2012 Nissan Quest LE: VQ35 Fuel Curiosity
November 09, 2012
Recently, Oldham and I were compiling one of the monthly fuel economy updates. The question came up: which grade of fuel does our longterm 2012 Nissan Quest use?
It's 87 octane, but the question had me thinking about the other Nissan corporate product in our fleet that uses the same powertrain as the Quest, but requires premium.
Both the Quest and our longterm 2013 Infiniti JX35 use Nissan's VQ35 3.5-liter V6 and CVT transmission. Ostensibly the exact same hardware plunked into a different package.
I started wondering why it is the case that one requires premium fuel and the other does not. And for some reason, I started hearing the voice inside your head:
"Well," you're thinking, "the JX probably makes oodles more power than the Quest as a result."
Not so much. The JX is rated just 5 hp and 8 lb-ft more than the Quest. Not exactly a huge difference, especially when we're dealing with a 260 hp engine as installed in the Quest.
"Well," you're thinking, "the JX probably returns significantly better fuel economy than the Quest as a result."
Nope. The Quest returns 19/24 city/hwy mpg. The FWD JX? 18/24.
"Well," you're thinking, "the JX probably weighs significantly more than the Quest. That's why its city fuel economy is a bit lower."
JX35 AWD: 4544 lb. Quest: 4592 lb.
"Well," you're thinking, "at 5.173, the JX's final drive is shorter than the Quest's 4.878. That's why its city fuel economy is a bit lower."
That's true, but the JX uses a larger rolling diameter tire package that nullifies its shorter final drive. The gearing between the JX and the Quest is effectively identical as a result.
Yes, WTF, indeed. So, I inquired with Infiniti as to why the JX requires premium. Maybe there's a big jump in output elsewhere in powerband that doesn't show in the peak numbers, I proposed. Here's the response from Infiniti:
"The Infiniti JX is programmed to run on premium. Smoother response, maximum power and torque. In their words, it helps give the 'Infiniti-ness the customer expects.'
If one chooses to put regular fuel in the Infiniti JX, power and torque will decrease slightly. Not necessarily exactly to the point you mentioned in the minivan offered by our corporate, mainstream brand, but it will decrease slightly.
As for that minivan, its programmed to run and be happy with regular. Quite the opposite of the Infiniti JX, however, in that if one does put premium fuel in it, it doesnt increase power and torque. Therefore, in effect, the customer is wasting their money by putting premium in that vehicle."
From what I can translate, the JX does indeed see a benefit to premium in off-peak parts of the powerband, but the Quest does not. I don't quite understand why this would be the case -- perhaps the Quest's exhaust has more backpressure and/or its intake is somewhat more restrictive. Yeah, it's not a terribly satisfying conclusion. Any theories?
Jason Kavanagh, Engineering Editor