Stavros

As per title really.
Obv most of you wont have a clue, but hoping some will (please no wild guesses, if no idea dont post, I know quite a lot about twin charging, but just wanna make sure about this bit).

Generally the accepted way to do it is the turbo blowing through the supercharger, the supercharger offers no real restiction to the boosted air, and you got the obvious benefits of having a turbo and a charger.

BUT is there any reason not to run the charger blowing through the turbo (ie the charger being the first in the chain)?

Theres not is there? I mean if the charger aint a restriction to the boosted air when the turbos blowing thru it, it wont be a restriction pre-turbo when the turbo is sucking thru it, right?

Just dont think ive ever seen it with the charger as the first thing, so wondered if there a reason for it?

An advantage I can think of is that turbos dont mind lots of heat as much as superchargers do, so better if the charger isnt the one that gets the hottest air thru it.

Main reason would purely for packaging reasons tho (ie its easier to plumb in that way).

Cheers

PhilM

I would have thought that due to the fact the supercharger will be rotating (due to being engine driven), it may offer a flow restriction to the air being sucked into the turbo - unlike a twin turbo setup, the supercharger's compressor is not free to accelerate/decelerate with the extra airflow, as a primary turbo would do in a twin-turbo setup, thus probably causing turbulence and a bit of a restriction.

I'd run the turbo first, then the SC. Though in real terms it probably makes little difference, wouldent take a great deal of re-piping to do some testing anyhow

big_wig_074

lookin at the delta s4 setup i can see here:
air filter,turbo,intercooler,supercharger,intercooler, inlet manifold!
its on here: http://www.carsfromitaly.com/lancia/index.html

Stavros

Wouldnt that be the exactly same if the charger was after tho phil? (as i know its no restriction at all when placed after the turbo)

I get your point tho, and thats what I was thinking.

The application we was thinking of was only possible (without wild amounts of work) with SC first tho unfortunatley, hence the question.

Greg- Yeah, all ive seen are like that. But trying to see why having SC first wouldnt work.



(BTW, might be interested to know the shit about bypass valves opening to let the air past the supercharger once the turbo is spooling is bullshit myth funnily enough! The supercharger bypasses only open at idle. Once on throttle the turbo always blows thru the charger at all times, no need for a bypass, supercharger dont cause a restriction, contary to popular belief!)

Anonymous

If its a displacement charger, like an Eaton M45 i would have thought it would be ideal to be after a turbo, as it will just move the same amount of air by volume, but it will be denser and hence result in even more boost in the plenum.

PhilM

Should be the same either way - the super charger isn't doing any work on the air when the turbocharger is running, so it should offer little if any flow restriction either way. The supercharger is only producing a mass of air, for a given engine speed, the "boost" is only produced when theres pressure from the engine not using the air as fast as it is produced, hence, pressurising the system. If the turbo is demanding (or producing) 10units flow of air, the SC is only rated to 3units flow of air, it won't be doing any work....either way the setup is aligned, that should be true.

Anonymous

Im not convinced in the case of a centrifugal charger, as the housings themselves tend to be quite small so could provide a flor restriction.
But im into the realms of guess there so willl STFU as requested by steven, lol

Stavros

Chip- Yes, purely talking about positive displacment chargers, not centrefugial ones.

Phil, replys like that i cant udnerstand at almost 1am

All i KNOW is if you fit a displacment charger AFTER the turbo, it spools up like a supercharged car, and then has the extra top end punch of whatever turbo you fit as well, with the car behaving at higher RPM just like a normal turbo, ie the charger giving no noticable restriction even though the turbo has to blow all its boosted air thru it.

Is the charger a restriction if fitted before the turbo? I cant see it being so, but unsure.

I think Phil probably explained either way, but its so late I dont understand him

PhilM

Chip, a centrifugal charger won't offer any flow restriction if there's a bigger turbo doing work after it, since the SC (or, small turbo) is not doing any work on the air, it won't offer any flow restriction.

If it is just being a "size of pipe" issue, then that surely won't matter too much, it'd just be a venturi, the pipe diameter decreases, the airspeed increases and the pressure drops, coming out the other side, the airspeed will drop and the pressure will rise again (but, remember, we are not interested in the "pressure" there as such, were interested in the flow rate). I am not certain though, if the airspeed in the venturi were to reach ~mach1, you may get a restriction. I don't know off hand the pipe diameter etc you'd need to approach that.

