Dyno Day 2

The owners manual for the 2005 Frontier recommends a minimum of 87-octane fuel but states that 91-octane or higher may be used "for improved performance."  Conventional wisdom on the Nissan bulletin boards is that the ecm in the VQ engine can advance ignition timing to take advantage of premium fuel, and some claim that gains of up to 10 horsepower are possible.  I decided to test that claim on a chassis dyno; for a description of the dyno testing process, click here

THE TEST:

I ran a few pulls with a tank of 87-octane gas and was very pleased with the results;  221.5 peak horsepower (SAE corrected) at about 5650 RPM and 230.10 ft/lbs  torque.  You can see the graphs of the tests here.  At the next fill-up I filled the tank with 93-octane fuel and ran two complete tanks of premium (from the same station that I bought the 87-octane gas) to allow the ecm to adjust and to ensure that there was no 87-octane gas remaining in the system.  I didn't notice any increase in performance by the seat-of-the-pants dyno, but I figured that the machine would be a more impartial judge.  We strapped the truck to the chassis dyno and ran three pulls; all were very consistent so I believe that we got a good reading. 

THE RESULTS:

You can see the results on the graphs below--allowing for the machine's margin of error, there was almost no difference in the two.  The test conducted with premium fuel showed 219 horsepower and 229 ft/lbs torque, both numbers actually slightly below the numbers posted on 87-octane fuel.  There were some gains in the lower RPM ranges, but peak power numbers were essentially the same.  I have been very careful to keep possible variables at a minimum, so I am at a loss to explain why there was no increase in performance with the premium fuel.  Even accounting for margin of error on the dyno machine itself the differences would have been small, certainly not enough to justify paying for the more expensive premium fuel.  You may draw your own conclusions from this test, but mine are clear; my truck runs very well on 87-octane fuel and no better on the high-priced stuff.  With gas prices high and getting higher I'm only too happy to fill 'er up with regular, thank you.