Turbo's

[z34_nut]

They have always been a mystery to me (not fully), but I still have no grasp on how to create the system, or what it takes to make a turbo set up.

Its the opposite with superchargers. I understand those 100%.

But I mean, Does any-one know of a good link that describes a turbo system, advantages, disdvantages, turbines, intercooling, wastegate, BOV, piping, and exhaust?


I mean, I just don't understand why they run so much more pressure vs. a supercharger. Why can it make so much more PSI then a supercharger, and not make the engine ignite?

I dunno, theres a million questions, but I was hoping some-one would have a link that helps answer some of my questions.

[sl3196]

http://auto.howstuffworks.com/turbo.htm

http://auto.howstuffworks.com/question122.htm

Some good info in there.

[z34_nut]

Thanks for the links, I read it and understand a little bit more now.

But twin turbo vs on large turbo, what would work better? smaller turbo's create less inertia, while the big turbo goes for the long run.

Could you mix sizes of turbos, one big and one small? the small one boosting low end, then the big one carrying out for the top end? I suppose if you didn't balance the two near perfectly, the little one could overrev, but couldn't it also help get the big turbo spooling faster because its creating more pressure in teh exhaust?

[slick]

Could you mix sizes of turbos, one big and one small? the small one boosting low end, then the big one carrying out for the top end? I suppose if you didn't balance the two near perfectly, the little one could overrev, but couldn't it also help get the big turbo spooling faster because its creating more pressure in teh exhaust?

Thats why you have the TT cars out there from the factory, to have boost at all times. Suprising as it may sound, the major upgrade is a larger single turbo. In this kit, I am assuming(not totally for sure) that it includes pistons that would increase the compression ratio some, so there will still be some low end kick, then once the larger turbo kicks in, it's all out balls from there.

[TurboSedan]

They have always been a mystery to me (not fully), but I still have no grasp on how to create the system, or what it takes to make a turbo set up.

Its the opposite with superchargers. I understand those 100%.

But I mean, Does any-one know of a good link that describes a turbo system, advantages, disdvantages, turbines, intercooling, wastegate, BOV, piping, and exhaust?


I mean, I just don't understand why they run so much more pressure vs. a supercharger. Why can it make so much more PSI then a supercharger, and not make the engine ignite?

I dunno, theres a million questions, but I was hoping some-one would have a link that helps answer some of my questions.

well a turbocharger has two basic parts - the turbine and the compressor.

everything starts with the turbine. exhaust gas is collected from all of the cylinders and enters the turbine side of the turbo tangently and exits axially. the exhaust gas hits the impellar wheel inside of the turbine housing causing it to spin very quickly. the shaft is connected to the compressor side, so it spins the compressor wheel at the same speed. this causes air to get sucked into the compressor side. anyways, after the exhaust gas goes through the turbine, it gets dumped into the downpipe. some of the exhaust gas exits through the wastegate, which is how boost pressure is regulated. IOW, when exhaust gas goes through the wastegate it isn't used to spin the turbine wheel therefore boost pressure doesn't keep rising. the wastegate is controlled by a boost controller, which may be controlled pneumatically or electronically. a boost controller tells the wastegate when to open. there are internal and external wastegates, but their job is the same.

now with the compressor side, air enters the compressor axially after (going through an air filter) and then exits tangentially and out through the compressor discharge. as the air goes thru the compressor, it is moving so fast and then slowed down through the scroll which creates pressure (and heat).

after the air leaves the compressor, it goes to either the throttle body and into the engine or it goes through an intercooler first. the intercooler is basically a radiator for the air. since the air gets heated up alot after it gets compressed, it is definately a good idea to have an intercooler. cooling the air causes it to become more dense, which means more power can be created at the same boost level. there are air-to-air intercoolers (most common) and water-to-air intercoolers like the Sy/Ty uses. their job is the same though. there is also chemical intercooling, such as adding water or alcohol injection. even nitrous is basically chemical intercooling. some people also spray CO2 at the intercooler to make it more efficient. the downside of an intercooler is pressure-drop through the intercooler. losing 1-2psi through the intercooler is common.

