Author Topic: Turbo Tech  (Read 6928 times)

Sentry

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Turbo Tech
« on: July 05, 2011, 09:26:27 PM »
Hey folks I'm gonna be doing a couple tech writeups in this forum about turbocharging. There's tons of topics to cover, but to start I'm going to explain what a turbo is, how it works, and what the parts of it are called and do. Some articles will be short, but in depth, tidbits on particulars of a turbo setup. Others will be longer such as this one.







An introduction, and some technical terms

So. This here's a turbocharger. It is a centrifugal compressor driven by a turbine on a common shaft that receives energy from hot expanding exhaust gases from the engine. It's not just volume and velocity, but also heat energy. A turbo will not spool if the engine has no load on it and is not generating heat energy, like if it is in neutral and free revving. Quicker spool times can be had from things that insulate the turbine and keep heat in, instead of radiating into your engine bay. It looks so peaceful sitting stationary, but being a perfectly balanced rotating assembly, can easily reach mind boggling speeds in excess of a hundred thousand RPM at relatively pedestrian boost levels on pump gas.



Let's take a look inside shall we?



The square flange on the turbine housing (A) is the turbine housing inlet and bolts to the exhaust manifold. Exhaust gas from your engine enters here, goes through the snail scroll of the turbine housing, and imparts force on the turbine wheel (B), thus spinning the fuck out of it. Exhaust gas exits the turbine housing at its outlet, in the case of this turbo, that nice round v band flange. The turbine wheel is attached to the compressor wheel (D) by a shaft that runs through the center housing (C). Inside this center housing is bearings and oil seals. Pressurized oil is pumped through the center housing to keep the bearings alive, and exits by gravity drain into the oil pan. All turbos have oil passages in the center housing. Some turbos also have a water jacket in there for additional cooling. The center housing, shaft, and turbine and compressor wheels are referred to together as the center housing/rotating assembly, abbreviated CHRA. The compressor wheel, now being spun like fuck by the turbine, takes "bites" out of the air through the compressor housing (E) intake. The intake is at the front of the turbo and the discharge is out the side. The spinning motion "flings" the air out radially (hey centrifugal compressor! get it?) and out the compressor housing discharge. It commonly discharges into an intercooler, then into your engine's intake. When your intake is pressurized above atmospheric pressure, it is "boosted", and taking in more air every time intake valves open than it would at atmospheric pressure. More air + appropriate fuel for proper combustion = more power.

The more air flowing into the engine, the more exhaust energy there is to spool the turbine, and the turbo spools at a faster and faster rate exponentially from the continuing cycle until it reaches the set boost level and stops climbing. This is what gives that nice ramp-up in acceleration that sucks you back into your seat, instead of a naturally aspirated punch and then just acceleration at a constant ish rate.

But with all that energy why doesn't the turbine just spin out of control?

The wastegate. The wastegate is a valve that allows some exhaust gas to bypass the turbine when target boost is reached. One style is called an internal wastegate, and consists of a flapper valve that is situated inside the turbine housing and vents into the downpipe. Another style is an external wastegate and is a poppet valve attached to the manifold that vents either to atmosphere or is re routed back into the exhaust stream inside the downpipe. I will cover these in detail in a later article.

Internal wastegate



External wastegate



Here is a closer look at a turbine wheel and a compressor wheel. Notice they both have a major and minor diameter. On the compressor wheel the minor diameter is the inducer and the major diameter is the exducer. On the turbine wheel the major diameter is the inducer and the minor diameter is the exducer. The importance of wheel design will also be covered in a later article.

Turbine wheel



Compressor wheel



Here is a turbo glossary:

Turbine housing - Assembled onto the center housing. Receives exhaust gas from the engine and directs it into the turbine for conversion into motion

Turbine wheel - Spun by exhaust gases, transmits motion through the shaft to the compressor wheel

Center housing - Contains bearings and seals. The shaft inside is lubricated by oil and sometimes cooled by engine coolant

CHRA - Center housing/rotating assembly. The center housing, shaft, and turbine and compressor wheels all assembled together, minus the compressor and turbine housings

Compressor housing - The "snail" of the operation. Assembled onto the center housing. Directs air discharged by the spinning compressor wheel out a nozzle

Compressor wheel - Intakes air and compresses it to pressurize the engine's intake

Wastegate - Valve that regulates turbine speed by allowing some exhaust gas to bypass the turbine

Downpipe - The pipe that connects the turbine housing outlet to the rest of your exhaust

