PDA

View Full Version : Octane ?



Sam
04-16-2006, 11:20 AM
What fuel octane are you running ? If I buy on the water it's typicly 89, if on land I do the same but from a brand name station.

mrfixxall
04-16-2006, 12:06 PM
i USE 93 ONLY,,,,I USE BP (AMACO) BECAUSE THEIR THE ONLY ONES THAT HAVE A SEPERATE REFINERY FOR 93 OCTAIN WHICH MEANS ONLY 93 FUEL GOES THROUGH THE PIPES AND THE 93 FUEL DONT GET MIXED WITH 87 AND 89 FUELS AFTER ITS REFINED....SO I WAS TOLD BY A FRIEND THAT WORKS FOR AMOCO...

Pismo
04-16-2006, 12:26 PM
Use only as high an octane as you need. If you do not have a high compression engine then you do not need high octane fuel. You will get slightly more power and speed using lower octane fuel. Like a stock 454/496/502 Merc with 9.5:1 or lower compression will not need 92/93 octane fuel. 87/89 is fine and will make more power. If you are 10-11:1 then you need 92/93, unless you have aluminum heads then you have some more room.

Sam
04-16-2006, 12:32 PM
Pismo, at the risk of sounding like a dummy, can you explain what you mean by "Have more room with aluminum heads.

THX
Sam

pmreed
04-16-2006, 02:34 PM
502/415 in my 22 C. 87 octane all day every day.

Phil

olredalert
04-16-2006, 05:05 PM
Sam,

-------Aluminum disipates heat faster, therefore the aluminum surface is less likely to prematurely ignite the fuel. Also the less sharp edges in the combustion area the less chance of detonation. Sharp edges stay slightly hotter during the combustion process.........Bill S

yeller
04-16-2006, 05:22 PM
Pismo, at the risk of sounding like a dummy, can you explain what you mean by "Have more room with aluminum heads.
THX
Sam
He just means with aluminum heads you could probably run 87/89 with a 10:1 compression motor because they dissipate heat faster than cast iron heads and therefore are less likely to cause detonation.

Oops...didn't notice Olredalert already answered the question.

Dr. Dan
04-16-2006, 06:08 PM
:smash: Like Phil posted I too run 87 all day long...when we had the 454 I too thought the higher Octane was gonna do me better performance...I went to 89 and the Soot on the Pipes and Transom went away.... I got tired of cleaning my money off the back end....and stuck it into the Gas Tank instead....some things never change.


Doc of Negative Cash Flow....as Gas PRices Go Higher :wavey:

blackhawk
04-16-2006, 06:43 PM
Use only as high an octane as you need. If you do not have a high compression engine then you do not need high octane fuel. You will get slightly more power and speed using lower octane fuel. Like a stock 454/496/502 Merc with 9.5:1 or lower compression will not need 92/93 octane fuel. 87/89 is fine and will make more power.

Well said! :D

MOP
04-16-2006, 07:14 PM
I have been using 89 with 9:125 I will try 87 next fill up, my transom has stayed clean but why waste the $$ if there is no gain.

Phil

Pismo
04-16-2006, 07:30 PM
Yes, the aluminum carries away the heat faster so it buys you 1 to 1.5 points of compression roughly. So a 9:1 steel head is equal to a 10:1 or 10.5:1 aluminum head. So you could use 87/89 on either where as a 10.5:1 steel head you may need to go up to 92/93.

blackhawk
04-16-2006, 08:03 PM
On a stock engine I will always run recommended fuel. Like Pismo said you will actually get LOWER performance running higher octane.

But, if I had a modified engine I would always run higher octane just to be safe. I will gladly throw a few $$$ and lose a couple hp to know my engine isn't running "on the edge"!

tiger lily
04-16-2006, 08:31 PM
i run premium with lead additive in my boat, mine pings if i put 89 in it for some reason, i trailer my boat always so its usually always filled up on land.

mrfixxall
04-16-2006, 10:27 PM
The only thing that scares me is the lower octain fuels have more alcohol in them,,so the pump say(may contain up to 25% alcohol)and we all know that its not good for the rings in the engine....

Cuda
04-16-2006, 10:41 PM
I run 87 in all my boats except the 302 Formula. It has 10:1 compression, only run 93.

Dickv
04-17-2006, 07:25 PM
I run 87 octane in my 87 Z21 454Mag 330HP with no pings, no knocks, no run-on.

My 89 Sea Ray with a 220HP 5.7 runs-on some times on 87 octane. When I remember, I add 2oz Mixi-Go fuel additive. It is not an octane booster, but evens the burn, dissipates carbon, and picks up any water in the gas. I've been using it for abour 20 or so years in all my cars that require premium fuel.
(regular 87 octane with the additive runs better than premium in my BMW M3 and in my Mercedes E-320. Most noticeable in the M-3). I haven't put any in the Z21 yet, but probably will to pick up any water accumulation during storage.

Sagbay32
04-17-2006, 07:35 PM
Silly question #2
If you had a 1/2 tank of 93 and you topped it off with 87, would you end up with 90? Or is it bad to mix different octanes?

Mike

Pismo
04-17-2006, 07:49 PM
As an engine gets older and develops deposits you may need to up the octane since the buildup can be a source of pre-ignition.

