525 EFI octane (Blue Mercury Racing Motor)

[Nord]

Running bone stock and was told that 89 was the way to go. Does this hold true?

 

[02HoWaRd26]

I run 87 without an issue, really glad i didn’t do the whipple tune this winter with the cost of fuel the way it is.
Also use Rev X with every fill up.

 

[racektm]

Mercury recommends 87

 

[parker guy]

I have always used 91, the reason is I don’t use all the fuel every fill up. So if the boat sits a couple weeks the fuel will still be ok.

 

[ridebig]

I also use 91 ethanol free. Cost's more but last's longer and was told better for the 525's life.

 

[farmo83]

I believe in one of his Podcast Teague mentions 525's run better with 87 then they do with higher grades. I'm sure it's not enough to notice for the everyday boater.

 

[hallett3]

87 in mine no issues.

 

[Racey]

I have always used 91, the reason is I don’t use all the fuel every fill up. So if the boat sits a couple weeks the fuel will still be ok.

This would be my advice as well. For the extra $20 a tank it's worth it to have a little extra octane for that margin

 

[BUDMAN]

When I purchased current boat with 525 I ran 91 thinking that’s what it needed, then I was told Mercury recommended 87. Been running 87 all last season without any issues. Then it was recommended by the service shop to run 91. Filled it up with 91 During Desert Storm and the transom had a lot of exhaust buildup. Going back to 87 on next fill up.

 

[azsunfun]

the awsome smell of 93 octane rotted dyno's

 

[DWC]

I believe in one of his Podcast Teague mentions 525's run better with 87 then they do with higher grades. I'm sure it's not enough to notice for the everyday boater.

An inmate saw me filling up with 91 and politely let me know that 87 is better for the motor. I figured the ethanol free 91 was better. Turns our not so much. Should have learned my lesson on the 496. The Magic transom was hammered running high octane.

 

[steamin rice]

I seem to get some transom soot if I run 91, and I can't notice any performance difference between 87, 89, and 91 in my 525efi's. If I'm putting in fuel that I don't expect to burn off quickly, then I'll put in 89 to give a little higher starting octane in case it degrades a bit before I use it up.

 

[schweeng]

87 - factory tuned to run best at that octane... I've been told i was wasting money putting premium in it.

 

[rivermobster]

I believe in one of his Podcast Teague mentions 525's run better with 87 then they do with higher grades. I'm sure it's not enough to notice for the everyday boater.

Yep. The higher the octane rating, the slower the burn. Incomplete combustion will give you less power, not more.

Mercury EFI is fat from the factory. They do that on purpose.

 

[H20 Toie]

87 is the way to go. no reason to use anything else

 

[done]

I believe in one of his Podcast Teague mentions 525's run better with 87 then they do with higher grades. I'm sure it's not enough to notice for the everyday boater.

Why would it run better, lower octane has to run less timing, to avoid detonation i would think. I think you can run 87, but i never did.

 

[Blubyu]

87


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[rivermobster]

Why would it run better, lower octane has to run less timing, to avoid detonation i would think. I think you can run 87, but i never did.

As stated...

The higher the octane, the slower the burn.

You Need a slower burning fuel in a high compression engine. In a low compression engine, slow burning fuel reduces power output.

The actual engine timing is irrelevant. If you have to reduce engine timing to eliminate detonation, you have a problem somewhere in the overall build, or, fuel not matching the amount of compression you are running.

Cam/valve timing is a factor as well, so you should Always go by what the engine builder recommends.

I'm fairly confident Mercury Racing knows what's best for the engines they build.

 

[Ziggy]

87 unless the efi module has been reflashed .

 

[farmo83]

Why would it run better, lower octane has to run less timing, to avoid detonation i would think. I think you can run 87, but i never did.

See RiverMobster's post

 

[4czn10]

Hijacking a little...i have a 525 with a whipple...octane?

 

[LargeOrangeFont]

Why would it run better, lower octane has to run less timing, to avoid detonation i would think. I think you can run 87, but i never did.

In a nutshell, the engines are running low compression and low timing, higher octane is not needed. Same reason your lawn mower runs better on 87 than 93.

 

[Wmc]

Run the cheap shit

 

[HST4ME]

Those motors are effectively 8.2:1. But hey whatever.

 

[azsunfun]

In a nutshell, the engines are running low compression and low timing, higher octane is not needed. Same reason your lawn mower runs better on 87 than 93.

gotcha what i thought, early in thread talking high compression, i have 10 1/2 :1 why i stated high octain

 

[douglasmarine28]

Stock 525's run better on 87. They soot up the transom if I run 93 but burn clean on 87. Plus, it's cheaper...

