Fuel Recommendations

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Surfbum
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Fuel Recommendations

Postby Surfbum » Wed Dec 12, 2018 1:00 pm

Running a DD stock Cadillac 500. Would ethanol free 90 octane or ethanol 93 octane be the better choice?

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pontoon outlaw
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Re: Fuel Recommendations

Postby pontoon outlaw » Wed Dec 12, 2018 1:03 pm

I run 4 gallons of av gas to 20 gallons of 93 on my branch 507 Cad...and it's only 8.5 compression..

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Slidin Gator
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Re: Fuel Recommendations

Postby Slidin Gator » Wed Dec 12, 2018 5:50 pm

Pontoon didn’t say why, but the better you feed it, the more advance you can throw at it. Assuming the fuel system is not original too ( so it is rated for ethanol), 93 should work fine. If you goose the fuel (Octane boost, AV etc.) you can tweak the timing etc.

The primary issue with Ethanol is not using the fuel, it does not store well. If you don’t use the boat 1-2x a month, then Rec fuel might be a better choice. Around me, AV gas is only 50 cents more, so why bother with Rec fuel.
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Re: Fuel Recommendations

Postby Surfbum » Wed Dec 12, 2018 6:25 pm

I already know this will open a can of worms from reading the other posts on timing a Cadillac 500. I have stock mechanical fuel pump(not sure if the pump can handle ethanol) I set the timing at 7.5degrees BTDC with vacuum advance disconnected. Hooked the advance back up and it ran great on 90 rec fuel, no detonation at all, but was quite hard to start. Set the timing back to 4 degrees BTDC and it starts much easier(I wouldn't say it fires up as soon as you bump it though). Boat feels and sounds pretty good to me, but I have very little experience with this suff. Would a higher octane make it crank easier so I could put more timing to it?

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pontoon outlaw
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Re: Fuel Recommendations

Postby pontoon outlaw » Wed Dec 12, 2018 7:11 pm

I don't use av gas mixture because of timing..the builder suggests it cause of the affect of the ethanol in the gas

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Slidin Gator
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Re: Fuel Recommendations

Postby Slidin Gator » Wed Dec 12, 2018 7:11 pm

No, if anything higher octane can make it harder to start. Are you running a choke?

It sounds to me like you found your start timing and need to work the rest of the profile from there. An adjustable vacuum can and a centrifugal advance timing kit will let you tweak things from the base timing needed to start.
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

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Slidin Gator
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Re: Fuel Recommendations

Postby Slidin Gator » Wed Dec 12, 2018 7:19 pm

pontoon outlaw wrote:I don't use av gas mixture because of timing..the builder suggests it cause of the affect of the ethanol in the gas

Ethanol burns faster and AV fuel burns slower (vs regular gas). Is that it, mix the three together to get an old school equivalent?
I grew up thinking I-10 was the Mason Dixon line.
1986 Airboat Engineering Inc., 14' Marsh Master. Refreshed narrow deck, SV O-540, 72” NGQ. A Bob Stossel original.

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pontoon outlaw
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Re: Fuel Recommendations

Postby pontoon outlaw » Wed Dec 12, 2018 7:20 pm

Could be. Lol

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Re: Fuel Recommendations

Postby SWAMPHUNTER45 » Wed Dec 12, 2018 10:02 pm

A properly timed Caddy with a good battery, cables and starter should spin over fairly easily.

Adding more initial timing fires the engine sooner which sort of makes the engine have to fight itself because the spark is sent prematurely. That fires the fuel charge and the piston still needs to go to TDC. That's why a locked dizzy is a bad idea.

Does this only have a hard start after it had been run and is at temperature ?

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Re: Fuel Recommendations

Postby One Eyed Gator » Thu Dec 13, 2018 11:19 am

My 1st caddy was a low compression motor I ran it with a mechanical pump. I bought a back-up mechanical pump but sold it with the last motor I built. The original pump I bought was still running 10 years later. Ran a little of everything through the low compression motor. Run fine on 87 til it got real hot.
Second motor with higher compression did not like the 87 at all. I like pontoon, I ran a little avgas (older motors liked the lead) with my 93octane. That motor loved it, but was tuned for it and I ran a good ignition.

Every once in a while I miss my old caddy. Till I realize it cost as much to rebuild my last caddy as it did my current ls 6.0.

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Re: Fuel Recommendations

Postby terrible ted » Fri Dec 14, 2018 12:42 pm

Slidin Gator wrote:Pontoon didn’t say why, but the better you feed it, the more advance you can throw at it. Assuming the fuel system is not original too ( so it is rated for ethanol), 93 should work fine. If you goose the fuel (Octane boost, AV etc.) you can tweak the timing etc.

