Turbocharger education - Diesel Bombers

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Old 10-14-2014, 06:06 PM
Diesel Fan
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Join Date: Aug 2014
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Default Turbocharger education

Hey guys and gals this is an awesome forum with a lot of good information, I have read hundreds and hundreds of old posts just to learn new things. One thing I haven't come across is more info on turbochargers other than people saying they have these mods and what turbo should I run. I would like to find more info on how the different sizes of turbine housings/wheels and compressor housings/wheels affect performance as well as what mods would be needed to run different turbos. I am also wanting to learn more about compound turbo setups and how they work as far as top charger bottom charger etc... As well as how the different sizes affect each other. Any info or links to info would be greatly appreciated!
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Old 10-14-2014, 10:26 PM
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Join Date: Jun 2014
Location: South West Pa
Posts: 541

This is a very detailed subject, to learn everything there is to know about a turbocharger will not happen over night. There is a lot of variables. You are looking for what the variables are, and what they alter in said charger correct?

Which Turbo Is Best For You
Here is a link that will get you a step in the right direction.

Unless somebody has written or remembers a specific thread you are going to have to look and read very many threads.

I will keep my eyes open for a good post for you

Last edited by RAW; 10-14-2014 at 10:38 PM. Reason: Added BB code for URL
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Old 10-20-2014, 02:05 PM
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Join Date: Jul 2013
Location: Hobart, WA
Posts: 669

There are a few books out there explaining how turbos work, and how to figure out their efficiency maps and what not. Turbolvr from cumminsforum is also a good person to learn from.

turbos and mods to run turbos all depend on the application and desired use...

I run compounds for the quicker spool, better street manners, and ability to tow without egt issues.

some basics:

smaller turbine housing and smaller turbine exducer = typically quicker spool, but higher drive pressure if not used in the correct application.

larger turbine housing = lower drive pressure, but may also cause lag.
larger turbine wheel = lower drive pressure, less low end power, but more top end power if you have the fuel to spool it.

on the compressor side... smaller inducer = faster spool, but may run out of steam in higher rpm of high HP motors...

larger inducer = slower spool, but more CFM for more power up top and cooler air.

compounds: ideally you want a 2:1 ratio for airflow.

the primary or "bottom" turbo is the larger of the two. it is the turbo that brings in fresh air and initially compresses the air.

now to understand the reasoning behind compounds you must first understand this:

our engines can only take in so much air into the cylinders at a given pressure in the limited time the valves are open...

so while you can run a huge turbo and push 36lbs boost from it only so much of that air actually makes it into the cylinder... and we cant just push a single turbo to 60-70psi without running it well out of its efficiency range (meaning after a certain point we are just pushing hot air and not gaining anything)

so to solve this problem we compound the pressure!

essentially the larger turbo brings in fresh air, and compresses it...

that air is then forced into the secondary turbo (smaller turbo) which is being fed compressed air.

it then re-compresses that air even further to effectively multiply the pressure without either turbo being out of their efficiency range or running excessive drive pressure.

This gives us that large volume of air from the large turbo, and gets that large volume to much higher pressures (65-85psi typically) without making the air too hot to be efficient...you will get a lot more air volume into the engine at 65psi than you will at 35psi...

the other reason behind twins is that large turbo all by itself is going to take forever to spool.. but with the smaller turbo present there, the smaller turbo spools first pulling air through the larger turbo. this helps the larger turbo get going and essentially jump starts the larger turbo until it catches up and starts pushing through the smaller turbo causing the compounding effect. so you get faster spool up but much more power.

then we have supporting mods... depending on size of turbo depends on how much fuel you need to spool the turbo. larger compressors and turbines typically need more fuel to get them going.

and then comes other supporting mods like valve springs. stock valve springs can only hold back about 50-60psi of intake pressure before the pressure overcomes the springs and allows the valves to float. being an interference motor: this is VERY BAD as valves can possibly contact the pistons. So when running higher RPM or higher than 45psi boost, stiffer valve springs are needed to ensure those valves stay closed when they are supposed to be closed and not blown open by intake pressure or exhaust drive pressure.

Another part that would need addressed with higher boost or performance levels is the head bolts... stock head bolts easily stretch and were not meant to hold down the head under excessive cylinder pressure caused by running larger turbo(s).. So typically Head studs are used to replace the stock bolts to give extra clamping force with minimal stretch possibility to ensure that head stays clamped down tight to hold the excess pressures and prevent a premature head gasket failure.

under compound boost levels typically you need to replace intercooler boots and clamps to heavier duty boots and clamps because under the excess boost pressures the stock boots will balloon out and end up either popping off, or getting sliced by the sheet metal edge on the passenger side next to the intercooler. Stronger reinforced boots wont have this issue as they wont balloon out...

there is a lot more to this stuff and some mathmatical equations like the one to determine the pressure ration for each turbo in a compound setup by just knowing elevation, primary boost, and total boost levels. but I think this is enough for one post to get your toes wet.
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