unleaded vs premium

[timmae2006]

hey all im having a debate with some people about using normal unleaded and premium unleaded fuel in the legnum.

I reckon premium but others are saying its not gonna matter which type i use

Any one out there with any suggestions

 

[pu-11-me]

*In a godly like voice over

Use the search button my son......

Lol

Premium only my friend!

 

[VR-04-TT]

Use 98 wherever you can.

 

[SiliconAngel]

Not just premium, but 98 only. As Dawso said, judicious use of the Search Button will bear dividends, but just to get the ball rolling, using 95 (or god forbid 91) your engine will be prone to detonation. Detonation is BAD. It will start with rubbish fuel economy as your ECU tries to compensate and lead to your engine not working anymore. Use low-octane fuel at your peril.

 

[timmae2006]

thats what i thought cheers all

 

[bratwurst_boy]

it would be nice if we had 101 ron fuel like japan

 

[frozen]

using 98 is already too low hence the ecu already richening the mix.. But its as good as it gets in australia.

 

[Hotwire]

not true about 98 not being enough... i've logged my ecu and knock never went over 2. 4 or more and it will pull timing and rich it up - so 98 is fine.

 

[happymatch]

how about E100

well, sound silly but how about E100 stuff? 100 octane but with some substitute

 

[Guest]

The Japanese run the Big gear, so not hurt you Legnum by running it on 91.

 

[SiliconAngel]

The Japanese run the Big gear, so not hurt you Legnum by running it on 91.

Sorry, WHAT was that, Steve? I'm having difficulty following your Engrish...

On the off chance you might be trying to say 91 octane fuel is ok for running in a VR4, let me set you straight - we have members who have logged high knock readings using 95 octane. 91 octane is substantially worse. Quite apart from the ECU compensating with over-rich fuel ratios, driving the car for very long on 91 in the summer on high boost will kill your engine as dead as driving it into a wall...

 

[Guest]

i would not risk it.. in summer its shell 100octain as thats the only 100 octain straight from the pumps.. maybe ill order a shit load of HKS race fuel, can i feel a group buy coming on.lol

 

[Guest]

On the off chance you might be trying to say 91 octane fuel is ok for running in a VR4, let me set you straight - we have members who have logged high knock readings using 95 octane. 91 octane is substantially worse. Quite apart from the ECU compensating with over-rich fuel ratios, driving the car for very long on 91 in the summer on high boost will kill your engine as dead as driving it into a wall...

To back up Trevor's comments, this is exactly the same as we've found on CVR-4. In the UK we have 95 unleaded, 97 'Super' and then Shell (and Tesco, bizzarely) do a 99RON unleaded.

We've had members use 95 and yes, the evoscan logs show significant knock - even on largely standard cars. God knows what it'd look like on 91!

 

[timmae2006]

the guy that imported the car for me has about 10-15 of them just sitting in his garage waiting to sell. he claims to put a tank of premium 95 ron and then 91 after that in all of them!!!! Krikey!!! i think he has issues luckily i got mine of him before he had a chance to curse my car like that How do you know if your getting knock without scanning the ecu for fault codes and how many tanks of fuel you guys reckon it take for ecu to adjust before it gets it all right???

 

[Zild]

Fill her up with 98, and then disconnect the battery. Flick headlight switch on then off to drain any remaining power from the car. Wait about ten mins.
The ECU will get its shit straight and reconfigure itself for the higher octane fuel.

 

[timmae2006]

yeah cool ill try that

 

[SiliconAngel]

the guy that imported the car for me has about 10-15 of them just sitting in his garage waiting to sell. he claims to put a tank of premium 95 ron and then 91 after that in all of them!!!! Krikey!!! i think he has issues luckily i got mine of him before he had a chance to curse my car like that How do you know if your getting knock without scanning the ecu for fault codes and how many tanks of fuel you guys reckon it take for ecu to adjust before it gets it all right???

Tim where'd you get your car from, if you don't mind my asking?

As suggested, just reset the ECU and you'll be fine. As for knock, you can hear it if you know what to listen for. You'll also notice the car running badly as it overfuels to compensate.

Hopefully he's not running them much on that, if its just used to move them around the carpark it won't do too much harm. But running them up and down the highway or hard takeoffs could well do serious damage.

 

[timmae2006]

yeah south freo imports is the place thats where i got mine from and the bloke has heaps just sittin there his name is stuart

 

[Sydo]

stick a logger on the ECU and check the knock on 95 - the engine will be running as rich as possible to try to reduce knock and end up in limp mode, which is terrible for both economy and power.

My interpretation of the data is a little different.

After keeping records for over 20,000kms, I can safely say there is no difference between using 95 and 98 ron fuel in regards to economy at highway speeds. None.
I get 10.5 - 11.5 ltr/100kms regardless of the fuel type.

The story is a little different when it comes to city driving.

After a little bit of messing with Evoscan, I have the following thoughts to contribute;


(Initial testing only.. using Safeway Vortex 95)


Engine knock appears only relative to airflow and engine load (not rpm).
Initially when knock is registered, nothing much happens within the ECU. The AFR map is reduced by about 1 degree, but I'm not sure what that means. Nothing else seems to change.

If you are to keep driving enthusiastically and knock continues, the car does begin to adjust the fuel map over time. I have seen a 13% reduction in the octane levels registered by the ECU after a 10 minute spurt around the back country tracks, with a knock level up to 14 under heavy load!
This will have a direct effect on economy and power.
This is the engine doing what it must to protect itself - but it does not happen straight away.


(I have no idea what 91 would do, and do not want to find out either)

The good news is however, the ECU will revert back to the base 100 octane fuel map over time with a more relaxed driving style.

So... My recommendation?
98 for city, fun and track.
95 for highway and other boring drives.



This week I'll be testing with 98.

 

[dimi_108]

Nice write up Andy thanks for the results.
Tim, I think it would be safe for you to stick with 98 octane.
Spend the extra few cents per litre for peace of mind and also knowing you're getting the best you can from your car on every fill up. After all, you're driving a VR-4, not a camry