Using lower octane

Dave M · 07-29-2008, 02:57 PM

There was a previous thread on using a lower octane than the boat recommended. I can't seem to find that thread. Just curious if there was any conclusion to the discussion. My boat shows 89 octane, can I use 87.
I have a 5.0L 8cy Volvo.

Thanks

Dave M

NightWing · 07-29-2008, 03:36 PM

The danger in using lower octane fuel is that you probably won't be able to hear your engine pinging under load, which is most of the time. It is like driving your car uphill in second gear all the time. There is no coasting, regardless of speed.

There is a reason why the lowest octane fuel available on the lake is 89. That is what the engine manufacturers recommend.

Why risk major engine damage in order to save a few dollars on fuel?

Now, there may be people jumping in here saying they have been running cat pee for years without any problems. At the end of the day, it is your engine that is at risk and you will have to bear the brunt of the repair cost.

As an afterthought, it would be a real sales point with today's high priced fuel if boat dealers could advertise that their new boats would run on 87 octane gas. I don't think that will ever happen.

BroadHopper · 07-29-2008, 03:43 PM

I was told by a mechanic, that the new engines controlled by an ECM has a knock sensor. The ECM will retard the timing to eliminate the pinging. Your engine will be less efficient tho. Not sure if that means burning more gas.

jrc · 07-29-2008, 04:10 PM

from the Mercury website:

2001 models and newer Mercury MerCruiser engines beginning with serial number 0M300000 will operate satisfactorily when using a major brand of unleaded fuel meeting the following specifications:

USA and Canada - Have a posted pump Octane Rating of 87 (R+M)/2 minimum. Premium gasoline [92 (R+M)/2 Octane] is also acceptable. Do not use leaded gasoline.

Cal · 07-29-2008, 05:59 PM

My engines are 4 years old and were originally design for 89 octane. They developed 647 HP on a dyno with MTBE added 89 octane fuel. After doing a rebuild on one this past winter , it was redynoed and retuned (timing and carb jetting) and wound up with 661 HP on ethanol added 87 octane. The other engine was retuned to the same specs.
It can be done but it's a risk for an amature

Disclaimer..."Don't try this at home"

http://videos.streetfire.net/video/5...-ON_159764.htm

VitaBene · 07-30-2008, 08:58 PM

Most newer engines adjust the timing automatically for the octane you are using.

For old boats like ours, I have a choice of what fuel I run but have to manually retard the timing if I want to run 87 reducing HP. I have run both 87 and 91- I see about a 15-20 HP (it is a rebuilt 260) difference, seat of the pants.

Woodsy · 07-31-2008, 07:45 AM

The newer engines with knock sensors automatically put the computer into a limp home mode.... retarding the timing and drastically reducing the power output so as not to damage the engine.

I would not run anything lower than 89 in a boat. A boat motor is CONSTANTLY under load, even when idling.

If you do the math seriously how much money are you going to save per fillup? $5? $10? Is it really worth risking your engine for?

Woodsy

VitaBene · 07-31-2008, 08:14 PM

Quote:

Originally Posted by Woodsy

The newer engines with knock sensors automatically put the computer into a limp home mode.... retarding the timing and drastically reducing the power output so as not to damage the engine.

I would not run anything lower than 89 in a boat. A boat motor is CONSTANTLY under load, even when idling.

If you do the math seriously how much money are you going to save per fillup? $5? $10? Is it really worth risking your engine for?

Woodsy

Really? Why do that? Why not just retard the timing a few degrees automatically until the knock stops? Interesting, looks like I will have to do some research.

I run 91 regardless because I need all the HP I can get in my old sled!

Cobalt 25 · 07-31-2008, 10:12 PM

I've been running 87 in my 2001 496 Merc since it was new. It has well over 700 hours on it and I have never had any difficulties related to using 87 octane. For the past couple of years I've had to use the ethanol blend required in MA.

What's more, the Tappet Brothers (Click and Clack) from National Public Radio say that in most cases you are wasting your money on higher octane. I submit my experience substantiates that thinking.

Peter

P.S. Speaking of saving money, check this out. I'm not sure how many Stop and Shop supermarkets are in the Lakes Region, though.

http://www.thehulltruth.com/forums/t...09508&posts=10

Audiofn · 07-31-2008, 10:19 PM

It has been my experience that I get more HP and more speed with the lower octane. Lower octane fuel burns with more power/faster then higher octain. What really determins what you can get away with is the compresion ratio. If you do not know how to listen for detonation then I would run the higher oct. fuel. If you do then it may be worth a try. Remember that Ethenol is an octane boster!!

