Blower or Exhaust?

A blowers power delivery is generally more liniar than turbo.

[StealthAu]

either way, the original question was blower or exhaust, exhaust will cost well under 1k,extractors to tip, fourced induction, blower or turbo, you wont have much change from 10k after engineering and all. exhaurst, i'm guessing about 10kw gain, other options 100+kw gain

[Casper]

Its actually a really odd topic to be honest. The options are poles apart.
It would be like asking"should I colour code my mirrors... or get a full respray in a new colour?"
The cost, results and effort differences really put the exhaust vs blower into such difference spheres of modification that its a case of "Do the exhaust if you have $1,000, do the blower if you have $10,000" as stockoau has said.

[chief]

If you want to supercharge on a shoe string budget read this thread and have a laugh http://www.fordforums.com.au/showthr...c+supercharger

[Casper]

god, that thread just wont die :

[JC]

Originally Posted by Casper

Which is actually a fallacy as you are aware JC. A turbo DOES cost the engine something to produce. It is an exhaust restriction, no different to shoving a potato in your exhaust. So while the SC is draining power from the engine from friction, not unlike an AC compressor, the turbo is draining power from the engine from being an exhaust blockage.
There are also different types of SC's, that operate on different principles, that have fundamental advantages over turbos and also fundamental disadvantages.
Both have benefits, both have down sides. It is effectively a cost/application/preference option as to which one you prefer.

Actually, it's not fallacy. Any exhaust is a restriction, and every car legally has to have one. A blower takes around 20% of engine power to run. A turbo does not. As both a s/c and turbo'd car must have an exhaust, then it is fair to say that the turbo doesn't rob any additional power to run it, whereas a s/c does.

[Casper]

Originally Posted by JC

Actually, it's not fallacy. Any exhaust is a restriction, and every car legally has to have one. A blow takes around 20% of engine power to run. A turbo does not. As both a s/c and turbo'd car must have an exhaust, then it is fair to say that the turbo doesn't rob any additional power to run it, whereas a s/c does.

A turbo takes about 1% of engine power for every psi it generates. Theres no such thing as free power, if it was there would be a thing called a "perpetual motion" machine in operation (something that makes more power than it consumes) and this is not the case. Given that a turbo (or any mechanical device known to man for that matter) is not 100% efficient then there is loss somewhere.

I could type it all out but Gunns posted something a year or so ago that explains it all pretty much.

Originally Posted by Gunns

Here is some other food for thought that goes to show that a turbo draws power from the engine just like a supercharger does to make power.

A supercharger does indeed require power to drive it. The power required is actually mass airflow times boost. You also need to include the extra power required due to efficieny losses in the blower caused by heating of the air above that which occurs because of compression. Also belt drive losses need to be taken into account.

If you do the maths you will probably find between ten and twenty percent of crankshaft power is lost driving the blower in a typical modern street engine.

Now a turbo also requires power to drive it. The power developed by the exhaust turbine is once again mass airflow times boost, plus efficiency losses, plus bearing losses. If your supercharger has 70% adiabatic efficiency, and your turbo runs at about 70% adiabatic efficiency then the actual shaft horsepower required is going to be identical !

But to drive the exhaust turbine there must be a pressure drop across the exhaust housing and turbine wheel. This is basic thermodynamics. you cannot get power out of something without putting power in.

If you have ever measured the pressure drop across the exhaust turbine you will find it will be typically betwwen twice boost pressure, down to the same as boost pressure if you are really lucky.

But how does this extra back pressure in the exhaust manifold effect engine power ? Well again research has been done into this and the results have been published.

Typically an engine looses 1% of crankshaft power for each psi of back pressure in the exhaust manifold. Surprise ! ! you are going to lose about ten to twenty percent of crankshaft power to drive your turbo, exactly the same as that required to drive a supercharger.

Ah but if you loose 1% of power per psi that means at 100psi back pressure you would have no power at all ? Yes indeed.

When the exhaust valve opens there may be roughly about 100psi left in the combustion chamber trying to get out. If there is no exhaust flow, the engine will stop. Hence zero output power.

The myth that superchargers draw power from the crank, and turbos are free power for nothing is just that, a myth.

[StAndArdAU]

this has been a pretty handy thread! good to see the pros and cons for both mods. especially for someone like me who is only very basically mechanically minded. all i know is a SC/Turbo makes cars go faster. But how fast do ya wanna go?

