Octane and compression discussion
 

I started this thread with myself and a good friend in mind. We both took our first runs of the season today and found out that the fuel docks we normally fuel up at, no longer carry 91 octane. We can only get 89. We have heard that there may be 1 place that may have 91. However, its a pain in the a$$ to get there, due to many long no wake zones. So, for now, lets say we are stuck with 89. Jugging fuel to the dock is not possible either.
Some may say, add octane boost. I am not a believer in that stuff. From what I know and have researched, the cost and the amount you have to add to make such a small difference in octane, doesnt make it sound to appealing. In the past, when I was into running high compression engines in street cars, I used to mix in some race fuel, maybe Cam 2 or VP, with pump gas. That was easy, after all, compared to a boat, a car sips fuel.
Now for our engine specifics.
My friends engines are the easier to describe. He simply has 575SCI's. Fresh rebuilt, nothing added, everything was built back to factory specs. Ofcourse, Merc recommend 91 octane. Has anyone run these engines on 89?
Mine is a bit more complicated. I am running new built, NA 565, 10 to 1 compression, aluminum heads, closed cooling. No EFI, no computer to control the timing. Just a simple Carb and an MSD. I normally run 36* advance, locked. With the closed cooling, my water temp runs about 180*. I am thinking I can lower the water temp some, that may help lessen the chances of detonation. I have aluminum heads, that has to help suck out some combustion chamber heat. The fairly large bore, 4.530 may help a bit. I suppose I can add a knock sensor. At least that will tell me if there is something going on. Does anyone run a simliar combination on 89?
The next question I have, does anyone have a successful, proven formula for increasing octane?
If I wanted to simply add some race fuel to the mix, is there a formula for calculating how much is needed to bump up 89 to say 91? Is it as simple as calculating the percentage of 89 and race fuel, to come up with the new octane. For example: 5 gallons of 100 octane added to 5 gallons of 90 octane would make 10 gallons of 95? That would be nice, but it seems that may be too simple a formula.

I have a similar set up as well but new motors this winter , we do have 91, my builder said to splash 10-15 gallons of 110 in there just to make sure you are above 91.

Fixx
 

Contact your local fuel oil distributor,some one who delivers fuel to construction companies tanks in their yards..see what it would cost for them to drive their mini tanker and fuel up yours and friends etc etc etc..if you can get enough boats together and your close to shore I'm sure thet will fill them up and it should keep the cost down..

That would be a good idea. Unfortunately, we both keep our noats at a local high and dry here on Long Island. The owner doesnt want to see anyone filling up their boats on his property. Insurance regulations I guess.

[QUOTE=LV;3111704]I have a similar set up as well but new motors this winter , we do have 91, my builder said to splash 10-15 gallons of 110 in there just to make sure you are above /QUOTE]
My engine is brand new as well. Until now, I was able to safely run 89 in my previous engine. The fuel docks by me, have carried 91 for as long as I can remember. Now all of a sudden, I buld an engine that requires 91 and bang.... no more 91.

Fuel distributors have to have a permit to be able to pump into a boat on water and around here it is a $50k slap on the wrist if you are filling anything other than a barge on water. As far as the ratios it really is as easy as percentages. If your local marine has switched to a 10% ethanol blend (which mercruiser states is safe for their marine motors) then your 89 is actually close to a 91 octane of they are splash blending. Anything over 10% has seemed to be a little to harsh for marine enviroments but most octane boosters are in fact ethanol or methanol based.

Another thing to consider, apparently Ethenol has a lower BTU for the same otane.

In Canada, all stations buy shell have Ethenol.

Also the ethenol has caused some problems with many EFI engines here on the lake. (it cleans out everything inside)

Gasoline:
1 Gal Gasoline (mid grade) = 125,000 Btu's

Ethanol:
1 Gal Ethanol = 76,000 Btu's

1 Btu= .293 watt
1hp = 746 watts

Therefore, 101hp/ gallon of Ethanol, and 167 HP/gallon gas.

http://www.cogeneration.net/FuelAndE...quivalence.htm

Correct....whenn your local fuel distributor switches to ethanol you need to change your fuel filters EXTREMELY reguarly for the first few fill ups. I changed mine every other weekend for 3 months when we switched. Rather be safe than sorry.

I have heard that you can use toulene(sp) but never used it.

I always put some 110 in at the start of the season just in case. Running 10.7:1 i don't want to take any chances.

http://www.motorsportsracingfuels.co...alculator.html

tolulene is a component of race gas so yes it helps raise octane. Lead is one of the larger factors in raising the octane of AV gas though.

i was curious what octane you mix your 110 with? Ive built new motor over the winter and ended up with about the same compresion..

