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 Turbochargers design and related parts

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FaselZ71
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PostSubject: Turbochargers design and related parts   September 1st 2009, 12:50 pm

The wise consumer makes a better purchase than the ignorant one, so if you are seriously interested in turbo performance you at least need to know the fundamentals. This article is dedicated to the turbocharger, ultimately the most powerful of all forced induction systems. Here I will try to identify each part in the basic turbo system, what it does and why you need it. I’ll also try to keep this on the lighter end of the technical scale, but it’s hard not to get deep into it with this subject.


TURBOCHARGER BASICS


The turbocharger is one complex little piece of work, at least until you get familiar with it. Although a turbo obviously functions as a single piece, it is commonly broken into these three sections for easy conversation…

COMPRESSOR SECTION:

The compressor section is identical in function to any centrifugal supercharger, the only difference is that the turbine section of the turbo drives it. One thing to know is that turbocharger compressor sections are (generally) significantly smaller than their supercharger cousins. This all has to do with efficiency and the chosen method of powering the compressor, so just know it’s the reason why you see turbochargers spinning such high RPM when compared to their centrifugal supercharger cousins. It’s all about necessity.

TURBINE SECTION:

This section bears a strong resemblance to the compressor section for a reason; it basically functions the same but backwards. The two main parts are the turbine housing and turbine wheel, and if this is an internally wastegated turbo, the wastegate also resides here (there will be more on that later). As exhaust gasses quickly move out of the cylinder and into the exhaust manifold, they are routed into the turbine housing’s scroll. If you understood the flow of air through the centrifugal compressor design discussed earlier, here it’s just the opposite occurring. As the hot and rapidly moving gasses attempt to find an airflow path through the turbine housing (with the ever decreasing scroll area), they come in contact with the turbine wheel on their way to the center outlet of the housing. As they rush through this airflow path and into the exhaust downpipe, they spin the turbine wheel, imparting a portion of their kinetic energy to the turbocharger. Especially notice that with this design comes variable RPM, the turbocharger itself is not physically strapped to any rotating part of the engine. This makes many different turbo shaft speeds possible at a single engine RPM, which is where the system’s basic performance characteristics and tunability are born.

CENTER SECTION (aka bearing section):

The center section is definitely the most complex of the three portions. This is what connects both the compressor and turbine sections, and where all of the cooling and lubrication of the unit occurs. Inside the center section is the main shaft, which is what the compressor and turbine wheels are directly connected to. This main shaft undergoes a great deal of pressure, RPM and heat, so the center section is unsurprisingly very specifically engineered to deal with these. The most common and basic center sections use what’s called thrust bearings to keep the shaft spinning, and oil flow from the engine to both lubricate and cool the unit. Two common updates to this proven design are becoming more affordable and widespread; ball bearing center sections and water cooling in addition to oil. The ball bearing center is both more durable and more efficient at transmitting power to the compressor wheel, making it better for performance and longetivity. The water cooling is more for reliability than anything else, helping to stabilize temperatures and prevent oil coking in the housing. Both are worthwhile additions to your turbo purchase if at all possible.



TURBO KIT BASICS


Although I say “basic” here, know that this is pretty much an oxymoron when dealing with turbos. There is nothing basic about a turbo system, as many different things concerning engine operation need to be addressed. The basic turbo system should come with a bunch of different things, and few systems effectively address all these unless your car was originally equipped with the system. Here they are, in no particular order (with the little things like vacuum line omitted), and notice I left out engine management from the list, because I want to deal with that separately:

1- turbo
2- exhaust manifold for turbo
3- wastegate
4- blow-off valve (aka bypass valve)
5- lines for oil supply and return
6- intercooler (optional)


TURBOCHARGER:

We’ve already gone through the basic explanation, but one more thing bears mention here. Ever hear the T25, T3/T4, T04e turbo designations? Well, these refer to the size and basic flow potential of the turbocharger. Garret and other manufacturers created turbo families, ones in which all members prescribed to certain physical characteristics. A T3 compressor section is one that prescribes to a specific characteristic set, such as overall size and design features. Generally speaking, larger numbers and higher letters mean a larger (and sometimes newer) family of turbos, meaning a potential increase in flow ability, power production and possibly even efficiency. The T3/T4 designation is an example of a hybrid turbo; one where a T3 turbine section has been mated to a T4 compressor section. This popular hybrid attempts to combine the excellent low RPM spool characteristics of the smaller T3 class turbo with the big flow potential of a sizable T4 compressor. Really it’s a “best of both worlds” attempt, which seems to be very successful on smaller displacement, high RPM engines. Now there are a few other considerations to turbo sizing, such as A/R ratio and wheel trim, but I won’t go into those unless someone really needs to know everything. The point here is simply to get a basic feel for turbo function and sizing, as the experts who designed the turbo kit or upgrade likely have already made an excellent choice in turbo size for your specific application.

