Turbo Question

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I have a friend who just got into turbos and he says that the purpose of having a twin turbo is to spool the other one. I was wondering if that is true. I thought that is true for an inline 4, but would you have a turbo on each exhaust manifold/header for a V6 or V8? Sorry if this sounds elementary.

posted by  cougdude67

The purpose of SEQUENTIAL twin turbos is to spool the big one up. For a V6 3 of the cylinder exhaust ports go into one turbo and the other 3 go into the other turbo. Same as V8 but 4 ports each.

posted by  CarEXPERT

A: I got a question too.. Does coolant flow through the turbo and the throttle body to keep them cool or not?

B: When you are driving, can you adjust the boost level anytime if you have a boost controller? If your driving can you set it at 0 psi if you wanted to? Why is there a negative psi on the boost gauge. Like there is 0psi then 20psi and then there is -20 psi.??

C: Does running lean cause higher temperature in the combustion chambers? A supercharger and turbo put out the same boost pressure, so which one will waste more gas? Do S/c waste more?

posted by  CarEXPERT

bsst...wrong on the sequential part. THe sequential turbos work like this, there is a smaller turbo which is designed to reach a boost level at the lower rpm range which gives way to a larger turbo, which was stilling spooling. Seeing the only production Sequential that i know of was the 93+ Rx7 i am going to use that as the example. It had boost levels that went 10-8-10. as in it hit 10psi, as the turbos changed over it dropped to 8, then hit 10 right after. but the setup has proved VERY unrelieble because there is alot of electronics and vaccum lines involoved to keep everything balanced. also, it requires the focusing of exhaust gases by an actuator. most people go to a large single for relieblity and more power.

THe reason people use two turbos and V blocks is because it is usually unpractical to plumb both headers to a single turbo. Also, that means less heat is placed into the intake charge because the heat is halved between the two turbos.

posted by  Low Impedance

A) most turbos today are water cooled which runs coolant through a water jacket around the turbo bearing. Many cars have the coolant flow throw the Throttle body because it warms the intake charge. which is not good for preformance, but allows for better cold engine preformance and therefore, better idle when cold. More of a comfort thing for the buyer market.

B)No you cannot control the boost of the car when driving. BAD BAD BAD BAD. you want to have your car tuned to a set boost level. you will still experience spikes and risk detonation if you change altitude or temperature drastically. plus, boost controllers actually add on to the boost level of the car, not take away. they delay the signal to the wastegate so more boost can build before the wastegate is opened. 0 psi is a n/a car. if a turbo is present you will hit vaccum, for an instance 0 and then a boosted level. the vac is created by the throttle plates being open just enough to let the car idle. this will create a pressure in the manifold that is less than the atmosphereic pressure. WHen the plates open that hits as close to atmospheric as can be. That is true about all cars, turbo or not. only turbo or s/c vechiles are able to power above the atmosphereic pressure, giving boost. usually vac is read as in. Hg. or inches of mercury. but that depends on the gauge maker, preference etc.


C)lean conditions refer to the ratio of fuel to the air (as im sure you know) just stick with me though. When you run too lean, you create a situation where you can have premature detonation of the charge. this is called detonation. What happens here is an explosion, 6 times more power than anything you can produce until control situations. the temperature can reach 1200 degrees in the center of the explosion and have pressures reach the thousands inside the cyclinder. "pings" are what some people call this becuase it sounds like a hammer hitting your engine. that sound is created from the shockwave of the detonation. Seeing there are no materials out that can resist constant detontation, you stop your car if you here pings. But that is why we tune are cars with wideband 02 sensors (the Autometer A/F are useless) but that is a hole other thing.

C part II) what do you mean by waste more gas? gas as in exhaust? i thnk you mean fuel. The s/c places MUCH MUCH less heat into the intake charge, but requires HP to drive it. then again, turbos create backpressure with also loses power. either way you have to make a sacrifice. Most S/C systems are not worth the time unless situations do not allow for a good turbo system to be utilized. THe BBM lysholm s/c ( www.bahnbrenner.com (http://www.bahnbrenner.com) ) is the only one i would ever use, but it is owned by BBM which makes only Audi and VW kits. IE get one from them and do everything yourself. but it can go 200,000 or more without any mainteince. The s/c vs. turbocharger is a BIG BIG debate. Google that and you can read for hours.

posted by  Low Impedance

Supra TT was sequential also but you could put both into twin mode if you wanted...

posted by  NISSANSPDR

A: What I dont understand is WHY the pressure will DECREASE as the atmospheric air go into the intake system then to the manifold then to the cylinder. What causes it to decrease? SO pretty much heat causes it?I know that when the piston moves DOWN from the intake stroke, there is a low pressure area in the cyliinder so it sucks in the higher pressure from the atmospehric air. I guessing this is why the the pressure will decrease as the air moves in the air filter to the pipe past the throttle body and into the manifold but im NOT SURE.
IM TALKING ABOUT N/A ENGINES FOR THE PARAGRAF ON TOP NOT BOOST.
I also thought that when the engine is at idle, the throttle plates are completly close so the air bypasses the plates? Can you explain to me what happens when the engine is at idle with your foot of the pedel.

