The basics (and the not-so-basics) of turbocharging...

[digitalsolo]

The Turbo:

Flanges
How To Read A Compressor Map
How To Calculate A/R
How to Calculate Trim
What Is Compressor Surge
Bearing Types

Flanges:

The most commonly available flanges are T3, T4 and T6, though there are many, many custom flanges out there on OEM and specific use turbos.   Most aftermarket turbos will use one of the below flanges, though there is a movement toward V-Band style flanges currently.    Flange size of the turbo is generally dictated by the size of the exhaust housing, which is, in turn, dictated by the turbine wheel.   Some turbos are available in multiple flange sizes with no other changes.   As a general rule, if a larger flange is available for your properly sized turbo, and you can fit it, bigger is better.

T3:



T4:



T6:



How To Read A Compressor Map:
By Jacob Isaac-Lowry

We?ll start by looking at a sample flow map.



From the top of the chart we can see that this is a Garret TO4B turbo with and S-3 compressor wheel.

Understanding the Axis:

1. First we will start by looking at air flow through the turbo measured on the x-axis.  Garrett uses lb/min on their maps while other companies like Mitsubishi use cubic feet per minute (cfm).  Since I think it?s easier to work with cfm, we?ll convert.  Every 10 lb/min is equal to 144.72 cfm, remember this.

2. The pressure ratio measured on the y-axis is merely the ratio of air pressure leaving to the turbo to air pressure entering the turbo.  Since atmospheric pressure at sea level is 14.7 psi, if you were to run 29.4 psi of boost, the pressure ratio would be 2. 

Understanding Information within the Map:

1. The oblong ovals on the chart or ?islands? as they are called represent the efficiency of the turbo in that range.  As you can see on this map, the most efficient operation (73%) is in the very center of the chart.  This is general characteristic of most turbochargers.  Without getting into the thermodynamics of adiabatic heat-pumps, we?ll just say that efficiency is a measure of how much excess heat the turbo puts into the compressed air coming out of the outlet.  So intuitively, more efficient is better.

2. Wheel rotational speed is simply the rpm at which the compressor wheel is spinning.

3. The choke point, which is usually not indicated on flow maps, is the maximum flow rating the turbo is capable of regardless of pressure or efficiency.

4. Beyond the surge limit on the left of the plot, compressor surge occurs.  In layman?s terms, this phenomenon is caused by a back pressure wave entering the exit of the compressor housing and disrupting flow through the compressor wheel.  Surge will kill turbos and is to be avoided at all costs.

Calculating your Engine?s Flow Requirements

Now that you can read and understand a compressor flow map, its time to figure out how to match a turbo to your engine, this involves selecting the proper compressor and turbine wheels along with the right combination of housing A/R.  A mismatched turbo could not only result is extreme lag, but also wasted potential as a turbo can easily outflow an engine.  I.e. bigger is not always better.

The only real calculation that needs to be done is to determine how much air you engine is actually flowing.  This depends on a number of things including the RPM, absolute temperature (Rankin, equal to 460 + Fahrenheit temp), absolute manifold pressure (psi, equal to boost pressure plus atmospheric pressure), and lastly the engine volumetric flow or EVF in cfm.

First to calculate EVF use the following equation:



Next we?ll use EVF to calculate the amount of air in lb/min the engine is flowing under boost and at temperature using this equation:



Where N is the airflow in lb/min, P is the absolute pressure in psi, and T is the absolute ambient temperature in Rankin.

Finally, multiply N by the volumetric efficiency of your engine (VE).  This compensates for the fact that upon every cycle of the engine, not all of the old air/fuel mix in the cylinders is forced out the exhaust.  Thus there is a difference between the actual airflow through and engine and the predicted airflow.  This discrepancy is equated to a VE.  There is literally thousands of hours worth of online reading about volumetric efficiencies for just about every production engine.  To get the most accurate results from this step I would suggest researching your engine and coming up with the most realistic VE possible as this does have a significant affect on engine flow.  If you are just messing around with compressor flow maps and need a value for VE just to experiment with, 85% efficiency is a nice conservative number for most modified turbocharged cars at high rpm (6500-7500).  Keep in mind though that on a forced induction setup VE can easily exceed 100% so again it will be very beneficial to research your engine.