Dumptube - The pipe of an external wastegate that dumps to atmosphere

Oil feed line - Line that feeds pressurized oil to the bearings in the CHRA

Oil feed restrictor - Some ball bearing turbos require lower oil pressure, so a restrictor is used to prevent it from blowing seals

Oil drain line - Line that oil drains out of the turbo through and into the oil pan by gravity

Charge pipe - Pipe that carries compressed air from the compressor outlet to the engine intake. Hot side charge pipe is before an intercooler, cold side charge pipe is after an intercooler

Intercooler - A heat exchanger used to cool the compressed air being fed into the engine so that it is denser (more oxygen molecules per volume) and more resistant to detonation

Lean - A combustion mixture with too much air, and not enough fuel. Too lean a mixture will lead to detonation, which will lead to broken parts

Detonation - Pre ignition of the air-fuel charge, before the piston has reached TDC

Rich - A combustion mixture with too much fuel for the amount of air. Too rich a mixture and you are killing power. Way too rich a mixture and you can foul plugs, or even wipe out cylinder walls/pistons from washing the oil off with fuel

Blow off valve - A valve that vents boost to atmosphere when the engine goes into vacuum from the throttle blade snapping shut. Used to prevent compressor surge during the moment you let off

Compressor surge - A condition when the compressor is bumping what is known as the "surge line" of a compressor map. This occurs when the compressor is outputting too much air for the engine to swallow, either due to a small displacement engine or from a throttle being shut. The air backs up and the compressor is fighting to pack air into something that is already "full". Compressor surge from shutting the throttle is only momentary. Compressor surge on load, in boost, (too big a compressor for a small engine) is very hard on the turbo and can destroy a number of things

Compressor map - A graph of a particular turbo's efficiency, shaft speed, and the volume of air (in cfm or lb/min) that it can flow at certain boost pressures

A/R - Effectively, the "size" of a housing, within its family of housings (T25, T3, etc) expressed as a ratio. I will go into further detail on this one later, but for now this will do. A larger turbine housing will spool later but offer a better top end, a smaller turbine housing will spool faster but choke out the top end

Trim - (Compressor inducer ^2 / Compressor exducer ^2) x 100. A number people like to throw around that gives a good general idea of what kind of power the compressor wheel can make
« Last Edit: July 15, 2011, 10:24:56 PM by Sentry »

92 Aristo - Borg S366, QSV, AEM V2, 12 psi - 410whp 360ftlbs
84 SVO - FMIC, straight piped, chipped/tuned LB3, 15 psi - 202whp 238ftlbs

Sentry

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Re: Turbo Tech
« Reply #1 on: July 15, 2011, 11:39:21 PM »
Wastegates



Back in the early days of turbocharging, boost pressure was limited by restricting flow through the turbine by using a small exhaust size to achieve the target boost. This of course was terrible for performance since the more air you flow, the more the tiny exhaust became a restriction. This meant slow spooling and shitty top end performance.

Once turbos started appearing on race cars and performance production cars in the 70s, wastegates came into play. A wastegate is a valve that allows exhaust gas to bypass the turbine and regulate turbine speed and therefore, compressor speed. This allowed it to spool right up to the target boost, then crack open to maintain that boost pressure right up to redline.

Wastegates are most commonly actuated by a diaphragm actuator. On one side of the diaphragm is atmospheric pressure, and on the other side a boost signal is fed in through a nipple via vacuum line. Spring pressure and atmospheric pressure hold the diaphragm in place, boost pressure works against the diaphragm to open the wastegate. Some wastegates on newer cars are actuated electronically by the car's ECU. Variable nozzle turbos do not have wastegates, since the vanes can be actuated to control boost.

An internal wastegate is a swing valve that covers a port in the turbine housing. The valve is opened and closed by an actuator bolted to the turbo. The benefit being that it is incorporated into the turbo in one nice little package, and are generally cheaper to manufacture and also buy. There is also less fabrication to be done since they vent straight into the car's regular exhaust, and are quieter for the same reason. While they are technically inferior to a good external wastegate, they get the job done, and they're all I've ever used. These aren't ideal on larger engines, unless you're talking twin turbos, because a single internal wastegate can't flow enough and a boost creep situation can be created.



An external wastegate is a poppet valve that covers a port in the exhaust manifold. This valve is opened and closed by a diaphragm actuator that is built into the assembly. The exhaust gas vented by this style wastegate can either be re routed back into the car's exhaust system to be muffled or dumped to atmosphere. Whenever your car is at full boost, the wastegate is venting, and with an open dump it can be LOUD. This can get annoying to daily drive and attracts unwanted attention from the po po, however it is the best option for performance vs re routed external and regular internal setups.





