New VF commodore

[Skylarking]

I can tell you the SV6 knock sensors are pulling timing out on 98 up to 3400rpm then again over 5000rpm. On 91, the engine would be running on the knock sensors with substantial power loss over 98.

So they are working as designed
And what’s substantial?

 

[RevNev]

So they are working as designed
And what’s substantial?

The point is, 98 has an insufficient octane rating for the ignition timing to reach it's maximum advance so 91's miles off for optimum efficiency isn't it?

 

[Skylarking]

The point is, 98 has an insufficient octane rating for the ignition timing to reach it's maximum advance so 91's miles off for optimum efficiency isn't it?

My understanding is that timing is advanced until the sensor detects knock at which point it’s pulled back a little... such checks occur multiple times a second for whatever fuel is used, be it 91, 95, 98 or a good blend of e85 (of the vehicle is e85 capable). Thus the timing reaches maximum advance for the octane rating of the fuel actually in the tank, as such, “optimum“ timing is relative to fuel used.

As to power, I’ve only seen Holden’s statement that the LS3 pumps out 304kw @ 6000RPM & 570Nm @ 4400RPM when running 98RON fuel. Unfortunately Holden don’t specify power/torque figures on 95 or 91RON fuel (LS3 doesn’t have an alcohol sensor nor e85 fuel maps).

It would be nice to see some dyno graphs comparing 91, 95 and 98RON, run on the same dyno on the same day. But I doubt there would be much in it within the normal RPM and throttle range someone would normally uses on a public road (which is why I questioned your “substantial power loss“ statement).

Mind you I’m not an expert though I try to avoid conformational bias. Guess it’s easy for such to sneak in when one fills up with 98 or does a happy dyno run after some mods...

 

[RevNev]

My understanding is that timing is advanced until the sensor detects knock at which point it’s pulled back a little... such checks occur multiple times a second for whatever fuel is used, be it 91, 95, 98 or a good blend of e85 (of the vehicle is e85 capable). Thus the timing reaches maximum advance for the octane rating of the fuel actually in the tank, as such, “optimum“ timing is relative to fuel used.

There's a base ignition timing map configured for maximum engine efficiency and the actual ignition timing following this map, is dependant on the octane rating of the fuel. 98's not that good in reality and I'd say that 102 race fuel would be required for the SV6 ignition timing to follow the map free of knock sensor retard. Running on 98, it's on the cusp where the knock sensors are pulling 1-3 degrees under load however, there's a detonation free window between 3400 and 4800 rpm where the engine produces maximum torque. An additional 4 degrees of timing can be added into that window on 98 on a custom tune to optimise torque.

Datalogging the SV6 engine clearly confirms that 98 is the preferred fuel for maximum efficiency and performance. Disabling the knock sensors is guaranteed to destroy an engine running on 91. Sure they'll run on 91 and 95 with knock sensor protection, but the engine's ultimately designed for a 98+ octane fuel.

 

[vr304]

I’m no tuning expert but 102 octane in an sv6? What a waste of race fuel and I bet you couldn’t physically feel any difference when actually driving the thing

 

[Terry57]

On this road trip 23000 klm towing a van with a 3 litre Evoke VF i started off running 98 premium and did this for maybe 15000 klm. I then changed back to 91 and can honestly say im at the point now where i notice no difference except saving money on fuel. It still cruises along on 90 kph on around 2000 rpm and has no problem climbing hills. Much more important is the regular and early changing of fluids.

 

[RevNev]

I’m no tuning expert but 102 octane in an sv6? What a waste of race fuel and I bet you couldn’t physically feel any difference when actually driving the thing

Nevertheless the point is, the 3.6 LFX engine doesn't run on 98 octane fuel detonation free and would likely take 102 race fuel to run without knock sensor safety intervention. It most definitely isn't an engine designed to run efficiently on 91 at the given compression ratio.

On this road trip 23000 klm towing a van with a 3 litre Evoke VF

I would've bought an FGX Falcon for towing vans, the poor old 3 litre VF's lacking torque for that job. I don't know why Holden fitted that 3 litre V6 then then tried to match a Falcon, they're nuts!

 

[Anthony121]

I would've bought an FGX Falcon for towing vans, the poor old 3 litre VF's lacking torque for that job. I don't know why Holden fitted that 3 litre V6 then then tried to match a Falcon, they're nuts!

The 3.6 SIDI engine was so much better. Actually the 3.6 was better all the way through from VZ, VE and VF.

 

[Forg]

I’m no tuning expert but 102 octane in an sv6? What a waste of race fuel and I bet you couldn’t physically feel any difference when actually driving the thing

Once you get used to how a car normally feels, the reduced power & torque from 91 is actually a little disconcerting. The car feels broken somehow, but it's like you can't quite pinpoint what's wrong & when. It feels like, when you're in a boat, the difference between just prior to aquaplaning & when the boat gets up on a plane - or, it's like you've got 5 more dead bodies in the boot than you usually carry around.

I'm not talking about full load WOT balls-to-the-wall acceleration, which is almost never used in a road car, I'm talking about when you're accelerating normally away from the lights, when there's a slight uphill incline and you need to use the accelerator slightly more with the 91 than with the 95 so it just doesn't quite feel "right".

 

[Skylarking]

There's a base ignition timing map configured for maximum engine efficiency and the actual ignition timing following this map, is dependant on the octane rating of the fuel. 98's not that good in reality and I'd say that 102 race fuel would be required for the SV6 ignition timing to follow the map free of knock sensor retard. Running on 98, it's on the cusp where the knock sensors are pulling 1-3 degrees under load however, there's a detonation free window between 3400 and 4800 rpm where the engine produces maximum torque. An additional 4 degrees of timing can be added into that window on 98 on a custom tune to optimise torque.

Datalogging the SV6 engine clearly confirms that 98 is the preferred fuel for maximum efficiency and performance. Disabling the knock sensors is guaranteed to destroy an engine running on 91. Sure they'll run on 91 and 95 with knock sensor protection, but the engine's ultimately designed for a 98+ octane fuel.

If the base map is such that the engine always needs the safety of the knock sensors to survice (even on 98RON), then the designers made the engine very dependant on the knock sensor to survive. I'd have ensured the system didn't rely so much on the knock sensors when running the recomended grade of fuel... but if that engine is e85 capable, then the settings of the ignition timing base map as was done is understandable.

In any case, engine efficiency is determined by and dependant on the fuel used, As such it runs as well as it can on the fuel in the tank. To conflate efficiency with following the base map without retarding timing is missing the point on these multi fuel (RON) vehicles.

I still wish the manufacturer would provide the engine power/torque curves for then engine with the various fuels it can run on as then it's no longer theoretical issue but something that's quantified so would clearly answer the question of how much better 98RON is.

For the most, i'd say there is bugger all difference beyween 91 & 98, though in some high air temperatures cases the engine may be a little doughy on 91 as compared to 98. However, for many people even that is probably OK as it's safe (thanks to the knock sensor) and saves $15 odd a tank per week (or $750 per year).. Crawling along in traffic, many find the $750 more appealing than any perceived efficiency improvements with 98RON.