andythejock01wrx

Hi !

I have just bought a UK 2001 WRX. No mods other than a WR exhaust.

Have been told using Optimax 97 Ron Super can give around 20 bhp more than 95 ron unleaded. Do you agree ?

Also, I was considering fitting a Revolution decat backbox and centrepipe but leaving the downpipe. Would then have an Ecutek3 done.
What bhp could I expect and will i be reducing the engine's lifespan sigificantly ? And would the car pass it's MOT without swapping exhausts
back ?

Cheers !

andythejock01wrx

bump

Yes, I know it's a silly question, but Newbies are allowed that aren't they ?!

Go on, somebody answer !

bluepolarbear

The car will run fine on NU. If you feed it on SUL it will give a little extra performance, about 50 to 100 miliseconds on the run up to sixty.

You makes your choice and pays your money.

nathanb

iTrader: (1)

20bhp extra? Absolutely no chance matey!

Opti will give you minimal performance gains over 95ron.

The main benefits of opti are a smoother, more consistent drive and a cleaner engine.

I have a uk 2001 bug and use both opti, tesco 99 and 95ron and I dont feel much difference with any of them!!

andythejock01wrx

That's weird. I thought magazines etc had said there was a bhp difference ?

Does anybody know the stats ?

Dave_68

Fifth Gear did a test a while back which showed a gain of 14 BHP when using Optimax compared to normal UL on an STi...

BedHog

http://en.wikipedia.org/wiki/Octane_..._octane_rating

Explains octane (RON) very well, and why it won't make much difference.

andythejock01wrx

So perhaps 10bhp on a 2001 WRX ? And are the bhp figures for these cars based on Unleaded or Super ?

MTR

The UK300 with a Prodrive Performance Pack either produces 230bhp on 95 RON or 245BHP on 97RON, Optimax is 98.4 Ron Minimum.

So it gains 15BHP.

See the attached image, which is a scanned copy of the Subaru literature produced at the time.
They cannot lie as they would be in breach of trading standards.
It is stated in the text towards the bottom of the page.

http://img.photobucket.com/albums/v201/MTR/uk300.jpg

Additionaly when I bough my first Impreza turbo in 1997 I phoned Prodrive who confirmed I would lose about 10BHP by switching from 98 RON as it was then to 95 RON.

It's strange that when people spend money and fit some modification to their car i.e back box or air filter, which in all probability give almost no extra power, but just increase noise, their car 'spools up' miles better and it goes like stink, yet when you switch fuels which DO ADD POWER nobody can feel any difference.

Perhaps its the 'kings new clothes' syndrome.
Its shiny and makes more noise so it must be better.
My Full decat on my MY00 lasted 5 weeks then came of as the car was slower and too damm noisy.
ECUTEK wasn't around at that time, or if it was I hadn't heard of it.

I know when I started using 98 RON, all I noticed was better smoother low speed running on changing fuel, but I have used it ever since to lessen the likelihood of detonation and engine failure.

Cheers
MTR

BedHog

Lower octane fuel than what the car is designed for will produce less power. The onboard knock detection will do this to protect the engine.

I'm not sure if it works the other way - i.e. will the ECU will advance the ignition with higher octance fuel than it was designed to run on?

It's possible, but somehow I doubt it - surely the manufacturer would stop this to protect the engine too?

MTR

The PPP ECU obviously does, so it isn't beyond the realms of possibility that the std ECU does as well.

What fuel is the Impreza Turbo engine designed to run on?
95/98/100 ?

The WRX and UK pre MY00 handbooks state they may be run on 95 RON minimum in the UK, but it doesn't say it was only ever designed to run at the power produced on 95 RON, as in Japan the same basic engine with different ECU settings/turbos etc run on Jap 100 RON which I believe is not the same as a UK 100 RON should it exist, but its certainly higher than 95 RON.

It won't do it any harm, and will certainly lessen the chance of detonation occuring, even if the power gains can barely be felt.

I class that as cheap engine insurance.
My MY06 STi states that I must use 97 RON as did my MY 02 STi PPP Prodrive.
I suspect more for engine longevity than producing more power.

Cheers
MTR

MTR

I suppose being pedantic, the PPP ECU is probably mapped for 97/98 octane fuel so it just drops the power down when run on 95 RON.

But the engine is certainly able to cope with the higher theoretical power gains possible with better fuel.

And Fifth Gear seemed to prove there was a gain, as posted earlier on this thread.