Ideally you want to reach your target boost level (lets say 10 psi for these examples) as quickly as possible, and then have it hold steady all the way to redline. There are five situations where this won't go as planned.

Boost creep - Boost climbs to 10 psi, then begins climbing higher and higher as RPMs increase.
This occurs when the wastegate cannot vent enough exhaust gas to regulate turbine speed, and the turbo continues spooling uncontrolled. This can lead to engine or turbo destruction on stock parts, but aftermarket parts can usually withstand spinning a little faster and running a little leaner. The solution is to increase the amount of gas the wastegate can flow, either by upgrading to a larger size or enlarging the existing port. Another cause is poor placement of the wastegate in an external gate setup. Venting exhaust from only one manifold runner may not be enough to regulate turbine speed versus venting from all of them.




Boost sag - Boost climbs to 10 psi, then begins dropping as RPMs increase.
Either the turbine housing is too small and choking out the engine at high RPMs causing boost to taper off, or the boost signal used for actuating the wastegate is not accurate to the boost the engine is actually receiving in the intake manifold. Commonly, boost reference is taken from the compressor housing. This is poor practice, since it does not account for pressure drop across the intercooler which becomes greater as flow increases. Boost reference line should be run from the charge pipe, after the intercooler, but before the throttle body. If the case is that the turbine housing is choking out the engine, the only solution is to change to a turbo with a larger housing. A restrictive exhaust would also cause this, but going larger would easily remedy the problem.

Boost fluctuation - Boost will fluctuate up and down and not hold a constant pressure.
Can be cause by not enough preload on the flapper of an internal wastegate.

Boost spike - The turbo spools past the target boost by a couple psi, then settles back down to it.
Often goes hand in hand with boost sag due to OEMs using tiny assed turbine housings on factory turbocharged vehicles in an effort to reduce "lag" and sell more cars. As in, the boost will spike above, then sag below the target. The other cause can be the boost controller you are using. Cheap boost controllers will spike, ones with a little R&D in them rarely do.

Excessive lag - The turbo is extremely slow spooling and not responsive enough.
Common causes of this are exhaust leaks pre-turbo, an exhaust leak past the wastegate valve, or a large boost leak. If the system is 100% leak free, then chances are the turbine housing is just too large for that size of engine to spool a turbine quickly through.

92 Aristo - Borg S366, QSV, AEM V2, 12 psi - 410whp 360ftlbs
84 SVO - FMIC, straight piped, chipped/tuned LB3, 15 psi - 202whp 238ftlbs

James

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Re: Turbo Tech
« Reply #2 on: September 07, 2011, 03:25:09 PM »
Make a few suggestions for corrections here.

This can get annoying to daily drive and attracts unwanted attention from the po po, however it is the best option for performance vs re routed external and regular internal setups.

Best performance setup is actually routing back into the downpipe.  Properly setup, the scavenging will have the wastegate performing like a larger unit and will have a scaling effect.

Commonly, boost reference is taken from the compressor housing. This is poor practice, since it does not account for pressure drop across the intercooler which becomes greater as flow increases. Boost reference line should be run from the charge pipe, after the intercooler, but before the throttle body.

Actually this is not correct.  If using any type of bleed-air referenced boost controller you want the service line where it will see changes in boost as quickly as possible.  This is because the differential between the compressor and actual manifold pressure is what is important for tuning purposes and setting up the controller.  The compressor housing is also the source for the strongest and most reliable pressure reading for the boost-controller to use.  Personally I wouldn't run a bleed-air setup on anything I would consider for street/strip purposes and run a regulated compressed CO2 or nitrous bottle.
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Sentry

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Re: Turbo Tech
« Reply #3 on: September 07, 2011, 08:33:27 PM »
Best performance setup is actually routing back into the downpipe.  Properly setup, the scavenging will have the wastegate performing like a larger unit and will have a scaling effect.
I've only ever seen evidence to the contrary. Maybe people manufactured the evidence as an excuse to be lazy and run open dumps. I like quietness so I've always had an internally gated turbo, and I can get away with it on such a small engine.

As for the boost reference, maybe it's a matter of preference, but I like my wastegate controlling the amount of boost the engine will see and not the amount of boost at the compressor housing.

92 Aristo - Borg S366, QSV, AEM V2, 12 psi - 410whp 360ftlbs
84 SVO - FMIC, straight piped, chipped/tuned LB3, 15 psi - 202whp 238ftlbs

Onyx Dragon

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Re: Turbo Tech
« Reply #4 on: September 08, 2011, 12:08:19 AM »
I've only ever seen evidence to the contrary. Maybe people manufactured the evidence as an excuse to be lazy and run open dumps. I like quietness so I've always had an internally gated turbo, and I can get away with it on such a small engine.

