Lots of good information thanks for the reply Milemarker60!!!

That's extremely interesting reading Dave, thanks for the information. Mequires seems to be the preferred product for most of the guys here, so these top of the line alternatives could certainly save some from a lot of hassles and heartache. I may even give that Turtle wax a go to get rid of some of my hard water spots I have accumulated.

Thankyou.

I use Super Strength, from the Dollar store. Belive it or not, it is VERY strong. I use it on all of our construction equipment to get the grease off of them. Be careful, if you let it sit on there in the sun, or dry it stains the surface. Have you looked into painting your boat? Our's is painted on the bottom because it use to sit in the water (now its in a lift) and it doesn't look beautiful going down the road but, it looks good when you pull it out!!:) Just a thought! Painting isn't cheap though. $2600 dollars (US)

mis4tun81, I do have silent choice but a small amount of exhaust does come out of the pipes at idle. I think due to back pressure of forcing down lower unit when not on plane.
I use 3M boat wax and it seems to work well, the soot wipes right off. My brother uses ICE and likes it, but he says it needs to be applied more often than other waxes or polishes he has used.
I have another related question.:confused: There is only two gas stations left in town that has gas without ETOH. One, Shell 87oct @ 4.19/gal and one truck stop with 91oct @ 4.18/gal. I know you shouldn’t run lower octane than a engine is rated for. But, I should have no problem running the higher octane in my 87oct rated engine all the time, Right? I would think it will give my more power and maybe burn cleaner.
Thanks for all the info!

You are absolutely right, running a higher octane in any engine (marine or road) will give you better economy, cleaner burning, longer engine life, and most important more power!
My cars handbook says - Vehicles with engine management systems will automatically adjust the motor to suit the octane rating of the fuel being used - dont ask me how it knows though!

Late model cars use a combination of knock sensors, oxygen sensors, air mass meter and various temp sensors to determine the proper fuel mixture and timing. The computer then adjusts the injector flow and ignition 'dwell angle' to the optimal settings for the fuel you are using as well other variables, i.e. humidity, intake temp, contamination of oil by fuel, etc.

The really neat thing is that the computer via the knock sensors is able to determine which cylinder is beginning to knock and adjust the timing on that individual cylinder. It is possible for the computer to set individual timing on every cylinder at the same time.

As far as boats are concerned, since the pollution controls are not required, my guess is that they use a much less sophisticated approach. :)

Graydog you posted as I was typing and thinking this out.:D

Hmmmm,

If this were a car or motorcycle forum I would disagree with you (dudders), ;)

which is why I waited a little to think about my response.

Cars know what the fuel octane is by using a knock sensor which listens to the knock or pinging in an engine and tunes accordingly. Most newer injected boat engines have a knock sensor as well.

However, normally aspirated non performance car engines are tuned to run best (within EPA limits) using the recommended fuel.

This is true, however most knock sensor & ECU's detune the car if a lower octane, or bad gas is put in the tank that increases knock, the ECU detunes the car by retarding the timing from optimum to eliminate the knock. Not generally the opposite.

Higher octane fuels reduce pinging by being harder to ignite, they contain similar amounts of energy, however it is harder to release that energy. Higher compression engines take advantage of that and are tuned more aggressively, without the fuel preigniting. They get more power by using more fuel in an engine that is built to use it, not the higher octane.

OK HERES WHY BOATS MAY BE DIFFERENT

Engines are more prone to preignition (pinging) under high loads at full throttle, especially at low RPM. Not as common in a car (unless you drive like I do:eek_animated:) but very common in a boat (especially if you drive like I so :D)

So with a lower octane fuel in these conditions, your engine MAY retard timing slightly at full throttle, if it does, a higher octane fuel might reduce this tendency.


Practically speaking,

I am chasing a low top speed/RPM (4200) in my 2001 454 MPI Z275 that I don't suspect is the prop selection, because it is original equipment.

So far I have only tried two things to improve it, one I cleaned my air intake/spark arrestor, and at the same time, put some injector cleaner in the tank, and decided to run higher 91 octane fuel to see if things would change.

They did, I lost another 200 RPM and 4 MPH.

Last night I pulled the distributor cap and the terminals are pretty corroded worn, so I will do a tune up, plugs, cap, rotor, maybe wires. And see if anything change.

But in my opinion and experience as with cars, you may not see an improvement by running a higher octane fuel.

The tune up will certainly not harm you, but I would wait until you have run enough fuel through the system to insure your performance is not being skewed by the fuel injector cleaner.

How long has it been since you changed your oil, contamination from a previously rich mixture can really screw up how your engine management system regulates itself.

Also, make sure your trim is working correctly and you don't have any drag on your hull (read "crap"). My experience is that performance problems are more often than not cumulative and not just based on one major problem.

What's the old saying, "The devil is in the details."

And when all else fails, check to make sure that you pulled your anchor before trying to reach top speed. :D

Thanks for the feedback,

Oil has 20 hrs on it and is clean, I suppose the injector cleaner could be tweaking the tune a little, I put a mild mix, compared to what I would do to a car or bike since it will be in there for a while. So I would not expect to notice a difference.

Boats clean, trim does what its supposed to do.

I will be putting the tune up parts in this weekend, the boat had 200 hours on it, and it looks like the cap rotor and wires at least are probably original, so as you said wont hurt.

The boat is new to me, so before I do something drastic I figured I would go over all the devils details, before I accept it or prop it.

Once I do the tune up I will know where I stand.

Thanks

Thanks for the replies guys, I stand corrected and will pass this info on to my mechanic who furnished this info to me in the first place. He owes me a beer now. Great.
Good luck getting your motor sorted missfortunateone. Happy boating over your summer period. Hope the floods we are hearing about arent affecting any of you guys.