5 speed gearbox + 400 bhp ??
 

Hi folks
I'm currently working on getting my Wrx RA built with a 2.1 CDB
My aim is to have the happy side of 400 outa this new build when I'm finished
My question is will the 5 speed take the power if unabused I'm a mechanic by trade so have a lot of mechanical sympathy for my cars I don't do track days as yet anyhow and am in no way gonna thrash this car the current 5 speed has 60000 miles on std RA non dccd with std power output
Will it survive normal daily driving with the odd spirited burst of acceleration thrown in

mechanical sympathy goes a long way IMO,

I ran an RA at 320 for a good while with no problems and the new owner destroyed it in 4 days

If you plan on using the 400+ hp and 4wd properly then I can't see it lasting long. The five speed box just isn't a strong box, shafts are long thin and unsupported and the gears are narrow and weak. Yes they last good enough, but why build a 4wd car with 400+hp if your not wanting to do the occasional 0-60 sprint, or drift it a bit round some bends.
Be as well getting a front wheel drive car for 400 hp if you only ever use te power in third upwards

Don't get me wrong I do intend to drive it but not launch it off the line at 6000 rpm or do rings in it on dry tar
It's gonna be my pride and joy when done and one reason not to go six speed if not needed is the shorter RA ratios which are part of the experience
If I have to I will I just don't want to

Well just drive it, worry about if when it breaks. Even on a third gear pull you may strip all the teeth off of third gear even with all the mechanical sympathy in the world

6 speed ratios are preatty short:

JDM Impreza WRX RA MY93TY752VB3BA 3.454 2.333 1.750 1.354 0.972
US Impreza WRX STi MY04 lateTY856WH4MA 3.636 2.375 1.761 1.346 0.971 0.756
JDM Impreza WRX STi Spec C MY05TY856WB6JA 3.636 2.375 1.761 1.346 1.062 0.842

JDMs have 5th and 6th shorter than UK/Euro specs.

5 speeds can get broken even at original power levels......start saving for 6 speed (had it in my gc8 at 350bhp and it was great upgrade).

Will put it on my things to do list
Was hoping I would hear from someone who had managed without six speed for a while at least

The later hawk 5 speed is a lot stronger, but still no where near 6 speed levels.

Is it? I've got one here with third gear ripped off it
Attachment 58929

How many horses did that take or was it horseplay

Plenty of launches and agressive driving destroyed that from what I read somewhere on here! :D

Yes, the later hawk 5 speeds are much stronger than previous 5 speed boxes. a few people here have taken them apart and validated that.

if you do drive them hard you will still break them. Goes without saying.

TY752 boxes do seem to be less sturdy than the later TY 754 boxes - maybe its the smaller number of bellhousing bolts allowing twist or something.

The 5 speed TY754 box in mine put up with 430-450bhp for many thousands of miles with no issues other than the typical 5 speed main layshaft nut coming loose ( which it can do at 220 BHP).

I don't do drag starts or hard launches, but that did include quite a few track days where you're generally rolling before the hammer goes down. I make progress on the road usually too so I think you'd be fine as long as you're not slamming it through the gears and sidestepping clutches etc. I ran an AP organic 5 speed clutch both with that box and after i switched to the 6 speed. great clutch which did over 18k miles before it cmae out for the exedy twin plate cera metallic that's in it now.

I eventually went '04 JDM six speed and that's pretty short ratio - it will pull to a real 165mph at 7500rpm (where bits begin to fly off the car in my experience...) but the 6 gears in that make for a good narrow spread, so when you're ready to go to 6 speed it would be a good choice for track/ b roads and motorway cruising isn't too bad either in 6th.

Quote
The 5 speed TY754 box in mine put up with 430-450bhp for many thousands of miles with no issues other than the typical 5 speed main layshaft nut coming loose ( which it can do at 220 BHP).

I like the sound of that cheers

I never broke it, plus you won't break third gear by launching.
420bhp did it after 93 miles apparently

2nd or 3rd will most likely loose their teeth at preaty much normal full acceleration.
You can try and see but you wont have good 5 speed box for sale if you are among 95% of people that tried pushing it.

Been there,done that.....at the end it just cost me 2 5 speeds befor moving to 6 speed:P

400+ bhp Is a big no no in a 5 speed gearbox,for it to last you would have to baby it I.e no launches etc...As the torque would eventually destroy it and the clutch.SJ.

Where's the fun babying it!? Six speed FTW!

LOL. Fair point! :lol1:

Plan b
Get stroker engine built and fitted and run in with std Vf 29 turbo
Max it out to 330/340 when getting Simtek fitted and tweaked
Live with this power till I can get six speed kit and decent brakes and big turbo fitted at the same time then map once more for all I can squeeze outa it and live happily ever after

Good plan. 6 speed is always the best way to go!

I have destroyed 3rd on 2 boxes running 370/350. Been running the current 5 speed UK turbo box for about 6k and it's fine. Now putting out 400/370 and a few track days under its belt. No launching though. Box had unknown history when i bought it second hand for 200 quid

I've broke a 6speed they aren't invincible :D

Good work fella, that's the spirit

:thumb: I do try my best!

.....but you did that with much more power than 400 or/and you were using your impreza with non existant mechanical sympathy,right?

I'd say it's luck of the draw with 5 speed boxes, there are a few that have ran 400+ and survived, also a few of those were being launched too. Harvey (rip) ran up to 450bhp I believe. Then you have those that have broken running standard power, as for those that have managed to break several boxes, i'd say a look at the driving style may help.

Wonder how a 5 speed would fare if it were frozen with that new fangled nitrogen hardening process and how much it would cost.:wonder:

It was just a general point that a 6speed is not invincible and isn't as strong as everyone makes out :thumb:

It was with a little bit more power...
http://youtu.be/_RzVviQZb0s

Anyone familiar with drag racing will understand that mechanical strength and not mechanical sympathy comes into it

Destroyed my 5speed within a thousand miles when I went from standard power to 340bhp...

Know loads of lads running 330 /340 with no issue one had trouble at 360 on a 2.5 extra torque would be part of that I'd guess
I'm gonna try it as is with a new excedy clutch
Box is only worth a couple of hundred anyway so not gonna make much contribution to a six speed setup when or if it blows i will go six speed
My last gc8 only covered 3000 miles in 18 months most of that just cruising to work
This one won't have an engine I'm afraid of blowing so might do a little more but I'm never gonna dog it after spending 4 plus stg building an engine