Trim Calculation Equation:

[(minor wheel diameter)x(minor wheel diameter) / (major wheel diameter)x (major wheel diameter)] x 100= compressor / turbine wheel trim

T04E 60 trim (inducer = 2.290", exducer = 2.950")

[(2.290)(2.290)/(2.950)(2.950)] x 100= trim
(5.2441/8.7025) x 100= trim
.6026 x 100 = trim
60= trim

An Illustration:

 
Determining Turbo A/R:

It is worth noting that many manufacturers list trim by letter (eg. P, Q, S) or stage (eg. 1, 2, 3).   This is a per manufacturer nomenclature, and is just their way of listing different trims.

2. Understanding housing sizing: A/R

A/R (Area/Radius) describes a geometric characteristic of all compressor and turbine housings. Technically, it is defined as: the inlet (or, for compressor housings, the discharge) cross-sectional area divided by the radius from the turbo center line to the centroid of that area.   See below for illustration:



The A/R parameter has different effects on the compressor and turbine performance, as outlined below.

Compressor A/R - Compressor performance is comparatively insensitive to changes in A/R. Larger A/R housings are sometimes used to optimize performance of low boost applications, and smaller A/R are used for high boost applications. However, as this influence of A/R on compressor performance is minor, there are not A/R options available for compressor housings.

Turbine A/R - Turbine performance is greatly affected by changing the A/R of the housing, as it is used to adjust the flow capacity of the turbine. Using a smaller A/R will increase the exhaust gas velocity into the turbine wheel. This provides increased turbine power at lower engine speeds, resulting in a quicker boost rise. However, a small A/R also causes the flow to enter the wheel more tangentially, which reduces the ultimate flow capacity of the turbine wheel. This will tend to increase exhaust backpressure and hence reduce the engine's ability to "breathe" effectively at high RPM, adversely affecting peak engine power.

Conversely, using a larger A/R will lower exhaust gas velocity, and delay boost rise. The flow in a larger A/R housing enters the wheel in a more radial fashion, increasing the wheel's effective flow capacity, resulting in lower backpressure and better power at higher engine speeds.

Compressor Surge:

What is compressor surge?

The surge region, located on the left-hand side of the compressor map (known as the surge line), is an area of flow instability typically caused by compressor inducer stall. The turbo should be sized so that the engine does not operate in the surge range. When turbochargers operate in surge for long periods of time, bearing failures may occur. When referencing a compressor map, the surge line is the line bordering the islands on their far left side.
Compressor surge is when the air pressure after the compressor is actually higher than what the compressor itself can physically maintain. This condition causes the airflow in the compressor wheel to back up, build pressure, and sometimes stall. In cases of extreme surge, the thrust bearings of the turbo can be destroyed, and will sometimes even lead to mechanical failure of the compressor wheel itself.
Common conditions that result in compressor surge on turbocharger gasoline engines are:

    * A compressor bypass valve is not integrated into the intake plumbing between the compressor outlet and throttle body
    * The outlet plumbing for the bypass valve is too small or restrictive
    * The turbo is too big for the application

Bearing Types

Journal Bearings vs. Ball Bearings
The journal bearing has long been the brawn of the turbocharger, however a ball-bearing cartridge is now an affordable technology advancement that provides significant performance improvements to the turbocharger.

The cartridge is a single sleeve system that contains a set of angular contact ball bearings on either end, whereas the traditional bearing system contains a set of journal bearings and a thrust bearing

Journal Bearings    



Ball Bearings
   


Turbo Response ? When driving a vehicle with the cartridge ball bearing turbocharger, you will find exceptionally crisp and strong throttle response.  Ball Bearing turbochargers spool up ~15% faster than traditional journal bearings. This produces an improved response that can be converted to quicker 0-60 mph speed.

