Low octane fuel (95 RON) and knock levels

[CJay]

Over here in Ireland (south) we have no choice but to use 95 RON fuel, SUL was taken out of circulation a few years ago. I run an FTO GPX as a daily driver and the ECU restards timing accordingly without any noticable detonation. I have an RX-7 (FD) for weekend fun, detonation kills rotarys pretty quickly so I decided to go the Apexi Power FC route and had it remapped accordingly . I should mention that knock wasn't the only reason I went for the Apexi, stage one mods had a bearing also. (318bhp @ the rear wheels without TCL can be scary at times!)

In terms of the VR-4, how does it react to low grade fuel, will the ECU do the business and retard the timing sufficiently? My main concern relates to driving on boost where detonation is bad news . I have very little faith in commercial octane boosters as a means to effectively increase the RON rating of a tank petrol, I'm considering purchasing a VR-4 and this is my primary worry right now.

CJ

[Nick VR4]

Hi and Welcome

Putting Low octane in a VR4 will cause the ECU to go into safe mode loosing around 40-60 BHP I think

I dont know what the effects would be to do this permanently to the engine if any

[Nutter_John]

I have used 95 ron in the past and not had any real issues with it , but as nick says it does lose a little .

For the last two years I have used 99 or 98 ron and it's been fine , but I'm over in the green isle next week and think I will have to turn the boost down a little seeingas you only have 95 ron

[Kieran]

Davezj posted some Data logs with 95RON petrol in the tank and the results were a little scary - Knock Counts through the roof at times!

The ECU does however react to this and will pull timing and start dumping fuel to keep a lid on it, but it's not foolproof - stick with 99RON and you'll be fine.

If you don't have Vpower nearby, then Tesco 99RON is okay too - I have seen a knock count of 1 with this fuel, and that was at really high revs just before the limiter on a quite warm (20 degree) day.

[Kieran]

In fact, the thread is in the member's area, but here's a snippet from that thread...


....as an aside i am using 95RON petrol, and i am getting knock sensor reading in the 70-80's not all the time, but under WOT at a ton, running standard boost, and octane reading is down to 88 after about 3 min blat...


....filled up with V power and knock sensor is down to 1 or 2 counts and octane is at 100 all the time.

[Nutter_John]

K They don't have Super UnLeaded in the Rublic of Ireland thats the reason for his post /pan

[CJay]

Thanks for the info guys. As I have no access to anything above 95, WOT driving could be an issue @ the top end.

Kieran, any idea what Davezj was using to extract knock level readings?

In terms of the VR-4, what sort of options are out there with regard to an aftermarket ECU (mapable).

CJ

[Kieran]

K They don't have Super UnLeaded in the Rublic of Ireland thats the reason for his post /pan

Yes, but he still needs to know that 95RON could bust his car up!! /pan /pan /pan

Cjay - Dave was using EVOScan I believe.

[bradc]

Lots of us guys in NZ use 95 octane and while it does result in less power it isn't that noticable, and I haven't had any big problems in any of my cars

[CANDEE]

I tend to run mine on 95 and have had no probs with it.. Doesnt seem to use any less fuel on 98 anyhow... :thinking:

[Davezj]

Yes evrything Kieran said about my results are spot on.

Vpowerall the way fro me.

The only time i would use 95 ron is if do a long trip and i am going to use a full tank of fuel getting there. I would have to ensure i did not boot it on the entire trip though.

Where's the fun in that though.

Dave

[Kenneth]

The ECU has high and low octane maps. It should run the low octane maps when it detects you are using low octane fuel.

If you are so inclined I would invest in a tool such as evoscan and log the knock readout using various fuels then stick with the fuel that gives the least knock.

Another thing to try out is using a bigger intercooler which should drop the intake temps much more on boost. One of the NZ members got a significant fuel savings after just installing a 600x300x76 Intercooler also.

You could also use water/ethanol injection.