The only issue I can see, is that the supercharger is being forced to spin at a set rate (engine driven), and this may offer some turbulence to the air passing through it, but shoudlent restrict things too much

Infact....if you look at an aircraft's air-conditioning system: you have an engine, or APU at one side, supplying bleed air, this is then ducted to the aircon packs, where it passes through a primary intercooler, then it enters a cold air unit (essentially a turbo), gets compressed, passed through a second intercooler, then passes through the turbine of the cold air unit, and out the back of it, then through a water extractor and into the cabin. The flow rate can't change, the flow produced by the APU/Engine bleed HAS to go to the cabin. If it doesn't, where does it go? It will cause a rise in pressure in the ducts and then blow the pipes apart....The only "energy" that drives the cold air unit is the heat from the air itself (hence it cools the air), not the flow of air itself (exactly the same for how a turbo works....by using the heat energy in the gas, not the flow of it through the turbine).

Sooo, based on that, I'd say no, wont make any noticable difference

DelboyTurbo

A turbo spins because of the mass of the air passing through the turbine.....heat only affects it by increasing the volume of the air....thus affecting required turbine size....or so i understand

If you place a turbo after the supercharger...youll be limited by the flow rate of the supercharger.......it cant freewheel to allow more flow when theres a negative pressure at the outlet (not that a turbo would really produce any).....its connected to the engine.


I think the supercharger will make the turbo redundant if its placed before it.

Rick

JesseT

Placing a displacement charger first in the line is an extreamly bad idea. Once the turbo starts coming in, there's no way it's getting any more air, since the crahger in only seeing 1 atm pressure on the inlet and producing flow equal to the crank speed.
The other way around, with the turbo feeding the charger, when the turbo kicks in it's feeding the charger with a higher pressure air, and even when the displacement charger is pumping the volume more or less dictated by the crank speed, the total mass-flow is increased dramatically by the turbo.

SimonT

Lancia S4 induction system:

Rob

well after reading this the biggest factor i can see is the throttle location, with a eaton the throttle will need to be suck through setup, and to be honest you'll end up stressin the turbo with it downstream as it'll only be working with what air it's supllied, lower RPM the blower withh be flowing more. high end the turbo will be flowing more. the the turbo upstream it will see far less stress.

the length of the induction would be fun and the throttle will be miles of pipework away from the inlet which will cause issues and can be ironed out with some good mapping however i think this would far from ideal.

With a turbo feeding a supercharger you wont be able to disengage the blower top end without a bypass as the blower will not flow suffciently with no drive. however it will happily spin over still.

it will work with the turbo downstream but i think it's about longtivingty as i really cant see the turbo lasting well, as it will be working harder in certain conditions where upstream it would be unstress with one side at atmos.

you want to spool the turbo up from an increase of exhaust gas and not from forcing it to spin up from air.

jacko

this looks so much easier when its layed out in front of you the only thing i dont know is what is that part pointing towords the first pipe on the cold side that looks like its bolted together is it some sort of valve that lets each charger do its part and how would this valve be operated

Jamz

It's a recirculating dump valve.

Stavros

Right, so basically my fears were probably right.

But, if thats the case, how does compund charging work if this wont? Where the far far smaller turbo (often rated at 500bhp less) is the first in line, but dont restrict the huuge turbo that sits downstream of it...


Surely the same? Or is a supercharger FAR more of a sealed unit than a turbo compressor?

Why? On eatons you can run the throttle before or after it? Makes no real odds, seen both done.

Would have no intentions ever of bypasssing the supercharger apart from maybe at idle, no need to, actually is a bad disadvantage from the testing ive seen.

Like i said, it isnt done, thats just popular myth.
Wasnt done on the S4, that bypass was for idle etc only.
Its like the "wastegate chatter" myth.

PhilM

Steve,

What JesseT said is very important! If the supercharger was a displacment type it won't allow the turbo to take any more air through it, that the SC is actually producing anyway. This woulden't be the case for a centrifugal one (I assumed you were on about centrifugal ones)....

Stavros

No, rootes style ones.

So yeah, basically as rootles styles ones are sealed units, you cant suck any more air past em, but cant feed more air thru em by the air already being pressurised.

