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kdvdub Wed Feb 19, 2014 7:09 am

Thought I would ask a question about AV gas for vw engines. The fuel we fly with is running a octane rating of 100/102.If used, has anyone had any head problems with the fuel? Do we have to use a different valve seat ?

Thanks Ken

[email protected] Wed Feb 19, 2014 7:26 am

The Mofoco Made in the USA heads that we produce are used for airplane applications as is.

tattooed_pariah Wed Feb 19, 2014 7:52 am

I don't know anything about the AV VW world and not trying to step on your toes Roy or steer kdvdub in any direction, just offering options I know of..
http://www.revmasteraviation.com/ has also been doing VW aircraft stuff for years if you want to research them as well, always nice to have options and decide for yourself.
I've never bought anything from either company and both seem to have good reputations.

Gurn Blanston Wed Feb 19, 2014 9:49 am

What is the application? Airplane, car, road use, racing, compression ratio, cam?

slalombuggy Wed Feb 19, 2014 10:08 am

New heads should have hardened seats and running unleaded fuel won't be a problem. I saw a few X-plane engines at the shop I worked at and cannot remember them having any problems with valves or seats.

brad

Bashr52 Wed Feb 19, 2014 10:10 am

The issue you will have is the lead content in the fuel. I would suggest going dual-plug to combat this. Ever cleaned plugs on an aircraft engine? The bottom ones are always full of burnt lead.

longboard511 Wed Feb 19, 2014 10:42 am

we ran av gas in the Renault 5 turbos we used to race totally std engines just gave us a bit of safety margin against detonation

they always had really nice combustion chambers on strip down and we never had any issues at all

midtravelmidengine Wed Feb 19, 2014 2:50 pm

wasn't all gas leaded when the VW engine was engineered?

Quokka42 Wed Feb 19, 2014 3:20 pm

Av Gas is a low octane fuel with a lot of lead added. This allows the engine to run at max power close to the ground, whilst still being able to operate at altitude where air is a lot thinner. While lead resists detonation, it doesn't accelerate the fuel burn so it is not optimal for road going use. Having said that, many have (illegally) used it successfully in turbos. Lead will eventually foul plugs, but in aircraft and cars running very high boost the plugs do not have a very long life anyway.

gt1953 Wed Feb 19, 2014 4:24 pm

Back in the day, last century my older brother used to put moth balls to boost the octane. Not sure how true this is or would work with the current pump gas.

scotth17 Wed Feb 19, 2014 4:29 pm

It would take a lot of moths because their balls are so small...

Alpha_Maverick Wed Feb 19, 2014 6:11 pm

You have to use Napthalene based mothballs, which are getting more rare these days, but yes, it does work.

SamT Wed Feb 19, 2014 6:21 pm

Run it in all my high compression sand rail engines and my turbo motor now.
I have never noticed any power difference in it and race fuel. Its a highly regulated fuel, its top notch quality, no water, no ethanol, and it lasts for years in a tank and wont gum up a carb. I use it exclusively in my lawn mowers and weed eaters. They crank first try after sitting all winter. I have a push mower thats 5 years old and never had the oil changed or plug cleaned.
I suspect it goes by the wayside soon lots of the little planes that run on it are buying some sort of tax stamp and running pump gas now.

Quokka42 Wed Feb 19, 2014 7:03 pm

Either your high comp engines don't rev very high or your seat of the pants measurement isn't accurate. The government here is trying to reduce the use of lead in aircraft and encouraging alternatives.

As for mothballs, I believe they did help to stop detonation, but the byproducts both in the fuel system and exhaust were pretty nasty. Burn naptha sometime and you'll get the idea.

udidwht Wed Feb 19, 2014 10:55 pm

Quokka42 wrote: Av Gas is a low octane fuel with a lot of lead added. This allows the engine to run at max power close to the ground, whilst still being able to operate at altitude where air is a lot thinner. While lead resists detonation, it doesn't accelerate the fuel burn so it is not optimal for road going use. Having said that, many have (illegally) used it successfully in turbos. Lead will eventually foul plugs, but in aircraft and cars running very high boost the plugs do not have a very long life anyway.