Who knows.
Its certainly not worth putting it on a dyno to find out.

Cheers
MTR

andythejock01wrx

Thanks for all the replies !

One thing i'm still not sure about - is the UK 2001 WRX DESIGNED to use 95 ron or are Subaru simply stating that it can cope with it ?
Is it's standard 218bhp with 95ron or 98ron ?

~ The Wikpedia article suggests that vehicles will not gain power by using a higher octane fuel than they were designed for.

tony95

on optimaxi tend to get about 210-220 out of a tank (my95)
on 95 ron about 175-190 ish
engine does seem to run better on optimax

Bob Rawle

The car is designed to use 102 ron fuel and is de-tuned for the European market, strictly a Eurospec should be run on 97 ron or Optimax to make full use of its ignition maps, using 95 ron WILL knock the performance as it will retard ignition, on a custom mapped car the difference is probably 8-10 degrees Optimax to 95 ron on a Sti. Thats huge. the quoted figs are for 97/98 ron, ie SUPER unleaded.

BTW BP Ultimate is still very detty on these cars.

bob

Shark Man

That wikipedia statement is only true on cars that do not have an ECU capeable of adapting to run on higher octane fuels. The Subaru ECU employs a suck it and see attitude....it brings the timing forward, if it senses detonation, it knocks it back again, it'll keep doing this until it settles down or reaches the limits of the ECU map (maximim advance or retard - too much RON, or too little RON).

An example of a car that wont benefit is a Metro running on optimax with stock ignition timing Infact, it is possible to lose power by having too much RON, as full ignition and peak explosive pressure could occur too late in the combustion phase. Also, the stock ignition system may struggle to ignite the fuel, causing misfiring. A good example of this is a car running on LPG (from 102RON upto 110RON?)with stock ignition set to 95Ron (or even 90Ron for some early/pre80's cars).

It has to be kept in mind a different RON fuel doesn't just mean resistance to "det" as many people here think (wikipedia does go into this a little). Lower octane burns differently; It burns faster, but it also ignites easier and thus needs different timing to burn correctly. Due to its characteristics it needs to be ignited later in the combustion stage as it reaches its peak explosive pressure sooner than a higher RON fuel. The common misconception is people think they lose power by switching to lower octane fuels. If the car has fixed ignition and fuel mapping, It will. As detontion is uncontrolled combustion, and results to power loss (amongst engine damage). Remember your retarding the ignition for lower octane fuel because it burns at a different rate, not just because it self-ignites easier.

A vehicle which has adapative fueling and ignition timing can accomodate for the lower octane fuel and optimise the burning charateristics by self retarding ignition, as it burns faster the timing needs to be retarded, so it occurs later on. A higher RON fuel burns slower so more ignition advance is needed as it takes longer to reach peak explosive pressure, the downside is it needs more spark energy to accomplish ignition.

Thus on a roadgoing engine correctly mapped for the fuel, power difference between fuels can be minimalised.

Higher RON fuels on only favoured because they are less prone to self-ignition under high compression and temperatures, combined with other factors that affect detonation, such as cam profiles, valve timing, valve sizes/angles, combustion camber design, piston crown design, inlect and exhaust design. A car manufacturer will take all of this into account.

This is why tuners favour higher RON: it makes their life easier when working with the constraints posed by a given engine design. As it allows higher boost levels to be used with less need for enrichning fueling to help quench and stabalise combustion chamber temperatures, so bhp increase can be maximised.

But on a stock car? Nope, a few horses at the most. Nothing to shout home about anyway

andythejock01wrx

Shark Man never sleeps !

I'm off to buy a Metro (3litre GT4 !) to save fuel !

Interesting argument - but how do you counter the fact that both Subaru and Top Gear have stated there is a a difference of around 15bhp on an Impreza between 95 Ron and Optimax (or equivalent ?)

Shark Man

15bhp in my book IS nothing to shout home about

Engine/combustion chamber design/hot spots, compression ratio, boost pressure and charge temps. Meaning the engine needs to run a few more degrees of retard than what would be optimal for the fuel.

It could be countered by using larger intercoolers, a turbo that doesn't transmit so much thermal energy to the charge air, a more thermally stable combustion chamber and piston crown design, spark plug heat range etc. etc.

But for a manufacturer, it's cheaper and easier just to run more ignition retard, over-enrich the fuel mixture at high revs/high load and slap on a SUL only sticker on the fuel filler