XR550 g23

[Zach@n3]

From what I see your 500 EFI only had 8.75 to 1 compression. Even with agressive timing you should have been able to run 87 in that thing all day long. At the point the timing created a detonation situation it probably would have been so reduced in power you would have let out of the throttle.

Even the new 525 shows 87 pump gas required. 6.0 L engine to output 450 hp is going to require a very large increase in compression ratio and timing to make that power where your 8.2 is a much larger displacement with big block port flow numbers. Original rating on the 500 EFI looks to be 470HP.

http://www.mercuryracing.com/sterndr...5efi/specs.php

[Clax]

PCM manual states for optimum performance and reliability on a 450 93 octane premium fuel is required. You run whatever fuel you want in your boat. Every PCM engine has knock sensors. It can and will pull timing if it senses pre detonation. (that's why it's there......)

Why would you care about saving 15 bucks per tank in a boat if you were trolling around in a 150k G boat? I'm sure PCM would laugh at you if you had a warrany claim and the fuel in the tank on a 450 was tested as 87.

Order a 409.

As I mentioned earlier, for me it's not about saving 15 bucks per tank. Premium is not available on my lake. I'd gladly pay the extra money for premium gas if it was available on my lake. As for the warranty claim comment, I guess PCM might have issues with several boats on our lake. The largest Nautique dealer in Canada is on our lake. PCM could laugh all they want, but their own dealer that sells their product does not sell premium fuel. By the way, my friend on our lake had a warranty claim with his PCM ZR450 engine last year, and the engine was replaced in 3 days. I guess they must have "forgot" to check the octane.

[jsta281]

Some people misunderstand what octane does and does not. It is a common misunderstanding. Octane does not make you go faster or make more power. It is not "better" in that if 89 is good 93 is better. More octane is only "better," if, as in this ZR450 discussion, if it stops the engine computer from pulling timing. If you don't understand this concept do some research.

Octane is related to cylinder pressure. More cylinder pressure more octane required to stop the air/ fuel from igniting before the spark plug fires. If your cylinders start detonating prior to spark its call "knocking" or "pinging" and your engine computer will "pull timing" or reduce timing to lower the cylinder pressure. Less timing, less cylinder pressure, less horsepower.

High octane gas does not burn or "explode" as well as low octane gas, that's the point.

[jsta281]

As I mentioned earlier, for me it's not about saving 15 bucks per tank. Premium is not available on my lake. I'd gladly pay the extra money for premium gas if it was available on my lake. As for the warranty claim comment, I guess PCM might have issues with several boats on our lake. The largest Nautique dealer in Canada is on our lake. PCM could laugh all they want, but their own dealer that sells their product does not sell premium fuel. By the way, my friend on our lake had a warranty claim with his PCM ZR450 engine last year, and the engine was replaced in 3 days. I guess they must have "forgot" to check the octane.

The point trying to be made is either run the proper octane (use an octane booster that works like the link I posted as opposed to some auto parts store product) or purchase a engine that will not be constantly relying in the knock sensors to pull timing to stop your engine from being damaged, thus reducing the HP down to a level more in line with the "smaller" (not really) lower hp motor.

[core-rider]

These engines have nothing (to my knowledge) that can tell the ECM what octane the fuel is. It doesn't see less than 93 octane and automatically de-tune the ECM. They only have sensors that can protect the engine if pre-ignition is happening that will then pull timing which will effect HP numbers. I believe this is why PCM recommends high octanes so you get the best performance possible.

Now if PCM recommends compared to outright states using premium fuel than it is up to them what the warranty claim decision should be. If they outright state only premium fuel and you choose to use lower octanes IMO the user doesn't really have an argument. If they only recommend it then there is room for error and discussion.

Higher octanes just raise the flashpoint of fuel. The higher the number, the higher the flashpoint. If you can run 89 instead of 93 and still not have pre-ignition engine performance won't change which explains your earlier scenario between identical boats not running differently.


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[jsta281]

These engines have nothing (to my knowledge) that can tell the ECM what octane the fuel is. It doesn't see less than 93 octane and automatically de-tune the ECM. They only have sensors that can protect the engine if pre-ignition is happening that will then pull timing which will effect HP numbers. I believe this is why PCM recommends high octanes so you get the best performance possible.

Now if PCM recommends compared to outright states using premium fuel than it is up to them what the warranty claim decision should be. If they outright state only premium fuel and you choose to use lower octanes IMO the user doesn't really have an argument. If they only recommend it then there is room for error and discussion.

Higher octanes just raise the flashpoint of fuel. The higher the number, the higher the flashpoint. If you can run 89 instead of 93 and still not have pre-ignition engine performance won't change which explains your earlier scenario between identical boats not running differently.


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This is exactly true. It is possible that under certain conditions a ZR450 will run on 89 octane and not need to pull timing. Higher altitude would would be a significant factor in the equation. However, the places where detonation is most likely to take place is where most tow boats spend their life. "Tip in" or going from idle to WOT, "pulling under load" and WOT.

Without data logging the motor under any given parameters there is no way to know if and how often and how much timing is being pulled. Could be none, could be alot.

[jsta281]

To clax, if I understand that you are in Canada what is your altitude? If you are at a higher altitude your octane requirements (to avoid timing being pulled) could mean little or no timing is being pulled on lower octane. Of course this also means that your cylinder pressures are not as high (do to the higher atmospheric pressure) so you are not making 450 hp like you would at sea level.

[gride]

if i were at altitude i'd absolutely want a supercharger. they also make these things called gas caddys that can be filled up at a gas station with whatever octane you want/require.

[Clax]

To clax, if I understand that you are in Canada what is your altitude? If you are at a higher altitude your octane requirements (to avoid timing being pulled) could mean little or no timing is being pulled on lower octane. Of course this also means that your cylinder pressures are not as high (do to the higher atmospheric pressure) so you are not making 450 hp like you would at sea level.

Our elevation is about 700 feet.

[wakerider107]

I would never run anything less than 91 in any wake boat, period.

[jsta281]

I would never run anything less than 91 in any wake boat, period.

Based on what?

[swc5150]

It's hard to find 100% gasoline in anything other than 91 octane in our area, which is why we run premium. Some may disagree with me, but ethanol is garbage fuel IMHO.

[shawndoggy]

ethanol increases octane. Octane has nothing to do with the amount of potential energy stored in a gallon of gas, just the gasoline's resistance to premature detonation.

[swc5150]

It also thrashes your fuel efficiency.

[ironj32]

Iron- could you notice a difference in 450 performance between regular and premium fuels?

I don't know that I noticed any difference with the fuel used. I always ran premium for that last couple months, so didn't do any "testing" with 87 octane. I also probably had inconsitencies with ballast setup every time out...nothing major, but I found that only having about 100-200 extra pounds in the rear, or if the rear bags were positioned even just a few inches further back that I noticed decent differences in performance.