Only way you could make a "supercharger first" setup work is to have a bypass that opens to let air past, making it no longer a restriction.

Itd be a right complicated thing tho, as you need a bypass on a supercharger anyhow to work at idle, and THEN youd need another one to work once on a set boost level, 10psi or so.
And when the one was open, the other would have to be closed. Complicated.

BTW, ive found a thread all about this, done by someone whos done it all, also tried a VNT turbo too, and found twin charging was far better.

Rob

Like i said you wouldnt be able to disengage the blower top end tho, with the blower free wheeling alot of engery and heat will be created from try to force air through it. air velocity would be seriously imparied. so like i said you'be better off keeping it driven.

and yes the superchargers are far far more of a sealed unit that a turbo impeller. if you locked a blower so the rotors cant turn the engine wont start. if you had a turbo impeller not spinning the car would run. I've seen both example first hand. the clearances are tight in the eaton because it is a positive displacement pump to avoid leakage back from the outlet to the inlet. if this wasnt the cas you may aswell have a nice ebay supercharger running from 12v

And as for eaton running suck and blow through. well i have only ever seen the setup as suck through and there good reason. with the inlet of the blower to atmos it will allways produce boost. unless u vent the boost off at the throttle you will have a massive build up heat the throttle plate and have a massive heat spike when it's opened. on part and light thorttle it would be rediculous the heat created and so much wasted horses pumping the air not being used. Look at every OEM installation of the eaton and tell me a single setup that is blow through. The only supercharger that lends items to blow though is the centrifugal type simple because it doesnt actually start doing much until a certain speed and that partly due the leakage from the compressor housing.

Jamz

If you haven't found it already have a look at http://www.geocities.com/MotorCity/Lane/1231/index.html when it comes back online (hour or so).

James

simon170

One of the best people to speak to would be Chris Todd at Power Engineering he built his own 12second FWD 1.6 Mk1 Fiesta years ago, using both a supercharger and a turbo.

Sure he could give plenty of helpful advice having done it a few times now

Stavros

Rob You wouldnt want to bypass or disengage it, both would be bad.

Heres some interesting stuff from someone who has already done it, and experermented a lot...

Initially I ran it with just a single throttle body at the blower intake, an intercooler feeding the stock EFI plenum, and no bypass. It was pretty horrible actually.

The large combined volume of the intercooler, pipework and plenum caused terrible drivability problems, especially during gear changes. Declutch, and back off suddenly on the throttle and the engine RPM took forever to drop. It felt as though it had a ten ton flywheel on the engine, quite disconcerting actually.

Also at constant speed light throttle, the blower acted as a large vacuum pump sucking furiously against the just open throttle. The blower was noisy, ran hot, consumed power, and increased fuel consumption about ten percent when driven carefully.

Hmmmm. So the challenge was to fix it, and a whole series of ideas were then tried. The bypass was the first thing to be added. I used a Garrett external wastegate, simply because I already had one, and this has proved to be ideal.

Choosing a suitable spring is an interesting compromise. It needs to be stiff enough so that boost pressure will not force the valve off its seat and create a giant boost leak. It also must be light enough that engine vacuum can hold the bypass fully open at idle and light throttle. The main feature to look for when selecting a suitable wastegate is a large ratio between valve area, and diapragm area.

As an example if you want to run 15psi boost, and you expect the bypass to hold fully open, say above 10"hg manifold vacuum (- 5psi), you would need the diaghpram area to be at least three times the area of the poppet valve. This might be a tall order, four times the area would be better, or even more if you can find or adapt something suitable.

If you have to buy new, the Turbonetics Deltagate has an area ratio of about 4.6 , or the larger and slightly cheaper Vortech Mondo blowoff valve also looks pretty good from pictures, but I have no idea of the actual internal dimensions.

With the bypass installed the blower was far happier at light throttle, and the fuel economy came back.

Next I replaced the original throttle body back on the plenum down stream of the roots blower, and connected the throttle cable back to this. The throttle body on the blower intake was permanantly held fully open. This was all purely experimental.

The results were actually quite good. Drivability was restored, and everything worked fairly well. With a boost gauge up stream of the throttle body the boost readings were "turbo like". At light throttle the bypass was open and massive amounts of air were circulating around through the open bypass, but with almost no boost pressure showing on the boost gauge.