Tests run on CART turbos have shown that ball-bearings have up to half of the power consumption of traditional bearings. The result is faster time to boost which translates into better drivability and acceleration.



Reduced Oil Flow ? The ball bearing design reduces the required amount of oil required to provide adequate lubrication. This lower oil volume reduces the chance for seal leakage. Also, the ball bearing is more tolerant of marginal lube conditions, and diminishes the possibility of turbocharger failure on engine shut down.

Improved Rotordynamics and Durability ? The ball bearing cartridge gives better damping and control over shaft motion, allowing enhanced reliability for both everyday and extreme driving conditions. In addition, the opposed angular contact bearing cartridge eliminates the need for the thrust bearing commonly a weak link in the turbo bearing system.

Other Ball Bearing Options ? Another option one will find is a hybrid ball bearing. This consists of replacing only the compressor side journal bearing with a single angular contact ball bearing. Since the single bearing can only take thrust in one direction, a thrust bearing is still necessary and drag in the turbine side journal bearing is unchanged.

[digitalsolo]

Piping (hot and cold sides):
 
-Hot side = all systems tied to exhaust maangement.
-Generally want to maximize pressure differential so big piping = good
-Key boost control is via the wastegate (manages exhaust flow so the turbo doesn't have the opportunity to overboost).
 
-Cold side = all intake parts
-Two types of pressure management exist, blow-off valves and pop-off valves
---Blow-offs are actuated by MAP pressure and exist to bleed boost and preventing turbo stall during shifts when the TB slaps shut
---Pop-offs are pure max pressure limiters and basically exist as safety devices
-Sometimes you run duplicates of the above for redundancy?  (or it is to help with flow?)
-Short runs = less lag (fairly obvious, but looks like the one big compromize of a rear mount setup)
 
Engine Information:
 
-Strength of assembly (iron block vs. sleeved aluminum)
-Displacement (bore and stroke have been mentioned but not what the pros and cons are of playing with the two values.  Does a 370 imply a certain combination?)
-Cam (and wide rules of thumb here?)
-Heads (gotta keep them clamped down if you want be numbers, check).
 
Boost Control:
 
-I honestly couldn't follow the comment about how timing matters to turbo spool, it seems to me that would be a function of exhaust flow, but not how you'd tune this differently than an N/A setup.
-Short runs (intercooler etc) help minimize lag.
-How are boost controllers used if the physical exhaust flow is managed via mechanical devices?
 
Heat Management:
 
-Comments on intercooler sizing would help
-Pros and cons of alternative fuel or water cooling?
-I know turbos usually use oil for both lubrication and cooling but not exactly how it's plumbed or how it gets oil pressure.
-Comments on oil line sizing would help as well.

[spacevomit]

  I have heard a guy who I would consider to be a genius, state that the majority of charge piping is sized larger than necessary, which they claimed induced extra lag (as well as cost and under-hood real estate). I'm pretty sure this guy was an engineer for turbofans, or something along those lines.
  On the other hand, LSx motors have a relatively enormous displacement compared to the M50/S50 series of motors (but those motors do have excellent flow with the stock heads, DOHC/4-valve, etc.). The impression I got was that you almost never need more than 2.5", maybe 3" for charge pipes, but that most people do not want to listen to this.
  For post-turbine-outlet, I have never heard anything but bigger is always better, velocity doesn't matter, etc.
 

[spacevomit]

I found this on Garett's website, and I thought it was interesting:

Race Updates

Garrett Fully Machined Compressor Wheels

February 09, 2009

The Garrett? GT5533R and GT5541R turbochargers are the only members of the GT family of turbos to feature fully-machined compressor wheels. Fully machined wheels are commonly referred to as "billet."

Why use a fully-machined wheel?

Higher Flowrates, Horsepower or Efficiency?

No. Garrett? compressor wheels are designed from the ground up to optimize performance. The blade shape and wheel diameter are the most critical factors to optimize to achieve high performance. Garrett? fully-machined (billet) wheels take their blade designs from Garrett? cast wheels. Regardless of the wheel manufacturing process, dedicated aerodynamic engineers spend countless hours using computational fluid dynamics (CFD) and finite element analysis (FEA) to design compressor blades.

