High Octane 91 vs Low Octane 87
 

I saw on a review today about the new Acura TSX wagon that it is supposed to use 91 octane fuel This is interesting news as I ran our 97 RL on low octane all the time unless I was going to drive in the hills.

Premium specified; regular OK temporarily, but Acura warns: "The long-term use of regular-grade gasoline can lead to engine damage."

Engine ping will damage valves, but I never had an issue using the low grade fuels. Now the '06 we have says to use high octane fuel and we run low octane around town and mid or higher on trips.

There should be a knock sensor in the block to retard the ignition if it pings. In fact, the knock sensor is so sensitive that you may not ever notice a ping.

So this is a technical question...why the high octane? Does the RL have a high compression engine?

I found a few threads on the same topic, hope these help.

Search results: https://acurazine.com/forums/search....archid=4739360

Threads:

https://acurazine.com/forums/showthr...ht=octane+fuel

https://acurazine.com/forums/showthr...ht=octane+fuel

From my understanding with the higher octane is that there is a longer carbon chain in the 91 rating. Engines that require the 91 octane rating have been engineered to take advantage of that and if a lower rating is used then maximum horsepower may not be obtainable.

Yes, it is a high compression setup. You don't want fuel to prematurely detonate do you?

And Alfa, I'm willing to bet you'd actually have saved money buying premium for your RL since the car's ECU would not be retarding the ignition. More miles per $$.

I agree. You will get higher mileage with engine designed for higher octane. You won't get higher mileage with premium in engine not designed for it.

I've been told in no uncertian terms that I should run premium through my RL.

After doing an intake removal and cleanout on my daughter's '99 TL (to remove all the carbon and other crap that had collected), and replacing the third EGR valve, I'm convinced. That was a big, dirty job and props to Acura for giving me the TSB with all the proper torque values for the manifold replacement!!

My RL gives me the same mileage estimate with mid and high octane. I've also use those supplement gas booster they sell at the dealer. Currently I might consider downgrade to mid octane to save $$$$. I love my RL but it's draining my pocket on gas but rules are if you want to play you have to pay.:ugh:

We don't get true high-test in SoCal anymore (unless you get the $9/gal racing gas at the pump in RSF), so my choices are 87,89 and 91 octane.

The RL gets 2mpg better on 91 than it does 87. I only run 91.

I filled up for a road trip this last weekend with premium. The mileage was about 26 mpg not using cruise control (broken switch) and the engine was quieter. If you figure 20 cent different for 87 vs 91, for 15 gallons that is $3.00 more for a tank. It isn't that much when you are looking at a $50 fill up. If you are driving around town, I would go with the cheaper stuff.

I just pump 56.00 tonight on a fuel tank but I drive freeway and city. It only last me 4 days after driving about 75 miles round trip.

That's about 50 miles off from what I get with my daily commute.

Guys, it's a $50k car. Okay, they're worth more like $15k-$30k now, but still, it is a luxury vehicle. Adding a few bucks to every fill up is well worth it. This thread reminds me of one of the nerve-wracking considerations when I buy used cars. I always wonder how the previous owner handled things like these. I baby my vehicles because I want them to last as long as possible. Adding a few dollars to oil changes and fill-ups gives me peace of mind.

if u own a RL and put 87 in your car, i think its time to down grade to an accord. u have to pay to play, if not the car aint for u.

TSX Owner's Manual states:

"Unleaded Premium, pump octane number 91 or higher is recommended.
Use of a lower octane gasoline can cause occaisional metallic knocking noise in the engine and will result in decreased engine performance.
Use of a gasoline with a pump octane less than 87 can lead to engine damage."

My understanding is that the knock sensor will count the number of times it detects pre-ignition and use that number to estimate the fuel octane and then select from a series of maps that determine ignition timing under various conditions. Lower octane will result in a map with retarded timing to avoid pre-ignition of the fuel/air mixture and the resulting engine knock. This will result in decreased fuel economy and engine horsepower under high load conditions. It is far less likely, with gentle driving and winter weather for knock to occur. The higher the ambient temperature and the harder you drive, the more likely it is that the engine will experience pre-ignition or knock. If those conditions persist, the ECU will resort to a less than optimal map that retards timing and the engine will not deliver full power or best fuel economy. If you do switch octane, there is a period of adjustment before the ECU is able to determine that the octane is higher. The owner's manual warns that octane below 87 can cause damage to the engine, presumably because the ECU cannot retard timing enough to avoid prolonged knock under high load conditions with octane below 87.

Refiners used to tie higher octane gasoline to a premium detergent package, but it is my understanding that this is no longer the case. The only real advantage to higher octane is resistance to pre-ignition. Before the advent of electronic engine controls with feedback loops, light pinging under load was the sign of optimal timing. It is now possible to develop a high compression engine that adjusts timing based on the octane of the gasoline being burned and thus provide optimum efficiency. The ECU has the ability to trade away performance and fuel economy in order to protect the engine as the octane is reduced and pre-ignition is detected.

My recommendation: Use 89 octane in the winter and 91 octane the rest of the year for gentle driving. The ECU should adjust to the lower octane with a map that prevents knock under high load, high heat conditions. To have peak horsepower available and improve fuel economy when driving aggressively, use 91 octane in the winter and higher octane once the weather warms up. Octane can be lower at higher elevations due to the reduction in density of the intake charge. If Acura increased horsepower using a larger displacement engine rather than higher compression, fuel economy would suffer and at least partially offset the added cost of premium fuel. The only real negative I am aware of with the TSX manifests itself in cold climates. The stock battery is just too small to cope with starting a high compression engine on extremely cold days. Hope this helps.

I find my RL runs best on 91 (which is midgrade around here). I really do think it runs better with 91 than 93. I have only put 89 in it once and didn't notice a different but 95% of the time I put in 89.

91 or 92 only. well thats if you like you car