running lower octane
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Category: General Correct Craft Discussion
Forum Name: Common Questions
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URL: http://www.CorrectCraftFan.com/forum/forum_posts.asp?TID=20452
Printed Date: November-22-2024 at 9:51pm
Topic: running lower octane
Posted By: aquaman766
Subject: running lower octane
Date Posted: January-24-2011 at 9:08pm
| I have used sunoco 93 octane in my boat and it has always ran well. With the price of fuel rising i was thinking of goiing to the mid-grage 89 octane. My owners manual calls for a minimum of 89. I have a 1993 Nautique with the 351 Ford. Have any of you guys ran the 89? How much difference in power? |
Replies:
Posted By: TRBenj
Date Posted: January-24-2011 at 9:13pm
|
If your engine is 100% stock- meaning the compression ratio has not been raised, the ignition system hasnt been modified and the timing is set per the factory recommendations- then you will not notice a bit of performance improvement by running anything greater than the minimum recommended 89 octane.
The only performance boost would come from advancing your timing, in which case higher octane would prevent pinging. Unless your engine is modified, just run 89. ------------- |
Posted By: aquaman766
Date Posted: January-24-2011 at 9:25pm
| Thanks, It has a Mallory distributor in it. I bought the boat used but i don't think thats a stock distributor. |
Posted By: wakeboardin2k4
Date Posted: January-24-2011 at 10:34pm
|
Are you familiar with using a timing light? If so you could check to see what your base timing is in the spring and let us know how many degrees before top dead center, btdc, the engine is idling at. If youre running stock timing then TRBenj is 100% correct about using 89 octane fuel! ------------- "I'm planning to bring my girl that rides on a trailer with me and leave my girl that complains about camping at home" |
Posted By: kapla
Date Posted: January-25-2011 at 4:49pm
|
if you have the mallory then your engine was reverted to a regular ign set up and the protec ign junked away.. ------------- <a href="">1992 ski nautique |
Posted By: Gary S
Date Posted: January-26-2011 at 12:07am
Here's what the '89 PCM manual says-
 ------------- http://www.correctcraftfan.com/diaries/details.asp?ID=1711&sort=&pagenum=1&yrstart=1966&yrend=1970" rel="nofollow - 69 Mustang HM SS 95 Nautique Super Sport |
Posted By: SNobsessed
Date Posted: January-26-2011 at 1:07am
|
I have an '89, run 87 octane (not ethanol). Timing is at 9 deg BTDC. No knocking problems at all. ------------- “Beer is proof that God loves us and wants us to be happy.” Ben Franklin |
Posted By: TX Foilhead
Date Posted: January-26-2011 at 1:52am
|
89 works fine in my 93.
As the price goes up the higher grades are cheaper percentage wise if your getting something from them. Doesn't make much difference in these old boats, but in newer cars you can save a little from the improve MPG you might get. The reverse example of this works in my truck, I can get E85 for 20% less, but it drops my mileage about that much so its a wash. |
Posted By: MI-nick
Date Posted: January-26-2011 at 12:02pm
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been using 89 for years in my '93 and '88...no problem... ------------- As far as I can tell, I'm not quite sure... |
Posted By: skidcl
Date Posted: February-17-2011 at 1:17pm
|
One factor regarding gas is the altitude. As the altitude increases the density of the air molecules diminshes, acting like lower compression.
At my running altitude, about 24000 feet above sea level, I considered using 87 octane, and tried some. However the noise and wind did not allow me to hear any knocking, even with an engine stethoscope. I gave up and continue to run 89 octane in my 1988 Dominique. To my mind, this "altitude derating" is a longetivity issue with the engine, allowing less power, but less stress on the engine and longer engine life. Same thing with the jetting on the carb. Sea level jetting means I run slightly rich, but likely avoid any damage from being over lean. The difference in gas price is a small part of the cost of running my boat and is cheaper than major engine work. |
Posted By: 8122pbrainard
Date Posted: February-17-2011 at 1:32pm
Dave, Wow, that is some high altitude boating!! Where do you boat?  ------------- /diaries/details.asp?ID=1622" rel="nofollow - 54 Atom /diaries/details.asp?ID=2179" rel="nofollow - 77 Tique 64 X55 Dunphy Keep it original, Pete < |
skidcl wrote:Posted By: C-Bass
Date Posted: February-17-2011 at 2:23pm
|
Must be somewhere outside of Maryland...Maybe somewhere up the side of the Himalaya's.
Maryland Elevation - Highest point Backbone Mountain (Hoye Crest)3,360 ft (1,024 m) Mount Everest Elevation 8,848 m (29,029 ft)  ------------- Craig 67 SN 73 SN http://www.correctcraftfan.com/diaries/details.asp?ID=6103" rel="nofollow - 99 Sport 85SN |
Posted By: skidcl
Date Posted: February-17-2011 at 5:04pm
|
Oops, my fault, that should be 2400 feet. My boat is on Deep Creek Lake in western Maryland. The lake is 2380 feet above sea level at it's highest level.
