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Old 12-29-2007, 12:28 AM   #1
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Default Process West TMIC and Air Splitter for '06 STi

Well all, after all the great things I've read about the Process West TMIC design and arguments made for efficient airflow and optimal core thickness design, I decided to plunk down the $1086 shipped from MastroWRX for both the TMIC and air splitter.

A note about my application: I have an '06 STi with a Cobb TBE and AP V2. I have in hand a part list including an FP Green turbo (ported, 2.4" inlet, 7cm exhaust, internally wastegated), 850 cc deatschwerks fuel injectors, 255 lph Walbro fuel pump, Buschur Racing CAI, and Buschur Racing uppipe. I wanted to run a a mid-high 11s daily driven street car with a stealthy top mount.

What really appealed to me about the PW TMIC design was the thought process involved and efficiency arguments. I really appreciated the way they considered airflow and heat exchange and weren't about to just cram the largest chunk of aluminum they could squeeze under the hood. The pictures on the website and other forums show a very impressive improvement over the WRX with substantial core size increase and truly impressive matching airsplitter designs, which truly are a very nice upgrade for a WRX. Dyno curves were supplied showing improvements and part of the promised testing was supposed to be a direct comparison of a stock STi TMIC with the PW TMIC. I am not able to find these test results. Anyway, I approved of the methodology and decided to go for it anyway. I called Mastro to ask about the TMIC and was told that it really was a substantial TMIC and would be a good upgrade for an STi. SOLD!

So, I received the PW TMIC and splitter on 12/17/2007. The following are photos comparing the stock STi components with the PW components:

TMIC comparison....

At first glance, I am hard pressed to tell any real size difference at all between the two. Sure, the internals may flow differently, but it's nowhere near as obvious an improvement as over the WRX TMIC. So I get out a measuring tape. Along the cooling fins, there is no measureable difference along the short direction and thickness that I can tell, and the PW is about 2 cm larger in the long direction. Also note that the stock TMIC has about 34 columns of fins compared to about 27 on the PW TMIC. In terms of heat exchange, the STi TMIC appears to have MORE surface area as more fins are packed into the same area/volume. The cooling fins on the stock TMIC are also connected by a wing shape as opposed to a block shape on the PW TMIC. The implication being that air would flow with less turbulence through the stock TMIC design. Of course, I cannot compare the internals. So this is my own external inspection.

***1/1/2008***More careful inspection of the stock STi TMIC shows there is a recess on the bottom that is 'hiding' the real stock thickness as Kevin points out, PW is 90 mm (or 3.5") and the stock is 60 mm (I measured ~65 mm /2.6"). This would give a core volume increase of about 35%. However, this neglects differences in fin density as the STi appears to have about 20% more. Therefore it is still unclear to me (although much less so) which would have superior heat exchange capabilities. Though the PW TMIC does appear to have the advantage. If the PW had the same fin density, there would be no reason for discussion, it would win hands down.

Top view:

Side view:

Again, externally there appears to be little difference.

***1/1/2008***Again, PW TMIC IS thicker by about 0.9" or 25mm. I show a more careful analysis and outline the estimated stock core then transfer it to the PW so you can get a feel for the difference. Of course there is some degree of error due to the angle of the photo, but you get the idea.

One major difference between the two TMIC's that I think is very clever of the stock STi TMIC is the lip which is actually designed to mate to the stock air splitter like a sleeve. I will show how this comes into play later.

Now I will directly compare the air splitters. I unbolted the stock STi air splitter and you are looking at the bottom of both of them (or the side that mates to the the intercooler). What is immediately striking is that the PW TMIC opening appears to be very similar to the stock STi air splitter. Actually the PW splitter is a bit larger and would sit on top of the PW TMIC or on top of the lip on the stock STi TMIC where the stock STi splitter is slightly smaller and designed to fit inside the lip. Another obvious thing is that the PW splitter does appear to provide far superior cooling to the turbo as seen on the left side of the picture. I should also note that I did not apply the seal that was included with the PW splitter as I was keeping the parts in mint condition for my inspection.

Another air splitter comparison.

Now shown is the PW air splitter on top of the stock STi TMIC for placement purposes. What is shocking to me is that after all the arguments about channeling max air flow through the TMIC that the design is reliant upon a seal resting in place. To me this seems inferior to the sleeve type design of the stock STi splitter/TMIC interface. It does not matter that the PW splitter is on the STi TMIC and not the PW TMIC. Its going to be press fit either way and the top of the PW TMIC actually angles DOWN away from the center of the TMIC. This design would be more prone to air leaking out than the stock design.

PW splitter shown on top of stock STi TMIC:

Stock STi splitter shown on on top of stock STi TMIC:

For fun, I took a side photo comparison of the two. Pretend that there is no lip and the seal is in place on the PW TMIC. To me it seems obvious that the sleeve type design is better. Nevermind that there does not appear to be any substantial gains in surface area to be had by the PW splitter.

As for the PW air splitter itself, I wasn't overly impressed with the craftmanship of the piece that I received. There were several warped areas in the metal. It just wasn't a quality piece like the PW TMIC. The PW TMIC was a very nice piece and the assembly work was top notch. Here are some photos of the PW air splitter that I received. The item was packaged poorly and there was a ding where it poked through the box and maybe you could attribute one slight bend to that. However, there were several unacceptable flaws in the construction. I spent a lot of money on my car and the PW product. It should be a nice flush finish without any bending required.