As for the boost reference, maybe it's a matter of preference, but I like my wastegate controlling the amount of boost the engine will see and not the amount of boost at the compressor housing.

Wouldn't it be better to know what boost the engine is going to see anyway?  If you're not getting the same boost at the engine that you are seeing at the compressor housing, then you could be under boosting, correct?

Sentry

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Re: Turbo Tech
« Reply #5 on: September 08, 2011, 12:58:49 AM »
I don't understand what you're getting at.

The difference between what the engine sees and what's at the compressor housing is just pressure drop, mostly from the intercooler.

92 Aristo - Borg S366, QSV, AEM V2, 12 psi - 410whp 360ftlbs
84 SVO - FMIC, straight piped, chipped/tuned LB3, 15 psi - 202whp 238ftlbs

James

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Re: Turbo Tech
« Reply #6 on: September 08, 2011, 01:04:06 AM »
I've only ever seen evidence to the contrary. Maybe people manufactured the evidence as an excuse to be lazy and run open dumps. I like quietness so I've always had an internally gated turbo, and I can get away with it on such a small engine.

I've seen the results on small block and big block turbo setups in the extreme street classes in this region. 

As for the boost reference, maybe it's a matter of preference, but I like my wastegate controlling the amount of boost the engine will see and not the amount of boost at the compressor housing.

Engine doesn't see that figure at either location.  Only reason to even pull a reference between the IC and TB is to check for a leak or see if the IC needs upgrading.  Would also create a situation where the controller would see a false surge when the TB was suddenly closed if the reference is after the BOV.   This is about a differential and the only number that truly matters in the one inside the manifold after the TB.  If you have 10 psi at the compressor, 9 psi after the intercooler, and 7 psi in the intake at part throttle which two numbers do you take into account?  The engine is only seeing 7 psi so it can care less what the other two numbers are.  The turbo is seeing the 10 psi it cares about.  When you are trying to control something you start at the source.  If you want more fuel pressure at the rail do you start with the filter or the pump?  Good boost controllers can keep you within 0.5 psi of target.  Great ones can keep you within 0.1 psi.  To do that they need a source that is strong and avoids variation due to BOV's, plumbing, and reversion at the intake manifold.
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Sentry

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Re: Turbo Tech
« Reply #7 on: September 08, 2011, 01:14:41 AM »
Who cares about part throttle? At WOT the biggest restriction is the IC. The more you push through it, the more it restricts and as a result the boost tapers off in the top end. Taking the wastegate reference by my method, it stays steady. Talking about manual/bleeder style only.

92 Aristo - Borg S366, QSV, AEM V2, 12 psi - 410whp 360ftlbs
84 SVO - FMIC, straight piped, chipped/tuned LB3, 15 psi - 202whp 238ftlbs

James

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Re: Turbo Tech
« Reply #8 on: September 08, 2011, 02:29:54 AM »
Who cares about part throttle?

Pretty much anybody who's had to tune a turbo car that wants to get the most out of it and the money invested. 

At WOT the biggest restriction is the IC. The more you push through it, the more it restricts and as a result the boost tapers off in the top end. Taking the wastegate reference by my method, it stays steady. Talking about manual/bleeder style only.

Yours is an odd case because in my experience the TB or MAF are the largest intake restrictions.  Anyway, if strictly speaking MBC's then in your case the source location doesn't matter since that is a passive system anyway. But for the sake of making a Tech thread it should be noted that that the compressor housing is a better choice at least when dealing with EBC's.  I know HKS and AMS specifically state using a port in the compressor housing.
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Sentry

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Re: Turbo Tech
« Reply #9 on: September 08, 2011, 02:49:49 AM »
MAF?

Speed density fo lyfe

92 Aristo - Borg S366, QSV, AEM V2, 12 psi - 410whp 360ftlbs
84 SVO - FMIC, straight piped, chipped/tuned LB3, 15 psi - 202whp 238ftlbs

quantum

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Re: Turbo Tech
« Reply #10 on: September 08, 2011, 01:21:08 PM »
Wastegates



Back in the early days of turbocharging, boost pressure was limited by restricting flow through the turbine by using a small exhaust size to achieve the target boost. This of course was terrible for performance since the more air you flow, the more the tiny exhaust became a restriction. This meant slow spooling and shitty top end performance.

