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PV, 120 (Amazon), 1800 General Forum for the Volvo PV, 120 and 1800 cars

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Will LL100 avgas work on B18D?

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Old Oct 19th, 2018, 01:41   #1
adarvasi
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Default Will LL100 avgas work on B18D?

Friends,

Will 100 octane Low Lead Aviation Gas work well and not cause damage on a B18D engine?

My concern is that that petrol is formulated to work with big bore, low RPM engines (usually 2,500 RPM)

If not 87 octane no ethanol will be acceptable or 91 will be better?

Thank you for your comments

Andres
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Old Oct 19th, 2018, 04:17   #2
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I'm no big expert, but I think you can run any of those unless you have a high compression engine, say 10.5 to 1 or greater.

I think the 100 octane Aviation fuel will be the worst, and perhaps a waste of money, as it is designed for high altitudes. I run a 100 octane race fuel in my '59 MG race engine, but even that is probably overkill since my compression is only about 10.0 to 1. I've never noticed any difference running 91 or 93 octane. But since I run quite lean, I'm playing it safe with the race fuel.

If both the 87 and 91 octane are non ethanol, then I think you can run either in a stock engine. If you have pinging under load with the 87, move up to the 91 and see if that runs without the pinging.

Try to avoid any fuels with ethanol as is separates, absorbs moisture and isn't good for old rubber parts.

Run leaded fuel if you can find it - even if your engine's head has been modified to run unleaded fuel.

On a slightly side note, I'm running a B16B in a PV444. Just by looking through the spark plug holes I can see that my pistons have a heavy carbon build up. And the shop manual recommends decarbonizing the head, I think, every 15,000 miles. I haven't put many miles on my car at all - much to my dismay. I've tuned it to run lean and it has been a big improvement with regard to fumes and exhaust gas. As some point when I can get it out on a race track or back road where I can run close to wide open throttle, I intend to run with the 100 octane race fuel as I think it runs very clean and will blow out some of that carbon on my pistons. At least that's my theory.

Edit: Running lean makes an engine run hotter.

Last edited by blueosprey90; Oct 19th, 2018 at 04:22.
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Old Oct 19th, 2018, 14:22   #3
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B18D engines appear to have been built in two versions, one w/a 8.5:1 CR and another w/a 8.7:1 CR and both versions will run just fine on 87 octane if the timing is is set correctly.

I have been rebuilding vintage racing and road car engines for over 40 years and have learned a lot and researched this subject over the years and found that a fuel with a higher octane than what needed can actually cause head and valve damage.

The higher the octane the slower the fuel charge will burn which is the exact opposite of what you might think. The reason for this is to keep the fuel charge from burning too quickly in high compression engines which can cause spark knock, detonation and engine damage.

When used in low compression engines, high octane fuel will still be burning when the exhaust valve opens and will damage the valve seats, valves and heat the exhaust port more than usual which can lead to cracks forming in the head and exhaust system in time.

I drive my 1800s with the original B18B engine here in the US on road and have stated running it in VSCCA races here in the US this year. The engine is not modified and has a 10:1 CR and produces 115 HP. It needs 93 octane fuel to run on the gas and 10% ethanol mix sold here without spark knock and running on.

Recently non-ethanol fuel has become available at a small number of gas stations in the US and it has transformed the 1800s engine from producing just OK power to what I estimate to be a 15-20% increase in HP. The timing can now be advanced five more degrees than before. Without the ethanol vapor lock when starting hot is gone and it now comes to like quickly when warm and the engine temp is now about 10 degrees cooler.

Last edited by Vintagewrench; Oct 19th, 2018 at 14:26.
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Old Oct 19th, 2018, 14:33   #4
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Vintagewrench. Are you David G? Of Mount Equinox fame? And the bitter dual with the drab white PV544 for Volvo honors that I read about yesterday?

Geez, with another grownup on the boards, I better start behaving and acting like an adult.