95RON fuel isn't the end of the world, it just means you will have to go to a bit more trouble (and expense... :( ) to keep detonation down

[d i c k i e s]

I tend to run mine on 95 and have had no probs with it.. Doesnt seem to use any less fuel on 98 anyhow... :thinking:

agree, but ive noticed with 98 its im getting alot more pull (ie, power) and its more responsive as to when i put in 95. 95 seems to lag a bit... like when you plant your foot with 95 in the car... it thinks a bit, then decides... ohh he wants to go faster. With 98 ive noticed alot... doesnt do all that. plus its cleaner, as it should be... you dont get all that combustion stuff on the back as much as you do with 95.

[Subaru ETA]

i run 95 at times, i just notcie the samee as dickies....

[CJay]

Thanks for the replies fellas, I'm gonna take it that either a bigger IC or WI is something I will have to consider in terms of keeping knock levels down, I know that the rotary guys get good results with both options. I'm pretty sure that Evoscan can be used on the FTO (I'm assuming that the the VR-4 also uses the MUT-II diagnostic protocol) so it would be a good investment.

CJ

[Kenneth]

Thanks for the replies fellas, I'm gonna take it that either a bigger IC or WI is something I will have to consider in terms of keeping knock levels down, I know that the rotary guys get good results with both options. I'm pretty sure that Evoscan can be used on the FTO (I'm assuming that the the VR-4 also uses the MUT-II diagnostic protocol) so it would be a good investment.

CJ

I have had evoscan working on the VR-4 if that helps you :)

[Eurospec]

Evo scan will work on your FTO and on your VR4.

Mitsubishi active knock control works like this:-

The ECU looks at the signal coming out of the knock sensor, this is simply a raw signal. It then looks at what noise it expects to hear at what rpm and (though i dont know this- i do suspect) the frequency of the noise itself. What passes through this filtering is a knock sum.

The ECU will react by pulling timing for any knock sum greater than 5. You could think that the engineers thought 4 was okay, but 5 was too high. The timing pull is quite drastic. If you watch it on the logger its not 1 or 2 degrees, its like 10. The ecu will also dump fuel in there too to try and hold down the cylinder temps.

So active knock control only does something when it detects knock. And when it does it boy will you feel the power drop off. There may well be long term trims in the ODB2 protocol which look at knock levels over extended time periods which would then trim the primary timing maps, but i have never looked into these. Even if their are, it will take time for the trim to move (ie like days) and all the time you will be encountering knock events.

Obviously it will only knock when you load the engine.

Both JDM FTO and VR4 primary maps are for 100 octane fuel. 99 being the closest we can get here. 95 is a big step down from that and i am not surprised at Daves results, certainly the VR4 will knock like a good un on boost with 95 in it. Even fto will be struggling when the revs get up. I've seen them knock like 7 counts on bad bp 98. Its just in non turbo cars the detonation event itself is not as destructive as in a turbo car where there is more of everything (Fuel, air, heat etc)

UK cars will probably have a less advanced timing map, though i dont know this for a fact, but the 3000GT for example does. In which case they will tollerate the lower octane level better.

Bottom line, better if you can get some sort of timing control just to pull a little out to be on the safe side.

cheers,

Ben.

[CJay]

Nice info Ben, thanks. Maybe I should limit my search to a UK prepped model :thinking2 (thus reducing my choice dramatically!)

CJ

[KHK]

there seems to have some additive (pills , or liquid form additive) in the market to raise the octane rating

[JJVR4DominicanRepublic]

Guys... I just wish I could at least get 90RON here in DR for my VR4... I have seen more than 50 times knocks of 250's...that's @8Psi. the PREMIUM gas here "THEY SAY" IS 87RON that's why when I push the boost to 20Psi I have to use VP Racing Fuel 109. there the SAFC doesnt register any knock. I should add that I have a big arse FMIC and I dont really know if there was a difference... average dayli temperature here is 30 C . Can you recommend which water/alcohol injection kiyt best fits our cars?Thanks!

