Comparing Fuel Octanes on MoTeC's Engine Dyno

Engine management manufacturer MoTeC recently undertook dyno testing of different street-available fuels. The testing was done on their engine dyno, the test mule was a Mitsubishi Evo IX engine, and the results clearly show the gains able to be achieved with specific tuning to match higher fuel octane. And the data also shows that without specific tuning, little gain is experienced....

Testing

Three different fuels were tested. Two, identified only as X and Y, were 98 octane pump fuels. The third was Shell’s V-Power Racing 100 octane fuel. Four separate fuel cells were used, the fourth used to contain waste fuel from the fuel rail obtained after flushing-out each old batch of test fuel. Each fuel was bought from the pump and then tested by a laboratory.

This testing gave the following results:

Test	Test Method	Units		VPR Racing 100	98 octane ‘X’	98 octane ‘Y’
Density @ 15 degC	ASTM D4052	g/cm^3		0.7714	0.7575	0.7554
Distillation	ASTM D86	deg C	IBP	40.3	33.4	32.7
			10% Evap	54.3	54.6	52.7
			50% Evap	109.3	107.6	105.7
			90% Evap	141.3	153.7	163.1
			FBP	173.9	184.5	190.2
			Residue % v/v	1.0	1.2	0.9
Research Octane	ASTM D2699	RON		101.1	98.2	98.4
Motor Octane	ASTM D2700	MON		87.8	86.7	86.5
Reid Vapour Pressure	ASTM D323	kPa		59.00	64.00	57.25

The engine was a standard Evo IX engine. Care was taken that the dyno cell installation closely matched the in-car installation: this included the use of the standard intake and exhaust front pipe, including cat converter. The dyno runs were made with an acceleration rate similar to that achieved in the road car in 4^th gear.

Results from 98 fuels X and Y were so similar that in the following text, no differentiation between them is made.

Standard on 98 RON

The first test was of the standard ECU on 98 octane fuel. This showed a peak power of 303hp (226kW). Interestingly, the power curve was a long way from being smooth...

...and the torque graph for the standard engine shows why. Torque peaks at 270 ft-lbs at about 3500 rpm, drops to 260 and then holds this figure until 5600 rpm, and then falls away at the top end.

This logged boost curve shows why the torque curve looks like it does. Boost peaks at 1.4 Bar but then falls to 1 Bar for most of the rev range.

Standard on 100 RON

So that’s the standard engine and ECU - what happens when you feed it 100 octane fuel? The answer is: not much. The 98 octane (blue) and 100 octane power curves (yellow) overlay almost perfectly, with just a slight gain (4 per cent) around 6000 rpm. And of course, with the power curves being much the same, there’s no change in torque either.

MoTeC M800 on Standard Boost

Rather than then tuning the standard Mitsubishi ECU for optimal performance on the 100 RON fuel, MoTeC then ditched the Mitsi ECU and plugged-in their M800 unit. That’s an expected move from the manufacturer, but wouldn’t necessarily be the next step for an Evo owner.

The first test with the M800 was to tune the boost curve to match the factory boost curve, set the variable cam timing to also match stock – but to then tune fuel and ignition timing to get the best safe outputs.

How well the MoTeC engineers were able to replicate the standard boost curve can be seen here, where the MoTec and standard boost logs are compared.

So how much gain was there from the M800 being tuned to give optimal power and torque outputs – but still on the standard fuel and with the standard boost curve? As can be seen here, the increase (shown by the purple line) was considerable right through the rev range. Over the standard ECU running the same fuel, power was up by 20-30hp over most of the rev range.

But what happened when 100 octane fuel was used and the MoTeC ECU was then tuned to suit it? Well, there was another gain (red line), but it was major only at higher rpm.

MoTeC M800 with New Boost Curve

MoTeC then decided to use the M800 to change both the peak boost and also the shape of the boost curve. The thinking was this: the anti-detonation properties of higher octane fuel would best be seen when a high octane fuel was actually needed. And increasing boost requires more fuel octane...

Back on 98 RON fuel, running 20 psi with a very differently shaped boost curve gave the power results than can be seen here. The new boost curve has given a massive increase in mid-range power.

And now the final result: 100 octane fuel, new MoTeC driven boost curve and tuning to suit the fuel. As can be seen by the green line, there is a very substantial mid-range power and torque gain – when cylinder pressures are highest, the higher octane fuel allows a much greater ignition advance to be run with the higher boost levels, in turn creating extra torque and so power. MoTeC engineers also make the point that if they’d changed the restrictor in the wastegate plumbing to allow the standard pulsed wastegate control valve to run higher top-end boost, even more peak power would have been gained.

In fact, on 20 psi boost, the 100 octane fuel allowed 7 degrees more timing advance at peak torque over the 98 fuel. In turn, mid-range torque improved by 11 per cent – on the same boost pressure!

The table below shows the massive gain in peak torque that was achieved over the starting point. However, as indicated above, the obvious interim step of tuning the standard ECU to provide higher boost and best results on the different fuels was not undertaken.

Fuel	ECU	Turbo Pressure (PSI)	Torque at 3950 rpm	% Max Torque Gain
Premium 98 Octane	Mitsubishi	14	265.0
100 Octane V-Power Racing	Mitsubishi	14	267.5	+0.9%
Premium 98 Octane	MoTeC	14	300.8	+13.5%
100 Octane V-Power Racing	MoTeC	14	311.0	+17.4%
Premium 98 Octane	MoTeC	20	328.5	+24.0%
100 Octane V-Power Racing	MoTeC	20	363.7	+37.2%

Conclusion

Just putting higher octane fuel into the tank of the standard Evo makes little or no difference to the performance that’s available. However, when specific engine tuning is undertaken to match the non-standard fuel, results start to appear. Run 100 octane fuel, more boost and suitable tuning – and then the power and torque outputs respond extremely well.

Contact:

www.motec.com.au

MoTeC fully paid for this testing – no financial support was provided by fuel companies.