just been reading through the threads i have a 95 wrx and normally fill her up with v power as i was told that was the best fuel to put in her.
i then noticed i was draining on fuel but thought it was because of the fuel prices and not getting as much for my money. so went down to our local asda garage and topped her up with normal unleaded she seems to run ok on that but as i'm travelling 500 miles per week would it be advisable to change to the t99 it approximately costs £65 pw to fill her from empty

 

I've sent an email to Shell, so hopefully they'll come up with some ideas

 

I filled my wrx to the brim with red diesel yesterday just to see what would happen. My findings were as follows:

-It now does 0-60 in a fortnight
-It shoots brown flames out the exhaust (and engine cover, or 'bonnet')
-I get 0mpg
-According to Subaru my warranty is now 'invalid'
-I have been able to remove my spark plugs, gearbox and engine with no noticeable loss in performance.

All in all a very affordable and worthy mod.

 

To date I guess I've used about 1.5 tanks of fuel since my MY99 JDM WRX has come back to the UK. I always used High Octane (100 RON) fuel in Japan and since it's been back I have put only Shell V-Power in it. So far in normal motoring I've seen no activity on the KnockLink, same as in Japan. I gave it a bit of a thrash last weekend and my mate said 3 lights came on at high revs, same as in Japan.

So currently I'm happy it's performing on V-Power pretty much as it did on Japanese 100RON fuel. I'm sort of reluctant for that reason to try Tesco 99, especially as it's a weekend car and the difference in cost is not really significant given limited mileage. I'm interested to follow this thread however to see if any firm trends develop.

To establish a pattern people would need to keep a good record of mileage/types of driving/type of petrol used over a number of fillups and then post that information together with UK/JDM and mod status. Without that info, there's no basis for making any judgement about which is the better fuel.

 

It will cost you more for a new engine when it goes POP! Don't use Normal UL in a Jap import WRX unless it's been mapped for it.

 

Filled up with T99 today and on the first run there was flat spot as it went through 4500rpm. Happened a couple of times almost randomly and seems to be okay now.

 

oh oh!! will have to quickly fill her up at tescos then!!

 

I've had a reply from Shell to my polite e-mail mentioning worse fuel economy with V-Power. See below:


Thank you for your email regarding Shell V-Power.

Below is some further information about V-Power Gasoline (VPG) and the differences when compared to Shell Optimax (OMX):

1. VPG has a RON Octane of 99 compared to the 98 of OMX - this will leverage either improved responsiveness and/or fuel efficiency in certain vehicles, particularly those with high performance engines - dependant on driving style of course

2. VPG has much higher detergent additive levels than OMX used to have, which keep the engine fuel system even cleaner - helping to aid increased fuel efficient burning.

3 VPG contains the Friction Modifier Technology additive that lubricates the piston to cylinder contact within the engine. This converts more of the energy released from the fuel into drive power, and FMT was not in our OMX fuel at all.

4. VPG has been created by further developing the OMX fuel, but does not contain an octane booster additive to achieve the 99 Octane. VPG actually contains a high octane hydrocarbon blend component to create a balanced 99 Octane fuel.

Given the above information, we are surprised at the comments noted as the fuel technology should give you increased mpg and/or improved responsiveness.
I hope this information helps to address your query.

Kind regards,

Mike Ward
Shell Retail Customer Services

 

You should send them a link to this thread!

 

I had exactly the same reply but didn't get a chance to post it earlier....

 

your ecu was prob adjusting to the petrol, which can cause a power loss then increase

 

Yes I agree, it is similar to what happens after an ECU reset, but I find it a little strange given that they are both 99 RON and if this happens every time I change my brand of petrol, it's not good for when I can't find a tesco

 

mine run crap on v power as well optimax no probs now i mix it i pt £30 v and £15 unleaded and it works it runs better than it did on optimax honest

donna x

 

Could we have that in English please.

 

All this is speculation unless anyone has some proof, ie delta dash, timing numbers before and after etc. Your ECU has to cope with many different parameters, including ambient conditions etc which will skew the effects.

Works fine on the Evo. Is it noticibly better than Optimax? Is it bollocks.

An extra octane point or 2 will allow you a touch more timing, which eaquals a few more bhp (im talking stage 1 tuned type cars) With that in mind, think of this: Most would notice if driving along and you put the aircon on, which probably saps a few bhp. Would you notice that same difference in power if you got in the car from fresh after not driving it for a day or two? I wouldnt.

MB

 

I have filled up twice now with Sainsburys Super, and apart from it being cheaper than V Power i also seem to be getting more miles to the tank. Its running no diff to when on V Power, and my new nectar card is also doing well.

 

Well, they've done it before with Formula shell, and it trashed a few engines. My driving instructor had plenty of problems with it.

From a random website.......

 

I think as some people in this thread have now noted; Fuel octane doesn't mean everything. It's just a small insight to the fuel's behaviour

The other important factors is the calorific value (bang per buck). Additives used in the fuel can affect that (call it dilution, if you want to gain a crude concept of what happens). Depedning on the additive, the fuel may have a higher, or indeed lower calorific value.

Also how fast the fuel burns is very important. The flame front speed or burn time/rate. This is loosly related to octane, but not in the way as you may think (octane being the resistance to detonation/knock). Higher octane fuel tend to burns slower due to the additives used. This slow burning is a way of controlling detonation (which is uncontrolled burning) of the fuel.