So, I felt like I had purchased a TMIC with quality construction. However, all of the air flow arguments no longer made sense to me and it was not clear in any way to me that this WAS in fact an upgrade for an STi. I looked around for a while and still can not find a single dyno plot where a stock STi TMIC was compared with a PW TMIC.

I decided to ask Kevin at PW about it. I PM'ed Process West at NASIOC and again emailed at the process west website. I wanted to give them a chance to make me feel good about my purchase and explain technically why this was an upgrade for an STi as I truly cannot readily see for myself.

I sent the following on 12/17/2007.
Hi Kevin,

At the recommendation of the Unabomber I just purchased your PW TMIC with the splitter from Mastro for my '06 STi. I must say, the workmanship of the actual intercooler itself is very nice and it looks like a very quality piece. However, I have some questions/concerns about this product. If you would humor my questions/comments:

1) I cannot measure a significant difference in core volume between your intercooler and the stock STi intercooler (maybe 2 cm in the longest dimension). Can you explain to me in technical terms what are the expected performance benefits of your intercooler (ie CFM comparisons etc).

2) The workmanship of the splitter itself is not up to par with the beautiful intercooler. The metal work is bent/warped in several areas. However, I attribute one of these bends to shipping damage as I feel it was packaged improperly. I can supply photos if you wish.

3) The dimensions of the new splitter that fit over the intercooler appear to be the same dimensions as the stock STi splitter. Is this splitter required for an STi or not?

4) The factory design of the stock intercooler with the raised lip where the stock splitter is forced to mate inside this lip appears to be a superior design to your TMIC/splitter design. In the factory configuration, the air appears to be forced into the stock intercooler better, where on your intercooler, the seal is dependent upon the splitter resting on top of the new intercooler.

5) I still cannot find any direct comparison of the stock STi intercooler configuration with your product.

Can you comment on these issues for me? My main concern is that any benefits from your intercooler are not masked by splitter fitment. I would also like to understand the technical reason why the Process West TMIC is superior to the factory STI TMIC.

Any response is greatly appreciated.

I received no response whatsoever. I still have not received a response and it is 12/28/2007. I wanted PW to tell me, yes this is an upgrade for the STi and here is why. Here is our test result. Because of this, I have to conclude that there are minimal if any gains to be had for the STi using this setup. So after 5 business days I decided enough was enough and called Mastro to express my concerns and inquire about sending the items back.

Funny enough, Manny at Mastro told me that he had the PW on his STi and did not see any power gains at all, but it 'ran cooler'. Well, being the empirical engineer that I am, that's not good enough for me. I asked to send the items back. Manny told me he'd check with management since he wasn't authorized to make that call and that they don't take performance parts back, but he'd have the manager call me back on 12/26/2007 since he wasn't in. Instead of a call, I got the following email on 12/26/2007:

Gregg, Unfourtunatley, we can not take ruturns on the top mount and splitter. I apologize if you're not satisfied with the complarible size of the intercooler. But after a tune you should see considerable gains and increased efficiency.
Now I'm pretty sure this email is from Manny who just told me he didn't see any gains at all with his PW TMIC on his STi. So I called back and asked to speak to the manager (Joe). He wasn't in. So I waited till 12/27/2007. I got the feeling from Joe that Manny never consulted him, and just told me they couldn't take the parts back. Joe helped me out. Thank you very much, Joe, for being a gentleman! I'm a fair guy. I'm not trying to take advantage. I wasn't asking for them to pay shipping. I'm not trying to get something for nothing. I offered to pay the restocking fee since I don't feel this intercooler is for me and I did not feel I should have to pay any restocking fee for the air splitter since I do not feel it was a quality product. Anyway, thanks again Mastro for taking the parts back.

To make a long story short, I believe the PW TMIC is a high quality piece and a very excellent upgrade for a WRX. I feel the PW air splitter is also a very good upgrade for a WRX, but the craftmanship of the piece I received was poor. Do I think it's worth $1086? Not really, probably you can get the same results for a lot less with the stock STi TMIC and air splitter. You can also drill your own holes in the stock splitter for better turbo cooling. However, I do not think that this product should be marketed as an upgrade for the STi until there is testing that shows a definite quanitfiable improvement. If there is testing showing this, then I apologize profusely, but this information should be readily available and shown very publicly.

***1/1/2008*** After receiving Kevin's input, I now understand that that PW air splitter was never meant to replace the STi air splitter, though that is how it is advertised on the Mastro website. I also can say that the PW TMIC has a ~35% core volume increase over the stock STi TMIC but a ~20% decrease in fin density. The net heat exchange advantage is 27/34 (fins) * 90mm/65mm = 1.10 or ~ 10% in favor of the PW TMIC compared to the STi TMIC. For the money spent on a PW TMIC, it would be nice to see just how much of a performance advantage is expected. Is it a very modest gain or not?

Thanks for reading, and I apologize for my hasty and incorrect original thickness comparison.
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Last edited by scoobienoobienoo; 01-01-2008 at 02:12 PM.
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