To test this, our engineers ran identically-designed compressor wheels on our gas stands. We removed as many confounding variables as possible; there were no vehicles, no engines, just a test cell and a turbo. The only difference between the wheels tested was the manufacturing process used to create them. One was a fully machined wheel (the red map) and the other was the standard, high-quality cast wheel (the blue map).


Looking at these maps side by side, it is evident that there is little difference between them. The differences seen are well within the testing tolerances set by our laboratories. When the maps are combined, the similarities become even more pronounced.

No noticeable gains in performance can be seen when testing a machined wheel vs. a cast wheel of the same design.

The grooved lines seen on fully-machined wheels are a result of the machining process and are not part of the wheel's aerodynamic design. They are the path that the cutter tip has taken to machine the wheel. There is no intention to direct airflow in any way using these lines.

Stronger?

Sometimes, in OE applications, fully-machined wheels can withstand higher centrifugal stresses due to differences in the base material. Forgings are inherently stronger than the typical casting in this respect. However, when Honeywell engineers choose a fully-machined wheel over a cast wheel, they are only doing so to prolong the wheel's life in extreme duty-cycle OE applications where the turbo speed is constantly cycled. A typical example is a city bus, in which the turbo is frequently subjected to rapid transitions between high-load (full throttle) and low-load (idle). Compressor wheels can fail in low-cycle fatigue (LCF) in these applications, which is where fully-machined wheels offer an advantage in strength and lifetime. However, the typical aftermarket turbocharger will not be subjected to such extreme cycling.

Cost and Time to Market?

Yes! The unique configurations of the GT5533R with its 94mm inducer, and the GT5541R with its 106mm inducer required unique wheels that could be created quickly. Creating cast tooling is typically an expensive and drawn-out process. In lower volume turbochargers such as these GT55Rs, choosing a machined wheel reduces the cost per wheel compared to a casting, and allows the turbos to be brought to market rapidly. For either of these turbos, a cast aluminum wheel using the same dimensions and blade designs would have performed equivalently in most aftermarket applications. In fact, cast compressor wheels are used in the vast majority of the 9 million turbos that are designed, tested and produced each year by Honeywell Turbo Technologies' 500 turbo engineers world-wide.

   

[FortuneLSX7-TT]

I found this on Garett's website, and I thought it was interesting:

You are correct, billet has no real performance gain over the same wheel in a cast version. However, billet wheels are stronger and have allowed companies like Precision to create more aggressive wheels for their billet versions and that is where the performance gain comes into play. The billet wheels also allow those companies to make changes to the wheels a lot easier. Which means they can R&D new wheels a little bit easier and faster.

Here is a competing argument from Turbonetics.

1. Billet aluminum wheels are much stronger than cast aluminum wheels for a couple of reasons. The first is that there are no porosity issues to have to worry about. This means that there is no chance of minute air bubbles being in the metal. Turbonetics uses a special process called HIP?ing. Hot Isostatic Processing that virtually eliminates porosity in its cast wheels but because the wheel is cast and the metal is still smushed together (laymans terms) the hotter the wheel gets, the faster it spins and the greater the pressure ratio conditions it runs at the greater the chance of metal fatigue, blade straightening or in the worst case bursting. The second is the metal material that can be selected to be used is a much stronger grade than the same cast material. This is where Turbonetics forged billet compressor wheels shine. They are even stronger than standard billet wheels because the grains of metal have been moved in such a way as to align in a specific direction. See article here on forging (http://en.wikipedia.org/wiki/Forging)
 

2. Because Turbonetics uses  Forged Billet to machine the compressor wheel on a 5-Axis mill, the nose and hub of the compressor wheel can be made significantly smaller to allow for a greater blade diameter for a givine inducer size. The nose is where the compressor nut gets fastened down and the hub is the area around the bore of the wheel that the impeller blades are attacheed to. A cast wheel has to have a certain size nose and hub to allow the wheel to be cast number one and secondly it has to be able to be pulled from the mold itself. So simply stated a 61mm Forged Billet turbo will flow more air and have the opportunity to make more power than the same 61mm turbo with a cast compressor wheel.

