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Old 05-08-2010, 11:53 AM   #11
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Quote:
Originally Posted by Ilikebmx999 View Post
My car weighs in at about 3000lbs and My tires have a treadwear rating of 240. I assumed with those two combined with high pressure would give me poor wear. Guess I'm mistaken
What size tires?

My 2008 VW Rabbit with 195/65-15 tires has done well with 51psi. The tires are at the end of their life; I've the same miles as most people get from them. Whenever I get the chance I try to make my tires louder than my stereo going around turns...it's the only excitement I get. The center is visibly more worn than the edge but it's not enough to say it has affected the life of the tires. On the worst tire, the tread is still visible in the center and at the edge the wear bars have been exposed for a long time.

The treadwear rating won't change how they handle extra pressure.

Additionally, in my opinion center wear isn't anything to worry about anyway; water will still channel out through the tread just as well, you'll still have plenty of traction for turning and stopping, even if the center is totally bald.
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Old 05-08-2010, 11:54 AM   #12
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This post was turning into a novel so I decided to break it up into a few posts.

Regarding aero mods:

- Taping panel seams (also gaps around headlights etc): I don't recall anyone ever measuring an improvement large enough to say it definitely helped. However, I suspect that it is a real improvement and would contribute to an overall effort.

- Blocking front airflow (generally called Grille Blocking around here): Some people have had definite improvements. I'm pretty sure it has helped me but I haven't been able to nail down numbers. You may have more cooling to worry about than other cars.

- The WRX's signature hood scoop probably costs a chunk of MPG but I don't know what the possibilities are for sacrificing it, nor would you want to.

- Those roof rack rails ought to come off unless you actually secure cargo to them.

- You might want to do some tuft testing.
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Old 05-08-2010, 12:00 PM   #13
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Since you have a lot of low speed stop and go driving, there's a lot of strategies you can use to improve.

- Roll through a green light at 15mph rather than blasting up to a red light at 35, if it won't cause so much road rage behind you that you end up dead.

- Don't brake for turns. Carry your momentum through so you won't have to re-accelerate.

- If you do have to brake, know your car's DFCO behavior. You may be able to just read it in the car's computer program...otherwise you'll need some sort of instrumentation to confirm it. A built-in MPG gauge, if equipped, may or may not detect DFCO accurately (and would probably display 9999 during DFCO); an OBD2 device like a ScanGauge II can detect Open Loop reasonably quickly; watching O2 sensor values may tell you. You want to maximize DFCO when you can but avoid wasting gas when you can't.

- You may be able to work some Pulse & Glide (P&G) into your drive. When you know the traffic and traffic light patterns it gets easy to predict when you should accelerate and then when you should coast in neutral. Depending on how hardcore you want to get with it you may be interested in Engine-Off Coasting (EOC) but you should not dive right into that one.

The big thing with saving fuel is that it's not about throwing upgrades at your car or using specific techniques that always work. It's not even about directly saving fuel at any one time. Rather, it's about knowing where your energy comes from and where it goes.

Higher RPM = extra engine revolutions to get to your destination. Every revolution comes with two losses that are measured per revolution:
- Engine friction - this reportedly increases exponentially with RPM.
- Reciprocating loss - gotta reverse the direction of those pistons twice in every revolution.

Commonly, intake and exhaust are singled out as reducing fuel economy (FE) by being restrictive, but I believe that attitude is incorrect except for people who always flow the maximum amount of air that the engine can flow - and those people aren't interested in FE. They're popular upgrades because they're easy to do and are marketed well but the throttle plate is a far, far worse restriction except maybe when it's wide open.
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Old 05-08-2010, 12:13 PM   #14
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My tires are hankook ventus v12's in a 225/45r17.

Yes the scoop is quite huge but unfortunatly that's where my intercooler is. I could get a front mount style but that's roughly $1200 and would be quite laggy with my small turbo.

The roof rails can come off as I don't use them but they leave giant holes in the drip rail. Not sure how to tackle that.

I've been thinking of making a belly pan for the front to replace the factory skid plate as it's riddled with holes and odd shapes. I'd like to start it closer to the bumper and bring it as far back as possible. I also plan on lowering the vehicle in the very near future.

I'll read up on more driving techniques and see if I can pull more mpgs out of driving habits. I'll have to look into what my DFCO number is set at in my ecu. I try to decelerate as much as possible (usually down to 1000rpms then clutch in and coast to a stop.
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Old 05-08-2010, 12:46 PM   #15
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The holes from the roof rails should respond to the same treatments that people use for holes from front license plate mounts that they've removed.

A belly pan may indeed be a good idea.

For DFCO, it's not as simple as how low RPM it will go to. There are plenty of conditions that will prevent DFCO or change its lower limit. For example, my VW usually won't DFCO directly after a shift (except, oddly, into 4th - though lately that seems to have changed). My GMC has an 8 second delay before it will DFCO, which makes it detrimental to try - during those 8 seconds it's using more fuel than it would at idle.
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Old 05-08-2010, 12:57 PM   #16
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By holes I mean 4" wide by 1" deep haha

I'll have to hook the laptop up and see if I can scan it and determine what it's doing under DFCO
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Old 05-08-2010, 06:46 PM   #17
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Nice Ride and welcome!!!

Its nice to see another turbo car looking for FE and Performance.

It is strange how performance sites don't understand why some of us will want FE also. The same can be said for most FE sites also.

With your tuning management system you should be able to take advantage of reducing pumping losses with your turbo engine.
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Old 01-19-2011, 04:11 PM   #18
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Re: New guy here with a Subaru!

well im back after a hiatus. not much has changed for the wagon mpg wise except ive added a block heater to help with cold starts. now i feel comfortable only warming it for a brief moment before starting my slow drive to work till its up to operating temps.

im currently getting 25mpg with my drives to work and back.

future plans (as soon as it warms up!):

new skidplate that goes from the bumper back to the trans mount (stock one just covers under the engine leaving a void under the bumper).

new struts and lowering springs. ive got some saggy butt issues on the wagon and i doubt thats helping anything. the suspension i purchased should give a bit of a rake stance.
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Old 01-20-2011, 04:45 AM   #19
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Re: New guy here with a Subaru!

Just fyi - I don't think adding a front mount will result in any lag so long as you plumb it with the appropriate diameter tube. 2.5" would be plenty.

Where you're getting the $1200 figure is beyond me... your car isn't extensively worked over so a $100 ebay intercooler is going to provide just as much cooling as your OEM top mount if not more. Now if you were running 400whp I'd say spend a chunk on a quality front mount, but for nearly stock you're not hurting anything by using off the shelf stuff. Instead of $1200 for a front mount, I could see you spending $150 total to get the job done, then spend another $200 on an extractor for the hood rather than the scoop. They're more functional anyway at removing under-hood heat and the scoop is at adding under-hood cooling; plus it'll be more aero friendly.
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Old 01-20-2011, 10:47 AM   #20
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Re: New guy here with a Subaru!



There's a decent amount of piping and couplers needed besides the IC. It's not the easiest setup out there that's for sure. I'd also have to hack up my front bumper and I don't want to do that....plus the lameness of having a front mount with a stock td04
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