6MT vs. built 5MT

[PhilSine]

So here's my dillemma...

I'm preparing to do a 400 whp build on my SS and have come to the understanding that the OE 5MT isn't really strong enough to support such hp for long. With this in mind I have two options and both (I think) will cost around the same amount of money.

Option 1: Do an STi tranny swap

Option 2: Upgrade the internals to PPG or Rallispec gears as seen (for example) on this page... RalliSpec Gearbox Parts

Now to me, PPG is widely known to be good but for what I'm doing (building a time attack car) which would best suit me? Will the STi 6MT hold up? Will the RalliSpec gears be suitable for my power goals? I'm not looking to see how much I can spend but I'm also not interested in cutting corners either.

Any experience and input would be greatly appreciated.

[93forestpearl]

People are running 9's on stock 6mt's, so it's durability is not an issue for you.


The gear ratios of the 6mt are not what everyone desires. That said, you can get the '07 6mt for very reasonable money brand new from the dealer. The '04-05 6mt's use a 3.90 rear diff, so that would be an easy swap for you. Later 6mt's use a 3.545 rear.


I have an '05 6mt and I don't have an issue with the ratios.




Don't waste your time with any of the RA gearsets. They aren't substantially stronger than a WRX transmission.

[Legacy777]

Yeah I'm keeping this in the back of my mind. Not sure what the power will be like when the Link is tuned, but I have questions about the stock tranny holding up.....

If I can get by with just swapping in the tranny & shorter drive train and leaving the rear end alone, I'd probably prefer that.

[93forestpearl]

I should add that if you want to go with a PPG gearset, you need a WRX transmission case.






If you watch NASIOC, an '04 or '05 6mt can be had for around $2500. I also see used PPG boxes go for reasonable money, compared to putting one together from scratch.

[PhilSine]

I should add that if you want to go with a PPG gearset, you need a WRX transmission case.

If you watch NASIOC, an '04 or '05 6mt can be had for around $2500. I also see used PPG boxes go for reasonable money, compared to putting one together from scratch.

I was wondering about that. I wasn't exactly sure if they were internally simlar. Finding a WRX case is easy enough for me.

[Grayguy]

If I get my SS to the point where I need a new tranny, I'm for sure going to do the 6mt swap. I think it will be cheaper, and if I went to the dealership and bought an 06'-07' it'd be way easier.

[93forestpearl]

No, you have to use a 6mt clutch. The tranny is a hydraulic pull style, meaning you need to change to a hydraulic pedal box. On that note, the OEM STi clutch didn't slip for me until the 325-350 lb-ft at the wheels.

If your '91 SS was already a 5mt, whouldn't you have a hydraulic setup, unless you changed it?

Also, you need an auto driveshaft for use with the 6mt.

Here is a STi flywheel: