E39 GMH 3.0 SIDI: 91 vs 98 Octane

[swingtan]

Just to separate this from the PID thread.....

I got down to 70KM to empty and figured it was as good a time as any to compare 91 and 98 octane fuel. The car had 460km on the clock, so is still very, very new. The comparison is still valid though.

Vehicle:

• Holden VE SII Sportwagon (Omega)
• 3.0L SIDI engine
• 6 speed auto
• E39 ECM
• T43 TCM

Conditions:

• Ambient Temp: 32'
• Rel. Humidity: 29%
• Barometric Press. : 97kPa
• 2 Adults and 2 teenagers on board.

Here's the log details, Note #1 is on 91, the "Chart Inspector" is in the middle of the tank refill and Note #2 is on 98.

Octane	91	98
RPM	2298	2350
ETCTP	52%	58%
APP	37%	40%
Spark Adv.	10'	15.5'
KR	2.5% (3' peak)	0'
MAP	95kPa	96kPa
VSS	56kmh	57kmh
MAF Air	57.95gm/S	54.78gm/S
IAT	37'C	47'C
Engine Trq.	235.0nM	237.5nM

So.... I think the difference is pretty obvious. Some of the really interesting points here....

• Spark advance came up 5.5' with similar engine load and RPM.
• MAF air speed was slightly reduced.
• Calculated engine torque rose slightly.
• No KR with 98 fuel.
• The ECM applied significant throttle torque reduction when shifting with 98RON fuel.
• All this occurred with an additional 10' of IAT.

The car also felt much better on the road, an indication that it's suffering badly from the lower octane fuel. I think Holden should have made this a 95RON minimum engine, really it's not happy with 91. Note also that the fuel trims also reduced, indicating it was running slightly richer on the 98, so maybe the use of 98 would get better value for money....... It's an interesting thought.

Simon.