Woodsy · 08-01-2008, 08:09 AM

Cars & Boats are NOT the same....

Click & Clack are spot on when they are discussing cars & octane. Just about every car in production has a knock sensor that will automatically retard the timing when it senses detonation (pre-ignition)... Boats are completely different! Boat engines are CONSTANTLY UNDER LOAD, there is no coasting in boats... when traveling at headway speed, your motor is under load. A light load to be sure, but under load nonetheless.

Vitabene, if your motor is rated for 89 octane, putting 91 octane in your tank isnt going to do much for you other than cost you $$$. Your motor isnt going to burn the 91 octane any more effeciently than the 89 octane. Thats the point Click & Clack are making.

Until recently, boats didnt have knock sensors.... and detonation is an engine killer. Knock sensors are relatively new to boating. Most newer boats with fuel injection and electronic ignition do not have adjustable timing. The timing advance is completely controlled by the computer. You have to put the engine in limp home mode to adjust the base timing if the base timing is adjustable at all.

Cobalts 25's 496 has a knock sensor and the computer controls the timing. If the knock sensor senses detonation, the computer will instantly retard the timing until the knock sensor no longer senses detonation then the motor will resume normal operation. If your on plane its pretty seamless... if your attempting to get on plane, or at WOT you will feel the loss of HP. 700 hours is a good number... You should plug the Merc scan tool in and find out how many hours were idling vs. how many were at WOT. It would just be an interesting tibit to know.

AudioFn.... your bit off!

Lower octane fuel burns EASIER than a higher octane fuel. It doesn't produce any more HP. In simple terms (there are other factors) compression ratio determines the required octane.... the higher the compression ratio the higher the octane required. Burning 87 octane in a motor that requires 91 octane with 10:1 compression ratio on a boat and you will be making a trip to the engine shop... In very short order you will melt the top of the piston or burn a valve....

The engine shops can use tricks to "fool" a motor, fattening up the mixture (so you burn more gas, but can use a lower octane) retarding the timing etc... the end result is that it is doable, but at the cost of engine efficiency. You end up burning more gas than its usually worth. Cal's motors are specially built HiPo motors that were tuned by an engine shop on a dyno. If you have a stock Merc or Volvo motor, leave it alone if you want it to live...

The difference between 87 & 89 at the pump is maybe .15 per gallon.... thats an extra $15 per 100 gallons of gas.... If you burned 1000 gallons of gas a year its an extra $150! Is it really worth fooling around with considering the cost of a replacement engine?

Woodsy

Dave R · 08-01-2008, 09:31 AM

Hey Cal,

I'd love to hear more about the parts in your engines. Compression ratio, bore and stroke, connecting rods, cam specs, valves, heads etc. Those are impressive numbers for 5400 RPM, normally aspirated, and a marine cam to prevent water reversion.

Audiofn · 08-01-2008, 09:57 AM

Woodsy Woodsy Woodsy you have drank the potion that is the high octane debate

When you coming back up to the lake so we can blast around!!

Lower octane fuels definetely burn faster, causing the retarding of timing to prevent knocking. However, if you run say a 330 motor you are MUCH better off running lower octane fuel and bringing the timing up as much as you can for the max power. If you raise compresion then you need to also as some point raise your octane rating to slow down the burn. As you raise preasure in the cylinder you have to slow the burn or you get.... detonation.

This is a nice artical that kind of explains it.

http://www.factorypro.com/tech_tunin..._vs_power.html

I have a few more if you would like. Get up to Maine and lets run the boats!!!! I am sick of working on my roof!!!

07-29-2008, 02:57 PM	#1
Dave M Senior Member Join Date: Jul 2007 Posts: 395 Thanks: 4 Thanked 26 Times in 24 Posts	Using lower octane There was a previous thread on using a lower octane than the boat recommended. I can't seem to find that thread. Just curious if there was any conclusion to the discussion. My boat shows 89 octane, can I use 87. I have a 5.0L 8cy Volvo. Thanks Dave M

07-29-2008, 03:43 PM	#3
BroadHopper Senior Member Join Date: Oct 2004 Location: Laconia NH Posts: 5,512 Thanks: 3,118 Thanked 1,090 Times in 784 Posts	Knock sensors I was told by a mechanic, that the new engines controlled by an ECM has a knock sensor. The ECM will retard the timing to eliminate the pinging. Your engine will be less efficient tho. Not sure if that means burning more gas. __________________ Someday may never be an actual day.