3. The specific metal material used in Turbonetics forged wheels also gives the wheel tremendous blade strength and lowers the chance of the blades straightening at high speeds (ie. high boost pressures). When the boost pressure is raised many things occur including causing increased friction with the air and thus increasing temperatures, the pressure the wheel is under and finally the great centrifugal force the blades are under spinning at such high speeds. These three factors can cause the blades to contact the compressor housing causing serious damage to the turbocharger and could possibly lead to immediate destruction or greatly decrease the life span of the turbocharger.

4. With forged billet impellers the blades of the wheel can be machined much thinner because they are so much stronger. This allows the wheel to have a greater efficiency range becuase their is less blade thickness to contact the air and heat it up. It also means that with less blade thickness and lower hub area that there is a greater area in-between the blades to squeeze more air and build boost pressure. The more efficient a wheel is the lower the intake temps and everyone knows the cooler the air going into the engine the more horsepower you can make.

5. Being a 5-axis machined part means that this wheel is not cheap as it takes a long time to machine these wheels and it is expensive to program the mill. Hence the increased price of the TNX line of Turboentics turbos but being a machined part allows Turbonetics to continually make improvements in a quicker manner and lower cost method than creating very costly tools and molds for casting compressor wheels. This gives us an advantage in that we can make small changes to the comp wheel and continually improve the airflow and efficiency of the turbo for specific types of applications.

http://turboneticsinc.com/blog/2009/12/15/why-are-billet-wheels-great-turbonetics-forged-wheels-even-better/

[spacevomit]

That makes sense. I wonder why Garrett does not make use of these potential improvements in efficiency.

[Speedfab]

That makes sense. I wonder why Garret does not make use of these potential improvements in efficiency.

LOL

No wait, L. M. A. O.

Garrett (encompassing the eras of AiResearch, AlliedSignal, and now owned by Honeywell) built/originated all of the stuff that the Turbonetics'/PTE's (and others) of the world licensed. copied, re-marketed, etc etc.  Just because Garrett doesn't hype and spin their technology the same way as the much smaller companies reselling and marketing it, doesn't mean they aren't doing the same things, and moreover, doing them first.  They just don't tend to throw as much bullshit and marketing hype around about it.

We saw billet machined compressor wheels for a few odd applications a good long time ago... Like at least 15 years ago.  I think the only reason it is getting more widespread and mainstream now is because of much greater accessibility and affordability of the full CNC 5 axis machines that can produce them.

[spacevomit]

My shame is great.

(Although I'm sure you could see how I got the idea that they don't make more efficient billet compressor wheels for commercial sale from that blurb. I also never actually tried to act like I knew anything about anything (nor do I, necessarily) - I just copy/pasted an article from their website).

[Speedfab]

My shame is great.

(Although I'm sure you could see how I got the idea that they don't make more efficient billet compressor wheels for commercial sale from that blurb. I also never actually tried to act like I knew anything about anything (nor do I, necessarily) - I just copy/pasted an article from their website).

Oh no sweat dude, you have nothing to be ashamed of, I wasn't laughing at you.  I see EXACTLY what made you think that...  It just cracks me up when somebody/company X puts this slick marketing spin on something originated by someone else, in an effort to make themselves look good.

[spacevomit]

I believe the marketing materials clearly show that the cnc machining of compressor wheels is a technology which can only be fully employed with the wizardry possessed and cultivated by Turbonetics, yet it somehow remains just out of reach for Garrett/Honeywell. 


 /sarcasm

[FortuneLSX7-TT]

Oh no sweat dude, you have nothing to be ashamed of, I wasn't laughing at you.  I see EXACTLY what made you think that...  It just cracks me up when somebody/company X puts this slick marketing spin on something originated by someone else, in an effort to make themselves look good.

