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Old 07-18-2008, 10:41 PM   #1
bulwnkl
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Member#: 41070
Join Date: Aug 2003
Location: Arizona
Vehicle:
2005 Black Tiger
(Black Turbo Baja)

Default OK, what's exact model # of the Baja's turbo?

As in TD04HL-52 (made that last bit up). Anyone? How about this: Is it the same (exactly, in all respects) as any other Subaru model?

What I'm really, really looking for is the compressor map. I want to calculate some stuff and need the compressor map. Thanks.
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Old 07-19-2008, 11:42 AM   #2
Hawk296
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Member#: 14555
Join Date: Jan 2002
Chapter/Region: MWSOC
Location: Troy, MI
Vehicle:
1995 Impreza L
Baja

Default

Quote:
Originally Posted by bulwnkl View Post
As in TD04HL-52 (made that last bit up). Anyone? How about this: Is it the same (exactly, in all respects) as any other Subaru model?

What I'm really, really looking for is the compressor map. I want to calculate some stuff and need the compressor map. Thanks.
Well I remember the WRXs as having a TDO4L-13T, And I was pretty sure we had something very similar if not the same. THere is a compressor map for that turbo on these forums somewhere.

But if you want to find out exactly what we have here it is:
14412AA451
49377-04502
TDO4L 040818112

The above numbers are copied from the ID plate of the stock turbo directly as they are stamped into it. This one is off of my 2005 model with manual transmission.

Make some calls and I am sure you can figure out what it is. When you do, please let us know what you find.

EDIT: the 14412AA451 looks very close to a Subaru part number, as other turbochargers in the Subaru line have "14412AA0xx" as a part number. However I cannot find this number when I look it up. Maybe this one has been superceded?

The middle number looks like the Mitsu part number.

Last edited by Hawk296; 07-19-2008 at 02:01 PM.
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Old 07-19-2008, 04:51 PM   #3
bulwnkl
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Member#: 41070
Join Date: Aug 2003
Location: Arizona
Vehicle:
2005 Black Tiger
(Black Turbo Baja)

Default

Thanks, Hawk! You're the man!

Yes, the middle number is the Mitsu part. The 49377 part means TD04L as far as I can tell (that's the turbine side), and the 04502 refers to the compressor (i.e. 13T). Since that part doesn't match the early WRX number, that almost certainly means the compressor is not the same. Not surprising, since our engines are bigger. The WRX switched to a different p/n in '06 which is only 1 number off of the Baja's for the compressor section (04505 vs. 04502). That coincides with the engine switch in the WRX, no? Now I'll have to try to find out what compressor wheel this is...
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Old 07-22-2008, 12:46 PM   #4
bulwnkl
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Member#: 41070
Join Date: Aug 2003
Location: Arizona
Vehicle:
2005 Black Tiger
(Black Turbo Baja)

Default

No luck so far finding any compressor info at my 'usual' sources. In fact, they wouldn't even be able to assure me of getting parts for this turbo. I'm trying some others; we'll see.

Let me summarize why I'm looking for this info and also try to consolidate some things into this one thread:

Our turbos are different from the 2-liter WRX turbos. This makes sense because, even at the same power output, we need equal flow at lower pressure ratios for our 2.5-liter engine. That indicates the need for a different compressor.

Why do I care? Factory turbo-ECU programming, if I understand what I'm being told and what I'm seeing properly, reduces boost pressure as altitude increases. The effect of this is to cause turbo Subarus to lose power faster than naturally aspirated vehicles. There is no good reason to do this, and in fact Subaru explicitly says that they do the opposite of this. Subaru says they compensate for altitude so that you get rated output as you go up the mountain. I'm trying to figure out whether Subaru is lying, or whether those who claim that Subie is reducing boost for altitude reasons are misinterpreting what they're seeing, or perhaps there's something else going on.

To illustrate why I take the position that there's no good reason to reduce boost at higher altitudes, let's look at the WRX compressor map (just to use an example). It can be had here (thanks, Unabomber!). Mitsubishi's compressor maps are nice because they use volume flow rather than mass. That avoids a need for additional conversion calculations when you're dealing with different temperatures and pressures from 'standard.'

For simplicity's sake and to avoid redundancy, I'll not go through any calculations right now. Suffice it to say that making power in the engine requires oxygen (from the air) and fuel.

As atmospheric pressure (density) decreases (which is what happens as altitude increases), there is less air mass per cubic foot of air. That means you need more cubic feet of air to get the same amount of oxygen into the engine. Looking at the compressor map, if you want to simply maintain rated power output, this need forces you to the right on the graph.

The Y-axis of the graph (up-and-down part on the left side) is the pressure ratio. It's essentially the ratio of the absolute pressure inside the manifold to the atmospheric pressure right before the turbo. Needing to cram more cubic feet of air into the engine, combined with lower atmospheric pressure at altitude, means that the pressure ratio must also go up in order to maintain the same amount of oxygen going into the engine. That pushes us up on the compressor map graph if we want to simply keep rated power output.

Now, see what has happened? In order to maintain rated power output as altitide increases, we must move to the right and up on the graph. Notice how that coincides nicely with the direction those oval shapes on the graph go? Those oval shapes are efficiency zones of the compressor. So, as we compensate for altitude, we follow the lines of efficiency for the turbo's compressor. The only thing the turbo has to do is spin a little faster. So long as we don't exceed the max wheel speed of the turbo, we're good to go. No loss of power, and no loss of efficiency. Clearly there are limits, but reasonable turbo selection results in the ability to compensate for very large altitude changes without significant negative impact on turbo efficiency.

We also need no concern ourselves with 'high pressures' in the combustion chamber causing knock because the engine 'sees' absolute pressure, not relative pressure. That is why normal cars up here run at least as well on 85 octane instead of 87, or on 88-90 instead of 91-92.

It is interesting to note that the same basic thing is happening when you simply try to get more power out of the stock turbo. You're moving the same directions on the compressor map, because you need more volume of air and you need a higher pressure ratio.

So, the fact that there is more power to be had with our stock turbos is outstanding evidence that the stock turbos can altitude-compensate very nicely. If anyone is still reading this post, thanks for your perseverance. Also, if anyone has or can obtain any specific information about the Baja's compressor, I'd really appreciate it if you'd share.
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