07-29-2008, 05:59 PM	#5
Cal Senior Member Join Date: Apr 2004 Location: Pitman , NJ Posts: 627 Thanks: 40 Thanked 21 Times in 12 Posts	My engines are 4 years old and were originally design for 89 octane. They developed 647 HP on a dyno with MTBE added 89 octane fuel. After doing a rebuild on one this past winter , it was redynoed and retuned (timing and carb jetting) and wound up with 661 HP on ethanol added 87 octane. The other engine was retuned to the same specs. It can be done but it's a risk for an amature Disclaimer..."Don't try this at home" http://videos.streetfire.net/video/5...-ON_159764.htm Attached Images __________________ Paddle faster , I think I here banjos

07-31-2008, 07:45 AM	#7
Woodsy Senior Member Join Date: May 2004 Location: Weirs Beach Posts: 1,949 Thanks: 80 Thanked 969 Times in 432 Posts	The newer engines with knock sensors automatically put the computer into a limp home mode.... retarding the timing and drastically reducing the power output so as not to damage the engine. I would not run anything lower than 89 in a boat. A boat motor is CONSTANTLY under load, even when idling. If you do the math seriously how much money are you going to save per fillup? $5? $10? Is it really worth risking your engine for? Woodsy __________________ The only way to eliminate ignorant behavior is through education. You can't fix stupid.

07-31-2008, 10:12 PM	#9
Cobalt 25 Senior Member Join Date: Sep 2004 Location: Cape Cod Posts: 213 Thanks: 219 Thanked 36 Times in 20 Posts	87 is fine I've been running 87 in my 2001 496 Merc since it was new. It has well over 700 hours on it and I have never had any difficulties related to using 87 octane. For the past couple of years I've had to use the ethanol blend required in MA. What's more, the Tappet Brothers (Click and Clack) from National Public Radio say that in most cases you are wasting your money on higher octane. I submit my experience substantiates that thinking. Peter P.S. Speaking of saving money, check this out. I'm not sure how many Stop and Shop supermarkets are in the Lakes Region, though. http://www.thehulltruth.com/forums/t...09508&posts=10

07-29-2008, 03:36 PM	#2
NightWing Senior Member Join Date: Aug 2004 Posts: 410 Thanks: 4 Thanked 6 Times in 6 Posts	The danger in using lower octane fuel is that you probably won't be able to hear your engine pinging under load, which is most of the time. It is like driving your car uphill in second gear all the time. There is no coasting, regardless of speed. There is a reason why the lowest octane fuel available on the lake is 89. That is what the engine manufacturers recommend. Why risk major engine damage in order to save a few dollars on fuel? Now, there may be people jumping in here saying they have been running cat pee for years without any problems. At the end of the day, it is your engine that is at risk and you will have to bear the brunt of the repair cost. As an afterthought, it would be a real sales point with today's high priced fuel if boat dealers could advertise that their new boats would run on 87 octane gas. I don't think that will ever happen.

07-29-2008, 04:10 PM	#4
jrc Senior Member Join Date: Apr 2004 Location: NH Posts: 2,689 Thanks: 33 Thanked 439 Times in 249 Posts	from the Mercury website: 2001 models and newer Mercury MerCruiser engines beginning with serial number 0M300000 will operate satisfactorily when using a major brand of unleaded fuel meeting the following specifications: USA and Canada - Have a posted pump Octane Rating of 87 (R+M)/2 minimum. Premium gasoline [92 (R+M)/2 Octane] is also acceptable. Do not use leaded gasoline.

07-30-2008, 08:58 PM	#6
VitaBene Senior Member Join Date: Jul 2007 Location: Moultonborough Posts: 3,532 Thanks: 1,574 Thanked 1,608 Times in 823 Posts	Most newer engines adjust the timing automatically for the octane you are using. For old boats like ours, I have a choice of what fuel I run but have to manually retard the timing if I want to run 87 reducing HP. I have run both 87 and 91- I see about a 15-20 HP (it is a rebuilt 260) difference, seat of the pants.