Once turbos started appearing on race cars and performance production cars in the 70s, wastegates came into play. A wastegate is a valve that allows exhaust gas to bypass the turbine and regulate turbine speed and therefore, compressor speed. This allowed it to spool right up to the target boost, then crack open to maintain that boost pressure right up to redline.



Just a small correction on the history...Olds used a integral wastegate on their turbo motor for the 62-63 model years.

Sentry

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Re: Turbo Tech
« Reply #11 on: September 08, 2011, 07:47:39 PM »
It's a tech article not a history lesson. :)

92 Aristo - Borg S366, QSV, AEM V2, 12 psi - 410whp 360ftlbs
84 SVO - FMIC, straight piped, chipped/tuned LB3, 15 psi - 202whp 238ftlbs

Scotty

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Re: Turbo Tech
« Reply #12 on: November 01, 2011, 10:31:53 PM »
Will turbocharging a stock car cause a CEL?
Please, please, please, let me get what I want. Lord knows it would be the first time.
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Sentry

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Re: Turbo Tech
« Reply #13 on: November 01, 2011, 11:06:31 PM »
The car doesn't "know" it's there, but if it's OBD 2 it may set MAF or MAP codes the instant it sees positive pressure or increased airflow.

If you just bolt a turbo onto a vehicle and have no way to add fuel or control timing, a light is the least of your worries. :)

92 Aristo - Borg S366, QSV, AEM V2, 12 psi - 410whp 360ftlbs
84 SVO - FMIC, straight piped, chipped/tuned LB3, 15 psi - 202whp 238ftlbs

Scotty

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Re: Turbo Tech
« Reply #14 on: November 02, 2011, 12:07:48 AM »
The car doesn't "know" it's there, but if it's OBD 2 it may set MAF or MAP codes the instant it sees positive pressure or increased airflow.

If you just bolt a turbo onto a vehicle and have no way to add fuel or control timing, a light is the least of your worries. :)

Well, yeah, was just a little debate I was having with a friend.  A tune should take care of all of that though, right?
Please, please, please, let me get what I want. Lord knows it would be the first time.
Quote from: sponty
I have no taste and blow dogs for quarters.
"in the depths were old ones lie, perhaps death itself may one day die"

Sentry

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Re: Turbo Tech
« Reply #15 on: November 02, 2011, 12:12:35 AM »
Some ECUs are not tunable. With them, your options are piggyback, or standalone.

Piggybacks can work alright but come with inherent issues, and most cannot control timing. I would say they're good for very mild setups.

Standalones of course are awesome but run anywhere from a grand to a couple grand. I don't count the "DIY" standalones like megasquirt because they are mostly junk.

92 Aristo - Borg S366, QSV, AEM V2, 12 psi - 410whp 360ftlbs
84 SVO - FMIC, straight piped, chipped/tuned LB3, 15 psi - 202whp 238ftlbs

Scotty

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Re: Turbo Tech
« Reply #16 on: November 02, 2011, 12:26:21 AM »
Car is a 2002 RSX, I assume one would have to go with a stand-alone like Hondata?
Please, please, please, let me get what I want. Lord knows it would be the first time.
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I have no taste and blow dogs for quarters.
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Sentry

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Re: Turbo Tech
« Reply #17 on: November 02, 2011, 12:27:30 AM »
K pro.

92 Aristo - Borg S366, QSV, AEM V2, 12 psi - 410whp 360ftlbs
84 SVO - FMIC, straight piped, chipped/tuned LB3, 15 psi - 202whp 238ftlbs

James

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Re: Turbo Tech
« Reply #18 on: November 05, 2011, 07:07:03 PM »
I don't count the "DIY" standalones like megasquirt because they are mostly junk.

Um, no.  In fact there are championship winning vehicles using some of those DIY standalones.  They are not junk as it's usually the user's fault 99.9% of the time.


SDS makes probably the simplest and most least expensive programmable standalone ECU and would be a good choice.
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Sentry

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Re: Turbo Tech
« Reply #19 on: November 05, 2011, 08:50:09 PM »
Installed and programmed by people who do it FOR A LIVING.

For a hobbyist I would never recommend a DIY EMS.

92 Aristo - Borg S366, QSV, AEM V2, 12 psi - 410whp 360ftlbs
84 SVO - FMIC, straight piped, chipped/tuned LB3, 15 psi - 202whp 238ftlbs

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Re: Turbo Tech
« Reply #20 on: November 06, 2011, 07:50:21 PM »
And I would recommend a DIY system to a hobbyist if that person has aptitude and wants to stick with it.  Simply a fact, EFI tuning is no longer a realm that is strictly for the "professionals".
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