OCTANE IN A MIX... AND AV GAS/PUMP 91/RACE GAS.

[mountainhorse]

Some info on AV and Race relative octane levels.


AV-GAS... 100LL is rated "100" on a special Aviation octane rating... and the 100 relates to a "lean mixture rating"
NOT AT ALL similar to motor fuel (road) ratings.

The "LL" relating to Low-Lead (low tetraethyl lead content, not to exceed .56grams/liter.... much lower than typical 110 race fuel)

100LL has a MOTOR OCTANE NUMBER (MON) of approximately 103. This will give a more accurate comparison for an "apples to apple" snapshot of this fuel compared to other motor fuels.

By comparison.

Sunoco 110 has a MON of approx 105. With a lead content of approx 4.0grams/Liter.


There are many different characteristics of the fuel, eg Reid Vapor pressure, specific gravity, evap temps etc.... Octane IS important, but only a small snapshot of the whole picture....But for this conversation in this thread... not really necessary since we have all had great reports of all of these fuels for use in our sleds over the years.... no need for an argument of these points for this discussion IMO.

Although I hate to use etanol pump fuel for mixing (for my own reasons), in my area... and many others, it is the only option... (and, yes, there are some that are blessed with non-eth in certain areas )

Using 100 as the octane number of AV-GAS, 110 for typical race fuel and 91 as your octane number of Premium pump full will NOT give you an accurate idea of the octane rating of mixture.

To Calculate fuel ocatane in a mix of two different fuels... you must first make sure that you are using the SAME OCTANE rating.... MON is a good place to start.


100LL MON = 103 MON (approx)
91 'Premium' Pump fuel with 10% ethanol = 88 MON (approx)
110 Race fuel typical = 105 MON (approx)


Those would be much better numbers to use with the following formula to determine your mixed octane number relative to the BASELINE of typical 91 pump fuel. Note that Non-Ethanol "Pump-91" fuel will have a slightly lower MON of approx 87 MON due to the increased octane of the added Ethanol.


( [ % Fuel A ] x [ Octane of Fuel A ] ) + ( [ % Fuel B ] x [ Octane of Fuel B ] ) = Octane of Mixture

For example... a 50/50 mix of typical 100LL to 91(10% eth) 'pump'.... would give you approximately 95 MON in your end mix.
[Lower than the 103 MON of the AV-GAS and higher than the 87MON of the 'premium' pump fuel.]




Also, as a side note... the word "PREMIUM" fuel has ZERO to do with the QUALITY of the fuel within a brand.... It is just a industry name that refers mostly to the Octane number of the fuel.

It is easy to LOSE performance...both in overall max power & throttle response ('torquieness' and throttle 'character') by using too HIGH of an octane.

Pump gas will, for our intents and purposes in mountain sledding, have better throttle character for our uses than 100LL... and that is not simply related to Octane ratings.
This is the reason I'm an advocate of MIXING pump fuel to 100LL to get the right blend for your uses....

Since MOST turbos sold today are lower boost (sub 8 lbs psig, on sleds used above, say... 5K feet.... you are losing performance using straight 100LL in a given sled... and mixing 100LL with Pump fuel will optimize your smile factor and get the most out of what you paid dearly for (sled and kit... and time off work !!)

You need to do your research...a little trial and error...or talk to people with the SAME sled/kit as you have... and, find the mix for you for the elevation and boost levels you are riding... To enjoy what you have !


Hope this helps.

My 2¢






















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[Jay]

Mountainhorse, you've always come across as a pretty smart guy, so I gotta say your 2 cents is probably worth more like 3 cents. thanks for the info it really does help. Jay

 

[Jreng87]

The “Hot Mix”

25 gal 100LL
25 gal 91
5 gal Tolulen
1gal oil

Braaap

 

[mountainhorse]

WHY?

Are you running high boost or a NA sled at 16:1?? (or sea level??)

100LL has as much as 20% toluene in it already (you can actually smell it).

Adding another 10% to your mix... does make it "Hot" in terms of solvent levels.

Toluene is also an aggressive solvent, higher Toluene levels have been shown to embrittle plastics and weaken rubber, and certain plastics and adhesives.

The approx 50:1 oil mix you've added on top of it all... I like that idea [or maybe a bit less] for longevity/piston lubrication... your resultant oil mix on an 800 CFI engine would be in the neighborhood of 25:1 - 30:1 IF, you have not already turned up your oiler.
A 50:1 premix would essentially double the oil to the piston
(still flows the same stock amount to the crank bearings however... as premix does not flow to the bearings in 800 CFi motor)
Richer oil mixes Lower octane of a fuel to a certain degree.


Something to ponder.














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[Jreng87]

10lbs at about 10k

This is the mix I was recommend to run by VOHK.

