Hi

Can't find a definate answer to this one elsewhere, so here goes.

I am curious as to what the main differences are between a MY98 UK and the equivilant WRX and STI engines are (Phase 1?).

I know that the WRX and STI engines have a bigger turbo, and difference manifolds, intercoolers, etc, but where do they differ in terms of block, crank, pistons etc?.

What is the safe limit for a UK engine in terms of boost (assuming correct fuel and ignition mappings), and output?. What is the limiting factor with the UK car?.

Are there any major mechanical changes to the engine internals to support the Jap car's 280ps output.

Thanks,

Alex

 

don't want to bore everyone with details but the wrx engine has some fundamental differences not all of which are purely cosmetic. These range from different water jacket (to aid heat dissipation)through to uprated pistons and valves (in sti form). The turbo is bigger and a high-tech coating is also applied to the turbo internals to reduce friction. The ECU is also different + there are numerous detail changes such as improved hoses on the intercooler to cope with the extra throughput.

All of which means that it is generally agreed that the jap spec engine is a better base for serious tuning (300 bhp plus) though the UK derivative is safe to approx 270 bhp (about the level of current PE phase 1 conversion) Any higher than this and it becomes advisable to consider a change of pistons, con rods and other engine vitals before going any further.

as far as boost goes - I would stay well clear of any bypass circuitry or teeing off of boost solenoid pipework as this is asking for trouble. That boost cutoff is there to protect the engine and should not be tinkered with unless re-mapping the ecu + verifying fuelling mixture etc. is done at the same time.

btw - the sti intercooler is just painted silver - entirely cosmetic - just like the red crackle finish on other engine bits - same kit underneath.

there are lower states of tune too - especially as fitted to Foresters - again essentially the same engine but different state of tune to reflect the perceived usage it will undergo.

an important consideration is the fuel type that engines are tuned for - ie UK car is lower output but is happy/safe on 95 RON unleaded whereas sti versions are partial to more exotic fuels and 98 RON SUL is only just acceptable.

hope this answers some of your questions - there is endless archive stuff on this subject if you do some searching on the bbs - also read Power Engineerings web site - some good info there.

Paul W

 

I presume from the above that it is not recommended to use a manual tap boost controller!

As for ECU remap on STI, will this give much performance increase on a totally standard car? I.e. no exhault, air filter upgrade. Is the STI ECU optimised alreadly?

 

Seraph my STi 2 whent from 240ish bhp before remap to 284 bhp after remap by PE , if the figures seem a bit low this is running on 95RON no other mods apart from Japanese back box that was already on the car, no idea what it is but it is much quieter than the Scoobysport item.

 

Running a peak boost of 1.25 - 1.3 bar. Was very glad to see that the Lamco guage agreed exactly with the guage that PE used when testing.

 

Paul, what boost are you running after remap?

My STI 5 is alreadly running about 275bhp on 98 octane, totally stock with boost beak at 1.05 bar.

 

Sooooo......

Do I conclude that the tuning potential of a UK MY98 is limited by it's crank, pistons, rods, cooling, turbo, and gearbox?

My car makes 241bhp and 229Lb/ft on PE's rolling road, with peak boost of 14Psi, and 12.5Psi held?.

What is that likely to turn into after PE Phase 1, and how much boost would it be running?. Am I likely to compromise the durability of the engine, transmission or turbo by increasing boost to say 15/16Psi?.

Thanks.

Alex

 

Hi there

Weaknesses vary between years, but for yours its the conrods, conrod bolts, pistons, lifters (you can suffer from "pumping" under high revs. Valves can be a problem too. The crank is reasonably ok. You will be putting a strain on the transmission.

Personally I would suggest an STI for a base car to start modifying... unless you are willing to spend alot of money and strip the UK car down and uprate everything and fit extra coolers.

The turbo will be running at full wack too..

Speak To Pete at C&K (subaru manchester) - hes knows a thing or two (tell him I sent you)

You'll be able to increase boost to 15/16psi ok without any problems....(just keep an eye on the fuelling)

The PE upgrade is the most popular and I've never heard of any problems. Its hard to say exactly what you would get from it, each car is different and individual mapped.

Cheers,

J.



[This message has been edited by firefox (edited 21-09-1999).]