained 9kW before bouncing the rev limiter to an unknown max power. Problem being the bottom end sucks nuts now, however it IS quiet...

My point? The exhaust is critical in it's design. Not only that, the way you muffle it too...

Gav.
and not only that - your catback exhibits weird behaviour that defys science =)
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Old 15-07-2006, 05:39 PM   #74
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I don't know about that, air speeds up around/over curves (NOT corners). This is why planes stay in the air. So with increased air volume, there would seem to be an increase in airspeed too. However, the way it's implemented is not so liveable in every day driving.
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Old 15-07-2006, 05:52 PM   #75
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I don't know about that, air speeds up around/over curves (NOT corners). This is why planes stay in the air. So with increased air volume, there would seem to be an increase in airspeed too. However, the way it's implemented is not so liveable in every day driving.
Planes stay up in the air because the air traveling over one side of the wing has a longer distance to travel etc... it creates a pressure differential and provides lift - its more to do with luminar flow and the speed of air at the boundary layer (layer of fluid or gas that "clings" to the surface of an object)

The distance the air has to travel and hte space/surface it has to "fill" has alot more to do with it.

I suspect a simillar pressure differential exists inside the curves of a mandrel bend - air on the outside of the curve has more area to cover to go the same distance as air on the inside of the curve thus speeds up (linear velocity - consider a CD... it spins at - say - 3000rpm. The inside of the disc has lower linear velocity than the outside, because hte outside has to travel further in the same amount of time) but I am no physics expert so i'll leave the finer points of whether or not this works with fluid in a pipe to someone else.

However - in a correclty designed system (headers and back), you cannot positvily affect power beyond the collector. It just cant be done. Because at the collecto the air is being compressed, accellerated, and sucked out - it is at this point that it is moving at its fastest speed. If you try to accellerate it further, you are doing so by creating a restriction.

I'd say your 9kW is more to do with - somehow - the xforce being less restrictive. This could explain why the cannon is more "torquey" - because it is allowing hte air out faster, but is unable to flow nearly as far as the xforce.... sound wierd though, given how contorted, twisted, and down right ugly looking the twin loop muffler is! - only way to put that to bed would be to put both mufflers on a flow bench and see...

If it were a simple matter of putting lots of bends in to get max power, we'd have spaghetti headers and exhausts.... the only reason some race cars appear to have such headers (F1s) is to equalise lengths.... getting equal length pipes in a 5-1 header design (for V10), with such short primaries isnt such an easy job!
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Old 15-07-2006, 06:13 PM   #76
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Blah blah blah, you agree with me, that's great.

Whatever the deal is with the XForce twinloop, I have no gripes with it, except that it should be the larger style like the OBX twinloop. I am torn between that and a Magnaflow next time...
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Old 15-07-2006, 06:20 PM   #77
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Blah blah blah, you agree with me, that's great.

Whatever the deal is with the XForce twinloop, I have no gripes with it, except that it should be the larger style like the OBX twinloop. I am torn between that and a Magnaflow next time...
Next time?????? you have 9 mufflers! isn't that enough! I think you need to goto a support group meeting mate
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Old 15-07-2006, 06:31 PM   #78
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I need a financial support group more than anything else...
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Old 16-07-2006, 04:13 AM   #79
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Quote:
Originally Posted by andrewgrazier
Oh come on for **** sake. exhausts on your car isnt going to make that much of a difference apart from noise.
i have a crush bent exhaust and having a look at the bends id have to say i might have lost like maybe half a cm from the bend of the pipe. WOW thats right. why pay like double the price. a lot of normal steel pipes are now coated and turn black when the car heats up. it protects it from rusting.
if your going to spend $500 on your car i would seriously look at other options.
just remember... no matter what anyone says. when thye mean MORE POWER from your exhaust.. you might get 2kw more . if you keep your car clean n take out **** from the boot it might be acheaper option hehe
:ets not also forget that if you cheap out here and get used to not spending the dollars on quality parts then install a cheap/underdesigned CAI, cheap/ un proven cams.........etc....before you know it you are falling waaay behind where your power figures really should be
Remember that each part in the engine/exhaust is designed to assist in making the mst of not only itself but each other part installed as well
Cheap out if you want but when you get blown away at the drags or on cruises etc you know only to blame yourself for it
And just remember that the rest of the car requires the same attention to detail to work correctly

For example I will have finished the body/ suspension on my SOHC BG with a stock engine /exhaust shortly and I challenge ANY BG SP owners to the hills no matter how modified they are
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Old 16-07-2006, 06:45 PM   #80
andrewgrazier
Senior Member
 
Join Date: Feb 2003
Location: newcastle
Posts: 586
Quote:
Originally Posted by LordWorm
Wrong.
Wrong.
Wrong.
Wrong wrong wrong wrong wrong.

An exhaust on its own will remove restrictions. Depending on how restrictive your stock pipe is (usually quite), will depend on how much power a sports exhaust "adds". Crushbends are NOT overly that much better than your stock pipe (which is likely crush bent anyway), because they add turbulence which slows the gas escaping the system down. Alot. This reduces power, and gives the potential for the dreaded "backpressure". Half a CM is a stack.. and its not just hte amount of pipe size you are losing, its the severity of the bends that is bad.

Depending on the car - an exhaust could release substantial power. (i say "release" because it all comes back to the manifold/header - an exhaust itself doesnt so much "add" more power, but allows the gas to flow more freely.. its not actually adding anything more on its own)


Headers,if designed correctly can add even more.

Hell, tests have proven that a racing COLLECTOR (the last part in the header, usually overlooked) have added as much as 9kW to a V8 motor ON THEIR OWN.

Mandrel bends are not overly that much more expensive if in mild steel. I've never heard of this magical turning black compound that protects from rusting, usually HPC coating (which is satin black or polished aluminium in appearence, depending on what you ask for, and stays that colour no matter how hot or cold the stuff is as long as it never exceeds its operating temp) is applied to stop mild steel from rusting. Its not necissary to coat stainless in it, but many do because it keeps the heat in the pipe which - er, guess what? adds power. Not much, but a measureable amount at least.

Now, if you are having a chop at my "potential power figures" of course an exhaust wont do that on its own - its common sense. What i said is that a given pipe size will allow the motor to flow to a maximum power dependent on size before the pipe becomes a restriction again. You do, of course, need to do other mods to get it to this point.

To say "exhausts only add noise" only shows you dont really have much of an idea on how things work. A poorly designed crush bent system is going to add alot of noise for very minimal gains, yes. Time for you to do lots of reading about how things work i think....

Oh and, for the record - it is quite possible for a decent set of headers to add upto 20kW to a stock motor - maybe more. Try adding that much power to the car through other mods, and see how far you get with the stock pea shooter exhaust. Not very, i'd imagine.


in my most professional opinion..... blow me
yes ******** you sure might be able to get an extra 20 kw from a stock motor
maybe if its a turbo car. but not a standard astina mate
give up
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