Tranny Modification Question - Subaru WRX Forum
 
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#1 Old 11-22-2009, 11:50 PM
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Tranny Modification Question

This may be the wrong forum, and if it is, please move it with my apologies.

First, I haven't autocrossed at all so far, but am looking at getting into it. The class which the car will be running in eventually is STU.

I was going through my spreadsheet and making sure that the list of allowed and disallowed mods was correct and ran across an interesting find.

As we all know, the 5mt isn't terribly strong. There are a myriad of upgrade options to make them stronger. I didn't see anything in the rules in terms of tranny modifications which I think would make them illegal. Would modifying the tranny by replacing the gears with a set of stronger ones be illegal given that the modification wouldn't be for any other purpose and would grant no performance advantage?

The rules do look like I could swap in a 6mt as a unit (no internal changes), any comments on the legality?

In addition, the rules state "Any mechanical shift linkage may be used" Does this extend to the innards of the tranny, such as the engagement type of the gears? For instance, could I rip my box apart, swap synchros for dogs, and run legally? Generally linkage only refers to the bits outside of the gearbox itself, however I'm attempting to split hairs (quite possibly unsuccessfully).

I hate the fact that the trannies in our cars are somewhat inferior. I'm not looking at running a boatload of power (goal is 290-310 whp) and would like to be able to use this without turning my 5mt into a collection of loose parts.

I suppose at the far end of things, I'd end up in a prepared class running a non-stock gearbox... That would rather suck, as I'm fairly sure a streetable WRX wouldn't stand a smoking chance in hell against some of the demons of the prepped world. I'm not the type who tends to compete with others, but knowing that I -could- win is kinda key.
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#2 Old 11-23-2009, 05:43 AM
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I just looked them over as well and your right there is no rule against building up a transmission...it only says if you do a transmission swap you must do no internal modifications...so I think your best bet would be to call the governing body of which ever autocross your interested in (I just looked up the SCCA rules so I'm sorry if your in a different governing body)

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#3 Old 11-23-2009, 05:49 AM
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Good stuff, just wanted to make sure my eyes weren't crossing so late at night pouring over rules!

I got the e-mail addy of the newbie guy for my local governing body, and I'll send him an e-mail shortly or tomorrow, whichever works out best. I looked at the straight SCCA rules myself, the local chapter's site didn't have anything posted which would suggest additional rules, however it never hurts to ask!

I made a similar thread over on NASIOC and it looks like there are at least a coupe of people well over my power goals who are still having success running on the stock tranny's guts in autocross.

Also a NASIOC poster noted that having better synchros and not needing to double-clutch or heel-toe to get into first for slow corners could be construed as an advantage. I'll be asking the local SCCA guy about this as well.

Thanks for casting an eye on the rules, I know there kinda on the dry side!
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#4 Old 11-23-2009, 02:01 PM
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Keep in mind that, if you want to compare others' experience with yours, 03-05 WRXs came with a 3.9 fd not 3.7 like you, so your tranny will be (theoretically) weaker. How much, I don't know, but I do hear 3rd is notorious for breaking.
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#5 Old 11-23-2009, 10:35 PM
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Yeah, I've read about a few 3rd gears out there letting go on the 06/07. I don't drive like a banshee on the street though, and doubt that I'd be using 3rd much in AutoX, as redline in second comes out to around 60 currently.

It is something to keep in mind though. Given the costs of stronger gearing though, I think I'm just going to keep the car's power goals on the low side, and tune for more driveablity. This would put me in the ST class where I'd like to be with as little risk as possible to my tranny. A couple of years down the road, if I feel ready to move up to SM, then I can get jiggy with the tranny.

I will be contacting my local SCCA to see what they have to say. I'm not interested in changing gearing, just making the components more durable.

The other option would be to just simply go that route and not say anything to anyone, but that wouldn't be completely honest, and that doesn't sit well with me.
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