a BOV is just a valve that opens after the throttle body blade shuts. it is controlled by a vacuum line on the other side of the TB blade (plenum side). when the TB blade shuts, the BOV sees the pressure diffrential between both sides of the TB blade. IOW, there is pressure in the charge pipes but no pressure in the intake. basically after the TB shuts the compressed air has nowhere to go which creates a pressure wave that sends alot of energy back to the compressor wheel. this slows the turbo down FAST and can hurt the bearings in the turbocharger's center section. the main purpose of a BOV is to prolong the life of the turbo. it also helps keep the turbo spooled between shifts (since it doesn't slow down so fast without the pressure wave coming back at it) and of course it sounds cool too!

[1990lumina]

very good explanation Josh

[TurboSedan]

I mean, I just don't understand why they run so much more pressure vs. a supercharger. Why can it make so much more PSI then a supercharger, and not make the engine ignite?

that's easy. first, the supercharger is belt driven and boost pressure increases as RPM increases. that's of course why people put smaller pulleys on superchargers - so it spins faster creating more boost at the same RPM. a turbo is different though. not only is it typically MUCH more efficient than a supercharger (meaning it doesn't heat up the air as much when compressing air to the same boost level), but more importantly boost doesn't increase with RPM. boost increases with engine load since exhaust gas is what spins it. for example, you could be at a VERY low RPM and still get high boost. drop down to 3rd gear at 20mph and mash the gas - boost level is almost certain to peak even though RPM is extremely low. it's also much easier to increase boost with a turbo, since you don't have to swap pulleys....just adjust your boost controller :)

whether the engine can handle it or not is a different story altogther.

[DaveFromColorado]

think of a turbocharger as a supercharger ... superchargers are driven directly from the engine by using a belt to spin the rotors/twin-screws/centerfugal fan - a turbocharger works indirectly from the engine using the movement of exhaust gasses and the heat and expansion of the gasses to spin a turbine which is connected to a shaft to spin the centerfugal fan on the opposite side of the turbocharger.

Turbochargers are prone to head-soak more then superchargers are, which is why they are usually cooled with oil, AND with coolant, some of the older turbochargers use only oil (like the one in my mustang)

as technology advances turbochargers have been made to handle greater and greater speeds allowing a smaller unit to produce as much airflow as some of the older bigger units which often ran slower and were more prone to "boost lag" a downside of having a turbocharger setup.

I hope that helps some.

stupid fact #1: most turbochargers can and at times do spin greater then 100,000 RPM's.

stupid fact #2: part of the noise from a turbocharger (only a very small small part) is the audible sound of the turbocharger blades breaking the speed of sound.

--Dave.

[z34_nut]

This is some GREAT information. Thanks a ton Josh and Dave. Those explainations helped alot. I accually feel like I learned some-thing today. This should be made into a sticky in the performance section :wink:

I have a question how-ever. Considering the different types of Intercoolers, Which is the most efficient.

What accually uses a Sequential Turbo set-up? I don't think I have ever noticed, unless it is commen for a TT set-up.

Why would one big turbo be better then a TT set-up? If a TT set-up is sequential, wouldn't it go hand in hand with the fact that it would be more efficent then one big turbo?

Thats all for now, I'll prolly try and squeeze as much info out of you guys.

[ShockTherapy]

This is some GREAT information. Thanks a ton Josh and Dave. Those explainations helped alot. I accually feel like I learned some-thing today. This should be made into a sticky in the performance section :wink:

I have a question how-ever. Considering the different types of Intercoolers, Which is the most efficient.

What accually uses a Sequential Turbo set-up? I don't think I have ever noticed, unless it is commen for a TT set-up.

Why would one big turbo be better then a TT set-up? If a TT set-up is sequential, wouldn't it go hand in hand with the fact that it would be more efficent then one big turbo?

Thats all for now, I'll prolly try and squeeze as much info out of you guys.

Front mount, 3KgtVR4,less complicated, and less pressure loss, no.

[AWeb80]

VW is looking at putting a supercharged and turbocharged motor in some upcoming cars.....i just read it in motor trend i think.