As you slowly increased the throttle opening boost would rise as the bypass slowly throttled the escaping air. It worked beautifully, throttle feel was excellent.

Next I reconnected the throttle at the blower inlet so it worked with the main throttle body on the plenum with a second throttle cable. This throttle was roughly synchronised, but was held open wider than normal at idle. As a result the throttle body on the plenum controls idle speed, fast idle, and so on.

The throttle body on the blower intake is open far enough to allow atmospheric pressure through the blower and intercooler to the "main throttle body". Just as with a turbo.

Now the interesting thing is that when you go to change gear at wide open full throttle RPM, both throttles snap shut. The throttle at the blower inlet greatly limits the airflow into the blower, and hence the airflow requirement through the bypass is reduced. It totally eliminates the small boost spike that had existed with only the upstream throttle operating.

So, the throttle on the blower is only a rough gross air intake control. It does not need any critical synchronisation adjustment. As long as it is open far enough at idle to not be a restriction, and be somewhere near fully open at full throttle, it will be fine. If it is large enough, it will not be an intake restriction even if it does not precisely fully open at max throttle.

The blower bypass modulates the boost upstream of the main throttle, and of course the main throttle body is what controls engine output torque directly, with good feel and precision.

All of this is a bit long winded I know, I must apologise. But it is difficult to explain in few words. It works superbly and is so easy to set up.

Later I fitted a four throttle body inlet system, that offered even crisper throttle response than the stock intake system. And later still, a turbo as well, He he he.

As for belt loads changing on the blower when the turbocharger is working as well, I have no idea. But in theory, total blower drive power = pressure ratio x mass flow x losses. So as the turbo spools up the supercharger will see denser air, and require more torque to drive it I suppose. But I feel the advantages of having it the way it is far outweigh any disadvantages.

It is interesting to speculate that the blower draws power from the crank, and the turbo creates exhaust back pressure, both of which are bad. But by adjusting the pressure ratio of each you can juggle things around quite a fair bit. It is quite easy to maintain full throttle boost pressure higher than total exhaust manifold back pressure, this is extremely beneficial to the engine. It also opens up the possibility of running some really respectable valve overlap, something that is far more difficult to make work with just a turbo all by itself.

Stavros

Other interesting bits...


It is a normal supercharger system that runs at perhaps half the desired final boost level. You then add a turbo, the exhaust turbine has the wastegate referenced to total final boost pressure after the supercharger. The turbo compressor directly feeds the blower intake.

It is a series flow system . The advantage is that the turbo thinks it is on a large engine, not a small supercharged engine. You can run a far larger turbo than you might think feasible without any of the big turbo problems. Also because the turbo only supplies part of the boost it does not have as far to spool.

When you open the throttle there is instant boost, the exhaust volume is also far greater and really kicks the turbo into action. By adjusting blower drive ratio, and exhaust a/r you can have any characteristics you want.


A blower bypass offers a vast improvement and is well worth the effort. I used a turbo external wastegate directly around the blower. External wastegates usually have two ports, one connecting with each side of the control diapragm. Two control lines connect to either side of the throttle body on the engine plenum. The idea is that the wastegate sees the differential pressure drop across the throttle body. At light throttle there is enough vacuum to hold the wastegate fully open. At full throttle full boost the differential pressure will be zero.

Also, the bypass flow area does not need to be as large as you might at first think. It is only required to bleed off unrequired boost, and a slight pressure drop is of no account. Try to imagine how much boost you might lose if your intercooler tank had a round 38mm hole in it.

At idle and light throttle the blower bypass is fully open so the supercharger has zero back pressure. Drive losses are very low, mainly frictional. As you increase throttle opening the wastegate smoothly closes allowing boost to rise. Remember this is upstream of the main throttle body. The wastegate movement follows the movement of your right foot, just as a vacuum gauge needle would.

The result is extremely drivable. By changing the wastegate spring you can change where boost starts with relation to throttle position. With the correct spring you can keep up with the traffic and never see boost, but that last 25% of throttle makes a big difference as boost smoothly comes in though !

When you have the supercharger system working properly, just bolt on that big turbo, and get some real action.

This is not all armchair speculation, I have done it, and will probably do it again. It is by far the best system I have ever had on any car to date and was the result of a lot of development.

