VR4 petrol do I use 91 or 95

[Ryan]

What are you two on about?

Nobody mentioned anything about mapping or driving. All I mentioned was the results of the EvoScan logging whilst fuelled with 95. *shrugs*

[Kenneth]

I think there is something in the fuel argument.

I wouldn't be surprised if there is a difference in the fuel rating scale, it would make a lot of sense.

IIRC V Power from shell is rated at 95 octane here.

In my opinion, a difference in fuel would explain all the differences we see between cars in NZ and UK. I think there are some differences in Oz too? don't quote me on that one though.

Occam's razor...

[bradc]

Nick, on Ryan's car the octane level drops to around 93 with 95 octane and stock boost, we couldn't get it to go any lower than that.

With 98 octane and increased boost it settles on about 94 or so normally.

[Rambaud]

BP do a 102 RON petrol at selected UK outlets, but cannot remember the price; ~ £2.50 a litre?

Anybody seen a car dynoed with a tank of 102 RON?

[Nutter_John]

102 ron on it's own will make no difference but if you have you car mapped ( like Bradc's then you will be able to get more out of the engine as the fuel is more stable ) .

Also at £2.50 a litre the petrol station would want to be right next door to the dyno

[Turbo_Steve]

The 102 stuff is really pricey - but not as pricey as C10!

Best bet if you want to go to this level is to run a seperate tank for getting to/from the dyno/trackday and switch the feed over, as well as to a different map.

TBH it's mainly used by "Trailer Queens" that get filled up on the back of the trailer and taken to the event, thrashed senseless, and brought back on their trailer. These generally have the fuel drained anyway in between events.

[Hank Scorpio]

VR-4's need more E85 love. A great fuel if you can set your car up properly

[Turbo_Steve]

A big IF though: we're pretty much talking a Standalone ECU to make the most of it!

[chariot]

I just got a VR4 Legnum and not sure what petrol the last owner used so as I've done with all my other cars I just put 91 in it. I don't know a lot about cars but is there any negative effects from mixing different petrol types? Obviously 95 and 98 are more expensive but I heard somewhere that if using your car can be more fuel efficient?

[Subaru ETA]

it doesnt matter if 95/98 is more expensive! if you are worried about fuel prices you should probably be driving a corolla!

all high performance cars should be run on the highest poss octane. in fact all jap cars should really because they dont have 91 octane over there so they are not mapped to run on it.

running 91 is going to cause detonation. to prevent that the ecu is going to pull the timing. the side effect is poor fuel economy, poor performance and a sick engine

[chariot]

Is a hissing sound and air coming out normal when I open the fuel cap? Never had this on any other cars

[Subaru ETA]

that is normal

[Ryan]

Is a hissing sound and air coming out normal when I open the fuel cap? Never had this on any other cars

I get it all the time if I let the fuel level get quite low.

[bradc]

Running 98 is cheaper than running 91 and having your engine explode.

[Archie]

What do you mean by "pull the timing"? It sparks earlier in the cycle? If so, isn't this just making sure early detonation happens?

[Nick Mann]

No. Pulling the timing means pulling it back. Losing advance. The spark happens later in the cycle.

Hope that helps.

[mattnz]

I don't think that early detonation is a good thing.

[Turbo_Steve]

No: pulling timing means "retarding" it, which means it fires later.

It's because the ECU measure the values in terms of "Ignition Advance". So you're pullng timing out.

[Turbo_Steve]

Early detonation doesn't really have much to do with timing.

Strictly speaking, detonation refers to "explosive / destructive" combustion.


You're talking about "early ignition" which can lead to detonation.
Pre-Ignition (or dieselling) will also usually lead to detonation.

However it isn't a given: it's just likely.

[Nick Mann]

It depends on what you mean by early. I'm not a scholar of these matters by any stretch of the imagination, but my understanding is that for optimum power at high load, the spark needs to happen slightly earlier than it would on a sunday afternoon cruise. The ECU recognises this so advances the timing under appropriate conditions.

The way I understand it is that if the timing is advance too far then detonation can occurr. The VR4 has a knock sensor that detects detonation and retards the timing. Again my simple understanding makes me think that lower octane petrol is more likely to give detonation. Certainly, with lower octane petrol in a VR4, the sensor detects more knock and the timing gets retarded more.

I'm trying to remember numbers from Evoscan - I think when on idle the timing advance is only about 4/5 degrees but when on full chat it can be well into the twenties. Please don't quote me on that - I can't check any logs on this PC.