[Turbocharged400sbc]

A (inline) Twin turbo setup is used on some diesels and Alot of the tractor pullers some rin as high as 100psi boost basically a large Turbo compresses a large amount of air to 2-40psi and then a smaller turbo behind it compresses it further to 80+ psi and diesels as you know run upwards of 16 to 1 compressions so in effect that engine has at WOT close to 40 to 1 compression that is why them tractor pullers make 1000's of HP but Make 4000+ Lb Ft of tq that drags that big ass sled down the dirt track!

the twin turbo Rx7's have a small and large turbo the small turbo provides boost at lower rpm's then the system switches over to the larger turbo at high Rpm's (where the small turbo would be a restriction) creating the best drivability for a factory car produced for the public. but the biggest Mod on these cars is upgrading to a single Large Turbo for more top end power. and the tuners tune the turbo lag so the engine makes as much power as it can without the tires breaking loose at the line. plenty of turbo cars tune the lag to keep traction off the line and fullboost not too far past the 60 ft mark...

Turbo's you can control this with dual/tripple stage boost controllers that limit boost in 1st gear and then bump it up in 2nd then full bore it in 3rd gear+ to keep the driveline components happy and alive as well as to prevent tire spin (which just slows ya down)

<---LOVE'S TURBO'S!!!!!!!!! :twisted:

and another design of IC (intercoolers) uses an Air to Freon system where the AC compressor (shuts off at WOT) works to compress refrigerant that is passed through an evaporator (very similar to the air to water IC's) that the Turbo outlet air moves through, chilling it down to ambient or below ambient air temps.
some of these systems pass through an Air to air then through an air to Freon ICoolers seen more than a couple out in cali

we will be using an air to freon IC on the rear 3800 when it gets Turbocharged this winter
BTW Ford has a factory air to Freon IC on the newer Lightning trucks (factory supercharged)

james

[z34_nut]

tuners tune the turbo lag so the engine makes as much power as it can without the tires breaking loose at the line. plenty of turbo cars tune the lag to keep traction off the line and fullboost not too far past the 60 ft mark...



thats very cool, never considered that. as is this,



Turbo's you can control this with dual/tripple stage boost controllers that limit boost in 1st gear and then bump it up in 2nd then full bore it in 3rd gear+ to keep the driveline components happy and alive as well as to prevent tire spin (which just slows ya down)



Now about Knock retard. Its a serious probelm with GTP's once they go into the smaller pully's and stock exhuast. But if a turbo is creating say 10 lbs of boost, then the pressure with-in the intake would be higher, along with compression. pressure creates heat, and heat will create knock.

But I see cars running around with a turbo, stock manifolds but 10-15lbs of boost with little or no knock. What gives? How can a car have pressure built up in the combustion chambers (or so I think) yet avoid the knock with stock manifolds and compression?

Does the turbo create a vaccum in the exhuast due to the turbine? Is that even possible? Or does the turbo operate solely on the manifold backpressure?

[Prospeeder]

well knock is when the gas ignites because of pressure before its supose to, not by the spark? well if so, they use higher octane fuel, that makes it withstand more pressure

[Turbocharged400sbc]

Now about Knock retard. Its a serious probelm with GTP's once they go into the smaller pully's and stock exhuast. But if a turbo is creating say 10 lbs of boost, then the pressure with-in the intake would be higher, along with compression. pressure creates heat, and heat will create knock.

But I see cars running around with a turbo, stock manifolds but 10-15lbs of boost with little or no knock. What gives? How can a car have pressure built up in the combustion chambers (or so I think) yet avoid the knock with stock manifolds and compression?

Does the turbo create a vaccum in the exhuast due to the turbine? Is that even possible? Or does the turbo operate solely on the manifold backpressure?

a roots typr SC is a fairly ineficient means of compressing air which means that to increase the boost it heats up the comprewssed air more per PSI than a turbo, a more efficient SC is the whipple design as it actually compresses the air as it goes through it (the SC) the roots type just "blows"=moves more air than the engine can injest which presurizes the air in the intake

a turbo (or belt driven centrifugal) dep on the compressor design can move more air and compress it without increasing it's outlet air temp per PSI as much as a roots SC and sice a turbo (usually) has lag when the engine is under the most load at lower rpm's the boost level isnt high enough to cause KR but when the engine revs up it has less load on it (dep on trans/diff gearing) so everything is happening at a much faster rate and there is very little time for the mixture to preignite
(most of the Top Fuel engines actually live under controlled detonation-thats why pistons rods etc get changed every 1-4 runs, that an ~8000Hp doesnt let components live that long...)