07-31-2008, 10:19 PM	#10
Audiofn Senior Member Join Date: Sep 2004 Location: Bedford, MA/Naples, ME Posts: 162 Thanks: 3 Thanked 2 Times in 2 Posts	It has been my experience that I get more HP and more speed with the lower octane. Lower octane fuel burns with more power/faster then higher octain. What really determins what you can get away with is the compresion ratio. If you do not know how to listen for detonation then I would run the higher oct. fuel. If you do then it may be worth a try. Remember that Ethenol is an octane boster!!

08-01-2008, 08:09 AM	#11
Woodsy Senior Member Join Date: May 2004 Location: Weirs Beach Posts: 1,949 Thanks: 80 Thanked 969 Times in 432 Posts	Cars & Boats are NOT the same.... Click & Clack are spot on when they are discussing cars & octane. Just about every car in production has a knock sensor that will automatically retard the timing when it senses detonation (pre-ignition)... Boats are completely different! Boat engines are CONSTANTLY UNDER LOAD, there is no coasting in boats... when traveling at headway speed, your motor is under load. A light load to be sure, but under load nonetheless. Vitabene, if your motor is rated for 89 octane, putting 91 octane in your tank isnt going to do much for you other than cost you $$$. Your motor isnt going to burn the 91 octane any more effeciently than the 89 octane. Thats the point Click & Clack are making. Until recently, boats didnt have knock sensors.... and detonation is an engine killer. Knock sensors are relatively new to boating. Most newer boats with fuel injection and electronic ignition do not have adjustable timing. The timing advance is completely controlled by the computer. You have to put the engine in limp home mode to adjust the base timing if the base timing is adjustable at all. Cobalts 25's 496 has a knock sensor and the computer controls the timing. If the knock sensor senses detonation, the computer will instantly retard the timing until the knock sensor no longer senses detonation then the motor will resume normal operation. If your on plane its pretty seamless... if your attempting to get on plane, or at WOT you will feel the loss of HP. 700 hours is a good number... You should plug the Merc scan tool in and find out how many hours were idling vs. how many were at WOT. It would just be an interesting tibit to know. AudioFn.... your bit off! Lower octane fuel burns EASIER than a higher octane fuel. It doesn't produce any more HP. In simple terms (there are other factors) compression ratio determines the required octane.... the higher the compression ratio the higher the octane required. Burning 87 octane in a motor that requires 91 octane with 10:1 compression ratio on a boat and you will be making a trip to the engine shop... In very short order you will melt the top of the piston or burn a valve.... The engine shops can use tricks to "fool" a motor, fattening up the mixture (so you burn more gas, but can use a lower octane) retarding the timing etc... the end result is that it is doable, but at the cost of engine efficiency. You end up burning more gas than its usually worth. Cal's motors are specially built HiPo motors that were tuned by an engine shop on a dyno. If you have a stock Merc or Volvo motor, leave it alone if you want it to live... The difference between 87 & 89 at the pump is maybe .15 per gallon.... thats an extra $15 per 100 gallons of gas.... If you burned 1000 gallons of gas a year its an extra $150! Is it really worth fooling around with considering the cost of a replacement engine? Woodsy __________________ The only way to eliminate ignorant behavior is through education. You can't fix stupid.

08-01-2008, 09:31 AM	#12
Dave R Senior Member Join Date: Jul 2004 Posts: 2,974 Thanks: 246 Thanked 736 Times in 438 Posts	Hey Cal, I'd love to hear more about the parts in your engines. Compression ratio, bore and stroke, connecting rods, cam specs, valves, heads etc. Those are impressive numbers for 5400 RPM, normally aspirated, and a marine cam to prevent water reversion.

08-01-2008, 09:57 AM	#13
Audiofn Senior Member Join Date: Sep 2004 Location: Bedford, MA/Naples, ME Posts: 162 Thanks: 3 Thanked 2 Times in 2 Posts	Woodsy Woodsy Woodsy you have drank the potion that is the high octane debate When you coming back up to the lake so we can blast around!! Lower octane fuels definetely burn faster, causing the retarding of timing to prevent knocking. However, if you run say a 330 motor you are MUCH better off running lower octane fuel and bringing the timing up as much as you can for the max power. If you raise compresion then you need to also as some point raise your octane rating to slow down the burn. As you raise preasure in the cylinder you have to slow the burn or you get.... detonation. This is a nice artical that kind of explains it. http://www.factorypro.com/tech_tunin..._vs_power.html I have a few more if you would like. Get up to Maine and lets run the boats!!!! I am sick of working on my roof!!!