If you were looking into the options you'd hafe to ask more questions, "am i going foir the land speed record, or do i just want to be able to pull away at the lights a bit quicker next time there's a ricecooker pulled up beside me but don't necessarily Wwant to beat him??"

IMO, get an exhaust anyways, then look at a forced induction route. but that's just me talking, and i once thought Aluminium and Aluminum were two different things... :P

If you really want to go faster, Get a lick of Red Paint and always wind your windows up

[JC]

My point is that a turbo does not rob as much power as a s/c. The difference is around 20% efficiency. So if we assume that the power a turbo robs is nil, then in comparison, a s/c robs 20%. For 7 psi for each, these figures may be 7% and 27%, but in relative terms, a s/c costs 20% more power than a turbo does, given the same psi rating etc.

[JC]

I am leaning back towards the turbo now, as it's a cheaper setup, even if it does require more work to set up. I reckon for under $6k, I could get a snort stage 2 (~$4k) up and running, including exhaust changes (<$500) and edit (~$1500). The base s/c kit is more like $7k, and that still needs an edit, so the turbo kit saves roughly $2.5k. And gives around 80rwkw.

Back to the original question, do exhaust now, and start saving for either route of forced induction.

[4.9 EF Futura]

Originally Posted by Casper

god, that thread just wont die :

Lol, nor should it!

I use a cobalt 27 turn motor to propel a 1.2 kg graphite RC car to... maybe 25 mph. Lol. They have around 200mm of torque!

Somehow that kind of force doesnt equate in my mind to... 984cfm... pressurised!

As both a s/c and turbo'd car must have an exhaust, then it is fair to say that the turbo doesn't rob any additional power to run it, whereas a s/c does.

A turbo is restricting the exhaust just as much as its pressurising the intake. Think about it. You think that exhaust turbine might be getting a *bit* harder to spin when the intake side is compressing air at 5, 10, whatever psi?

This has a HUGE impact on the efficiency of these air pumps we call engines.

Like a turbo, the amount of energy used to spin a blower depends on the boost... not an arbitrary figure of "x" %...

[Casper]

Originally Posted by JC

My point is that a turbo does not rob as much power as a s/c. The difference is around 20% efficiency. So if we assume that the power a turbo robs is nil, then in comparison, a s/c robs 20%. For 7 psi for each, these figures may be 7% and 27%, but in relative terms, a s/c costs 20% more power than a turbo does, given the same psi rating etc.

no, not true. A S/C will rob around 20% of power outright.. from idle to redline. It doesn't change as it is a solid connection. Its like the A/C compressor. The faster you go does not increase the amount of power loss by any significant margin. If anything the overall percent will drop as the engine creates more power but the load from the A/C (or Supercharger) remains relatively static.

This is the opposite of a turbo. To start with the amount of psi you get back (lets say 7psi) will take around 14psi of exhaust pressure to generate. That equates to 14% on load. As the exhaust gasses increase the actual turbo "blockage" becomes significant too, far more than a standard set of extractors.

As I said, its horses for courses and each has an application and a down side. Neither are "free" power.

[StealthAu]

i don't quite get what your on about as in perpetual motion, using exhaust to increase airflow, isnt perpetual motion. Your using the force of air from the exhaurst to spine a turbine to increase air intake. that is where there is a power loss, from the transfer of fource from the exhaurst to fource of induction. Considering the gasses expelled from the exhaurst arn't in use, you realy are not taking power from the engine to gain boost.

[JC]

Originally Posted by stockoau

i don't quite get what your on about as in perpetual motion, using exhaust to increase airflow, isnt perpetual motion. Your using the force of air from the exhaurst to spine a turbine to increase air intake. that is where there is a power loss, from the transfer of fource from the exhaurst to fource of induction. Considering the gasses expelled from the exhaurst arn't in use, you realy are not taking power from the engine to gain boost.

Yep, that's the way I was looking at it, but apparently that is wrong. I don't agree it's wrong, but if someone thinks they know better, then I'm happy to let them. Reality is, after all, an illusion caused by lack of drugs. :yeees:

[Sourbastard]

Originally Posted by stockoau

i don't quite get what your on about as in perpetual motion, using exhaust to increase airflow, isnt perpetual motion. Your using the force of air from the exhaurst to spine a turbine to increase air intake. that is where there is a power loss, from the transfer of fource from the exhaurst to fource of induction. Considering the gasses expelled from the exhaurst arn't in use, you realy are not taking power from the engine to gain boost.