and yes exhaust restriction factors into the equasion but there are many variables that come into play with non IC turbocharged cars...

an excellent book is "Maximum Boost" by Corky Bell (amazon.com etc)
this will give you an idea of the math, and fluid dynamics involved in turbocharging a vehicle properly....

cam profiles, head flow all play into the total system design...and aas with most things mechanical there is a bit of compromise...street drivability or maximum HP....

the turbo doesnot create a vacum on the exhaust..the turbo is using the hot expanding gasses (which is wasted energy on an NA engine) to turn the turbine, a properly tuned Turbo system will have a bit of backpressor if the turbine is sized for the engines VE and airflow requirments a turbo with too much backpressure is not an efficient turbo system...

I highly rec the book i stated earlier as it can answer ALL of your questions....

James

[Turbocharged400sbc]

Octane is the measurment of a fuels resistance to ignition... it doesnt make the fuel burn slower (on higher quality fuels) but yes this contributes to knock resistance on both turbocharged and SC engine's...
but so does combustion chamber/piston face design....as well as if the chambers have any carbon buildup....

[DaveFromColorado]

an other way to reduce knock in an engine that's "charged" (supercharged or turbocharged) is to lower the static compression ratio, remember, if you're charging the air or forcing it into the engine you're basically making the engine think* it's bigger (for lack of a better way to put it) which will raise the compression ratio (can't remember the word for it when it's in motion, I wanna say dynamic compression ratio, but that doesn't sound right)

as for twin turbo setups, sometimes two small turbos are used to move more air at lower engine speeds, this works, but the smaller turbos will generate more heat then one large turbo.

the two vehicles that come to mind when thinking about sequential twin turbos are the Toyota Supra's and the RX7's both use the sequential turbochargers, one small one for slow speeds and one large one for higher engine RPM's with the smaller turbos doing almost nothing, the coolest thing about this setup is hearing the "pre-spool" stage of the second larger turbo - those setups do not have one turbo feeding into the other like someone else said (altho there are setups like that usually in tractor pulls and other type of highly modified engines) the downside to the seq. turbo setup is sequence timing is very important, pre-spool is extremely important, and keeping those things together is a hard accomplishment. Also, the two turbos together will hold a LOT more heat near the engine.

if I think of anything more about them later I'll post that.

--Dave.

[z34_nut]

Maximum boost was only $23 at amazon.com. i'm going to try my local bookstore first. I just hate shipping.

[Canada]

In all honesty, I wouldn't both reading about turbocharging on the internet. Awhile back I bought a book. Maximum Boost by Corky Bell (http://www.amazon.com/exec/obidos/tg/detail/-/0837601606/qid=1120833344/sr=8-1/ref=pd_bbs_ur_1/103-8016197-4024603?v=glance&s=books&n=507846).

He is a very good technical writer and actually knows what he is doing. The book isn't written for the engineer (which is nice) and he sort of wrote his view of certain aspects into. Do it. ;)

[TurboSedan]

i need to get that book!

[Turbocharged400sbc]

It's a great book, mine's getting old though....

BTW I just found a new Turbine housing design with a segmented housing design and a swing valve that closes at low speed for faster spoolup and swings open for maximum exhaust gas flow to the turbine....found it mentioned in a 4x4 mag
fairly pricy though but it gets rid of one of the hardest compromizes...lag and overal flow....

[Canada]

Thats why I like VNTs.....like on the LLY Duramax.

[Turbocharged400sbc]

Ah but long term the VNT Turbo has issues with the vane controller components (the older Mopar's) the new one's have modern materials and engineering.... but the design i just saw has one moving part vs 18-30 .... yes VNT's are great...

but as the saying goes, ..yeah i can make you go fast.....how big is yur wallet? :mrgreen:

[88Regal Limited]

Damn you guys know alot! Good information!