Stavros

More good stuff from same person...

If you wish to try a twincharge setup, the best way to go about it is to first just fit a low boost supercharger system to it, and sort out all the problems with that. Mounting and driving a blower successfully is never an easy task, but do that first and get it all out of the way.

It will then feel flexible and reasonably torquey but the top end power will be very disappointing (after having had a peaky turbo engine). It will feel more like a stock five litre pushrod V8 to drive. Low end balls, but rapidly fading out at the top end.

But it WILL behave like a five litre engine down low. The turbo will also think it is on about a five litre engine too, and even a big one will rapidly spool at unbelievably low Rpm. And it will produce all the top end airflow you could ever wish for.

Remember too, the turbo only has to provide maybe half the total boost pressure, so you will see full boost at something around perhaps 2,000 Rpm rather than 4,500 Rpm with just that same turbo all by itself.

There is no "switchover" point as you put it.

The turbo compressor is in series with the roots supercharger, both see exactly the same airflow as the engine sees. Both provide some boost, but total boost is the combined compression of both.

The turbo wastegate is referenced to total combined boost pressure, and sets the final boost pressure reached in the normal way.

How much boost each contributes, and where in the Rpm range, depends on how it is all set up. You can change supercharger pulley drive size and exhaust turbine a/r to get it working any way you want it to work.

For instance it could be mainly supercharged and have a very flat torque characteristic and no lag, and only have the turbo start to produce slight additional extra boost at the extreme top end.

Or it could only require a small amount of additional supercharger boost just to get sufficient exhaust flow to really spool up that MASSIVE turbo early.

I have heard the argument that the supercharger would restrict the turbo flow. Not true ! If the supercharger has a higher measured outlet pressure than inlet pressure, it cannot be restricting flow.

Another old wives tail is that two stages of compression make the air twice as hot. Not true either.

Suppose you compress air to 7psi boost at 70% efficiency in a turbo, and then compress it again up to 14psi again at 70% efficiency in a supercharger. The final air temperature will be exactly the same as compressing it in either a turbo, OR supercharger straight up to 14psi in one step (if the efficiency figure stays at 70%).

In practice the efficiency of both supercharger and turbo vary over a fairly wide range, but final discharge temperature will not be significantly different than when just using a turbo. Any decent intercooler will make discharge temperature a minor issue anyway.

Now the myth about crankshaft drive power.

Ever thought about how much crankshaft power is lost due to turbocharger turbine back pressure ? I will tell you, very roughly 1% per psi.

Suppose you run 15psi boost with your turbo, and you fitted a pressure gauge to your exhaust manifold and discover there is 20psi required to drive the turbine. I am telling you that that turbo is sucking probably 20% crankshaft power from your engine.

If you fitted a larger a/r exhaust cover to it, it will make far more top end power, even if boost is not raised, why ? Well the reason is that the exhaust back pressure has been reduced, and less crankshaft power is required to pump the exhaust out through the turbine. Too bad about the increased lag and boost threshold though.

Nobody ever talks about how the turbo sucks power from the crankshaft, but it is true.

The horrible truth is, that any sort of engine driven air compressor requires power to drive it, and that power must come from the engine. Exhaust energy is not free. Back pressure increases engine pumping losses fairly dramatically.

About the first thing anyone learns with turbo engines is how much better they go with a free flowing exhaust. If exhaust back pressure makes no power difference, why not keep the skinny factory exhaust system ? Never believe that the exhaust turbine runs off free energy.

Everyone I know that has fitted a pressure gauge to their exhaust manifold for the first time has been truly shocked at what they see. A production road car typically runs twice the exhaust back pressure compared to boost pressure. Winding up the boost on a stock engine can easily force exhaust back pressure up beyond three times boost pressure. A competition engine may have exhaust back pressure approximately the same as boost, but the turbine would need to be really large to do that.


Oh yes, the idea of suddenly de-clutching a supercharger that is producing a significant amount of the total boost and airflow at full throttle is silly. It would feel like instantly cutting off the ignition to several cylinders.

If a supercharger is placed after the turbocharger, and increases the boost pressure further it cannot possibly be restricting the flow.

As to horsepower required to drive a supercharger it can be either more or less than the power required to drive a turbocharger depending mainly on turbo sizing and what compromises you are prepared to accept.