B: ?Detonation occures cuz the a/f ratio is lean WHITCH MEANS the cylinders chamber will be hoter so after the next stroke the fuel will ignite it self cuz of the heat?
IS THIS TRUE: when the air/fuel ratio is 14.7:1 then there will be no air and no fuel left at the end of the combustion? So if you lean the mixture say to 15:1 then there WILL BE extra oxygen after the combustion so the cylinders will heat up and cause detonation?

posted by  CarEXPERT

"The s/c places MUCH MUCH less heat into the intake charge, but requires HP to drive it"
Isnt this just because turbos make more compression which means more air pressure? If both the boost pressure of the turbo and s/c are the same wouldnt the both of them create the same heat when they are both compressed? Is one of the way the turbo air gets hot because of the exhaust gasses running thorough the turbo? The ROOTS supercharger makes the most heat out of all the superchargers but WHY DO YOU SAY the s/c makes less heat?

Is it true that s/c makes LESS boost than turbos? I think turbos can go up to 30s PSI but s/cs cant. With a s/c (roots or twin screw NOT centifugal) does in a s/c installation the intake manifold is replaced with the s/c?
With 6-8psi boost, the air pressure in the cylinders will be the same as atmosphric pressure or a little more right?

If the s/c is driven by the crank pulley, at idle wouldnt it still make boost which means s/cs waste more fuel?

IS THIS TRUE: Is it posible to run a engine with no exhaust manifold or pipes, which means the gasses will just go out of the atmosphere? But is it true that haveing a exhaust manifold and pipes under your car will create a low pressure there so the gasses will be sucked to the pipes when the piston is going up on the exhaust stroke?

With a turbo isnt it easier to adjust boost when you want to cause you have a boost controller while a s/c can only adjust boost if you get a smaller, or bigger pulley.

posted by  CarEXPERT

A: Coolant for turbo is for shutdown; the oil is the normal cooling medium. Coolant in TB is used two ways and not necessarily in combination = a) to deice the throttle plate contact surface b) to regulate a wax element for an air port.

B) With the right boost controller and solenoids you can dynamically adjust the boost levels within the constraints of the turbocharger performance. The negative pressures are the vacuum region that usually occur on low load (part throttle) condition.

C)Running lean within a small band of stoich will generally lead to hotter combustion temps and lower EGT. There comes a point where there is insufficient fuel to sustain high temperatures. Det and preignition do like lean conditions to breed. A supercharger is less efficient in terms of fuel consumption for a constant boost.

posted by  Wally

[QUOTE=Wally] The negative pressures are the vacuum region that usually occur on low load (part throttle) condition.

I dont get what you mean Wally.
I asked why there is a negative psi pressure on the PSI GAUGE. Like when you shift gears the needle go all the way down to negative. How can you have a NEGATIVE pressure? Where do they measure the pressure at witch the PSI GAUGE, in the manifold or cylinders or turbo outlet?
If it was the valcuum whcih makes the pressure low, it still cant make the pressure negative right?

posted by  CarEXPERT

OK you want to pedantic and I have been told off by other members for being so and that I must not try talking in tongues.

The gauge, in fact, reads in PSIG. The "G" stands for gauge and is interpreted to mean the pressure in relation to atmospheric pressure. As usual the auto industry doesn't tend to include the G on the faceplate. If you were reading in absolute pressure your gauge would be calibrated to read approx. 14.69 PSI where the "0" currently is.

When you read the pressure at the manifold you are actually measuring the static pressure drop of the air (in relation to atmospheric pressure) as it travels to the cylinders via the intake piping, choke plates, bends etc. This is a novel concept to many, but you must think in terms of air actually being forced into the cylinders, on the "suction" stroke, by atmospheric pressure; a vacuum is created by the piston displacement.

posted by  Wally

Wally you are really hard to understand.
Are you saying that the PSI gauge is measured at the intake manifold?
So if the PSI gauge needle goes to 10psi, then is the turbo compression outlet making 24.7psi or what??

posted by  CarEXPERT

I am not hard to understand if you did some homework. If I keep the bar where I have it you will be certain to reach it one day and wonder why I was not more technical.