You sure?

madmike Thu Feb 20, 2014 4:20 am

AV Fuel is made for low RPM and is never consistent(plane adjust their mix on the fly :wink: ) If you want performance fuel get some VP that is made for racing

longboard511 Thu Feb 20, 2014 6:35 am

we used to make our own blend with super unleaded and added toluene that worked well too we did a 20% mix toluene to super unleaded

udidwht Thu Feb 20, 2014 10:14 am

madmike wrote: AV Fuel is made for low RPM and is never consistent(plane adjust their mix on the fly :wink: ) If you want performance fuel get some VP that is made for racing

100LL is 100 octane which is neither low octane or intended specifically for low RPM use.

Define low RPM?

ap_sand Thu Feb 20, 2014 11:24 am

100 Low Lead has twice the lead that the highest pump premium had. It also has a bromine based (ethylene dibromide?) lead scavenger to keep the plugs, combustion chamber and valve faces free of lead salts. This is to prevent chamber "hot spots" and avoid pre-ignition. It transports the lead down stream and you find it on the back of the exhaust valves and in the exhaust system as a crusty, white deposit.

The scavenging occurs at chamber temperatures above 850 deg F, which is why the deposits are found downstream where things cool off. Here is an example of a lead fouled plug:



In the 2 o'clock position you see a chunk of the "scavenged" lead, the whitish lumpy piece. Beneath it in the plug and just visible below it in the photo, you can see a more typical deposit as a round ball of previously molten lead salt. This plug shows a whole lot of more operational and maintenance issue than just lead in the fuel...

Some aircraft engines seem to be resistant to lead fouling their plugs, others not so much. For those that have issues, proper operation includes ground taxi with the mixture leaned to within a blond c-hair of cut off, and raising the idle speed to 1000 rpm for 15 seconds and then leaning slowwwwly to cut off when shutting down.

Gasoline is not a simple fraction that comes off the distillation tower at a specific level. It's an engineered product that can be formulated in thousands of way to meet specs. As any commercial product, the formula used is the cheapest mix that meets requirements and can change daily based on the market pricing of the components.

Racing and aviation fuel doesn't burn "faster", "hotter" or have more energy. It's formulated to resist spontaneous combustion under high temperature/pressure conditions (detonation). Higher octane ratings ARE directly related to the "activation energy" needed to initiate combustion. High octane fuel may have trouble igniting in low temperature/pressure conditions or with weak ignition systems. Using these fuels where the extra octane is not needed accomplishes nothing but drain your wallet faster. Because of EPA requirements that change seasonally, automotive gasoline no longer needs to be formulated to remain stable very long. Aviation gasoline specs have not changed significantly since WWII, and a key one is that it is very stable. There are documented cases of fuel that has sat for 50 years still meeting specs. This is largely due to using higher grade, more expensive formulation components, specifically toluene.

Octane measurement of the two fuels is different too. Auto fuel (in the USA) is sold showing it's "AKI" (Anti-Knock Index) which is the numerical average of it's RON (Research Octane Number) and MON (Motor Octane Number). Aviation fuel is designated by two running numbers, rich and lean. Rich being a rich mixture operated in a supercharged engine and lean being more normal operations. The lean rating corresponds to a MON rating, up to 100. The full designation for 100 LL is 130/100 LL.

There are many operators that are using car gas in their aircraft because of the price difference. 100LL is running from $5.75 - $9.00/gal. To do so, the airframe/engine combination needs to be approved under an "STC" (supplemental type certificate). This is because the lighter, more volatile, aggressive solvency compounds and attack fuel system components and degrade them (these are the same compounds that evaporate off in time and allow the "varnish" to plate out). Additionally, it's vapor pressure is lower and can result in vapor lock at altitude, depending on the fuel system configuration. This insures that the particular aircraft model has been tested and found not to have issues.

Two other operating requirements are first (and official) is that the auto fuel need to be alcohol free. Second (unofficial) is that the aircraft is used frequently so that the fuel doesn't have time to become "stale".

Andrew
N2206Y '68 C-177
BCAG Engineering Operations

kdvdub Thu Feb 20, 2014 12:20 pm

Hi guys I m sorry about the first post. I hit the send button before redoing my question. I m building a sand rail and the engine package will be a 2276. I m able to get AV gas easy and wanted to know if there any side affects with using this fuel?. Being 100 octane can we run 10.0 comp and be ok?

Thanks Ken



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