Reckless

so what is the best to use then optimax or bp ultimate ? ps what is the rating on bp

Bexlee

I respect your opinions & everything, Bob, but how do I do this without a boost gauge? What is a GC8?

Dark Blue Mark

Optimax. Its not that BP Ultimate is bad, its just not as good as Optimax if you go by the knocklink. Its 97 and Optimax is 98 min (allegedly)

Bex, GC8 is the classic shape scoob, and you cant do as Bob suggests without a boost gauge.

MB

Bob Rawle

GC8 is a MY92-00 car, GDB/GDA is MY01 onwards, you need a boost gauge, borrow one for the purpose idealy as to diagnose the problem we need data.
DBM having tested Ultimate in my car 8 degrees retard from the equiv Optimax blend was diabolical, ok so I'm extreme but the indicators are there, every car I've mapped with Ultimate has never managed the ignition that Optimax contributes, not only Scoobs but Evo's as well.

Its just not suited and doen't have the det resistance.

cheers

bob

Ninnybobs

Bob,

Interested in your findings on mapping with different fuels.......

Have you mapped anything using Tesco's 99 ron yet.

My reason for asking is that I am on my third tank of 99ron petrol and have noticed a lot more knocklink activity as opposed to using optimax.

Any thoughts?

Martin

captain ted

[quote=Bob Rawle]GC8 is a MY92-00 car, GDB/GDA is MY01 onwards, you need a boost gauge, borrow one for the purpose idealy as to diagnose the problem we need data.


Why we on about a GC8??

Its a MY 01 !!!

Check the data on the origional post first!

Bexlee

Thanks ted, I thought I was going nuts!

Dark Blue Mark

Chill out Ted, think of it this way - Bob is the expert here, and has taken the time to reply and anyone doing a search on this thread in future would now find how to diagnose a sensor fault on both classic and bugeye scoobs. Check Bob's post - it says hold at - 0.15 bar vac but if its a CG8 then 0.4 bar....

But maybe im just thick.

I learned something.

MB

Bob Rawle

I did check out the post however if I read every thread from start to finish I would have a full time job BUT this bbs is for everyone so I always try and accomodate ALSO not every poster gets his model year correct which is why I "test" things some times.

Still since you decided to slap me ...

Martin .. yup mapped quite a few with very good results, I rate it above Optimax in a straight fuel for fuel fight. Sure you been getting 99 ron not 95 from wherever ? (just a stupid thought)

bob

Robocop

Bob

In your view, if a car (MY04 STi PPP in my case) is remapped whilst running on Optimax, what can I expect in changing to Tesco 99 with regards to ignition timing etc? Will it provide less advance than before, because of the fuel make up of Tesco 99?

I ask this because somewhere you mention that Tesco 99 burns differently to Optimax.

Your thoughts would be valued. Thanks

captain ted

Ooohhhh!!

dowser

You all need to try Shell 100 RON

Richard

Bob Rawle

When I map to a fuel I normally leave the car at AM 16 with a touch of negative in the mid range, that tells me that the ecu's learning systems are actually working (they don't always) and allows for a small amount of headroom if better fuel is used but strictly the map you get (from me) suits the fuel in the car at the time. If Tesco99 is used after an Optimax map then it won't cause anything to pull back, I have seen a few guys back for map upgrades who have switched onto the Tesco and have seen no negative learning over and above anthing expected, in fact mostly come back at zero i.e. max ignition. To start with I sense checked by resetting the ecu concerned to eliminate all learnt correction and, again, no negative effect.

Richard I wish !!!!!

bob

Robocop

Bob

Thanks for the reply.