TURBO EXHAUST MANIFOLD:

In order to mount the turbo to the engine, the first step is to route exhaust gasses through it. This is where the special manifold comes in, dumping exhaust gasses directly into the turbine housing (provisions for mounting an external wastegate should also be found here). Usually these are fairly crude looking log style cast iron manifolds, instead of the nicely shaped and finished stainless steel header piping. But there’s good reason that virtually every car to come off the production lines with a turbo follows this example: it works. Turbos build up a tremendous amount of heat and pressure in the initial part of the exhaust system, and the thick cast iron manifolds are perfectly suited to reliable performance in this environment. Also, space considerations often prohibit the use of nicely tuned tubular exhaust primaries, so there’s little reason to go to the expense of crafting them. The point here is this: there are possibly some finely crafted tubular manifolds available for your application if you want maximum performance and don’t mind the extra money, but these are largely unnecessary for a typical street setup. Ugly cast iron manifolds are routinely found on 400-500hp cars.

WASTEGATE:

In the most basic of terms, a turbo system is self-feeding. That is, as the system creates more boost, it also creates more exhaust flow. This exhaust flow is what powers the turbocharger, so if left unchecked the turbo system will quickly spiral out of control. Now it takes time and a specific amount exhaust flow to start creating boost, but once this point is reached (called boost threshold), either exhaust flow to the turbine is regulated, or the system keeps building pressure until something gives, usually a hard part in the engine. Which is where the wastegate comes in.


Controlled by vacuum signal from the manifold (or more correctly, positive pressure in the manifold), the wastegate’s job is to re-route exhaust flow around the turbine wheel to control boost levels. Remember, the turbo creates boost by extracting energy from exhaust gas flow, so this is the prime location to regulate turbocharger RPM, and therefore boost levels. What a wastegate does is provide an alternate path for exhaust gasses to flow through that doesn’t cause them to contact the turbine wheel. This prevents the exhaust gasses from contributing to boost production, thus regulating boost to preset levels.


There are also two main types of wastegates, internal & external. Both are there to perform the same task, the only difference is location and effectiveness. Internal wastegates are located inside the turbine housing itself, and although effective at re-routing exhaust gasses around the turbine wheel, they can impart a good bit of turbulence to the exhaust flow path. This increases exhaust system pressure and hurts performance. The external wastegate, the true performance choice, has provisions made for it’s mounting before the turbo on the exhaust manifold. An entirely alternate flow path is created where exhaust gasses skip going through the turbine housing altogether, contributing much less to turbulence in the system. They also tend to be more accurate at controlling exhaust flow and turbo boost; combine these two attributes and you have a recipe for superior performance.

BLOW-OFF VALVE:

This is both the insurance policy of the turbo system, and it’s protector. Two things are governed by the blow-off valve; maximum boost levels and pressure spikes in the intake tract. While the first job is primarily handled by the wastegate, in the event of a big enough overboost, the blow-off valve will vent excess pressures to help maintain safe levels of boost. Basically, the blow-off valve is a springloaded poppet valve contraption that will bleed off and excess pressure that builds up in the intake system. This can occur due to either boost creep or a sudden closing of the throttle body when boosting (such as during full throttle, high RPM shifts), but either way it’s the blow-off valve’s job to prevent pressure spikes in the intake tract. This serves two functions: one, to prevent serious engine damaging overboosts, and two, to prevent airflow from reversing direction into the turbocharger itself. The second one is it’s principle job, to keep the intake tract from building up large pressures during sudden lift throttle situations (such as shifting). When the engine is at full boost and full song, the turbo is spinning madly to supply air to the intake system. The momentum of air and turbocharger are not easily stopped on a dime, so when the throttle body is suddenly slam shut, things tend to get interesting in the intake system. There is an immediate pressure spike between the turbo and throttle body, putting great stress on the compressor wheel which is still trying to pump air into a closed system. To keep the turbo’s RPM up and the pressures in the intake tract down, the blow-off valve vents this excess pressure for maximum performance and reliability.