Stupid question: Could you turbocharge a supercharged engine? or would that create too mutch heat and effectively melt the pistons in the motor?

PS: when did you guys decide to make this section? :oops:

[digitaloutsider]

It has nothing to do with the heat, it has more to do with the fact that the supercharger would just more resistance than it would help. You've got two moving lobes (or screws depending on the supercharger), they'd do nothing but in the way of the air the turbo is trying to push. You could do it, it'd just be incredibly stupid and a waste of time.

[dbtk2]

ZZP put a turbo on an L67 with an M90. It has two intercoolers (one under the blower and a front mount for the turbo). They run a 3.4 pulley on the blower and it helps build up cylinder pressure so the turbo spools quicker. Once the turbo spools past X psi the wastegate for the blower opens to allow the air from the turbo to flow through there...or at least thats how I understood it when they explained it. The car makes insane power, although they still have lots more to do with it, they are still playing around with the turbo/supercharger combo.

Shawn

[TurboSedan]

how does a wastegate for a supercharger work?

[mfewtrail]

how does a wastegate for a supercharger work?

"The Eaton supercharger system incorporates a specially designed bypass valve, which is actuated by a vacuum motor near the throttle body, and recirculates the supercharger air flow when boost is not required. During typical driving conditions, the engine is under boost around 5% of the time, which means the remaining 95% of the time the engine is under vacuum, allowing for better fuel economy and a quieter ride. In addition, the helix angled rotors, along with specially designed inlet and outlet port geometry, also reduce pressure variations resulting in a smooth discharge flow and a lower level of noise during operation. The associated ducting and mounting used in installing the supercharger can play a major role in reducing the noise emitted by the supercharger. "

[z34_nut]

Thanks again for all this great info!

I went to my local bookstore they didn't have it *go to hell waldenbooks* so it looks like I'll be buying it off amazon.com.

P.S. This thread is jumping around every-where!

[slick]

Maximum boost was only $23 at amazon.com. i'm going to try my local bookstore first. I just hate shipping.

It's a good read. I have it laying around here somewhere.

[z34_nut]

Bumped for an odd reason.

[TurboSedan]

i better go out and adjust my overboost eliminator tomarrow.....


<-----noob.

why would over boost be bad and doesn't the waste gate protect from that?

i'm not intuned w/ FI....i know the basics though


well i went through this thread and didn't see anything that would answer your question about overboost Adam. so i'll try my best to explain it to ya :wink:

an "overboost condition" is a built in safety feature that is programmed into the chip from the factory so people don't raise the boost themselves, which could result in blowing their engine resulting in warranty claims....and auto manufacturers definately wouldn't like that! but first of all, i'll post some basic info before i go into what an overboost eliminator is....my apologies if i'm posting info you already know, i just want this to be as understandable as possible for others interested.

a MAP sensor is used on "speed-density" controlled engines (as opposed to mass-airflow [MAF] controlled engines). IOW it meausures airflow indirectly by using the crank posistion sensor to measure engine RPM (speed) and the MAP sensor to measure engine load (density). both my Cutlass and my GTS use the speed-density system of measuring airflow into the engine. a 1-bar MAP sensor (used on NA cars) cannot sense pressure - only vacuum. therefore its 0-5 volt output signal has a greater resolution than 2 or 3-bar MAP sensors which is beneficial to driveability (but anyways...i'm getting off topic here since we're talking boosted engines and not NA).

anyways, onto 2-bar MAP sensors....which are used on boosted engines utilizing a speed-density system. a 2-bar MAP sensor's 0-5v output signal doesn't have as much resolution as a 1-bar MAP sensor due to the fact that the 0-5v output signal must now be used to span both inches of vacuum and up to 14.7psi boost pressure levels. most factory turbocharged cars experience the factory programmed "overboost condition" at around 10psi depending on the engine of course. this overboost condition is used to limit boost level and it does this by cutting fuel to the injectors. this causes the engine to suddenly feel like it dies since it momentarily has no fuel (the overboost condition can sometimes be a very harsh feeling and can almost make your head hit the steering wheel!). the result of course is that since there is no more fuel, the engine has no exhuast gas to feed the turbine, and therefore boost cannot go any higher. the fuel supply is only cut off momentarily but long enough so the turbo has to re-spool all over again. cutting fuel to the injectors is a rather crude way of creating an overboost safety feature and can sometimes be damaging to the engine becuase since the fuel supply is cut off at a relatively high boost level, it could result in a momentary lean condition. but it does work.