Placing the supercharger in front of the turbo makes no sense for several reasons, and I have never ever seen it done that way.

In any compound compressor system, the first stage always has to pump a higher volume than second stage. The mass flow is obviously exactly the same, but the air is squeezed down in size for the second stage.

Centrifugal compressors (turbos) are small compared to the volume of air they can flow. Positive displacement compressors are always much physically larger and heavier for a given job. It makes far more sense to place a physically smaller supercharger after the turbo, than to place a physically larger supercharger ahead of a smaller turbo.

Another less important reason is that a "normal" turbo can be used with respect to compressor and turbine trims and specifications. If the turbo compressor is to be presented with already compressed air out of the supercharger, the compressor wheel and housing would need to be much smaller with respect to the exhaust side of the turbocharger. That would require a more difficult to design custom hybrid turbo. All compressor flow maps I have seen apply to air at standard sea level atmospheric pressure at the intake.

As soon as you start feeding very hot already boosted air into a turbo compressor, the standard flow maps no longer apply. You would be pretty much alone in trying to design or size a suitable compressor.

Actually, in a series system with the turbo compressor ahead, the supercharger actually INCREASES its contribution as Rpm and flow increases.

The reason is that positive displacement superchargers work off absolute pressure. When the intake pressure of a supercharger is increased, it works in a much denser medium and it will require more power to drive it, as well as greatly increasing it's mass flow per revolution. Sort of like supercharging the supercharger if you know what I mean.

The volumetric efficiency of a supercharger certainly falls off with increasing Rpm, just like the engine does, whereas a centrifugal just keeps blowing harder as compressor wheel Rpm rises. Placing the centrifugal compressor in front of the positive displacement compressor is a much more efficient way to do it.

You are probably right in that if the supercharger was placed ahead of the turbo, the falling Ve of the supercharger would restrict the turbo somewhat, but only if the supercharger was grossly undersized. Much better to place it after the turbo, which is why it is always done that way.

The beauty of it is that the supercharger has very good low speed characteristics and the turbo very good top end airflow. They compliment each other so well. Both blowers and turbos have their own particular weaknesses, but combined, the result is more than just the sum of the parts.

It may seem difficult to size blower and turbo to get it working properly, but my experience has been that pulley drive ratio and turbine a/r can be altered to get whatever boost/speed characteristics you want.

The best way to do it is to first just fit the supercharger, and get that working properly by itself. There will be plenty of small problems to overcome mainly with the drive system and drivability issues, pipework, the intercooler and so on. Get that all sorted out to run at approximately half the final anticipated boost level.

Then fit the turbo as a last step. It will absolutely transform how it goes. You will also be quite surprised at how responsive a really large turbo will be with the increased low Rpm exhaust flow provided by the supercharger.

A turbo external wastegate makes an excellent supercharger bypass. Just connect the control diaphragm with two hoses so it responds to the differential pressure across the throttle body. Replace the spring with a weaker one that closes the wastegate at around 5 to 8 inches Hg. (2.5 to 4Psi).

Only thing you need to watch with this, is that the control diaphragm diameter is at least twice the poppet valve diameter for it to control properly. Some of the cheap crappy Chinese wastegates do not have a suitable diaphragm/valve area and will not work properly.

My own experiences with butterfly type supercharger bypass valves is that they can flutter and be very difficult to control. For excellent drivability the bypass must be smooth fast and progressive in operation. I have been experimenting with supercharger bypasses for literally years, and an adapted external wastegate is the most reliable, best behaved, and simplest to get working.

If you have ever driven with a sloppy or sticking throttle cable, that is what a badly behaving supercharger bypass feels like. It absolutely must work smoothly and accurately.

Eaton use a butterfly built into some of their roots superchargers, so it can be done. I have not had any success at all with it myself, only problems. I would strongly recommend trying an external wastegate first, to anyone planning a future supercharger project.

Every production supercharger that I know of has some sort of effective bypass system fitted.
With the bypass wide open, the blower is completely unloaded and drive power, noise, and heat buildup drops to near zero even if the rotors are still left spinning.

There is absolutely no need to bypass the supercharger while it is producing boost, as explained previously.