That is a great calculator. Thanks for sharing. I had the thought of contacting tech support @ VP race fuels today. I asked him how to accurately mix different octane fuels. His answer was as simple as my first post. In a mix of different octane fuels, the octane will be an average of the fuels mixed, by percentage of mix. Meaning, 5 gallons of 90 mixed with 5 gallons of 100, produces 10 gallons of 95. The equation is simple to do. Now that by u boy has added the neat calculator, its even easier. The problem is it takes a good amount of race gas to raise the octane of pump gas. In my case, I have an 80 gallon tank. It would take 15 gallons of 100 octane , to raise 65 gallons of 89, to 91. Not easy for me to do, when I cant fuel up at my marina for insurance reasons. I was hoping that it would take alot less race gas to bring up the pump gas. I am sure I could get away with adding a few gallons at the yard, but 15 may be a bit much.
My friend who is in the same situation as me, came across a stroke of luck today. He found that a local fuel dock, will be getting a shipment of 91 delivered tomorrow. If it sells enough, he will keep getting more. If that is the case, all our problems are solved. Maybe I should hire a sign plane to fly by the ocean beaches advertising for this guy. May as well start here... Anyone looking for 91 in the area of Jones Beach, head over to Scotty's in Point Lookout..

I run 8.9 to 1 comp & 36 deg timing with iron heads. I use 89 octain and have not had any issues. Keep your fuel fresh and only buy what you will use in a couple of weeks. I learned my lesson with old E10 fuel, I took out the tops of my rod berrings.

interesting thread, I just bought 500 gal. of 90 octane premium fuel with no ethanol. my engines call for 93, my fuel dist. told me because this fuel has no ethanol is should be fine. I have some avgas was thinking of mixing some in, what do you fuel guys think? should I add some avgas or is the high test 90 good?

as most of you know I operate a fuel distributorship and we make and blend our own race gas. I will be more than happy to attempt answering your questions. If it were me I would mix mixed race gas instead of just av gas. It will take more av gas ratio than race gas. Your beat option is to buy some higher grade race gas and mix it. That way you could raise the octane level with smaller quantities of fuel

So you think I should add some race gas to it? I like the idea of what I have now having no ethanol or additives, less water issues etc. Does not having the ethanol help with detonation? Can I get by with the 90 as it is? Hard to get good race fuel around here, can maybe get Torco or Cam2 somewhere or have to drive an hour to the refinery and by a 55gal drum of the good stuff.

The anchorage in lindenhurst has good gas !! I think they even have 100 rite at the dock .

Piece of Mind
 

I think you answered your own question with the knock sensor set up. Everything else is just a guess....or expensive.

It should only be necessary to install a knock sensor on one engine. As a base like, test with 89 as is. If you detect any knock, start dialing the timing back. We see minimal HP change in the timing on 9.3 CR and iron heads....maybe 10 HP between 34-38 degrees. If you still have detonation and you aren't willing to give up the HP, you can blend in 110 race fuel in five gal increments until you like the answer.

Share the results and everyone on OSO that reads will all buy you a beer :drink:

I run 93 and only add the 110 to the fuel that sat in the tank all winter. I put about 5 gallons to the 60 gallon tank. After that I just run 93 and have had no problems. I did snap a crank last summer and have not pulled the motor yet:angry-smiley-038:

I found this interesting write up on octane. You guys thinking of avgas, beware, page 2 says it may contain lead. Not that many of us, if any, run cat converters. Its just good info to know.

http://auto.howstuffworks.com/fuel-e...question90.htm

zzsupeboat,
Didnt know the anchorage has good fuel. Thanks for the info.:drink:

Mixing race gas is definitely the best way to know exactly what you're getting, but the "NOS racing formula" booster works really well. We've tested it on the dyno and the track and have used it in the boat for two seasons with 89 octane. I've heard the Torco stuff is good too and you can buy it in five gallon pails but have never tried it. Also, on your engine an option would be to contact Bob Madara and see if he could design a cam for you that will bleed off enough cylinder pressure to run 89 and not cause reversion. I've got a couple customers running 10.2:1 on 89 whithout any issues. Good luck either way :ernaehrung004:

Wow I'm surprised someone else has heard of toluene! I used to use it in my high compression jet boat in the early 80's. I mixed 1 Qt. to every 10 gals 91 octane and it ran great. I ran that boat for about 3 years hard with no problems. There are a lot of articles on mixing it if you do a search. I also ran 50/50 AV gas with 91 octane with good results.