now an overboost eliminator is simply a device that limits the voltage signal from the MAP sensor to the ECM. it's called an adjustable zener diode and sometimes referred to as a "MAP clamp". there are zener diodes that aren't adjustable but i wouldn't bother with them. by limiting the MAP sensor's output voltage, the ECM is essentially fooled by not 'seeing' the raised boost level (done by turning up a manual boost controller etc). so let's say factory overboost condition occurs when the ECM sees a 4.75v signal from the MAP sensor. with the overboost eliminator, you can limit the output voltage from the MAP sensor by adjusting it to a level just under 4.75v. adjusting the overboost eliminator to just under whatever the factory set overboost voltage limit is is very important because if you adjusted it to say....4.3v you would be limiting the max amount of fuel since the ECM would interperate that 4.3v as 9psi when in reality you have your MBC set to say.....15psi. that would obviously result in a lean condition and likely a melted piston or two. so if your factory set ECM overboost condition occurs at 4.75v (example), ideally you would want to adjust the overboost eliminator to something like 4.72v....giving you basically 99.9% of max fuel available to the injectors and of course, the ability to raise boost without hitting the overboost condition (which usually sets a trouble code and an SES light btw).

a VERY IMPORTANT thing to consider is that IF you raised the boost level past 14.7psi (IOW, above the maximum pressure a 2-bar MAP sensor can read) is that you still have done nothing to add extra fuel for the extra boost you are now pushing. since the overboost eliminator essentially fools the ECM, it has no way of knowing to add extra fuel past 14.7psi. adding extra fuel can be done in various ways, such as chip tuning, larger injectors, AFPR (adjustable fuel pressure regulator), RRR (rising rate regulator aka FMU), adding extra injector(s), or alcohol injection or a even combination of some (or all) of the above. some cars even have 3-bar calibrations available which makes things really nice and easy. a professionally tuned 3-bar calibration is probably the best way of adding fuel & boost (not to mention timing and everything else) if you want raise boost levels above 14.7psi.

adjusting an overboost eliminator is kind of tricky. i've done this a few times on my brother's cars (Bossman429 actually installed the one on my GTS). FIRST, go for a drive with TWO people in the car - one to drive (doh!) and the other in the passenger seat with a DMM (digital multimeter) with the DMM probes attatched to the output signal wire and ground wire off the MAP sensor. before you go for a drive, adjust the boost level just slightly higher so you know it will definately hit the overboost condition. you need to see what voltage setting the overboost condition actually occurs at on your particular car. then have the passenger take note of the voltage that is displayed the exact moment the overboost condition occurs. now install the the overboost eliminator inline between the MAP sensor output wire and the ECM and ground it of course. go for another drive and adjust the overboost eliminator by turning the trim pot screw until maximum output votage to the ECM is about .03v below where the overboost condition occured on the first run. this will likely take a few test runs to get it dialed in just right. IMPORTANT - DO NOT raise the boost level any more until you know you have enough fuel to support the higher boost, ECSPECIALLY if you are adjusting the boost higher than 14.7psi since that is the maximum pressure the 2-bar MAP sensor can read and the ECM would have no way of adding fuel past 14.7psi.

that pretty much covers it. every once in awhile a readjustment of the overboost eliminator may be needed to account for colder weather or altitude changes etc.

[kuntzie]

turbo sedan i didnt read your post but my car was getting overboost aswell cecause the stock boost conntrollere wasnt keeping enough boostt to open my wastegate

[TurboSedan]

yeah i won't bother installing an overboost eliminator on my Cutlass since the stock turbo is no good for above 12psi anyway not to mention you can easily get rid of it via chip tuning (unlike my GTS). i think Jay raised or completely removed the overboost cut-out in my chip since i've run at least as high as 13psi and never did hit overboost once.