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Old 06-14-2010, 04:07 AM   #1
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Default Noob question about compressors?

I recently ditched my T3/T04E .50 trim for a smaller but more reliable Garrett T3 ".42 .48". It spools much faster but does offer some very unexciting top end results. It sees full 10psi by 2800-3100 on my stock 1.8 but just falls flat from there on out.

I gathered what I believe is the correct compressor map for said turbo above and started to work on finding out just how efficient this compressor was for my engine. (correct me if I'm wrong on this map)

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Now according to some of Corky's calculations and mine as well from his book Maximum Boost, I figured up the following calculations and numbers.

Pressure Ratio = 1.68 (for 10psi)
Calculating airflow rate in "cfm" for my particular setup without boost I came up with the following the numbers.
1.8 = roughly 112cid.
My own personal redline set at 6600RPM.
An estimated 85% volumetric efficiency (real VE unknown).

Plugging in his formula to calculate these, I came up with a CFM of 181.80, with the basic flow rate established I can figure out the CFM under boost. Using said PR above of 1.68 multiplied by 181.80 I come to a boosted CFM of 305.43. Now to find out the correct value to read the compressor map I must have 2 things, the PR and a number to represent my pound of air per minute. I found pounds per minute by simply googling a conversion and come up with .070 x 305.43. This gives me 21.38 pound of air/minute. Do correct me if any of these formulas are wrong, but using the said numbers I made a rough sketch on shown compressor map above.

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For turbo's sake, am I really that far off the compressor map? Is efficiency really that bad on this small displacement engine? If so, are things as simple as swapping on a new compressor and wheel, what kind of equipment other then hand tools do I need to be able to do that? Or should I be looking for a different turbine?

Last edited by na8psi; 06-14-2010 at 07:13 AM.
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Old 06-14-2010, 10:16 AM   #2
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You should see the compressor map for the stock turbo on my Forester XT. I was wondering why boost goes from 12psi at 5000RPM to 9psi at 6500RPM-- the EBC pulls down the boost to follow the shape of the compressor map, which is shaped pretty differently than your map. Basically, it's a midrange turbo :|

Your calculations look correct to me. It's not like your turbo isn't working off the map though, it's just not being very efficient. I don't know about swapping compressor wheels etc or much about your turbo but my guess is that a 2871 or 2876 would run efficiently to redline without comprimise up top?
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Old 06-14-2010, 10:20 AM   #3
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the 45 trim will act like a 2554.

I'm running a 50 trim myself and it's running out of steam a lot earlier than my s60trim ever did. But it's spooling a little faster and making more mid-range torque like I was hoping for.



Solution: run more boost at higher rpms!

easy math for wheels is this:

If the efficiency island ends at 25 lb/min, then 25 * 10 = a 250BHP turbo. or you can do 25 / AFR / (.55/60) = 237BHP



Basically if you're making more than 200rwhp or so, you're pushing hot air.

Let me show you an example of this:



This is Paul's dyno running at 14psi and then 17psi...you can see he's clearly making more TQ at 17psi, but it's apparent there's just no more efficiency range left in the turbo to output much more power. It's maxed.
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Old 06-14-2010, 12:40 PM   #4
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yes I see this, being its a T3, can I just simply swap out to a bigger compressor housing and sort of balance the turbo better?
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Old 06-14-2010, 12:43 PM   #5
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I absolutely LOVE the spool characteristics, but would like some more air on the big end, and not HOT air...
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Old 06-14-2010, 01:57 PM   #6
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all you need to do is swap on a compressor housing and wheel from a 50, 55, 60 or s50 trim wheel and have more top end. Spoolup change will be trivial.
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Old 06-14-2010, 02:00 PM   #7
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Quote:
Originally Posted by Braineack View Post
all you need to do is swap on a compressor housing and wheel from a 50, 55, 60 or s50 trim wheel and have more top end. Spoolup change will be trivial.
Is doing so as easy as it looks? I'm assuming everything needs to be rebalanced? I just wasn't sure if things were that easy.
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Old 06-14-2010, 02:04 PM   #8
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rebalanced?! crazy talk.

