Indmar Vortec 8.1

(john_prine) · (john_prine) **Join Date: Nov 2006** 02-10-2007, 9:48 PM

What Fuel do you guys use..........89 91

(xaggie) · (xaggie) **Join Date: Nov 2002** 02-11-2007, 12:09 AM

Anything not Crude oil

(bennygoodx) · (bennygoodx) **Join Date: Aug 2006** 02-11-2007, 8:07 AM

89 is fine with that motor.

(ryan27r) · (ryan27r) **Join Date: Oct 2006** 02-11-2007, 1:00 PM

89 or 91 whatever you want

(john_prine) · (john_prine) **Join Date: Nov 2006** 02-11-2007, 1:14 PM

I heard the motor will knock if you put anything less then 91

(xaggie) · (xaggie) **Join Date: Nov 2002** 02-11-2007, 3:48 PM

Hahah Shell 87 is all that goes in mine and I've NEVER had a single problem.

(john_prine) · (john_prine) **Join Date: Nov 2006** 02-25-2007, 1:15 PM

Power house

(mhsb1029) · (mhsb1029) **Join Date: Jan 2004** 02-25-2007, 4:33 PM

87 Never had a problem with the engine knocking with 87. However, we did have a problem with one of the knock sensors last year. The problem was that one of the knock sensors(8.1 has 2) was taken off when the boar was winterized (most likely service guys who needed one and forgot to replace it). Was a real pain in the ass, took almost a month to find out why the damn engine light was coming on, and only figured it out because we diagnosed the problem ourselves.(Had access to code reader)

(ryan27r) · (ryan27r) **Join Date: Oct 2006** 02-25-2007, 6:36 PM

91 in all watercraft

(john_prine) · (john_prine) **Join Date: Nov 2006** 02-26-2007, 2:07 PM

Egine runs better with 91......Who wants to cheap out with 87

(xaggie) · (xaggie) **Join Date: Nov 2002** 02-26-2007, 10:03 PM

Why does my engine run better with 91? It's not a high compression engine that needs the extra octane, nor can I safely advance the timing to take advantage of a higher octane content gasoline. By all means though let me know so I can stop being cheap.

(rallyart) · (rallyart) **Join Date: Nov 2006** 02-27-2007, 8:00 AM

It's easy to test if you have a boat. Run flat out with 87 and see what your top speed is. Run flat out with 91. If you have knocking and maybe can't hear it you'll be down on power and so down on top speed. If you don't have knocking you will run the same or faster than you would with 91. Too high an octane burns slower and gives you a tiny bit less power and economy. Any knocking drops power lots.
Boats are nice, we have built in water dynamometers

(mcsammamish) · (mcsammamish) **Join Date: Jun 2002** 02-27-2007, 2:39 PM

What Art said and also with too high an octane you will get late burn and get the black soot all over the back of the boat around the exhaust. It also depends a little on how long the gas will be sitting around.

(xaggie) · (xaggie) **Join Date: Nov 2002** 02-27-2007, 4:29 PM

I was being quite sarcastic really when asking about running better with 91. It's true about knocking ART but the loss of power, at least on this engine would come from the computer pulling timing out due to Pre-Detonation (knock). Apples and Oranges and both are caused by using gasoline with to low of an octane percentage. More so that WOT testing, I find that if performance suffers when the air temp/density changes (cold and crisp in winter to hot and humid during summer) you tend to know you are using too low of an octane gas. This is especially exaggerated in our boats since they use typically closed loop systems that go off pre-programed tables instead of a more efficient "Mass Air" system as you see in automobiles today. It's just ignorant to make a blanket claim that your engine runs better with 91, especially when in reference specifically to a low compression big block that rarely sees the bright side of 5k RPM. Besides in Texas it's 87, 89, or 93. Minimal difference between 87 and 89, and I certainly don't need 93.