If you are measuring at the plenum your gauge will be measuring slightly lower than the outlet pressure of the turbo. If you have an intercooler the reading may be 2 psi lower again, BUT the pressure drop is highly dependent on your flow and fitting losses. You can measure where the wasteate control port is if you like, but it isn't telling you what the pressure in the plenum is.

I don't know why you are being so specific about the pressures?

Your next question is where to measure for boost control and BOV?

posted by  Wally

Well for starters I'd like to say CarExpert you should deffinately take a basic physics class. It would probably explain most of the stuff my friend Low Impedance has said and maybe if your up for it, take an automotive class. If anything get an automotive textbook from your local vocational school. I'm not trying to be mean here but this is all very basic material that anyone who performs any forced induction tuning on their car should know.

As for your questions on throttle plates the throttle plats are either bypassed with: a bypass air vlave, a hole in the throttle plate, or even sometimes there is a little screw that stops the throttle plate form closing completely. On the newer vehicles there is a motor on the throttle body that opens and closes the throttle body for the idle. Even newer there is drive-by-wire which has no linkage to the actual throttle body, all done with motors and sensors.

posted by  High Impedance

umm....no. yeah the oil does take heat away while it lubes the bearing but the real cooling comes from the water going through the water jacket. Why do you think the oil only turbos from days since past only last 20K miles?

posted by  Low Impedance

Wow, this threads frickin sweet! :laughing:

posted by  Zalight

no. it is because the s/c is not powered by exhaust gases. the turbocharger has heat penetrate to the compressor side of the turbo. That heat amount changes depending on what the peak efficency is and where you are in the rpm. s/c still make heat from moving parts but nowhere neat what a turbo creates. That is why s/c do not need a IC unless a air-water is desired. the intercooler helps to lower the charge temperature coming from the turbocharger. That heat can cause detonation.



well first the s/c will make the same amount of boost as a turbo. only i makes it in a constant increase. where as the turbo has a stepper rise. that is because the s/c will make boost lower in the rpm band. usually, right off idle. if the manifold is replaced, it is at the will of the kit maker. it is not required. if you have 8psi at the manifold, then yes pressure in the cyclinder will be higher than atmospheric. A s/c might produce boost at idle, the throttle plates are closed so it is not going to reach the cyclinder.



you must have some exhaust piping. you cant just expel the gases into the engine bay, BAD! exhaust temps are very hot, loud and hot. the exhaust gases are pushed out by the piston coming back up. and the turbo is easier to adjust boost level, but again there are considerations here. different methods to get the same job done.

posted by  Low Impedance

Has anyone ever thought about prochargers? I'm not too knowledgable on them but i konw a lot of domestics use them on their big engines

posted by  High Impedance

isnt that basically a supercharger though?

posted by  Low Impedance

I think you had better contact a manufacturer and pose that one. Trust me when I say the water jacket is not there for primary cooling. The bearings and seals that are in contact with the hot side are pretty much only cooled by the oil. The water jacket is there to provide convective cooling during the off cycle.

I seem to recall the Honeywell Garrett site has cooling water info, as I had someone question this a while ago.

As a side issue did you know in days past (when dinosaurs walked the earth) turbochargers ran on babbitt bearings and therefore the engine was "run on" to circulate oil for gradual cooling. Today we don't have babbitt metal bearings in turbochargers, but people still buy run on timers for their precious turbo.

posted by  Wally

i remember me and some of the other members once made a nice thread explaining all of this in very simple terms..... cant seem to find it.



EDIT: finally found the damn thing.... or one of the threads....

http://www.car-forums.com/talk/showthread.php?t=4873&highlight=turbo

posted by  Inygknok

Um ppl alwaies say turbo " Kicks" in.. what does this mean.. does it mean the turbo doesnt start working till a high RPM when it spools up? can anyone explain to me briefly of how this works..and if it kicks in does it mean the extra HP the turbo gives is not permanent and is only given wen it kicks in?

posted by  vuhuynh109

must resist getting technical . I would guess the term "kicks in" is to describe the sudden acceleration the driver feels when the compressed air finally reaches a point where it's mass exceeds normal aspiration rates. Being essentially a mixed flow fan the pressure/volume increases fairly rapidly once effective pumping starts.

posted by  Wally

Do s/c cost more or turbos? assumimg they give the same power

How do you make the boost pressure go up in a s/c. I know you have to get a pulley but do you get a pulley that underdrives the s/c? So the s/c pulley cicle thing will be smaller?

