Too Much Octane???

[tittyman]

Nevermind...just called our small local airport...100 low lead avgas is 4.31 and our local supplier of race fuel is 5.75 for 110 oct...
Question still is... most of you guys with 12:1 compression have you ever figured out what the min. octane level you can safely run at..I assume some where between 98-100 is that about right??? Thanks again for the help..

[born2burn]

Nevermind...just called our small local airport...100 low lead avgas is 4.31 and our local supplier of race fuel is 5.75 for 110 oct...
Question still is... most of you guys with 12:1 compression have you ever figured out what the min. octane level you can safely run at..I assume some where between 98-100 is that about right??? Thanks again for the help..
Like Mostly Crue was trying to explain to you .........it depends on the "brand" of fuel rather it be TRICK or VP or TORCO or UNICAL the list goes on and on. First you need to decide on a brand of fuel then go to there website get the phone number and call and talk to them about your application and "they" will recommend what fuel would best suit your needs. As for AV-Gas as was mentioned before lots of guys are running it in blown and high compression NA engines with no problems. However, it is all in the jetting and tune up. Av-gas is dry and requires and additive such as Miracle oil for lubrication. I used it with my 598 13.5:1 motor with no probs.

[rrocky]

What is the price of avgas with race fuel..thanks..$ 3.23 gal. in Va Beach Va.

[pw_Tony]

Avgas does work for keeping detonation down. But Avgas is not really meant for a higher power motor. Avgas runs much hotter than normal Race leaded fuel. Avgas is meant for Jets at over 20,000 feet where the air is cool. Bring that down here and run it in a boat that's constantly at 3500-4000 R.PM in 120 degree heat is not good. Yea alot of people run it and say it's just fine, which sometimes it is. But after using it for a while next time you take off your heads you'll see tons of pitting to your pistons and chambers, especially if it's aluminum heads! Again tons of guys use it and maybe they turn out fine. But working on the dyno day after day using all sorts of fuels, they combustion space got tore up, but then again we mostly worked on Aluminum head motors.

[tittyman]

Quick question..if you have a choice between av-gas or a good quality boost with lead, which would be better. The price ends up about the same. Just a matter of convience..
Second question...does av-gas burn cleaner than pump gas with boost or are they about the same or does it even matter?

[VDRIVERACING]

Quick question..if you have a choice between av-gas or a good quality boost with lead, which would be better. The price ends up about the same. Just a matter of convience..
Second question...does av-gas burn cleaner than pump gas with boost or are they about the same or does it even matter?
Avgas is MINIMUM 100 octane, but typically is much higher. Each batch is tested individually, and the hose jockey at the airport can tell you what it is. I've seen 120 before. I guarantee you you'll never notice the difference in "slow burn" by too much octane.
110 is about twice the price of avgas. Mixing different grades of fuels is not reccomended. Lead additives are a pain and expensive. Unless you're racing and pushing all the edges, go with the avgas. Just make sure you jet and time accordingly. If you're on the river in 115 degree sun, you might want to bump it back a couple of degrees. Check the plugs with a magifying glass once in a while and look for little silver dots. Those would be bits of aluminum from your pistons, tells you your too lean. We all go through this process...

[mostly crue]

T.M. Just do yourself a huge favor and just bite the bullet and buy just race gas. The money you save by mixing fuel is going to hurt you in the long run.
with 12to 1 comp ratio you owe it to your engine. Just think of it as cheap
insurance.

[RumRunner]

Octane:
Too much octane as stated will burn too slowly, and sacrifice some HP. How much depends on the actual engine that you’re working on. We’ve run Super Charged engines that have actually picked up as much as 30 HP, and cooled down in temp when decreasing to the optimal octane.
Optimal octane? The problem here is that just stating 12:1 or whatever number isn’t going to tell you what is the optimal fuel to use since different cam profiles will change your actual cylinder pressure. Different head, block, and gasket materials will change the detonation points. And different fuel blends (even with the same octane) will burn differently.
Now there are formulas to figure out what octane you come up with when you blend fuel. Such as 1 gallon of 100 octane 76 and 1 gallon of 92 octane 76 should give you 96 octane. Now to do this you really need to talk to the fuel vendor you’re using, mix it right before you use it, and only mix enough for what you’re going to use.
Avgas… Aviation fuel works extremely well, however it is designed and engineered to run at a much lower RPM range than where we run power boats. Usually the increased octane will overcome detonation at this point, however using the proper octane in an automotive rated fuel will generally produce more HP, safer.

[IMPATIENT 1]

Avgas does work for keeping detonation down. But Avgas is not really meant for a higher power motor. Avgas runs much hotter than normal Race leaded fuel. Avgas is meant for Jets at over 20,000 feet where the air is cool. Bring that down here and run it in a boat that's constantly at 3500-4000 R.PM in 120 degree heat is not good. Yea alot of people run it and say it's just fine, which sometimes it is. But after using it for a while next time you take off your heads you'll see tons of pitting to your pistons and chambers, especially if it's aluminum heads! Again tons of guys use it and maybe they turn out fine. But working on the dyno day after day using all sorts of fuels, they combustion space got tore up, but then again we mostly worked on Aluminum head motors.
jets run jet-a fuel which is closer to kerosene or diesel than race fuel .avgas is good, i ran a 11 to 1 bbf with a 300hp shot on avgas and never had any ill results from it.

[VDRIVERACING]

Just wondering how you/they determine/measure the octane rating, as you mention you have seen 120? Also dyno results show a fair amount of power loss with too much octane. But hey what do I know...
On the octane, I just take their word for it, just like any other gas I buy. It's been a while since I used avgas, but used to ask them the octane and they would bring out a clipboard and tell me exactly what that batch was. Maybe that has to do with FAA requirements, I don't really know why they do it or how they calculate the number.
As far as your dyno numbers, I'm not in a position to interpret them or discuss them. You know how dyno experiences go, engine to engine, dyno to dyno. My comment was directed at recreational use, I doubted he would notice the difference under those conditions. When one considers all the variables with occupant/gear load in the boat, weather, water conditions etc., a notciable difference would have to be pretty great.
110 leaded is probably the best fuel for highest performance, but question is, is that what is needed here? I use 110 because I run limited distances on a motor that is being pushed for every decimal of power it can deliver(racing). While racing components/fuels/etc can be used in other circumstances, I do not believe they are necessarily cost justified. That's just my opinion, but others, no doubt, have significant merit.