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#1: 01-27-2012, 07:09 AM
What turbo? wiki... with a twist
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Title: Royal Pain in the Ass
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Car: '08 1.5XTR+meth 6MT GH8
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Every day there are new threads asking for help choosing a turbo. Most of the time they start out either with no power targets or targets that are unrealistic. Then the questions come up on what mods are needed to support a given turbo, and a lot of turbo choices are made and then abandoned when the person realizes the extent of supported mods needed to run said turbo and the targets are revised or abandoned when the parts bill is added up. Most of us now realize that buying a bigger turbo is not the only expense in a project and that the parts list needed gets longer the bigger the blower we bought, and that's before anything goes pop.

A lot of discussions on which turbo to buy for which power level and so on end up in disarray because of differing supporting mods applied. You can’t easily compare two turbos if they are supported differently.

Here I want to try a different approach and explore some of the limits of the stock systems in our cars, and how they should affect our purchasing decisions. Call it a turbo chooser matrix if you like but it’s more about entire systems. Any of the knowledgeable members will tell you it's not individual parts that make a strong car, but parts that work well together.

I’m going to pick some points which may seem arbitrary but I think many people shop system setups in this way. A lot of people have some kind of deal-breaker that sets a threshold that they won’t cross, or won’t cross until that part has failed or worn out already.

Laid out below are some scenarios which to me represent the limit of some fairly important or hard to replace part which represents a threshold of complexity or expense. From this would-be builders can hopefully plan their setups more easily / realistically. Note that power and torque figures are going to fall into a wide range because of varying factors like supporting mods, atmospheric conditions, fuel quality used, dyno correction factors, heartbreaker dynos, the time of the month and phase of the moon. Please use your discretion and by all means look for plots which support the numbers you think are reasonable. I suggest we level the playing field here by assuming we are using pump gas of 93MON, reasonable temps and pressure as per sea level.
Of course tuning is a big factor in final output so I will again assume that timing is within a degree or two of knock, and AFRs are in the 11:1 range since this is what the vast majority of us are doing.

The scenarios laid out so far are:

1. Stock turbo is maxed out
2. Turbo upgraded, stock injectors / TMIC / clutch maxed out
3. Sensible limit for stock block?
4. Time to go built short-block?
5. I just got divorced and I want to go crazy

For purpose of comparison I’m using the following factors:

1lb/min = 14.27cfm
1liter air = 1.0914g
1ft3 air = 0.0682lb
1cfm = 30.90g/s
1lb/min = 7.35g/s

Since the best way to get good information around here is not by searching or asking, but by posting wrong or incomplete info and then waiting for those who know to come out of the woodwork, I'll start with a few scenarios for you guys to critique / fix.

What I'd like to happen is for the mistakes to get corrected, more turbos to be suggested (along with data to support their categorization). Unique turbos can be added to the scenarios which best describe the mods required to support them. More scenarios can be added to expand into the bigger setups. Hopefully like this people can get a ballpark idea of what is going to be required to reach a given power range beyond an actual turbo.
Obligatory 'build thread'
Buy my 13:1 rack!

Last edited by fahr_side; 01-27-2012 at 11:04 PM..
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