Does turbo give you lag when you switch gears?

When you are idling and you fllor the throttle does the boost start to work when a certain RPM is at or time? Does lag depend on RPM or time?
Cuz if you are at a stop can you rev the RPM to get the turbo spinning and then launch?

posted by  CarEXPERT

depends on the make and style of the turbo or s/c. they can be cheaper, similiar or more expensive.



if you use a set size for the main pulley, then the smaller the pulley on the s/c, the more boost that will be produced. if the diamemeter of the main pulley changes, this will affect the total boost. A small main will make less boost than a larger one, given the same size pulley on the s/c.


dpends on what rpms you find yourself in after shifting. there will still be a throttle response time as the intake (turbo out, through ic, into manifold) rebulds pressure after the BOV releases, but this is minute.



you can build boost by reving but the exhaust gases will not have the same energy as if the car was under load (ie moving) The amount varies by car and the exacting turbo setup. a s/c will make a set boost at a set rpm because only the rom of the s/c pulley matters. The lag is measured in seconds but, it relative to the rpm. meaning that say at 2000 rpms, you will have no boost building, but if you accelerate from idle to 4K rpms, you should starting building boost. the time it takes from idle to the rise in pressure above atmosphereic (boost) is the lag time. Not sure on that last question. never tried but ideally your traction would be better if you were not making power from the turbo until you started moving. boost = wheelspin if not handeled correctly.

posted by  Low Impedance

Just to clarify the boost rpm thing: an engine in a stationary car reving at 4000 rpm will be choked off more and with less volumetric efficiency than a car under load at the same revs. The mass exhaust flow and pressure will be a lot less in the stationary car.

posted by  Wally

a side note on turbo lag. the lag is actually determined on how well everything is set up, type of engine being used (bigger engines obviously can push better than smaller engines), etc. etc.

now.... smaller turbos generally produce less lag. in fact, if im correct, SAAB now produces wat they call "light pressure" turbos. SAAB claims that they either produce EXTREMELY little lag, or even no lag at all (havent heard any evidence on this to prove the "no lag" theory, but i do believe them in the almost no lag theory).

posted by  Inygknok

yeah but they reach their efficeny very low. unless they are trying to do something VATN in nature. Many people would find the preformance of a small turbo very dissapointing unless you want low speed pickup. Then there is always the heat increase after going beyond the efficency point.

posted by  Low Impedance

There is also a ball bearing turbo which has less friction cuz it replaces the thrust barings.
Anyone heard of a turbo that is at the back, underneith the car near the tailpipe? That is supoost to give you way more cold air and if you dont have room in the engine bay than you can turbo it and the turbo will not be in the engine bay but the back of the car.

When your reving your engine at a RPM and drive at a RPM wouldnt it be the same exhaust power? Doesnt RPM on the tach mean the crankshaft revolution? On an idle in neutral air and fuel is still going in right and making the same power? When you rev it in neutral why will it be less volumetic efficiency than with load? Isnt the throttle body opening the same when your in gear and in neutral?

posted by  CarEXPERT

When your reving your engine at a RPM and drive at a RPM wouldnt it be the same exhaust power? No

Doesnt RPM on the tach mean the crankshaft revolution? It means number of crank revolutions (rotations) per minute

On an idle in neutral air and fuel is still going in right and making the same power? Not sure what you are asking, but an engine without load will obviously use less fuel than one under load at the same rpm.

When you rev it in neutral why will it be less volumetic efficiency than with load? I thought I already answered this simply. The intake air velocities, exhaust gas velocities, cam overlap, etc are not running at optimal levels. To understand these would take you to another level of proficiency, if you are indeed a beginner.

Isnt the throttle body opening the same when your in gear and in neutral? No, think about taking a car up a hill and what you have to do with the throttle to maintain revs

posted by  Wally

the thing about those setups are the exhaust gases reaching the turbine will lose alot of the energy needed to drive the turbo. The heat is lost on the way to the turbo, meaning alot of energy is also lost. Also, all of the extra piping means that the responsiveness of the turbo will suffer. They say you dont need an IC but that is mostly BS. The piping will not provide enough contact to get the air particales to cool down like an IC will. They are supposed to work but i dont like the idea of the turbo charger being exposed like that. Would not survive the weather or the roads in Ohio.

posted by  Low Impedance

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