87 or 89 Octane in 99 pro air nautique?

[vtncsuskier]

We have been running 87 octane in our pro air for a while now....but I read in the owners manual that the min octane should be 89. I can tell no differences in performance when running 87 vs 89. Is there any long term advantages to running 89 vs 87. Possibly better on the engine/fuel pump?? Any insight on this subject would be helpful. I have friends that run both grades in their newer boats. Ours is the GT-40 EFI engine. I think it has 310 hp.

Thanks in advance

Brandon

[DRAGON88]

I run 87 in my boat (99 Sport Nauti with the GT-40) and I dont think it does any harm, some people will run fill up with 89 and once it gets halfway empty fill up with 87, then when that gets halfway empty it gets filled up with 89 on and on...

Basicly I dont think it hurts it any thing, But when you look at how insignificant (the price diffence, about 3-4$) puting plus in your boat is not a bad thing to do every once and awile, I only run 87 beacause thats what the marinia sells, but I would probably do the half 89 half 87 trick if they sold plus as well.

Heres a thread on Wakeboarder.com about octane ratings. Octane rateing thread

[thevogt]

Call PCM. I spoke to Mark today regarding the lead/no lead discussion in the maintenence forum. He was very helpful. 803-345-1337. BTW, if you use a 5/8" socket to pull your plugs, you don't need a lead additive. If you use a 13/16" socket, get the lead additive so you don't ruin the valve seats in the heads.

Gary

[patoloco]

I have a '99 air and it says to use 89 octane, which I do.....but the other day, after filling up and hitting the lake, the engine seemed to be running a tiny bit rougher and have ever so slightly less power.....I kept trying to figure it out and after I got home I realized that I had accidently put in 87.

The next day I put in a full tank of 89 and did not notice the problem. I could definitely be imagining things, but it seemed to make a slight difference in performance.

[Rock_Toy]

You're imagining things. The only difference would have been that your motor would be pinging and your acceleration would suck. Unless you have rebuilt the motor and increased the compression in your motor, you should be fine with 87. Read the thread that is linked on Wakeboarder.com and you will see what I am talking about.

[SGY]

I agree with Rock_Toy. The slightly less power you were experiencing was due most likely to air density and other variables that change from day to day with the weather. The GT-40 takes a sniff of air at start up and adjusts timing etc to accomodate. While the fuel injection/computer controlled motors do adjust better to changing conditions, the fact remains that if you have less air, you have less horsepower.

The rough running motor might be just bad fuel or just your imagination. Sometimes just the right amount of small chop makes me think my boat is running rough.

[vtncsuskier]

ok...a little clarification on this subject....I called PCM directly and they said they reccomend running 87 octane in all of their PCM engines regardless of what the correct craft users manual says. I would think they would know what they are talking about over any correct craft rep

hope this helps

[thevogt]

I agree. They are the engine builders. Correct Craft buys their product to install in the boats. That is why CC told me to call PCM about the lead/no lead questions we were all having.

Gary

[AirJeff]

Just an FYI, we were wondering the same thing, and don't have manuals for our boat yet. So, I cracked the engine cover and right on top of our GT-40 there is a PCM sticker that says 89 octane. So, that's what we are putting in now.