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Old 11-29-2017, 06:43 PM   #1
Raszaron
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Member#: 235727
Join Date: Jan 2010
Chapter/Region: MWSOC
Location: Papillion, NE
Vehicle:
2000 2.5RS Coupe
Blue Ridge Pearl

Default First Autocross - FP

I got to participate in my first autocross with my 2000 Subaru Impreza 2.5RS (coupe/5spd).

I have done a lot of things to reduce the weight in the car, went from 2840lbs with 1/2 tank of gas to 2520lbs with a full tank of gas. Additionally, I have reduced a lot of rotaitional mass (wheels: RPF1s, tires: SuperSport, crank pulley: GrimmSpeed) with the following going to happen this winter (DSS 1pc CF driveshaft, Exedy Racing flywheel, 2pc DBA 5000 series front rotors, 1pc DBA 4000 series rear rotors, etc.)

I've also done a lot of interior mods and got it prepped for road course racing.

Anyone else run in FP?
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Old 04-03-2018, 04:51 PM   #2
Vancouver98STi
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Member#: 459287
Join Date: Dec 2016
Chapter/Region: VIC
Location: Vancouver BC Canada
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1998 JDM Impreza STi
White GF8 wagon

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Originally Posted by Raszaron View Post

I have done a lot of things to reduce the weight in the car... crank pulley... with the following going to happen this winter... Exedy Racing flywheel
Just in case you're not aware of it, I understand that it's not a good idea to have both a lightweight crank pulley and a lightweight flywheel installed. Apparently, below a certain level, less rotational mass will trigger a code due to the engine not idling smooth enough RPM falling too quickly.

Last edited by Vancouver98STi; 04-03-2018 at 05:44 PM. Reason: Made a correction.
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Old 04-03-2018, 05:06 PM   #3
subydude
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Join Date: Jan 2005
Chapter/Region: South East
Location: Columbia, SC
Vehicle:
2000 2.5 Auto-X RSTi
What's A Head Gasket?

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On a stand alone ECU it's fine. On the stock ECU it sees the RPM falling too quickly as a misfire, but that's it. It still works ok as I had both lightweight crank/flywheel on my car for years.
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Old 04-03-2018, 05:28 PM   #4
Vancouver98STi
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1998 JDM Impreza STi
White GF8 wagon

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Originally Posted by subydude View Post

On the stock ECU it sees the RPM falling too quickly as a misfire, but that's it.
So it doesn't go into "limp mode" or dial back the ignition timing or anything?
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Old 04-03-2018, 05:32 PM   #5
subydude
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What's A Head Gasket?

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Not that I'm aware of. Just set's a CEL.
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Old 04-03-2018, 06:14 PM   #6
Vancouver98STi
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1998 JDM Impreza STi
White GF8 wagon

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Not that I'm aware of. Just set's a CEL.
I'm surprised to hear that.

I have no personal experience to draw from, but I've read numerous times in various forums that it's definitely not advisable to have both a lightweight crank pulley and flywheel installed. The consensus seemed to be that it affected engine performance (after throwing the code). So, I dunno...
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Old 11-11-2018, 09:34 PM   #7
Na nonsense
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Location: Albany, NY
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1999 2.5 RS
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I have a 99 2.5, with a lightweight act flywheel, and an unorthodox underdrive on which I've had the AC grooves machined off. It would frequently throw a CEL. Other variables did include high compression pistons and aggressive cams. But, in any case, after installing a rallitek ECU, problem disappeared.
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Old 11-12-2018, 10:02 AM   #8
Homemade WRX
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96 in the garage
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Default

If it's a racecar, I wouldn't sweat it. If it were a street car, you daily drove, lots of stop and go, etc. I'd keep the weight. I personally do on my street car...and I'm an uber engine nerd. At the same time, I've designed a race engine that had an ~7" flywheel and a quad plate AP 4.5" racing clutch...it's all about application.


However Dom put together a decent video hitting on the subject. Basically the pulley is a damper (which is true) and the flywheel is mass devise to reduce the rapid acceleration and deceleration that the engine sees (which is also true).



Sounds like you have a fun, punchy, NA set up. Future plans for more power or drivetrain upgrades?

Last edited by Homemade WRX; 11-12-2018 at 10:13 AM.
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