 

[Bigbore500r]

As stated...

The higher the octane, the slower the burn.

You Need a slower burning fuel in a high compression engine. In a low compression engine, slow burning fuel reduces power output.

The actual engine timing is irrelevant. If you have to reduce engine timing to eliminate detonation, you have a problem somewhere in the overall build, or, fuel not matching the amount of compression you are running.

Cam/valve timing is a factor as well, so you should Always go by what the engine builder recommends.

I'm fairly confident Mercury Racing knows what's best for the engines they build.

They just did a great "mythbusters" style episode on Engine Masters, testing the effects of different octanes / fuels in a controlled Dyno environment at Westech. Higher octane did not kill power, contrary to beliefs. They left timing and jetting untouched, the only variable was octane.

 

[azsunfun]

They just did a great "mythbusters" style episode on Engine Masters, testing the effects of different octanes / fuels in a controlled Dyno environment at Westech. Higher octane did not kill power, contrary to beliefs. They left timing and jetting untouched, the only variable was octane.

don't believe you can do accurate dyno , with out those adjustments!!

 

[Bigbore500r]

don't believe you can do accurate dyno , with out those adjustments!!

You can't tune an engine without adjusting timing and jetting, but once it's tuned.....

Low compression engine, timing and jetting optimized for max power. Increased octane fuels tested in succession. No loss of horsepower.

I'd share the link, but it's on Motortrend app only. If you have it, check out the show it's pretty interesting

 

[schweeng]

As stated...

The higher the octane, the slower the burn.

You Need a slower burning fuel in a high compression engine. In a low compression engine, slow burning fuel reduces power output.

The actual engine timing is irrelevant. If you have to reduce engine timing to eliminate detonation, you have a problem somewhere in the overall build, or, fuel not matching the amount of compression you are running.

Cam/valve timing is a factor as well, so you should Always go by what the engine builder recommends.

I'm fairly confident Mercury Racing knows what's best for the engines they build.

yeah.....what he said.....

 

[DaveH]

They just did a great "mythbusters" style episode on Engine Masters, testing the effects of different octanes / fuels in a controlled Dyno environment at Westech. Higher octane did not kill power, contrary to beliefs. They left timing and jetting untouched, the only variable was octane.

this is correct.

octane isn't the "burn rate" of the fuel.

octane rating is the fuels resistance ability to "self ignite". as cylinder temps and compression goes up.......the fuel wants to start burning on its own (early, before the spark event) which leads to catastrophic detonation.

higher octane fuel buys you insurance against detonation. as an example.....if your fuel pressure goes down....or maybe a single injector gets slightly clogged on a single-cylinder.....the lean condition will elevate cylinder temps increasing the likelihood of detonation.

 

[Outdrive1]

Love reading these threads. Lots of good info. [emoji106]


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[SBMech]

this is correct.

octane isn't the "burn rate" of the fuel.

octane rating is the fuels resistance ability to "self ignite". as cylinder temps and compression goes up.......the fuel wants to start burning on its own (early, before the spark event) which leads to catastrophic detonation.

higher octane fuel buys you insurance against detonation. as an example.....if your fuel pressure goes down....or maybe a single injector gets slightly clogged on a single-cylinder.....the lean condition will elevate cylinder temps increasing the likelihood of detonation.

It's actually a measure of how fast the flame front is affected from ignition. Pre-ignition is what you are describing, and fuck yes it causes detonation.

Talking about octane leads into static and dynamic ratios and how camshaft timing and ignition timing affects it, and why aluminum heads allow you to run more compression and we'll loose focus.

Fixed timing setups run as they were designed for. Adding octane without being able to take advantage of the timing advance you could add to the ignition event to add more power is obviously a waste, as shown by the sooty butts.

 

[Bullet28]

87

 

[lbhsbz]

Why would it run better, lower octane has to run less timing, to avoid detonation i would think. I think you can run 87, but i never did.

Fuel should match the motor. Lower octane doesn’t have to run less timing advance, it has to run the correct amount. There is a certain point, around 14 or so degrees after top dead center where cylinder pressure should be at its highest. The least amount of timing you need to hit that mark will create the most power. With domed pistons, you need to chase the flame around the dome...which is why a flat top piston with a smaller chamber needs less timing advance than a dome piston with a bigger chamber...the objective is to get peak cylinder pressure at the right time

Running a slower burning fuel will require you to run more timing advance, but with no benefits at all unless the higher octane is needed to control detonation/pre ignition.