At the end of the day then, I don't need to concern myself over anything. At one stage I thought about resetting the ECU when Shell actually get round to delivering some Optimax to our area, but from what you're saying, don't bother.

jerf

hi mate,after reading treads on the site you seem to be reguarded as one of the best to ask any question for an accurate answer.at the risk of sounding like an idiot (i am a complete novice on impreza's,on my 1st one) what is "maf" "knock" and "det" and what should i check to make sure i keep all these present and correct?
when i was looking to buy my first one i thought it would be best to buy an unmodified one.so i did.i bought a totally standard low milage '95 classic and apart from a few teething problems i love it (apart from the fuel costs 50 miles from a tenner,is this right?) its an import too by the way.anything you can tell me will be appreciated.cheers mate.

Bob Rawle

No need to reset, the ecu will instantly change the fine learning and knock retard/advance levels to suit as you drive.

MAF ... mass air flow (meter) a device for reporting the amount of air that is flowing into the engine to the ecu (engine control unit), it sends an analogue voltage (0-5v usually) output which is derived from an unbalance in a four leg wheatstone bridge (put simply).

Knock and det are the same thing, not to be confused with "detonation". Both relate to conditions in the engine cylinders which result in the air/fuel mixture combusting at the wrong time or in the wrong way, this results in extremely hot local areas on the piston crown which can then eat away at the aluminium.

Detonation (in my terms) is a cataclismic "event" that takes place in micro or nano secs, most often caused by a ring land breaking when a piston picks up. There is no real warning and almost nothing you can do since its so fast to happen. If you are lucky then some knock or det occurs first giving warning. Once its occured the piston crown looks as though a plasma torch has been at it.

hope that helps

bob

Andy.F

Well I certainly don't agree with that Bob ! Not the best evening for an arguement though so I'll leave it for a bit

Andy

Bob Rawle

Andy I expected you would post to that effect since you have made a point of tracking and denegrating, where you thought you could, my comments, I don't see why its an inappropriate evening, whats your point apart from "being pointed" ? As far as I'm concerned its an evening like any other. Perhaps I'll track you.

bob

Ninnybobs

Thanks for the suggestions Bob.

The fuel I have been using over the last couple of weeks is purchased from a newly converted Tesco's garages.

The difference in performance and KN activity was noticable within a couple of days.

KN lights up like a xmas tree in lower gears around the 4-5k revs mark on WOT.

The garage is selling 95, 97 and 99 ron petrol. I can only think that the fuels have been put into the wrong tanks.

I will give it one more tankful, then revert to the trusty Optimax

Cheers

Martin

Andy.F

Det is short for Detonation, nothing more, nothing less. Knock is the sound given off by detonation.

It is normally the destructive force of detonation (call it det or knock) which would cause a ring land to break (not the reverse as you claim)
This breakage may or may not result in a hot spot which can cause Pre Ignition potentially leading to runaway surface ignition (RSI) which in turn can melt pistons.

Andy

jerf

thanks bob,things a bit clearer now thanks.didn't mean to kick off a ruck though!!
just one thing.if the maf sensor has never been checked/cleaned from new at 38,000 miles could it be the cause of a warm engine missfire when boosting,seems ok when cold.

Bob Rawle

Andy your comments are valid of course, I claim nothing mind, but the effect of a piston catching in a bore is one of the most effective methods of causing a cylinder to detonate due to the disintegration of the weakest part of the piston, the ring land, for the rest play on words ... like calling a spade a shovel ?

jerf don't worry about the banter its always going on, if your maf is that old suggest just replacing if the car is a MY99-00 or cleaning if its an earlier one (hot wire). Brake cleaner is good for that (spray from Halfords).

cheers

bob

Engineer@Uni

I felt like i should add my little bit to this very interesting thread:

1) Misslabeling or not, the british WRX should safely run 95 octane with no warning-lights or misshaps. Yes, it prefers 98, but surely if my MY05 STi's manual states "will run on 95 octane, though slightly reduced performance may be observed under certain occasions" then the less-highly strung WRX should not malfunction with it.

2) Something a lot more common in my native Greece than over in the UK is fuel-bootlegging. It is unlikely but possible that the fuel is diluted with (cheaper) diesel in a small percentage so as to make for more amusing proffit margins. As stated by someone early in this thread, you should have gotten the suspect fuel tested at the time.