But until then, here's a link to a video of me working a set of Vredesteins. You can get a sense of what it takes before they let go.


https://youtu.be/nEDB3qV2tT4
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Old Oct 19th, 2018, 15:40   #5
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Blueosprey69 and Vintagewrench,
Thank you both for your answers and explanations.
I live in Mexico City upper parts (8,000 feet or 2,400 meters) so I definitely will have to lean the mixture. I am familiar with increase in cylinder head temp (CHT) rise when leaning.

Anecdotally: in aircraft engines there is a technique called lean of peak (LOP), where you lean beyond the peak exhaust gas temp (EGT) and the temp and internal cylinder pressure decreases considerably as well as HP output and fuel consumption, of course this will not be possible in a car engine unless that you have a mixture control in the cab as most piston engine aircrafts do, moreover, is hard to achieve with carbureted engines, it works great with fuel injected engines where the injectors have been balanced to have no more that 0.5 gallons per hour difference between cylinders (consumption on a 540 cu inch engine at cruise altitude LOP is around 15 GPH).
I am enclosing a picture of piston aircraft power plant management that explains the concept.

I asked the question because of the vintage engines requirement for leaded gas which Avgas could solve, but also because, believe or not, in Mexico is cheaper than automotive. In any event, as I am not planning to use the car for daily driving, the cost of gas, among everything else, becomes a lot less relevant. As previously mentioned, in Mexico right now there is no fuel containing ethanol.

I am relieved to hear that low compression (8.5:1) engines can work well with 87 or 91 octane unleaded.

Thank you again

Andres
Attached Images
File Type: jpg LOP chart.JPG (129.4 KB, 8 views)

Last edited by adarvasi; Oct 19th, 2018 at 15:52. Reason: Add picture
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Old Oct 19th, 2018, 15:41   #6
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Blueosprey69, Great video! one question; why the tire squealing? could it be pressure differential between tires? congrats
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Old Oct 19th, 2018, 21:31   #7
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Quote:
Originally Posted by blueosprey90 View Post
Vintagewrench. Are you David G? Of Mount Equinox fame? And the bitter dual with the drab white PV544 for Volvo honors that I read about yesterday?
https://youtu.be/nEDB3qV2tT4
Yes, thats me, although I'm not guilty as charged. Jon is a good long-time friend of mine and at no time did we battle door handle to door handle.

I was only able to see my lead increasing in the rear view mirror on the front straight at Lime Rock Park on every lap.

Photos of the car in action below at Mt Equinox and Lime Rock.



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Old Oct 21st, 2018, 14:39   #8
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Why are my tires squealing so much?

I think I was using 89 Octane gasoline for that run and the car was just complaining about it.


. . . No, on another forum, Vintagewrench (under an assumed nom de plume) had raised a question of whether he should run Dunlop bias ply tires on the race track. Of course, since I race in true 1950's fashion from the very, very bottom rung of the racing ladder, the Dunlop tires are beyond my budget. So I had suggested Vredesteins - a very nice summer performance tire - but then other posters were complaining how a radial tire tends to "let go" suddenly in the corners without warning. Since I thought Vintagewrench and that other guy on the other forum were one and the same person, I posted the video for his benefit. It was just my example of how much warning the tires actually give - and to be honest, when they let go, it was my driving, not the tires (I was too tentative because I'm simply deathly afraid of Turn 7).



Tire pressures were good. The screaming tires were more a product of the track surface and layout. The tires aren't so noisy at most other venues.
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Old Oct 23rd, 2018, 18:21   #9
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Quote:
Originally Posted by blueosprey90 View Post
here's a link to a video of me working a set of Vredesteins. You can get a sense of what it takes before they let go.
https://youtu.be/nEDB3qV2tT4
Does the MG suffer from a bit of oversteer or is it the front tires losing their grip at the 1:00 minute mark?
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Old Oct 23rd, 2018, 20:27   #10
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Oversteer at 3:30 when the rear end wanted to come around. I should have been on the gas instead of lifting for the corner. Some understeer going up the Toe of the Boot at 1:00, but mostly the noise is related to track surface.
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