Any cylinder pressure created due to combustion BEFORE top dead center is actually slowing the piston down...the closer we can light the fire to TDC and still hit peak cylinder pressure at the right time, the better.

 

[LargeOrangeFont]

They just did a great "mythbusters" style episode on Engine Masters, testing the effects of different octanes / fuels in a controlled Dyno environment at Westech. Higher octane did not kill power, contrary to beliefs. They left timing and jetting untouched, the only variable was octane.

Correct.. The fuel octane difference does nothing for power on its face. Tuning for a specific octane of fuel gains power.

 

[azsunfun]

politics, let's let er fly!!! life is exactly that

 

[185EZ]

had a carbed 500 blue motor for 22 years
87 everyday
Just like was printed on top of the flame arrester

 

[ToMorrow44]

Hijacking a little...i have a 525 with a whipple...octane?

91 at a minimum. My TCM 825 is built for 91 but I always just run 93 pump gas in it. I keep some Torco octane booster in case I get stuck and can only get 89 or 90 on the water.

 

[rivermobster]

They just did a great "mythbusters" style episode on Engine Masters, testing the effects of different octanes / fuels in a controlled Dyno environment at Westech. Higher octane did not kill power, contrary to beliefs. They left timing and jetting untouched, the only variable was octane.

I dig those shows. What engine did they use?

 

[rivermobster]

It's actually a measure of how fast the flame front is affected from ignition. Pre-ignition is what you are describing, and fuck yes it causes detonation.

Talking about octane leads into static and dynamic ratios and how camshaft timing and ignition timing affects it, and why aluminum heads allow you to run more compression and we'll loose focus.

Fixed timing setups run as they were designed for. Adding octane without being able to take advantage of the timing advance you could add to the ignition event to add more power is obviously a waste, as shown by the sooty butts.

Yep.

Its actually called flame propagation. When the plug fires, the a/f mixture does not explode, the plug ignites a flame front that burns across the top of the piston.

The higher octane fuels have a slower flame front, and as Dave said, also effectively resist pre ignition.

The way it was explained to me was...

Pinging is actually 2 different flame fronts running into each other over the top of the piston!

Not good.

 

[Springfield]

Run the cheap shit

...... says the guy with twin eggbeaters on his float.

 

[rivermobster]

FF to the 3min mark. Super cool vid...

 

[done]

My 2- 525 s ran 5200 RPM on either fuel,

 

[done]

They just did a great "mythbusters" style episode on Engine Masters, testing the effects of different octanes / fuels in a controlled Dyno environment at Westech. Higher octane did not kill power, contrary to beliefs. They left timing and jetting untouched, the only variable was octane.

Thank you !

 

[rivermobster]

Thank you !

Yeah well...

Contrary to what Jerry said, they changed the tune everything they changed fuels! Doh!

https://www.facebook.com/video.php?v=744265356291138

And then of course they used an LS engine. Was the variable valve timing in place? Did they use a knock sensor?

This is an apples and oranges comparison to an old school bbc with a map based ECU.

 

[02HoWaRd26]

Yeah well...

Contrary to what Jerry said, they changed the tune everything they changed fuels! Doh!

https://www.facebook.com/video.php?v=744265356291138

And then of course they used an LS engine. Was the variable valve timing in place? Did they use a knock sensor?

This is an apples and oranges comparison to an old school bbc with a map based ECU.

Doesn’t the Merc 525 use basically an LS style efi system on a gen 6 bbc?

 

[Bigbore500r]

Yeah well...

Contrary to what Jerry said, they changed the tune everything they changed fuels! Doh!

https://www.facebook.com/video.php?v=744265356291138

And then of course they used an LS engine. Was the variable valve timing in place? Did they use a knock sensor?

This is an apples and oranges comparison to an old school bbc with a map based ECU.

Where did you see them change fueling and timing across the sweeps? Maybe we watched something different? And what does an LS have anything to do with it? Lol

 

[rivermobster]

Where did you see them change fueling and timing across the sweeps? Maybe we watched something different? And what does an LS have anything to do with it? Lol

I didn't watch it yet, but I probably will next week sometime.

I did watch that clip I posted though. Fryburger said they changed the timing for every fuel.

And you know as well as I do what an LS has to do with it! Apples and Oranges.

Unless......

You're trying to say an LS is no better than a og bbc?? Is that really what you believe??

 

[HCP3]

Running bone stock and was told that 89 was the way to go. Does this hold true?

Here is your answer (87):