3) If your car is standard, unmodified and hence under warantee, it is to your advantage to rally -for- the quality of fuel. If indeed it was the fuel that caused the damage then you almost certainly will lose any chance of getting any damage fixed under warantee. For this same reason, if the mechanic isn't 100% sure what's wrong and is affraid you will demand warantee work, he will very likely point his finger towards the fuel. In order to establish this it would be wise to seek out a second oppinion from an indipendent garage.

Good luck with it all and hope no damage comes to your car in the end mate!

Andy.F

Not a problem Bob, as long as nobody is misled.
I'll continue to consider det and detonation as the one and the same thing and that det is the primary cause of ring land failure.
We will just agree to disagree again

For what its worth, the main reason for a piston picking up in the bore is overheating, usually due to bad tuning or pressing for too much power from a particular set up.

Bob Rawle

No worries Andy I'm sure that won't happen, "main reason for a piston picking up in the bore is overheating, usually due to bad tuning or pressing for too much power", or to tight Subaru clearances which cause even conservatively mapped cars to have a problem, don't forget that (especially New Age cars).

cheers

Bob

Andy.F

Apparently so, although I have yet to come across any issues there.

I was under the impression that the logic behind the ultra tight bore clearance was that the very thin linered block bores expand at a similar rate to the hyperutectic pistons although I have never actually measured the thermal expansion rates of said items.

Andy

Bob Rawle

The logic behind the tight clearances is tight Subaru management not wanting to spend out thousands on warranty replacement short blocks like they did over 1998 cars which suffered from pistoin slap for a past time. Now we design those sort of clearances in when uprating the engine. The "gross" example is the EJ257 short block, soo many of those have failed over this issue. Fortunately I have mostly only ended up remapping them after the rebuilds not before. I think the expansion logic suffers from a miscalculation when the engines are run harder, you could be correct up to standard power levels but not more.

Bob

jerf

sorry to break up your detailed dicussion on the life and times of the internal combustion engine bob/andy!! i can see you enjoy trying to get one up on each other!!
i'm not quite as advanced as you two on scoobies (you dont say). bob you suggested that i just replace the maf if it was old (its a '95) and clean it if its a "hot wire".what is the "hot wire" type and how do i distinguish it from the other.also when cleaning as suggested with the halfords spray do i just remove the maf (carefully) spray it,wipe it and put it back as i found it or is there a more involved way of doing said operation?sorry to seem so dull but i just dont want to **** it up altogether costin me money at christmas (2 kids,house etc)cheers mate.

Bob Rawle

As a MY95 its a hot wire, to clean start by just giving the element (seen in the barrel, a good blast with the aerosol, when actually cleaning I use a cotton bud soaked in cleaner but you need a delicate touch, if you damage it they are expensive unlike the MY99-00 or MY01 onwards items. the hot wire device is actually self cleaning, whenever the ign is switched off the hot wire is heated to burn off any deposits.

bob

MaDaSS

I too have suffered with crap Optimax but only once. It was just my luck i had it in the tank as i took my car for its bloody remap. They told me my car was hardly if at all boosting as the ECU had reset to whatever it considered correct for the fuel. They had to reset ECU, and whatever else you do, before they could then run the car to see how it would "perform".
The saddest thing is, i had been thinking, "i am sure this car aint performing, feels ****" LOL. Anyway, the stranger thing is, the car was then mapped with the fuel still in the tank, and i drove it home more than happy at the result.
So what i want to know is, if the fuel was ****, how can resetting the ECU suddenly make it all right? It cannot surely? But my car really was driving on bugger all boost until they reset the ECU.
Imho, which aint much, surely **** fuel should have hampered a remap?
So that then beggers the question, if the fuel was ok after all, what the hell caused my car to back off so much as too not even give me any power?