So far so good,

 

[KAWGRN]

So what octane are we really trying to get to? I mix to get 96 on my Wallace calculator and it’s been running great at 7 psi

 

[LongHorn XC]

Fuel Ratio’s

Using VP110 with pump gas (octane/quality?):

I have done my homework on figuring out ratio’s of fuel. I did it per MH’s MON-RON with octanes and compared that to a Silber recommendation chart. That basically checks out for how much Octane is needed per boost and elevation.

I studied up on another thread post that came up with a different way to calculate for simple terms. They used atmospheric pressure to figure out how much ‘extra’ octane to add. This is a little ‘rougher’ to estimate what you need, but should get you close to the same ratio as mentioned above (MON-RON-Chart).

0’ elev = ~14.7psi
8000’ elev = ~10.7psi
————————————
Difference of ~4psi
If you add 7lbs of boost at 8000’ elev you’d be at 17.7psi
17.7 - 14.7 = 3psi

Add .5 gallons per 1psi that you are above 14.7psi

7lb spring, add 1.5gal or about 13% (I’d add 2gal to be safe)
5lb spring, add .5 or add 1gal to be safe

At sea level:
I run 3lb to make it easier on my sled parts.
3lb spring, add 1.5gal or add 2gal to be safe

This is a way that another member calc’d ratios. I use VP110, so using 100ll these numbers will vary. I’ve ran my sled out west and in the UP without ever seeing a DET code. I tend to add a small bit of octane when in doubt.

Others can chime in here, but this method seems to work for me.

Someone posted their ratio mix is 96 octane. That would be adding 4gal of 110. That would mean that he is running 19lbs of boost at 8000’. If he is, great. But he might be over octane for his purpose at 8000’. If he was at 0’ elev, then he’d be at 8lbs of boost. That would be more realistic.

Please chime in if this does not seem correct. I don’t want to mis-lead anyone.

This has worked for me. You still need to verify your MON/RON values of the fuel you are using.

YB

 

[mountainhorse]

So what octane are we really trying to get to? I mix to get 96 on my Wallace calculator and it’s been running great at 7 psi

96 MON?

96 R+M/2 ??

For your calcs:
What octane rating are you using for the 100LL?
What octane rating are you using for your Pump fuel, and what is the pump rating?



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[KAWGRN]

96 r+m is what I’m shooting for my sled, at 7psi ,I’m `using the pump rating at the station in Laramie that has 93 non ethanol fuel and I have 110 octane rocket brand fuel and in my gas dock I mix 8 gal of 110 and 22 gal of 93 and sled runs great! Ocassionally a slight gurgle telling me I’m on the safe side, It’s all good!Im using wallaceracing.com

 

[mountainhorse]

TTT for some summer reading.

Best to read from the first post.

 

[papashawn]

How much 110 race fuel with 91 prem non eth

I'm running a MTNTK turbo on 10 lbs boost at 9K ft Island park area. How much race fuel should I mix with the 91 oct prem non ethanol?
It sounds like I've been wasting race fuel because Ive been mixing 20 gal race with 30 gal premium

 

[sledcaddie]

aviation fuel for storage

I've read that aviation fuel is good for long term storage of any vehicle, and stabilizer isn't required. Is this true? Got any info on this MountainHorse?

 

[gmustangt]

What’s the word on vp’s Octanium?

Heard some are running it

 

[LongHorn XC]

I'm running a MTNTK turbo on 10 lbs boost at 9K ft Island park area. How much race fuel should I mix with the 91 oct prem non ethanol?
It sounds like I've been wasting race fuel because Ive been mixing 20 gal race with 30 gal premium

My post above will describe the amount you need for VP110 with pump gas.

YB

 

[mountainhorse]

TTT .... it's that time of the year!

Best to read from the first post.


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[rick5150]

I've read that aviation fuel is good for long term storage of any vehicle, and stabilizer isn't required. Is this true? Got any info on this MountainHorse?

No stabilizer needed
I’ve been out 3 seasons with knee surgeries
100% Avgas put in oct 2015 I did start/run sled on stand every 2-4 months (indoor heated storage)
I’ll pump it out, put new proper mix in and finally be riding this season again[emoji1417]


Sent from my iPhone using Tapatalk

 

[revrider07]

Silbur at 7 lbs 2000 miles on 800 pro i like to error on safe side running 80 percent av 100 with 2 oz of oil per gallon. I had my waste gate stick shut one day 22 miles in didnt have right tool to pull apart with me. Hit the det a few times getting out but did not hurt the engine. I know if i would have been running on the edge with octane motor would have been toast. Bottom end sufers some but runs soo much better than the old turbos ive had. Ive bought enough pistons and jugs before this setup.