Toluene sells for about $35.00 5 Gals. and can be found at petroleum distributers and paint stores.

Toluene has an octane of 114, so plug that into your formula. It is probably the best option. The other real options are either race fuel or the Torco octane boost.

80 gallons of 89 octane and 7 gallons of Toluene puts you right at 91 octane.

Ethanol will make the fuel burn quicker that is how it attempts to make up for the loss of btu's... Unfortunately I can tell you that every motor runs a little different. We build stock 03 cobras with some running to the chip and one will run great with 102 and the other will want 105... Fuel is something you just have to pick a median and play around with until the motor runs smooth. If you can still find torco then It is a pretty good fuel but they have been in the process of shutting the doors. Let me know where you are located. We have distributors in 23 states and ship to your door also.

You can also use Xylene instead of Toulene. You can purchase Xylene at Home Depot and Lowe's.

Kemco Oil's Supreme 130 is good stuff but it will clog C02 sensors.

Torco's unleaded Accelerator is a good concentrated race gas.


http://www.easyperformance.com/Tech_...d_Content.html

That is a cool chart!! Great info...

I add some of the Supreme 130 (TEL) at the begining of the season and then again mid season to coat the top end with lead.
As for the 10:1 @ 36*...89 would be fine, I would take out 2* of timing for peace of mind or drop 1 heat range on the plugs. F all that mixing sh*t.

http://www.hi-flow.com/HPOP4.HTM

http://en.wikipedia.org/wiki/Tetraethyllead

Wow, this thread came back to life again. Since I started this some time ago, I have been running 89 octane, but with the timing set to 32*. I keep the mixture richer than I would normally as well. I dont run the engine hard. I keep it to max 3/4 throttle. The plugs are looking great. The timing burn is just right. I may be too cautious but I run alot of miles each time out. I would rather run safely today and still be able to run it tomorrow. My plans are a new set of pistons for this winters project. I have been working with Wiseco on having a set made that match my current pistons exactly, with the exception of the dome. Bore, pin location, ring package, even the weight, can be duplicated. That way, all I have to do, is swap pistons. No need to rebalance the rotating assembly, no need for new rings or even honing the bores. Remember, this engne was newly done just last winter. If the bores look good, I plan on just swapping pistons. I have calculated what I need to make the compression ratio a safe and conservative 9.25 to 1.

I would leave it alone.

Funny, I was talking to a fuel rep last week, he was telling me todays fuels only maintain there octane rating for 30 days...then fall off..so be aware sitting on fuel or where you buy if they do not move it fast....Vinny, I still think you are really close with the comp you are running with that much timing, the aluminum heads will help some as will the cam...they can grind the cam so the engine "thinks" it has less static compression..although might not be a good cam for your marine app. I said this before I would run a good water/alcohol injection system, it would give you extra insurance over the fuels...Rob

Who's got toluene experience? I've never run it but have access to it. Does it raise octane or is it oxygenated?
any dyno experience?

Other things that you can do to prevent detonation include, getting cooler air to the carb, a scoop or something. Lower your water temps. If you have fairly wide piston clearence, you can run without a thermostat or with a 120 deg. from Arizona Speed and Marine. Less ignition timing, but be careful, below 30 and your exhaust valves will start to heat up negating any benefit. Richer fuel mixture. Ever take a sparkplug out of a carbed Mercruiser? They are always dark. Much richer than a street car or a drag racer. Good luck.

I run a conservative 33º total timing with 10:1 compression, Aluminum heads, and 93 octane. I can go with more timing for sure, engine builder says another 2 or 3º, but how much hp would that actually gain?

I dont plan to add more timing, as I would rather have it live than eat itself alive, just wondering how much I am leaving on the table. The engine is a 598ci N/A, 10:1, Dart Pro 1 345cc heads worked over, Dominator 1050cfm, Comp hydraulic roller cam .647/.647 252/262 112LSA. Has a crossover with no thermostat. Should be right around 725hp right now based on speeds.

I agree with your engine builder. You're set up pretty conservative. That cam is bleeding off some compression also. Try it and find out.

That is the thing, I know I can run more timing, but for what gain? 10hp with 3º or 50hp? Then i run the risk of getting bad gas and burning up a piston or two.

I am just wondering if there is any real benefit to be gained.

Back to the Top for Keith
 

I have very similar engines, same size, compression etc. I am at 32 degrees total advance.

We can't get 93 here. Engines were tuned on a dyno with 92 which is no longer readily avalible.

I add 5 gallons of toluene to each 100 gallon tank at fill up as a safety precaution. Any more octane, and I am loosing energy since I only have 10;1 compression.