Winter mode
IMG-20121220-00217 by
SplatSTi, on Flickr
Now the gearbox has been upgraded, for taller gears and I did this for the following reasons. When getting on the highway, there was only a 500rpm drop from 4th gear to 5th gear, and another 500rpm from 5th to 6th. This means when getting on the highway, It felt like I needed another gear. The new gears now drop 1000rpm's from 1st to 6th gear, cruising at 70mph is now at 2600rpm's instead of 3000rpms. All the syncros and new bearings were put in as well and the stock gearbox oil was replaced with Motul Gear300 75w90 oil.
The stock synthetic subaru oil was also replaced Shell Rotella T6, which I use in both my 05 STi and this one, and the engine respons well to this oil.
Tuning:
I had a discussion with my tuner regarding the dual AVCS cam system in this car. Apparently this generation of STi uses more gas due to EPA regulations and emissions, with extra pumps on the engine etc. The tuning they did went along with it. I had a custom map created to basically turn off the dual AVCS and basically turn it into a single AVCS system.
The Theory:
Quote:
Having your cams open so high in such low load creates the effect of reverse scavenging. A typical scavenging effect you may be familiar with; when the cams timing on exhaust and intake advance enough or retard enough for exhaust, to assist in the flow of combusted gasses and non ignited gasses through the combustion chamber. The scavenging effect uses differentiating pressures to help evacuate the combustion chamber more efficiently, as well as increase the gas velocity of evacuated gas. Or you may know this more commonly as wave scavenging. You can also see this effect or rather the same theory with ram tuning, or scavenging headers on NA cars.
The reverse scavenging effect im speaking of allows exhaust gasses to be pulled back into the combustion chamber to be re-burned. Thus the EGR effect. To a point this CAN be a good thing for emissions and sometimes fuel economy. However with the crappy winter blends everyone receives with mighty E-10 now a days, we need all the help we can get.
Eliminating the EGR effect in subarus AVCS, I have seen MPG as high as 36 in the summer on a 2.5 5 speed. My sti is now hitting 27 mix with sunnoco 93 varied temps of 30-50 (this also includes some idle time for warm up).
Once you have adjusted your avcs 40* bump in the low load area to smooth to the surrounding timing of the cams, it may also be beneficial to you to run different ignition timing. Remember you have less hot gasses entering your combustion chamber now. DO REMEMBER > use det cans down low as the low load knock can be a pain in the flat four 2.5's.
IF you are not familiar with MBT then please leave this adjustment to your tuner. You may do more harm then good.
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We have also made an additional map with no boost and I will need to test this as well. Since I am going to get protested in Indiana this weekend, Im going to test my "Economy" map there and then get protuned and see what the mpg difference is on the way back. I do expect the protune to be better, these cars like more hp and they become more efficient when tuned that way as well.