Garret may be the OGs. Turbonetics may be overhyping their billets as they're the only ones capable of doing it. But Garret is also trying to downplay the billet turbos of its competitors. Both are marketing campaigns that need to be taken with a grain of salt. Turbonetics is going the billet is the best and is the latest and greatest route. Garret is going the billet offers you nothing, so our competitors are selling you snake oil route. The truth is somewhere in the middle.

For the other smaller, newer companies, their billets are different wheels than their cast counterparts. This is where they get their performance boost. It just so happens these upgrades get marketed under the name of "billet". So "billet" wheels do make more power, but its just because they're different wheels, so companies like Turbonetics and Precision are correct, their billets do make more power than their cast wheels. Likewise, Garret is correct billet by itself does not make more power.

That then brings us to whether you think the extra power of the "billet" wheels is worth it. That's more of a personal question based on goals, and constraints. Personally, I went with Precision's "billets" because I wanted the most power I could squeeze out of two 76's and didn't feel like I could fit much larger twins up front without drastic work. That and I got a great deal on them.

[spacevomit]

Agreed. Garrett is sort of being intellectually disingenuous with that article; the lack of mention of things which they must know to be true is conspicuous. (However much one adores Garrett, it is hard to deny that they are omitting info which would be relevant to the average person reading a primer on machined wheels. I think this is probably due to their business strategy, as much as Turbonetics' article is based on their own.)

[383mazda]

Piping (hot and cold sides):
 
-Hot side = all systems tied to exhaust maangement.
-Generally want to maximize pressure differential so big piping = good
-Key boost control is via the wastegate (manages exhaust flow so the turbo doesn't have the opportunity to overboost).
 
Just to clarify, maximizing pressure differential by uing bigger pipe is for after the turbo correct?  Not that you want tons of back pressure before the turbo to begin with (or rather a huge exhaust to boost pressure ratio...)  The rule of thumb has always been a big free flowing exhaust after the turbo - is there a "calculator" for exhaust pipe sizing before the turbo?



** Don;t know how I quoted everything on accident???  the stuff in italics is what I wrote, everything else is what I tried to quote

[talkstometal]

  Keep in mind though that on a forced induction setup VE can easily exceed 100% so again it will be very beneficial to research your engine.

great post.

since most here are dealing with ls1/2 etc do you have any info on that?  what calculation did you use for your build?  any sites to look at?

[professor_speed]

Piping (hot and cold sides):
 
-Hot side = all systems tied to exhaust maangement.
-Generally want to maximize pressure differential so big piping = good
-Key boost control is via the wastegate (manages exhaust flow so the turbo doesn't have the opportunity to overboost).
 
-Cold side = all intake parts
-Two types of pressure management exist, blow-off valves and pop-off valves
---Blow-offs are actuated by MAP pressure and exist to bleed boost and preventing turbo stall during shifts when the TB slaps shut
---Pop-offs are pure max pressure limiters and basically exist as safety devices
-Sometimes you run duplicates of the above for redundancy?  (or it is to help with flow?) Both, but normally because you need more flow

-Short runs = less lag (fairly obvious, but looks like the one big compromize of a rear mount setup)  rearmounts are slower too spool mainly because the exhaust loses alot of energy on the way to the turbine (It cools down which in turn reduces volume and available pressure differential. The actual time it takes to fill the longer pipes are minimal, calculate pipe volume vs. cfm and you will see its minimal   

 
Engine Information:
 
-Strength of assembly (iron block vs. sleeved aluminum) aluminum ls block are damn strong, is iron stronger? yes if you are not planning more than 1000hp I don't see the advantage of iron ls1 and ls2 have been at least 8.10's @3500lbs with  stock sleeves thats in the 1500hp range, and at least one has gone 7's(now that being said the fastest ls engine is a 4 bolt iron block will all pro heads) If you are running a GM or non thick deck casting head that will be your limiting factor

