Car with a 9.6:1 Compression Ratio - What Fuel to use?
 

I have a 1996 Acura TL 2.5L Inline 5 with a compression ratio of 9.6:1

I know that people often tout 10:1 or higher being the threshold for using premium fuel, but my car does recommend the use of Premium only.

Im wondering if anyone has done the work to find out if using the recommended fuel would benefit me over saving a few dollars a tank.

I have a scangauge so I may just give it a test after this tank.

If you have true E10 (as opposed to "may" be up to 10%) then it might run as good on regular, provided regular is 87 Octane nominal, ethanol seems to skew effective octane upwards.

i think it mostly has to do with the way the ecu alters the timeing.

in engines set up to use regular fuel the ecu won't alter the timeing beyond a point where this would cause nock with regular fuel. even when they're running premium. engines wich recommend premium can alter the timeing to a point where this would cause nocking with regular fuel.

i'm no expert in these things but that's how i understand it

My 92 Nissan 240SX recommends high octane (stated on the inside of the fuel filler door)- But I've run 87 octane through it for the last 140K miles with no problems/spark knock.

try regular first, it it doesnt knock, your fine. if it does, then switch to mid grade, then premium if mid grade still knocks.

You might wanna test different brands as well, for instance, I would think Sunoco regular would run well in that but shell regular might be a bugger. That's based on who I think more likely has more ethanol in their gas, and the tendency for Shell to seem to carbon up my motor in winter city crawling and then start knocking.

My girlfriend’s Acura has the inline 5 in it. She put 87 Octane in it when she first got it, because she didn’t know she was supposed to use Premium. She started having a lot of starting problems and the car seemed to keep running worse every time she drove it. She started running 93 Octane, without ethanol, and within a couple of tanks all her starting problems were gone and her car was running fantastic again.

Usually if the manufacturer specifies Premium it is usually because the engine will perform best with it because it is tuned that way (no matter what the CR is). My experience has been that running Regular in a Premium recommended engine lead to uneven acceration (pulsing) and reduced overall power. On my Neon R/T there was a big hit on the FE. With Premium I averaged 32 with Regular I averaged 28. Paying 6% more more Premium was worth the 14% better Fuel Economy. I saw a news article about people with Premium recommended vehicles resorting to Regular to save money. When in fact they were now putting in more fuel (due to reduced FE), so they were paying more at the pump and not realizing it. Right now there is only 5% difference per gallon at the pump.

as suggested on cleanmpg.com by a member, i was watching the IGN and at an even LOD and on a flat road with the same TPS and a steady RPM the IGN number was jumping around.

I think im going to try and use premium when I fill up tomorrow and see if that doenst make a different. Im pretty sure that the IGN moving around so much is the engine adjusting the timing and ignition on the car.

LET THE INVESTIGATION BEGIN!

10% ethanol required her. My wifes 06 Murano, 245 HP V6, owners manual recommends premium. She has never used premium. Mileage averages 22.8 MPG.

I drove it to our daughters house and back one day with 5 passengers, cargo, and a dog (360 mile round trip). At 70 mph average speed on the Interstate it got 25 MPG, which was the old EPA highway rating. Never noticed anything that I could directly attribute to regular fuel.

I would experiment with both grades, and use premium if the mileage improvement justified the additional cost.

regards
gary