[bradc]

your petrol over there is likely to be MON though isn't it?

http://www.carbibles.com/fuel_engine_bible_pg2.html

[omar]

In Ireland Maxol are rolling out E5 which is 99 octane, if you go on to their website they have listed 99% of their garages as pumping it but the reality is really about 10 % if even. You can e-mail them and they will tell you exactly which garage in your area is pumping it. Be warned though as some of them have it on pumps but aren't pumping it till Decemberish! so mail them for definite list.

[Kieran]

Can you recommend which water/alcohol injection kiyt best fits our cars?Thanks!

Well, as usual there's nothing "Off the shelf" for the VR-4!

Sounds like you need an ERL Aquamist system. They are well regarded, and they're sold in the UK and the USA, so it might be cheaper to get one from Ebay USA (I've just checked and there's a few for sale in the USA).

There are several versions available, you can see information about them here:

http://www.aquamist.co.uk/cp/cp.html

From their FAQ section:

System1s is triggered by boost only, the trigger point is determined by an adjustable pressure switch installed in the manifold (3-30psi).

System2s comes with an electronic controller (MF2), mappable between 2000-9000 RPM at 1000 intervals, load signal is either supplied by an adjustable pressure switch or a MAP sensor (not supplied) for a true 3-D mapping, water flow is progressive with pressure. The water line is pre-pressuised (adjustable between 4-8bars) at start up, flow quantity is regulated by a solenoid valve via MF2.

System2c is designed for users with their own custom ECU, mainly for racing cars. System comes without electronic controller.

Given that your knock levels are so high (scary high!!) It might be worth addiing a bit of Methanol to a water injection system - But You'd need to research that.

[Turbo_Steve]

Eeek those Knock levels sound terrifying!!!!
Water injection is a great idea, but I'd be looking to piggyback an ECU and master the timing and fuelling: it's a definite solution (if set up correctly).

[JJVR4DominicanRepublic]

your petrol over there is likely to be MON though isn't it?

http://www.carbibles.com/fuel_engine_bible_pg2.html

Interesting... but for your surprise , they dont even bother to put a sticker saying which of these you are using. great article though ! cheers

[JJVR4DominicanRepublic]

thanks kieran for the always so good replys and help offered. I will check eBay tonight to buy one of the sistems(most suited to my pocket) ;)

Yes turbo steve, I will soon be buying a Greddy eManage, but first I have to rebuild the trans and install external wastegate !!

but first things first.... WATER INJECTION!

[Nevman]

What about UK supplied RalliArt ones?
Are their maps prepared for the local fuel?
The problem is that the best fuel I can get in my area is 97 OCT frm Tesco.
Is that good enough?
The closest Shell garage is around 10 miles from my place and after reading this thread I'm thinking about going there for petrol but it will cost me abut 9 quid to get there and back... That makes it VERY expensive fuel...

[bradc]

Surely you could talk to your petrol suppliers head offices and see what they say.

[Robotnik123]

From reading this I gather that running 95RON in a VR-4 will reduce power, but what about fuel consumption? Will running 95RON increase fuel consumption over running 98RON?

[Kenneth]

From reading this I gather that running 95RON in a VR-4 will reduce power, but what about fuel consumption? Will running 95RON increase fuel consumption over running 98RON?

If the ECU detects detonation, it is likely to use the rich fuel mapping, which uses more fuel at various RPM/Load points. This being the case, then yes you will use more fuel as well as reduced power.

This means that you may actually spend less money per km using 98 over using 95.

[Robotnik123]

If the ECU detects detonation, it is likely to use the rich fuel mapping, which uses more fuel at various RPM/Load points. This being the case, then yes you will use more fuel as well as reduced power.

This means that you may actually spend less money per km using 98 over using 95.

Bugger, just as I feared!

I've been shopping at Countdown a lot lately and collecting Shell fuel vouchers and Shell only do 95RON. I face something of a dilemma now - if I want fuel vouchers say for 98RON BP Ultimate, then I must shop at New World...:inquisiti