RS25 tranny + rear diff

[Splinter]

My friend wants to sell me his spare RS25 tranny. Its in decent shape.

$450

I was going to drop it in now, then try and track down a WRX tranny and get it sent to BAC5.2

As long as Im not bombing it, it should be able to take the power, right?

AFAIK its a push-type clutch. So I'd have to swap the clutch afterwards.

[georryan]

My brother is running that tranny. He also has a 4.111 rear diff. Make sure you get that as well.

He is running a sport clutch for his added power, but other than that he is having no problems. People run stock NA trannies on their turbo cars as well. Thawa converted his NA to a turbo, and is running a 4.111 tranny. It can be done.

[AWD_addict]

Would it make sense to use a stock clutch with the 4.111, so that the clutch would be a weaker point than the transmission?

[douglas vincent]

A stock clutch is WEAK to start with...but really only if you do hard launches. I only had problems with me new "stock" clutch when drag racing and rallycrossing.

The cheapest option, and possibly safest, is to keep you pressure plate but upgrade to the cheap $97 6 puck.

[Splinter]

Im probably not going to have this tranny for that long, 2-3 months.

Maybe a little longer.

[dzx]

I ran it for a long time, it's a nice transmission.

[georryan]

Honestly I don't know what you'd want to do with the clutch. My brother is running the hydrolic version, and Thawa is running the Cable version. Both are holding up just fine so far. Neither of them are dropping the clutch or anything like that, though. If you only want it for a few months, and you treat it right, you should be ok with either route I'd imagine.

-Ryan

[mhrallyteam]

I,m running a 2,5RS 4.111, i bought it cheap because she's a bit noisy, but it,s been 6 months now and no problems whatsoever. I use the cable system with an upgraded clutch, works fine with 220hp

[555BCTurbo]

That's a lot of money for a used NA 2.5 tranny...

I paid $500 for my JDM Legacy RS 4.11 tranny, which was 100% bolt in, no clutch mods were required, and it has tougher internal bits.

[206er]

A stock clutch is WEAK to start with...but really only if you do hard launches. I only had problems with me new "stock" clutch when drag racing and rallycrossing.

The cheapest option, and possibly safest, is to keep you pressure plate but upgrade to the cheap $97 6 puck.

how is this setup on the street/in traffic?

[BAC5.2]

The JDM legacy RS 4.11 tranny doesn't have tougher internal bits. If it's a post-99 tranny, it actually has wider gears but weaker synchro engagement hubs.

All OEM Subaru trannies have been, basically, the same over the years. I've seen inside enough of them to know.

Even the "invincible" 6-speed is fairly weak when faced with over 400whp.

[Splinter]

That's a lot of money for a used NA 2.5 tranny...

I paid $500 for my JDM Legacy RS 4.11 tranny, which was 100% bolt in, no clutch mods were required, and it has tougher internal bits.

I need clutch mods because it's an auto.

[555BCTurbo]

The JDM legacy RS 4.11 tranny doesn't have tougher internal bits. If it's a post-99 tranny, it actually has wider gears but weaker synchro engagement hubs.

All OEM Subaru trannies have been, basically, the same over the years. I've seen inside enough of them to know.

Even the "invincible" 6-speed is fairly weak when faced with over 400whp.

I know for a fact the innards of the Turbo 4.11 trannies are different than the 4.11 NA Trannies, as far as the metalurgy of the gears...

Basically, the tranny lasts as long as you want it to...and depends greatly on how you treat it.

[BAC5.2]

Do you have proof that the gears are different, from the metalurgy side of things? Proof beyond heresay, I mean.

If I'm wrong, I sure would like to know about it.

The only differences I've HEARD between turbo and N/A gears, is the heat treating.

Aside from width and synchro hub engagement design, the gears from my 94SS tranny, a 99 Forester tranny, and a WRX tranny all looked very similar.

[555BCTurbo]

Do you have proof that the gears are different, from the metalurgy side of things? Proof beyond heresay, I mean.

If I'm wrong, I sure would like to know about it.

The only differences I've HEARD between turbo and N/A gears, is the heat treating.

Aside from width and synchro hub engagement design, the gears from my 94SS tranny, a 99 Forester tranny, and a WRX tranny all looked very similar.

Well...my evidence is from my uncle, who is a very prominent engine/race car builder in Auckland, New Zealand, and he actually owned a 1990 Legacy RS, and he race preps A LOT of Subarus. Anyway, I was discussing the whole tranny thing with him before I changed over to 4.11, and he said to definately use that tranny over an RS one, because the Turbo Tranny has case hardened and shot peened gears, where the NA trannies don't.

I believe you that the gears don't look any different, but differences in metalurgy and treatment of metals is not always apparent just from a visual inspection. Even just tempering the gears would make a huge difference in their strength. When I was in engineering school some friends and I did some experiments on steel with heat treating, and found that tempering steel can drastically change its hardness. A good example is tool steel, which is just heat treated hot-rolled steel, which we use to make lathe toolbits.