BigGrizzly
04-17-2006, 07:58 PM
I have tested many engines on dynos testing the octane theorys. It is true use only the octane requires. However if indoubt go up one. We have actually pulled more horsepower on some engineswith lower octane fuels providing they were ser up for it. If you set the engine 9.5 or better on a dyno with 93 then unlesw you back off timming it could be a problem. My partedular 502 with 9.5 and a procharger was set upvery well on a dyno and it will use only 93 octane without a major change. With all the efi boat engines (stock) there is a knock sensor as lame as they are they do work pretty well. All the Mercs That we have tested on the dyno tend to run fat-too much fuel. The reason you can run lower octane fuel on a fat engine is because lower octane fuel burns hotter and faster. This is where the trouble starts. Draw your owne conclusions. In 1974 A motor cycle racer and friend of mine Gary Nixon was racing for Kaw. At Datona they were having trouble going as fast as they needed. Gary's mech said to gary that the engines were only 8:1 compression and with 106 octain the plugs were too hard to read. Gary jumped up anr ran off and came back with a 5 gallon of 87. they mixes upthe oil(2 stroke engines) and went out and pulled another 5 mph the next practice session, leaving the rest of the tean in disbeleaf.

FISHIN SUCKS
04-17-2006, 09:11 PM
So I have always run 93 octane, get no carbon on my transom (a little inside the pipes if I wipe my finger in there), no engine run-on, and she starts right up, is this my test? 454 has been bored 30 over and sounds healthy, but don't know the compression. The previous owner built the motor and said he has run nothing but hi-test (93). Do I run 87 to get my answers or do I just stick with what seems to be working?:lookaroun

blackhawk
04-17-2006, 09:52 PM
IMO when in doubt run higher octane. Cheap insurance!

Like Big Griz said lower octane burns hotter. Heat=HP. But too much heat = melted/detonated/broken parts!

I used to have a "play" snowmobile that I strictly raced. It was 925cc twin that was about 190-200hp. Had 185-190lbs of cranking compression with a .055" squish and needed a minimum of 110. We also raced our bone stock sleds and ALWAYS ran 87 when racing. Guys would come up and ask to buy some 110 octane for their stock sleds because they thought "race gas" would make their sled faster. :rolleyes: If we had enough I'd sell them some. Then they'd wonder why my stock 600 just handed it to their modified 700. :D

CHACHI
04-18-2006, 06:08 AM
Lower octane burns faster. It is this reason that lower octane sometimes offers more power. Because of the burn rate of lower octane fuel you will get a more complete burn of the incoming fuel charge before the exhaust valve opens. If the exhaust opens before the charge is completely burned the flame will start travelling out the exhaust port causing more heat and producing less power due to less energy pushing the piston down.. Ignition timing has an effect on this as well as cam overlap and duration, and compression. Using 93 octane in a motor designed for 87 octane is a waste of dollars. Ken

Sam
04-18-2006, 09:57 AM
Soooo in my case where I’m running aluminum heads with 10:1 compression could I assume that a safe compromise would be to continue to run 89 octane which is what most all marina gas is ?

THX
Sam

MOP
04-18-2006, 11:37 AM
Ok my iron head 383 with 9:125 comp and timing set 32 max should run 89 is that is correct?

Phil

roadtrip se
04-18-2006, 01:25 PM
so that is what I do, even though it is rated for 87.

Seems to burn less rich with the better go juice and the transom does come out of the water with less gunk on it.

King of the post-launch quickie detail.

cday@crescentschool.org
04-18-2006, 08:22 PM
does anybody know what the compression is for the 6.2 MPI Merc?

smoothie
04-19-2006, 10:46 AM
Soooo in my case where I’m running aluminum heads with 10:1 compression could I assume that a safe compromise would be to continue to run 89 octane which is what most all marina gas is ?
THX
Sam
To many variables to assume yes:biggrin.: like timing,plugs,carb jets and air temp,find out the old fashion way run it and look at the plugs....JMO! I have aluminum heads and about 10:1 compression and always run 93 like Clint Eastwood would say "do ya feel lucky"...

MOP
04-22-2006, 11:48 AM
I was just looking over the Scorpion spec's in the Scorpion post, it was interesting to see Merc calling for 92 octane with only 9:1 compression. Makes you scratch your head!

http://www.donzi.net/forums/showthread.php?t=44582

Phil

Patrik Sweden
04-22-2006, 03:02 PM
I use 99 Octane from Shell.. it is the highest octane you can get from traditional Stations here..

smoothie
04-22-2006, 04:45 PM
I was just looking over the Scorpion spec's in the Scorpion post, it was interesting to see Merc calling for 92 octane with only 9:1 compression. Makes you scratch your head!
http://www.donzi.net/forums/showthread.php?t=44582
Phil

I believe they still call it CYA,,,cover your ass!

Gearhead99
04-23-2006, 06:33 PM
mrfixxall, couple of posts back you said that 25% alcohol is bad for the rings.

Never heard that one, do you know a reason?? Or did someone state that to you about your engine??

Just curious as to the thoughts why they feel it's bad.

Sagbay32
04-23-2006, 06:35 PM
Silly question #2
If you had a 1/2 tank of 93 and you topped it off with 87, would you end up with 90? Or is it bad to mix different octanes?
Mike


Does anyone have a guess on this one?

Thanks
Mike

Blue Bullet
04-23-2006, 08:35 PM
When my baby cruises up to the bar, she gets a mixed drink...
2 parts gasoline
1 part octane boost
1 part lead additive
but my babies a H/M 427 side oiler!:smileybo:

smoothie
04-24-2006, 01:24 PM
Does anyone have a guess on this one?
Thanks
Mike
This article is should help ya out!
http://www.cartalk.com/content/columns/Archive/1993/March/17.html

smoothie
04-24-2006, 01:28 PM
Does anyone have a guess on this one?
Thanks
Mike

Heres a chart

blackhawk
04-24-2006, 02:05 PM
Does anyone have a guess on this one?
Thanks
Mike

That is correct. Just figure out the average to get the new octane.