INTERCOOLER:

This is the most important performance part you can add to a forced induction system, and is well worth its price if boost numbers rise beyond 8 psi. Compression equals heat, and blowing hot air into the engine is neither efficient or reliable. An 8 psi forced induction system can produce air inlet temps over 200 degrees farenheit, making the engine a detonation machine. The greater amount of space between the air molecules also lowers charge air density, meaning the 8 psi of air isn’t as potent as it could be. The solution lies in cooling the air charge before it enters the engine, and that’s precisely what the intercooler does. Two types of these are in production, air-to-air and air-to-water intercoolers. Air to air intercoolers are inexpensive and easy to maintain, but they can be very large and must be in a good airflow path to be effective. They are also rarely over 80% efficient, meaning the charge temps only get to within 80% of ambient during engine operation. Air to water systems are more compact but also more complex, their biggest advantages lie in placement freedom and efficiency. An air to water intercooler does not need a supply of fresh air and can be well over 100% efficient (when filled with a cooler than ambient liquid), but they do need an external reservoir of coolant and some means to extract heat from that coolant. Traditionally, air to air units are preferred for simplicity, reliability and effectiveness in street cars, while the superior cooling and placement possibilities of air to water systems are most at home in drag vehicles (or ones that only see occasional boosting, where heat soak isn’t an issue). There are of course exceptions, and in fact the Jaguar XJR uses air to water intercoolers, but these are few and far between. At any rate, either system is universally a good thing if you plan on running even moderate levels of boost.

OIL SUPPLY:

A lot of people pass this part up when explaining a turbo system, and yet it’s one of the main things you will have to deal with on any turbo install. The turbo needs both a supply and return line, where the supply line is generally in the form of a sandwich adapter mounted between the oil filter and engine block. The return line is usually the pain in the butt, since the oil pan of the engine needs to be removed and fitted with provisions for this line to connect to. Some aftermarket oil pans have NPT bungs on them ready for this type of use; I highly recommend you think about buying one of these (which is always a good investment even without the turbo) if you are planning on a serious turbo buildup


Info courtesy of Automotive Techinal
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johnboggs21
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PostSubject: Re: Turbochargers design and related parts   October 21st 2009, 4:22 pm

Some more good info here. It has caused some gears to start turning in my brain lol!


Now just how hard would it be to custom make exhaust manifolds for a turbo......then I could use a powerstroke turbo on my truck which are a dime a dozen.............hmmm ideas, ideas.
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PostSubject: Re: Turbochargers design and related parts   October 22nd 2009, 10:09 am

Well now building a custom turbo header depends on how good your fabbed skills are because aren't turbos on fords up by the firewall? That would take quite abit of custom fab work!
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PostSubject: Re: Turbochargers design and related parts   October 22nd 2009, 10:30 am

Thats where they are stock, but if I'm custom making my turbo setup I reckon i could put it anywhere I want.
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PostSubject: Re: Turbochargers design and related parts   October 22nd 2009, 12:09 pm

Couldnt you just take a pair of manifolds off a Turbo'd 7.3L?

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PostSubject: Re: Turbochargers design and related parts   October 22nd 2009, 12:27 pm

HAHAHAHAHAHA!!!! Got to love when someone wants to go custom!!! Design yourself an STS turbo setup!!! It's a fairly easy setup no custom header no need for an intercooler unless you really want one but it's kind of pointless... It's gonna take a minute so sit back and enjoy the paragragh as I get one step close to carpotunnel in my hands and fingers from typing these long articals!!!