Really. What forces the gas out of those exhaust runners and past that big restriction. Fairy Dust? Magical Moonbeams? The Ghost of James Brown? Lemmiwinks? Just cause they arent in use, doesnt mean that suddenly they just wander around down the exhaust pipe of their own accord. They are filling a pressurized system, to exert pressure on the turbine. To keep the pressure up, the engine works harder to force more exhaust out into the restriction until the impeller spins up. Those pressures just climb as the system spins faster.

An Engine is an airpump. A supercharger is another airpump, as is a turbo charger. They all do the same job in different ways. They all have different efficiencies and different characteristics to the way they work together and they way they effect engine power.

No matter the method used, you lose some power, to gain some power. End of story.

[Walkinshaw]

Originally Posted by sourbastard

Really. What forces the gas out of those exhaust runners and past that big restriction. Fairy Dust? Magical Moonbeams? The Ghost of James Brown? Lemmiwinks? Just cause they arent in use, doesnt mean that suddenly they just wander around down the exhaust pipe of their own accord. They are filling a pressurized system, to exert pressure on the turbine. To keep the pressure up, the engine works harder to force more exhaust out into the restriction until the impeller spins up. Those pressures just climb as the system spins faster.

An Engine is an airpump. A supercharger is another airpump, as is a turbo charger. They all do the same job in different ways. They all have different efficiencies and different characteristics to the way they work together and they way they effect engine power.

No matter the method used, you lose some power, to gain some power. End of story.

$10 on James Taylor singing about Moobeams being the cause/effect.

[StealthAu]

so what your saying, is there is no air pressure at the end of the extractors on a non turbo car? It dosn't take much but you really have me confused

[Walkinshaw]

Originally Posted by stockoau

so what your saying, is there is no air pressure at the end of the extractors on a non turbo car? It dosn't take much but you really have me confused

Yes there are pressure waves at the end of naturaly aspirated collectors and at a turbo housing outlet.

N/A exhaust design is primarly based arround proviing low pressure at the valve face upon opening of the valve to aid in the pressure drop at the back of the valve face.

Now say you pressurise the back of the valve with exhaust gas at xpsi above what would be seen with the N/A setup. The effective pressure drop accross the valve face is xpsi less than was achieved with the N/A setup, thus causing two things

(1) increases the force the exhaust stroke expells to push the exhaust gas out of the cylinder
(2) reuces the effect of valve overlap has on drawing in the next intake stroke.

[Sourbastard]

Originally Posted by stockoau

so what your saying, is there is no air pressure at the end of the extractors on a non turbo car? It dosn't take much but you really have me confused

Stop arguing. Start nodding.

[StealthAu]

supercharger/turbo its all crap anyway, acourding to the link above the only way to go is get a pc fan

[Sourbastard]

i suggest you buy two.

[Jason50]

Originally Posted by stockoau

so what your saying, is there is no air pressure at the end of the extractors on a non turbo car? It dosn't take much but you really have me confused

If you were able to put say 7PSI of boost into the intake of an engine that did not have a supercharger or a turbo, you would find that it would make more power than an engine supporting a turbo or supercharger.

[Sourbastard]

Originally Posted by Jason50

If you were able to put say 7PSI of boost into the intake of an engine that did not have a supercharger or a turbo, you would find that it would make more power than an engine supporting a turbo or supercharger.

I read the same thing in Harry Potter.

[Jason50]

Originally Posted by sourbastard

I read the same thing in Harry Potter.

This is not magic :

[Sourbastard]

Originally Posted by Jason50

This is not magic :

If you can create a method to introduce boost into a system that draws no power from the engine or elsewhere, I assure you, it is.

[StealthAu]

as i said pc fans, or does the current drawn cause extra drag through the alternator?

[Casper]

Originally Posted by stockoau

as i said pc fans, or does the current drawn cause extra drag through the alternator?

no, but it is an intake blockage and since they are fans and not compressors the net result is just a pretty spinny thing in your intake.. till it explodes.. then its lots of shiney plasticy things in your manifold.

[Sourbastard]

Originally Posted by stockoau

as i said pc fans, or does the current drawn cause extra drag through the alternator?

To combat the extra drag, I suggest you wear a prettier dress while driving sweety.

[poolkeeper]

What a read

[Walkinshaw]

Originally Posted by stockoau

as i said pc fans, or does the current drawn cause extra drag through the alternator?

Bingo.
What’s the Efficiency of the PC fan?
What’s the Efficiency of your alternator
Does the gain cover the 30bhp loss for being ***edited***?