If you want to do this for some really peculiar reason, you will need to figure out what is going to happen when the boost level suddenly drops down to about half. The sudden extra surge of acceleration you expect from the reduced supercharger drive losses, may actually not happen. More likely acceleration Will drop significantly when the boost suddenly falls away.

I certainly don't see that as an improvement, and cannot think how it could possibly be helpful.

Just like any other supercharger application, there are really two choices where you mount the throttle.

If it is a V6 or V8 and the blower is mounted on top of the engine, the throttle goes directly on the blower intake, there is really no other alternative.

Where there is an intercooler and SIGNIFICANT pipe volume between the supercharger and engine, that simply is not going to work. The throttle must be located as close to the engine as possible or the drivability will be horrible, usually in the original standard location is always easiest.

Quite obviously throttling the output of a positive displacement supercharger is not going to work without an effective supercharger bypass system. If the bypass is working properly, an upstream throttle located close to the engine will offer far better throttle response, and it will work just as well as with a centrifugal supercharger or turbo. A multi throttle system is the ultimate for throttle response, even with a supercharger.

As I stated in an earlier post, sort out the supercharger first. Then when it is all installed and working really well, just add a really large turbo to it. The turbo will behave exactly as if it were fitted onto a much larger capacity engine. It is much more effective than boring and stroking the engine.

Stavros

Oooh, last lil bit...

What determines the maximum possible airflow rating of a supercharger ? It is really maximum permissible supercharger operating Rpm times air volume pumped per revolution (allowing for blower Ve).

As Kingsley has already correctly pointed out, if a given supercharger can pump say 400 Bhp worth of air (about 600 CFM) with atmospheric pressure at its intake, up to some specified boost level, that may define a theoretical power and airflow rating for that particular supercharger.

If if the supercharger intake sees already compressed air, it still passes a given volume per revolution, but that volume is actually many more air molecules per revolution already squeezed down by the turbo compressor.

Suppose air density at the blower intake was made double atmospheric air density. Then your 400 Hp rated supercharger would then be able to flow 800 Hp worth of air. And it would do it easily, and still raise the boost pressure by the expected additional pressure ratio. All that happens is supercharger drive power would approximately double, but then airflow has doubled too.

That does not really matter, provided the supercharger drive belt can cope with the extra torque.

Any supercharger that is large enough to produce some boost all by itself must be displacing more air than the engine. Placing a turbocharger ahead of the supercharger will not change that. In essence the supercharger can never restrict the preceding turbo no matter how large that turbo is.

Rob

itsmeagain very interesting read, however i will say that i run a eaton M90 on my V6 and it's suck through and i run the cofiguration described, ie throttle -> blower -> intercooler -> plenum and i do not get any of those issues. without know much about the setup it's difficult to comment but that is very interesting all the same even if it seems to be a over kill. What type of supercharger is it? the pipe work could be excessive compaired to mine and i dont think mine is exactly short! and thats using 2.5" pipework throughout.

You seem to be getting the wrong end of the stick. I do not beleive in disengaging the blower but if you did you'd need a bypass. I'm not saying you need a bypass i'm saying you dont need to disengage the drive

Rob

only thing i will add to large volume of inlet is i had issue with getting a stabalised idle as it caused the car to hunt but was totally unrelated to fueling, which took many hours of mapping to sort but it cured through mapping

Also i dont run a bypass as I have experimented with a few and have never been able to find anything that effective.

Stavros

I didnt post any of that to tell you your wrong Didnt think much of it applied to anything you said

I posted all that to show everyone details of what someone did and the expererments and findings he had.

BTW the car he did it on was a 1.6 16v 4wd turbo thing, a Ford Lazer IIRC.

Rob

tbh i only saw the first post that address me directly of the interesting info when i replied. the rest is very interesting. I'm a big boy now i dont read into things too much

Where i see what he has done and it quite ingenuios and does sound a lil over complicated i think the issue he has maybe accounted for from possibly blower size, blower type, and type on engine. but i guess my engine comsumes far more air at lower engine speeds.

Well a 2.9 12v (such as mine) has 172lbs/ft standard which may contribute heavily to the drivability. obvious mine runs more than this but it's give u a taste for the type engine used, especially when torque peaks around 3k. and whats a ford "lazooooooor"

jacko

when i wanted to know about doing this the other mont rod tary slated me calling me a dreamer wonder if he has red this post at all( who needs nos )