Hi!

Got an STi V4 @ stock @ 60k miles (engine, clutch, gearbox)

How much bhp are possible without cracking the gearbox or damage the engine?

Here is a list of my aftermarket parts which wait for fitting :

- 255l/h Walbro
- SARD FPR
- TD05H 16g
- uprated intake hose
- Apexi Air Filter
- FMIC or stock TMIC good enough?
- Power FC
- header
- 2,5" DP
- Blitz Nur Spec R
- parallel fuel rail mod
- stock 440cc injectors or 820cc (i think they are too big aren't they?)


Wanna hit the 400bhp mark (i know that the turbo is too little for that)..
is that possible?
Car will only be used on the road and a little bit drag race (2-3 times a year)!
What turbo for the 400bhp? TD05 20g from andy f. ?


Did I forget anything ? what parts would you add?

Greetings
Steve

 

You won't run 400bhp on standard internals for long...

 

hmmm... 350bhp should also be enough

 

imo you`d be better with a gt30 type hybrid for 400bhp. 550injectors? 800`s sound a little excessive.

From what I understand, the reliability of the gearbox at 400bhp will depend largely on how its driven.

 

550s are maginal for 400bhp.. 440s too small.. nismo 740s are good..

what make are the 820s you are looking at?

AFP 20g is a pretty good stopping point on standard internals and should just cope of 550cc injectors.. the 400+ garrett hybrids will kill the internals eventually.. depends what you want of course..

Simon

 

I think a GT30 will be too large for my build..

the 20g will be good as you said Simon!

What you think about the gearbox? Don't want to kill it..
It'll be better to sell the "good" box and get a 6-speed as selling a broken one..
But that 400bhp will be the maximum for me.. 380 is also ok.. don't want to spend too much money for my build..
what you say whats a good choice that my parts live more than 10t miles?
I also don't want to have too much turbo lag..

Hope you understand what I mean

Just looked after the injectors they are 850cc.. from daz..

maybe I'll sell them and get 550s or better 740s?

 

Gearbox is 100% a must IMO. There is no point in aiming for a power figure and not being able to use it in fear of breaking the box.

Best way as suggested would be to sell your current box in good working order and source a 6 speed.

I would also consider the long term set up, if you have no plans to tear the engine down for a rebuild in the future then i would lean towards a 18g rather than the 20g you will also have slightly faster spool up.

From your list above
370bhp
550cc injectors
TDo5 18G
STI8 TMIC modify the splitter and enlarge scoop/ Or GT spec FMIC
SX Fuel Reg
3” down Pipe
Straight through exhaust Blitz, H&S etc
Apexi Power FC
Induction in the wing if possible.
Parallel feed not 100% Necessary but good for changing fuel hopes to run higher pressure.
Walbro/Bosh fuel pump

 

thanks un-ink for your help!!

Talked with a mate from me he said a higher redline will be also good for performance!
And what gearboxes kill is the torque..
than higher I can rev the more bhp I have don't I?
What about the redline?
should it still be at 8k? or is it bad/better to get a little bit more? 8,5k or 9k?
Or is it not good for the engine/cams etc. to rev higher than stock!?

Or can't I change the redline with the power fc??

What you think about it?

I'll go for "Stage 1" now - get the 16g fitted and it will be good for a while.. the gearbox should also stand it.. i hope.. 340bhp won't be a problem I think..

@simon the 850s are Denso!

 

No point it’s not just a case of upping the rev limit to gain more power it doesn’t work like that not to mention the added stresses on the motor. The 16G will be well out of gas by 8K I would even aim lower on that turbo, ultimately a power graph will determine where to set your RPM Limit or whoever Is mapping the car will advise you, unless of Corse you plan a build from scratch.

Most Subaru’s motors even high spec that I no of still retain around 8000-8500 RPM Limit, to make good use of more you would need a very substantial turbo GT40R and some.

 

thanks mate! I'll keep the redline at 8k..

 

what about my injectors? can I use the 850s? or are the tooo big?
The car will be mapped with PFC can't I use the 850s with a lower duty cycle?

Simon help me!!

 

440cc injectors along with supporting mods will be good.

i think that ur car has a close ratio gearbox?? if thats the case keep it at say 340bhp and ul keep ur cost down and be very happy with ur performance for what u need it for.

another thing, the extra 50 or so bhp that u want will be pricey to obtain and will only really kick in after 70mph... ul be maxed out at 125mph(ish) if u do have that close ratio box. is it worth it

 

you cna but 850s will well out flow your requirements and you may find idle lumpy etc

550 would be better or 740 if over 400bhp

 

On my car (a 94 WRX) I run
550 injectors
TD05 20G
Pace FMIC
Standard crank and rods (rebuilt with new bearings at 70k miles, now at 110k)
Cosworth Pistons
STIV heads
Equal length manifold
3" turbo back exhaust
6 speed (Jap spec) gearbox

My engine produces 400bhp/350lb/ft. The 5 speed gearbox let go when I got 330 bhp/300 lb/ft and I am very mechanically sympathetic. Red line is set at 7500rpm on the Apexi, but rarely need to rev past 6500, with the close ratio box thats drops you right back in the meat of the torque.