-Displacement (bore and stroke have been mentioned but not what the pros and cons are of playing with the two values.  Does a 370 imply a certain combination?) This all based on how you want the car to drive. Also the turbo and power you want plays a role. Some may disagree but the turbo should be know before you build an engine I like to define the power goal, then decide what turbo is needed and what size engine is need. Biggest engine that will work with the turbo system is what i like to see. if all you can fit is a tc78 and you want a 402 you need to know that you will make less power than a 346, BUT you will make your power at lower revs and less boost. most turbos are happiest (most efficient) around 2:1 - 3:1  pressure ratio (15-30psi)  Lots of variables here but the big one is that back pressure starts to sky rocket and kills power (more on this later)

-Cam (and wide rules of thumb here?) match cam to the turbine section with displacement in mind big turbine I like to see a big cam, small turbine I like see a small cam I like to see overlap of less than 10 degrees @.050 (wide lsa helps) also advancing the cam will help larger cams spool big turbos. error on the small side for most cars works well. Again I like to see cam specs that match up what the car would run na. VA speed and Speed inc. have good off the shelf cams. Most cars will make power in spite of the wrong cam assuming overlap is not crazy

-Heads (gotta keep them clamped down if you want be numbers, check). if you have GM castings run arp'a torque specs, if you have thick deck heads add 10lbs, also after torquing heads down wait at least an hour and back the nuts of half a turn and re torque   you will get another 1/4-1/2 a turn with out over yielding the studs (i'm sure the is a scientific reason why this happens but I don't know it) I was told to do it a to my surprise every time the nut went further before I hit my torque spec. running the engine is not necessary IMO,

 
Boost Control:
 
-I honestly couldn't follow the comment about how timing matters to turbo spool, it seems to me that would be a function of exhaust flow, but not how you'd tune this differently than an N/A setup. It can drastically change exhaust temperature and cylinder pressure which in turn changes exhaust volume, which can increase pressure at the turbine inlet 

-Short runs (intercooler etc) help minimize lag.
-How are boost controllers used if the physical exhaust flow is managed via mechanical devices? waste gates use  boost pressure to open, basically you block the signal to stop boost from opening the gate until a higher boost is reached

 
Heat Management:
 
-Comments on intercooler sizing would help rx7 are space limited so you almost cant go too big, thicker intercoolers are only marginally better at cooling the charge, but they flow better. 

-Pros and cons of alternative fuel or water cooling? methanol > ethanol > water cooling they absorb more heat and in turn make more power and keep pistons cool, also they are increase the resistance to knock allowing for more aggressive timing and even more power, but  Meth and Eth require a larger volume of fuel for a given power level so more expensive injectors and pumps bigger lines etc. Meth is very corrosive an requires certain lines pumps etc. Eth more corrosive than gasoline but normal gasoline fuel systems work fine. 

-I know turbos usually use oil for both lubrication and cooling but not exactly how it's plumbed or how it gets oil pressure.
-Comments on oil line sizing would help as well. -3 or -4 in on most turbos 1/2" or larger exit some turbos require a restrictor plumed in to engine oil system, oil pressure sender T works well or ls engines have a block thing by the oil filter that loves to be tapped

Now back to displacement vs back pressure thing this my post from another forum
You guys are missing the pressure ratios. The exhaust volume will be close and the back pressure will be close. Now on the intake side the pressures wont be anywhere near the same. (back pressure RATIOS are very important, the actual back pressure only matters in its relation to intake pressure)

lets say we have a 400hp 6.0l it will need double the air to 800hp. (14.7*2 -14.7=14.7psi) Lets say that at 800hp worth or air this turbine will be operating at 44.1psi. this gives us a 3:1 exhaust vs. intake pressure ratio. Great for response but it choke low in the rpm range.

Now lets say we have a 200hp 3.0l it will need 4 times the air to make 800hp. (14.7*4 - 14.7= 44.1psi) Now the turbine is still moving 800hp worth of air. the back pressure will still be 44.1 giving this engine a back pressure ratio of 1:1. sluggish response but it will scream when the turbos finally spool.

This is a very simplified example, but shows you why a larger engine needs more turbine than a smaller one at the same power level.

http://www.yellowbullet.com/forum/showthread.php?t=217271&highlight=turbine+800hp