The engine is a 351 Ford, with a slightly modified ignition (Pertronic) and a MSD spark box to deal with my slightly overich running. It is timed at the normal 10 degree BTDC. It uses the stock distributor. The boat is a Dominique, a 351 engine in a BFN hULL. The deep v hull runs better on a choppy lake than a flat bottoom, but the large wake (good for tubing, wakeboarding or barefooting (never tried it, probably not enough engine) suggests to me that the engine/hull arrangement is not very efficient. I really spent some time trying to see if 87 octane would cause pre ignition, but did not trust myself to be able to hear it, my only means of detecting preignition. I could not hear any knocking at idle, but at any speed, it is just too noisy and windy in the boat to trust anything I heard, or didn't hear even with an engine stethoscope. I then thought this was dumb, you are risking the engine for the sake of a dime a gallon of gas. Not worth it. |
Posted By: TX Foilhead
Date Posted: February-17-2011 at 10:30pm
|
I've always felt that my Excel it thrifty on the fuel because of the shape. Similar hull to yours with the V, and I also have the SB Ford instead of the BBC. My thought was that it is designed to get out of the water for speed where most of the other boats want to push the nose down to get a smaller wake at skiing speeds. Don't know if that's true or not, and there wasn't a similar slalom boat to mine so no real way to test.
I did run across something related sorta last night. It was test reports from a boat testing site who had tested various boats over the years with different motor options for the same models. The Tige's were interesting because they switched to PCM motors last year and the fuel economy improved. The other thing I noticed was the fuel economy also improved upgrading from the 343 to the 409. I don't know if it was enough to justify the cost of the motor or not, but interesting since I've heard these claims but never seen actual proof. They were simply looking for the most range at what RPM and MPH, but quite a few were around 24 to 26 MPH which is our usual riding speed. I think the best I saw was a little over 4 MPG and there were some Mastercrafts down in the 2.5 MPG range. Unfortunately there were no Nautiques tested. |
Posted By: skicat2001
Date Posted: February-17-2011 at 11:11pm
|
I run 89 octane in my 85 now. I had to have a carb rebuild and used to use 87 octane. I do not know wheter that was due to 87 octane but feel 89 is better and will suit you fine. ------------- 1985 CC 2001-SOLD Lee Michael Johnson |
Posted By: horkn
Date Posted: February-18-2011 at 3:19am
Ethanol e10 87 works fine with no knocking as well as regular non ethanol 87. ------------- 78 martinique- refloored, reinforced, stringers re glassed, re engineered interior GT40P heads Edelbrock Performer intake acme 4 blade http://img.photobucket.com/albums/v64/horkn/fish/nautique.jpg |
Posted By: eric lavine
Date Posted: February-18-2011 at 10:51am
|
c-bass, you been to Brokeback mountain? ------------- "the things you own will start to own you" |
Posted By: C-Bass
Date Posted: February-18-2011 at 11:29am
Never heard of it. I'm assuming you've been there?  ------------- Craig 67 SN 73 SN http://www.correctcraftfan.com/diaries/details.asp?ID=6103" rel="nofollow - 99 Sport 85SN |
Posted By: wakeboardin2k4
Date Posted: February-18-2011 at 11:47am
He owns a timeshare there...  ------------- "I'm planning to bring my girl that rides on a trailer with me and leave my girl that complains about camping at home" |
Posted By: 63 Skier
Date Posted: February-18-2011 at 2:01pm
Yuck. I'm not doubting your results, but I'd either burn the gas quickly or treat it. I'm still a fan of 89 in boats over the 87. ------------- '63 American Skier - '98 Sport Nautique |
Posted By: skutsch
Date Posted: February-18-2011 at 3:05pm
|
My understanding on octane is that the higher octane burns slower. So at was stated above if your timing is advanced (beyond factory spec) or if you have made mods to increase compression then you would want to compensate for a slower burn (with higher octane) or flash point. If the fuel burns to early then you increase the chance of detonation or pinging which is caused when the fuel flashes (due to heat and compression) before the piston reaches TDC and the spark plug fires. This slams the piston back down and as you might imagine can cause all sorts of damage. In a lot of instances you don't "hear" the pinging (especially in the case of 2 cycle engines - snowmobiles, etc).
So if you are stock or running stock timing with no mods to increase compression, I would run the recommended 89. Running anything higher does not increase your performance and other then being pre-cautionary, really doesn't get you any gains. Running lower then recommended definitely puts you at risk for detonation (that you may or may not hear as pinging). ------------- Our http://www.correctcraftfan.com/diaries/details.asp?ID=4669" rel="nofollow - 98 Sport Nautique My Dad's 63 Ski N |