technically the compressor wheel should be balanced independently of the turbine wheel/shaft, so bolting up a new one shalln't matter.
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Old 06-14-2010, 02:17 PM   #9
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Quote:
Originally Posted by na8psi View Post
Is doing so as easy as it looks? I'm assuming everything needs to be rebalanced? I just wasn't sure if things were that easy.
I can't speak for Garrett turbochargers with certainty, but mitsubishi turbos are all component balanced and can have parts swapped without the need to re-balance. YMMV, but I've definately known a few people to rebuild garrett turbos and run them for quite a while.

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rebalanced?! crazy talk.

technically the compressor wheel should be balanced independently of the turbine wheel/shaft, so bolting up a new one shalln't matter.
In theory, theory and practice are the same. In practice, they are not.
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Old 06-14-2010, 02:26 PM   #10
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Quote:
Originally Posted by Jeff_Ciesielski View Post
I can't speak for Garrett turbochargers with certainty, but mitsubishi turbos are all component balanced and can have parts swapped without the need to re-balance. YMMV, but I've definately known a few people to rebuild garrett turbos and run them for quite a while.



In theory, theory and practice are the same. In practice, they are not.
I've read that the way to notice if the turbine/shaft has been balanced seperate of the compressor wheel is to see if both the turbine "nut" and the compressor "nut" appear to have been ground off then they were balanced together and if the compressor nut is not ground off then they were done seperately.

If its as simple as unbolting a few things and throwing on a new housing and wheel and then drive it, then i'm all ears...
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Old 06-14-2010, 02:59 PM   #11
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ask me how many times I've swapped compressors and CHRAs and **** around, then ask how many times I've balanced the turbo or had a failure.

To make it easy: My t3 came with a 45 trim wheel, that I swapped with a to4b-s wheel, then a t3 50 trim, then a t3 super 60. I had one failure due to under oiling when I started using a .040" restrictor where I replaced the turbine and everything was fine again...and not "balanced"

one of these days ill get un-lazy and swap my garret turbine and 50 trim or super 60 compressor wheel into my chinacharger's turbine housing and CHRA.
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Old 06-14-2010, 03:05 PM   #12
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Quote:
Originally Posted by Braineack View Post
ask me how many times I've swapped compressors and CHRAs and **** around, then ask how many times I've balanced the turbo or had a failure.

To make it easy: My t3 came with a 45 trim wheel, that I swapped with a to4b-s wheel, then a t3 50 trim, then a t3 super 60. I had one failure due to under oiling when I started using a .040" restrictor where I replaced the turbine and everything was fine again...and not "balanced"
Wouldn't happen to have a blowup diagram of a T3 so I could reference to when I do decide to replace mine? Maybe also a good source to find a compressor housing and wheel lol?
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Old 06-14-2010, 04:09 PM   #13
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aint much to it.




the biggest thing is figuring out what compressor seal you have.
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Old 06-14-2010, 04:55 PM   #14
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Quote:
Originally Posted by Braineack View Post
aint much to it.




the biggest thing is figuring out what compressor seal you have.
Ok I don't even have to take apart the center section then huh?
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Old 06-14-2010, 05:05 PM   #15
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no. just 4 bolts holding on the back plate to the chra, the 8 bolts to the compressor housings, and then the compressor wheel itself (reverse threading).
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Old 06-14-2010, 05:09 PM   #16
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Are any of these bolts torque-to-yield? Specific torque specs? How about I drive to arlington with a case of beer and watch your expertise go to work haha.
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Old 06-14-2010, 05:11 PM   #17
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Make sure to drink all the beer BEFORE working on the turbo. Its the only way to ensure top notch service
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Old 06-14-2010, 05:26 PM   #18
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Old 06-14-2010, 05:33 PM   #19
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Quote:
Originally Posted by 18psi View Post
Make sure to drink all the beer BEFORE working on the turbo. Its the only way to ensure top notch service


Hahaha your invited too my friend. As well as y8s.
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