Hi all, just bought an STi V5 and just wondered what boost levels are safe on standard internals/cooling.

Is it possible to make 400bhp with a FMIC and larger turbo? Do any internals need uprating?

Thanks

 

To put into context, John Banks tuned his UK spec V5 (not forged pistons or higher duration cams like the STi5) to over 400 bhp and I think its still going strong.

The block will take 400 bhp IMHO, but the life of the engine may be compromised. Just let it go pop and replace with a US 2.5 block

The question of getting to 400 bhp is not just around the engine, the gearbox and clutch will become the next weakest link, as will the the brakes. I think 340 ish is a good target and readily achievable with the right breathing and engine management mods. After that you really step up a level and have to ditch the standard VF29 and intercooler, fuel pump / reg, injectors etc.

As for safe boost, its best left well alone unless you are raising it by remap or similar ingition timing / fuelling control device.

All IMHO

MB

 

Thanks for that m8,

Only had the car since sunday, was not sure what to set the boost controller at.

Was on rollers yesterday, have set it to a safe 16psi which made 295bhp. Boost curve and fuelling looked good.

 

Should be fine there. Mine boosts to 18 psi peak, 16 held at the moment

Are you aware that you should only use Optimax and octane booster is also strongly advised? jap imports are mapped for 100 ron fuel and anything much less with kill your engine.

MB

 

PS - what mods does it have at the moment and what rolling road did you use?

MB

 

is it a type r or saloon??

 

Its a saloon.

yes have been running it on optimax and octane booster.

Used Clive Atthowes rolling road in Norwich, think website is www.engine-tuning.net They specialise in servicing imprezas, gave it a full service and checked it over.

Only mods are Grenade Cat back SS Exhaust, HKS induction kit, Blitz SBC-ID Boost controller, previous owner said it had a remap, although i guess there is no way of verifying this. Havent really had a proper look under the bonnet as its always bloody dark this time of year lol, pretty sure its got a aftermarket DV as its fairly loud.

 

Best to get someone to check all the mods, and what they're doing. I personally dont like what VTA dump valves do to the car, for example. The HKS induction kit is also a real worry too. These are well known to kill the MAF (mass air flow sensor) in the air intake pipe after the filter. This device controls the fuelling when the car is running on boost (or over 0.5 bar or wide open throttle (WOT) to be precise)

Failed MAF's have killed hundreds and hundreds of these cars! When they fail they lean the mixture out until its starts detting badly, and mr piston lets go and damages the internals. The only reputed indution kit to not damage MAF's is the K&N. Other than that a good panel filter (K&N / Green Cotton / STi) is well up to the job.

Verifying a remap might not be that tricky... If its the standard ECU then the only remap available is called TEK3. Any ECUTEK mapper should be able to plug into it and look to see if its a standard map or not... If its been "chipped" you will need to take the lid off the ECU and post a pic up of it so we can see whats inside.

Not to worry you on all this, but with the wrong mods these cars can be a disaster! In the right hands they can be very reliable and very capable.

MB

 

Please could you elaborate why the hks induction kit will kill the MAF? im guessing it is because it is not that great at filtering dirt etc?

I could not locate the ECU in the engine bay, is it under carpet in passenger footwell or similar?

Could not found the dump valve either, looked all around near the intercooler, found solenoid for blitz boost controller. where in the engine bay would the dump valve be situated?

Thanks again

 

They apparently give an irregular airflow over the MAF, and definately known to vibrate which the MAF doesn't like. The K&N has a bracket which mounts to the bulk head to stop the cone vibrating. And the fittration isn't great, Jap stuff tend to think in power terms and everything else later! More air in etc etc..

I monitor the MAF via an AFR gauge - if not id change it every 18 months as a matter of safety - they are pretty poor! AFR gauge is a good idea and quite a cheap install. Autometer do them.

ECU lives under the passenger carpet.

Dump valve is bolted onto the front right hand side of the intercooler.

Hope that helps!

MB

 

Thanks for your help m8, not my first turbo car but my first impreza so still finding my feet a bit lol.

The HKS filter is bolted to the the bulkhead via a bracket though? However think i will go for a K & N. Do you know how much a new MAF is? and best place to get it from?

i must be blind if i didnt spot the dump valve, will have another look tommorow.

 

The MAF is probably fine now, though clean it with some carb cleaner for now.

Put the airbox back in and use an ITG dry air filter for the best gains (approx!).

Dump valve is just to the right of the throttle body connecting onto the intercooler.

Jon.

 

ITG They're not dry Jon, one of the biggest MAF killers due to the amount of gunk on them... The STi and K&N are probably safest / lightest oiled.

The K&N cone also appears to have quite a big surface area so will draw more air in over the HKS. However.... It gets pretty hot under the lid, hence the standard airbox is extremely good at stopping heat soak. The standard filter is really only a restriction above circa 350 bhp so worth considdering going back to the airbox, depending on your power target.

If you can fashion some form or heat shield (carbon fibre surround) to segragate the filter from the surrounding engine bay, that may be best. There are a number of people on here with a good setup, think Harvey has one?

A MAF can be got from Xtreme Scoobies or similar for about £80.

Depending on what ECU you end up buying, you may not need the MAF. Link and GEMS dont use the MAF, so the filter you choose is less of a worry in respect to MAF damage.

Note - generally its just MY99/00 MAF's that are a problem, other years either side seem much more reliable.

When I bought my STi5 (and I swore id never own one due to the amount of blow ups due to MAF!) the forst thing I did was replace the 02 (lambda in downpipe which also break for a pasttime) and MAF - new air filter and all fluids. Next step was monitoring gear such as Knocklink - boost gauge - AFR meter. At least I kenw where I was with the car then.

PM me if you need any help and I can talk you through various bits, and there a number of more clever people on here who can help.

MB

 

Christ I shouldn't post on here when under the influence :s

K&N are just as bad though from past experiences. 100% agree with the STI though.

As for ECU wise the standard one is very capable with an ECUTEK remap. Plus you don't have those wonderful cold start issues that GEMS and other aftermarket ECUs can provide..... All depends on how much time is spent mapping though.

Jon.