Ok so the term STS turbo setup comes from the company that designed the setup. Any turbo can be used for this setup. Now one an STS setup it takes the turbo from underneath the hood to another location of your choice on the exhaust system. This is done by first choosing the best place for the turbo then cutting the exhaust building a custom flange to mate with the turbo and the exhaust pipe you then mock the turbo and design a bracketry to hold the turbo in place. Next you need to setup an oil scavenging system to get oil to your turbo and back to you motor. STS sells the oil systems but they are pricey it's best to do the research and design your own as it will cost half the price. Probably the easiest system would be to tap into you oil filter pickup somewhere where the oil comes out and then run a steel braided line back to your turbo then buy a small scavenging pump and install that under you truck near your turbo then run a steel brided line back to you oil pan and drill and tap a hole in the oil pan. No need to worry about an oil cooler and the distance the oil has to travel and the steel braided oil lines help disapate the heat of the oil. Also the air intake can be mounted underneath your vehical or in the bed of your truck surrounded by a protective box to prevent damage. Then when plumbing the compressor lines along you frame for protection back under the hood to the intake. This is where there is no need for an intercooler because the distance the air has to travel cools the air. Now an intercooler can be used to help lower AIT's even futher however than you begin to go back into losing boost psi due to the resistance of the intercooler. Also the location of turbo under your vehical removes the turbo from under your hood and from being located so close to the motor. This makes the turbine run cooler because the air that is passing through the turbine is cooler and due to the fact that the air is cooler it is also more dense which ultimaly cooler denser air not only makes the turbo run cooler it also makes the turbo spool faster and reduce turbo lag. Unless the turbo has an internal wastegate the wastegate will have to be placed under the vehical if you decide to use and atmospheric blow off valve then that can be placed under the hood or under the vehical hawever if you chose you vent the blow off valve back into the intake system then the BOV will needed to be plumbed under the vehical near the turbo so it can be connected to the intake side of the turbo... However if your truck has a mass air flow sensor you may run into problems there and would have to research and disign a system to make the MAF usable. Also having the turbo so far away from the motor helps to reduce the noise and generates back pressure so the choice would be yours as too whether or not you wnated to retain your stock muffler. I know on vettes and camaros that have STS the turbos go in place of the muffler. So after the turbo has be mocked into place and all the nessasary compents like vacuum lines and boost control and oil and air lines have be put into place and the tailpipe leading out of the turbine has been mocked up it'll be time to finalize your installation button up loose ends and make sure everything is in check then it's time for a test drive!!!!


P.S. Now this isn't a simple process and I've only listed an introduction and simple install process now if your fabbing skills aren't up to par with this level of install I'd highly recommend a friend to help you out. But more than anything please do the research read anything and eveything you can even if it pointless posts on a message board from 3 years ago every little bit helps... And before you even grab a wrench please buy all the parts you need check double check and recheck again to make sure you have all the parts you need because I'd hate to see you half way thru the install and find out your missing a critical part or find out you bit off more then you could chew...


So I hope this helps you and I hope you enjoy reading it because I have fun typing these kinds of things keeps my info fresh in my mind so I don't forget things. Any other questions just ask.

You can get more info on the STS turbo setup at www.STSturbo.com
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PostSubject: Re: Turbochargers design and related parts   October 22nd 2009, 5:37 pm

A remote turbo has crossed my mind before. Im pretty good at fabriaction, but ive got a buddy thats real good with it if i get in trouble. lol

As for robbing heads off a turbo 7.3, the ones off a PSD wont work, and if I was gonna get em off a turboed IDI then id get the turbo and everything else I need.
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PostSubject: Re: Turbochargers design and related parts   October 23rd 2009, 12:03 pm

Not the heads, just the exhaust manifolds and crossover pipe. Those should bolt right on.

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PostSubject: Re: Turbochargers design and related parts   October 23rd 2009, 1:58 pm

Yeah I agree with merlin on this one... Wouldn't the exhaust manifolds of a turbocharged 7.3L bolt right on then you'd have everything you'd need right there... I'm no diesel guy but I'm pretty sure you wouldn't have to change the heads to fit new manifolds on would you... unless there's a signficant difference in the internal working of the TC'd heads.
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PostSubject: Re: Turbochargers design and related parts   October 23rd 2009, 4:33 pm

The heads themselves are different, but the manifold bolt pattern I believe is the same. Should be pretty easy to bolt on a turbo.

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PostSubject: Re: Turbochargers design and related parts   October 23rd 2009, 4:50 pm

But will a non TC'd motor hold up to the forced induction?
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PostSubject: Re: Turbochargers design and related parts   October 23rd 2009, 5:43 pm

Absolutely. He would need to turn the IP up and I wouldnt get crazy with the boost, but you'll have no trouble at all John.

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PostSubject: Re: Turbochargers design and related parts   October 23rd 2009, 9:24 pm

Ok, I musta had a moment before. Everywhere that I typed "heads", I mean manifolds lol.

Cut me some slack, i had a long day yesterday lol
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PostSubject: Re: Turbochargers design and related parts   October 24th 2009, 10:33 am

FaselZ71 wrote:
But will a non TC'd motor hold up to the forced induction?

