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Old 03-22-2009, 01:49 PM   #13
Scooby Specialist
Member#: 4498
Join Date: Feb 2001
Chapter/Region: NWIC
Location: Portland, Oregon
WRX H6-3.0 Turbo


Originally Posted by kellygnsd View Post
If you can get some BC's installed for $200 I'm all for it but for the money his upgrade ain't to shabby.
What year and model STi where these out of? USDM STi cams are the same duration as USDM WRX cams ('04 at least)
Just to help you guys out a bit:

First, let's look at the part number history for the intake cam:
02 WRX 13031AA101/102
03 wRX 13031AA390/391
04 WRX 13031AA391/392
04 WRX 13031AA490/492
05 WRX 13031AA490/492

06 WRX 13031AA350/351/352
07 WRX 13031AA351/352
04 STI 13031AA350/351
05 STI 13031AA350/351
06 STI 13031AA350/351/352
07 STI 13031AA351/352

As you can see the 02-05 WRX cams are of course different from the corresponding year STI cams, but in 06 when the WRX went to the 2.5L motor it follows the same cam part numbers.

Looking at the specs:

04 WRX

04 STI

07 WRX

07 STI

From this, we get:

04 WRX
240 duration intake
240 duration exhaust
17 degrees overlap

04 STI
240 duration intake
240 duration exhaust
0 - 20 degrees overlap

07 WRX
240 duration intake
240 duration exhaust
0 - 40 degrees overlap

07 STI
240 duration intake
240 duration exhaust
0 - 30 degrees overlap (* note difference from above WRX. This is an ECU programming difference)

As you can see, the change from 04 STI to 07 STI is only in the amount of AVCS advance.. Not a physical thing but instead an ECU map change. However, note that the duration of the WRX and STI cams are the same. What is different however is the overlap. WRX cams have a fixed 17 degree overlap, while the STI cams can be changed from 0 to 40 degrees. (Lift is also different)

If you put STI cams in WRX heads, you will be running them with 0 advance, so the will be the 'max retard' values.

How does this effect power:

WRX cams in WRX heads will have greater power rolloff up top due to excessive overlap.
STI cams in WRX heads will have better top end power, but worse spoolup due to lack of overlap.
STI cams in STI heads will have the best of both world. Yummy.

This, btw, is part of the reason for the difficulty in tuning the hybrid 257+wrx head/cam engines.

Jeff Sponaugle
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Last edited by sponaugle; 03-22-2009 at 02:01 PM.
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