The understanding of what is happening here is critical, if the combustion doesn't reach its full flame front at the exact right time (in terms of piston position) the engine loses power and wastes the fuel's potential. So the ignition system has to have the correct timing for a slower burning fuel. Generally, the slower the flame rate of the fuel, the sooner it needs to be ignited...thus the more ignition advance that is needed.

Now. If the car was mapped specifically for that fuel. You'd probably find you not have any problems. If it is not mapped for that fuel, then there are too many unknowns in the engine's stock ECU map tables to catorgorically state if it is actually capeable of fully adjusting to the fuel's properties throughout the entire rev range and load scienarios. Older IMpreza ECUs can advance and retard ignition timings as well as adjust fueling in closed loop mode, just like the new ones. But as with both types, the longer they are operated without a reset, the more averaged (and thus safer and accurate) the values for the ignition timings and fueling stored in the map tables are. This is how a car can appear to compensate for a semi-failing MAF sensor - as it relies on stored data.

Keep changing fuel type every odd week is going to have unknown effects, so any observed outcome (in terms of comparsion) is going to be invalid. Unless you start from a common point, and that would be with a standard factory ECU with no previous "learned" data stored in its map tables to rely on. Call it a clean sheet, if you will.

 

In Australia, VPRacing runs leaner due to its ethanol content. I dont know the composition of UK fuels but this causes the car to run leaner pre and post boost. As a result, boost comes on slower and response isn't great before boost, and more fuel is used in closed loop. Post boost above 3000 revs, the stock wrx runs conservatively rich, so using VPR brings it back to a slight leaner more efficient afr. This makes it a better drive at max power, but at the discount of lower rev response. You need a remap to get best benefits out of the extra ron and oxygenation on both ends and the extra RON is bonus

Again, this is based on VPR in Australia, we run E5 and is rated 100 RON.

 

I run my car on Vpower and it fabulous - a lot more torque and a shade more power. Indeed this has even been measured

The car has is an unmodified Spec C and with Vpower is knocking out over 360lbs of torque around 20lbs up on Optimax.

Regarding an earlier debate I am still waiting to hear an explanation of how an ECU needs to compensate for higher octane. Needs being the key word.

Of course it is advantageous to compensate for it (more power) but to suggest it needs it is odd. I am sure that I could put 110ron race fuel in mine and it would run OK, albeit with less power due to the high octane burn characteristics.

Of course the in the original thread of that discussion Andy disputed it and Bob chose not to respond when asked the question directly as to why the ECU would have to compensate for higher octane fuel. As I have said elsewhere I would love to be educated as I do not understand what mechanism that might be.

Will keep using Vpower as it is the sweetest fuel in my car.

Rannoch

 

Prana,

I fully understand that you can map in more advance with higher octane fuel and therefore get more power. The question is not whether you can it is whether you must as it would prevent the car from running well. It is not my experience and was 'disputed' by Andy F who certainly knows performance mapping.

Can you explain why using higher octane fuel (in this case only 1 or 2 RON 'over' the map limit) would make it run leaner?

When chucked in a whole bottle of NF for a track day there was certainly no issue with running at all even though there was a much higher octane limit than had been mapped for.

Rannoch

 

Rannoch - rewording to answer your question better.

It doesnt neccessarily run leaner because of octane levels, the correlation to me is not established nor implied (perhaps by another posted?). But in the case of VPR, it runs leaner. My post above alludes to ethanol content. Ethanol has an atomic element bonded together in the ethane, which during combustion, combines with the C and H to form your exhaust gases, which accounts for the leaner mix. All blended fuels have different make up, some have more complex HC additives, which varies both the lambda and resistance to knock.

Let me know if that doesnt answer it, I'll try again

 

So the compensation will be an enrichment and is nothing to do with the ignition compensation at all. Indeed a lot of new high octane fuels contain bio-ethanol.

However, I presume that once the enrichment is appropriately compensated then ignition compensate can, but not must, be used to provide power gains.

I guess my MY06 Spec C is lucky in that it has no issues running lean when using Vpower - indeed it is much smoother than any other SUL fuels available here in the UK.

Thanks for you explanation which I would have understood if I had read your first post properly

Rannoch

 

There is one more complication which I should add but don't know enough to make a 'definitive' comment. The burning process of oxygen richer mix such as ethanol, DOES make burn faster. Conventional petrol burn converts much of the gaseous into CO before reconverting into CO2, whereas alcohol immediately burns hotter and quicker, so the compensation of ignition timing btdc for petrol is diluted a little. Where timing has been made conservatively for Petrol, this also means quicker burn to reach maximum expansion, a slight 'apparent' change in timing.

This is not mechanical and cannot measured by the ignition BTDC itself as its chemical exothermic characteristics, hence the complications in measurements, I would think back to basics, on the dyno and find theoretical best ignition timing vs careful monitoring of knock.

 

Mine seems fine on V power.
My 03 STI Type uk

 

i aint read all the above posts but, is the any mappers out there that have found any differance?

 

All the mappers I am aware of reported a measurable improvement with Vpower.

 

I've kept pretty good records of fuel use and mileage for all 40000+ miles on my 05 wrx, including fitting PPP at around 10k.

If anyone wants to see the data they're welcome.

Anyway, there is no mpg difference at all (on average) between optimax and vpower on my car on all the journeys I do (a varied mixture of short and log journeys).

Does vpower really feel any different? Not at all...

 

I enquired with shell when v-power was launched, they said it contained no bio-ethanol or other oxgenating components.

 

mines an my99 uk turbo and runs crap on v max. will an ecu reset sort this out?