Ya they are built heavy enough to handle the boost. The only difference between the N/A IDI's, and the TC'd IDI's is that some of the TC'd ones had bigger crankpins.

The big thing is, if I want to run more than 10 lbs of boost I need to replace the stock head bolts with some ARP head studs. Otherwise itll lift the heads and blow the head gaskets.
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PostSubject: Re: Turbochargers design and related parts   October 24th 2009, 10:34 am

merlin5577 wrote:
The heads themselves are different, but the manifold bolt pattern I believe is the same. Should be pretty easy to bolt on a turbo.

Well did a little looking around, and it turns out PSD manifolds will NOT bolt onto an IDI motor.
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PostSubject: Re: Turbochargers design and related parts   October 24th 2009, 4:07 pm

johnboggs21 wrote:
FaselZ71 wrote:
But will a non TC'd motor hold up to the forced induction?

Ya they are built heavy enough to handle the boost. The only difference between the N/A IDI's, and the TC'd IDI's is that some of the TC'd ones had bigger crankpins.

The big thing is, if I want to run more than 10 lbs of boost I need to replace the stock head bolts with some ARP head studs. Otherwise itll lift the heads and blow the head gaskets.

The main problem with FI on a IDI motor is cylinder pressure. The IDI has a much higher compression ratio then the later DI engines. When lots of boost (15PSI seems to be the threshold) is added, the heads actually lift (like John said) causing all kinds of problems.

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PostSubject: Re: Turbochargers design and related parts   October 24th 2009, 4:51 pm

Yup, mine has a compression ratio of 21.5:1. Some of the older 6.9s were at 24.5:1
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PostSubject: Re: Turbochargers design and related parts   October 24th 2009, 7:21 pm

with turbo deseils its a different relm but i know a thing or 2 about forced gas motors now and i know if your compression ratio is more then 9 to 1 then it isnt a good idea.. when i built my 4.3 i had to get a lower compression cause i have ever intent to procharge mine.. i had to change the crank, rods, and pistons to accomplish this.. that gave me plenty more power already but its only just begon.. once i bolt on the charger it will make close to 500 hp and get even better mpg..
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PostSubject: Re: Turbochargers design and related parts   October 24th 2009, 7:37 pm

I think there is some confusion here. I am talking about cylinder pressure, which is the force applied to the piston during the explosion when the fuel ignites. Compression ratio has a mild effect on it but no as much as boost does.

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PostSubject: Re: Turbochargers design and related parts   October 24th 2009, 7:45 pm

compression ratio has alot to do with it cause with to much you will blow your engine into toothpicks.. lol
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PostSubject: Re: Turbochargers design and related parts   October 24th 2009, 7:46 pm

Oh Joe. lol! This is going to be one of those things we just arent going to agree on.

Compression ratio applies much less force on internal parts the cylinder pressure. When parts scatter, its because of cylinder pressure. Regardless of fuel type, the only way to change compression ratio is to swap pistons or head components. On the flip side, numerous things (like boost) can effect cylinder pressure.

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PostSubject: Re: Turbochargers design and related parts   October 24th 2009, 9:02 pm

yeah but if you already have a high cylinder pressure cause your compression ratio is 11.1 or so on then its not really boostable past 8 psi..

in a way they go hand and hand.. lol
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PostSubject: Re: Turbochargers design and related parts   October 25th 2009, 5:48 pm

Joe, compression ratio is the air or (air&fuel) being squeezed by the piston as it travels up.

Cylinder pressure is caused by the explosion of fuel and is the force applied as the piston as it goes down.

Compression ratio does play a part in cylinder pressure, but does not effect all engines the way cylinder pressure does. Take for example your 4.3L and my 6.6L. Your 4.3L has IIRC 9.5 to 1 compression ratio, and a cylinder pressure of about 90psi. My 6.6L has a compression ratio of 17.5 to 1 PLUS 28lbs of boost, and a cylinder pressure of 125psi. See the difference?

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PostSubject: Re: Turbochargers design and related parts   October 25th 2009, 8:02 pm

you got me man.. lol. im lost on that one i guess.
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PostSubject: Re: Turbochargers design and related parts   October 25th 2009, 8:05 pm

the way i understand it, a turbo essentially raises your effective compression ratio. The higher your compression ratio, the higher your cylinder pressure. Correct me if im wrong in my thinking.
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