The primary issue with Ethanol is not using the fuel, it does not store well. If you don’t use the boat 1-2x a month, then Rec fuel might be a better choice. Around me, AV gas is only 50 cents more, so why bother with Rec fuel.




The problkem with ethanole is the corrosion that comes with it. Not recomended for a carb system

If you dont need the octain its wasted money.



Ethanole may be cheaper per gallon but for my bay boat (2 stroke) it was cheaper to run rec fuel. The economy worked out at 1 dollar per gallon cost was more economical, in just millage on the water of recreation fuel verse ethanole.
The cost was way chaper to use marina to fuel my boat then to fuel on the way with ethanole. luckey now you can buy recreation fuel at stations.

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Re: Fuel Recommendations

Postby terrible ted » Fri Dec 14, 2018 12:45 pm

pontoon outlaw wrote:I don't use av gas mixture because of timing..the builder suggests it cause of the affect of the ethanol in the gas

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because its eating the fuel system away?

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Re: Fuel Recommendations

Postby SWAMPHUNTER45 » Fri Dec 14, 2018 3:07 pm

Something must be lost in translation. First is Pontoon has a Series 3 LC engine that is a pump gas engine. It should live a long life on fresh 93 octane fuel.

As it relates to Aviation fuel in a Branch engine the builders guide line is 10% to 25% based on need. Need is driven by compression ratio, operation environment (temperature) and head material. The reason that he limits the blending to 25% is in the Cadillac head on the exhaust area use beyond that 25% blend has caused slight erosion. Not sure if it is because the fuel is "dryer" with less oil based lubricants or just a other anomalie. Personally I run a blend of 20% and add in a few ounces of Lucas Fuel Treatment or Marvel Mystery Oil as a cushion.

Unrelated to Mr Branches position years back I met an older fellow who had used AV has in auto engines. Back then he told me if I was ever going to use it to add in some 2 cycle outboard oil. I have always used the Lucas or Marvel and never had a issue.

Ethanol is bad for a few reasons one being it attracts moisture. Another is it degrades rubber and corroded metals. I think it is wise to use the aforementioned additives to lubricate and protect.

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Re: Fuel Recommendations

Postby Capt steve » Fri Dec 14, 2018 7:18 pm

Ethonol will wick moisture from the ambiant atmosphere and lead to water in the fuel system as well as caustic to rubber and plastic.
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Re: Fuel Recommendations

Postby SWAMPHUNTER45 » Fri Dec 14, 2018 7:24 pm

Capt steve wrote:Ethonol will wick moisture from the ambiant atmosphere and lead to water in the fuel system as well as caustic to rubber and plastic.


The actual scientific term I am told is "Phase Separation." It is why I run a traditional marine spin on separator style filter.

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Re: Fuel Recommendations

Postby Rick McC. » Fri Dec 14, 2018 10:42 pm

I run 90 octane ethanol free gas with PRI-G fuel stabilizer in everything but my autos; which includes outboards, motorcycles, airboat, and all my smalll engine powered “stuff.”

I’ve done that for many years now, and have never had any fuel related issues with anything.
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pontoon outlaw
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Re: Fuel Recommendations

Postby pontoon outlaw » Sat Dec 15, 2018 1:43 pm

SWAMPHUNTER45 wrote:Something must be lost in translation. First is Pontoon has a Series 3 LC engine that is a pump gas engine. It should live a long life on fresh 93 octane fuel.

As it relates to Aviation fuel in a Branch engine the builders guide line is 10% to 25% based on need. Need is driven by compression ratio, operation environment (temperature) and head material. The reason that he limits the blending to 25% is in the Cadillac head on the exhaust area use beyond that 25% blend has caused slight erosion. Not sure if it is because the fuel is "dryer" with less oil based lubricants or just a other anomalie. Personally I run a blend of 20% and add in a few ounces of Lucas Fuel Treatment or Marvel Mystery Oil as a cushion.

Unrelated to Mr Branches position years back I met an older fellow who had used AV has in auto engines. Back then he told me if I was ever going to use it to add in some 2 cycle outboard oil. I have always used the Lucas or Marvel and never had a issue.

Ethanol is bad for a few reasons one being it attracts moisture. Another is it degrades rubber and corroded metals. I think it is wise to use the aforementioned additives to lubricate and protect.
6 years and counting. Lol..and I run the dirt off the the hill...

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