Rear diff and clutch and valve advise for a 500lb/ft forester sti
 

Hello all,
I have been wrecking my head searching through the forum with the search function with no joy!
Not so many scooby owners running 450+hp in Ireland at the moment,
So it's very hard for me to get first hand information,
I would appreciae any advice,

As above, I have a 2006 forester sti, she has a forged 2.5 with Acl bearing, crower rods (I think) and wiesco pistons (8.9:1 comp) MD321t+
I'm getting 14mm headstuds now (due to head gasket failure) and while she is in bits, I was thinking of upgrading the valves,
So that's my first question,
Why should I do this, they are the same heads as the Ej20 which revs to 8,200rpm so revs aren't the issue?, does the bhp or torque affect them??
What is the advantage?

Also, I was running an Exedy organic clutch, but that s dow to about 20% after only 6 months, So twin plate is the way to go,
Which one is the easiest to use, ie. closest to oem feeling,??
The lighter te pedal the better, (the car is wifes daily driver, and she hated the organic)

Lastly I have her setup for tail happy driving style, (on track) loads of front negative camber and 22mm rear antiroll bar at tightest setting,
Result is she turns in perfectly and lets the rear swing out nicely,
But as soon as I get on the power, she pulls straight, I beleive the inside back wheel spins up and so the rear tyre that is on the ground doesn't get the drive! I had a 98 jap forester turbo auto before that locked the rear diff with any drive at all, ie. pulling out of my drive at full steering lock and the rear wheels would be locked together (perfect)
So that is what I'm after, a diff that stays open when not under load, but locks the rear wheels together under driven load, so even if the inside wheel is in the air, she'll still drive the tyre that has the grip!
So if there is a model of scooby that has a suitable diff that will bolt straight in, that would be ideal! (the forester has longer gear ratios then the impreza 6speed)

Thank you very much for taking the tie to read this,
And your opinions are greatly appreciated!
Dan

Ps, See you's at scooby sprint finale 20th sept

cant tell u the answer but i enjoyed reading the above, lol

Jonny

Do you think I should split up the questions into different threads to get replys??
Thanx
Dan

Hi Dan, I have a Hawkeye STI running a very similar spec to yours and I have an Exedy twin plate . It will easily handle the torque you are running but it isn't exactly user friendly . I have considered ditching it many times and going for an uprated organic clutch but as you have discovered they just cant take over 500lb ft of torque for very long ! ACT do an organic rated at 515lb ft which might be a more wife friendly option but I dont have any experience of these.

What heads are you running? the EJ25 heads are not as EJ20, nor are they the same as the better valve train/porting heads on STI EJ20. STi (and late leggy TT) have nimonic (sodium cooled) exhaust valves, stock EJ25 heads do not, with stock valves your temperature limiting part is the exhaust valves.

The Foz Sti uses a centre (50:50) and rear viscous couplings, so it responds more like a WRX than an STi despite having a 6 speed box, I would suggest uprating the rear LSD to plate as a first step, but ultimately to get rid of understeer you need the rear biased torque split of the DCCD diff from an STi.

Simon

Helix twinplate its supposed to be very light in use. Enginetuner do them.