Leaded Fuels

[UnexplodedCow]

Does anyone have any info concerning the use of high octane leade fuels? I know that having leaded fuels will mess up a catalytic converter, but since I have none, I'm wondering if there is any chance of burning the valves or valve seats. I wouldn't be running straight fuel like that, just maybe 1 in 10 gallons of 93 octane pump gas. Anyone have any info or ideas?

~ Cow

[GTP Dad]

Leaded fuels will not hurt the vehicle as long as you have a car that does not have a converter or O2 sensors. The lead will foul them just like the converter. Lead was originally designed into gasoline to provide lubrication for the valve seats. As the use of unleaded gasoline became the standard, the metal in both the seats and the valves were changed so that lead was no longer needed. Hope this answers your question.

[A. Souphound]

Originally Posted by UnexplodedCow

Does anyone have any info concerning the use of high octane leade fuels? I know that having leaded fuels will mess up a catalytic converter, but since I have none, I'm wondering if there is any chance of burning the valves or valve seats. I wouldn't be running straight fuel like that, just maybe 1 in 10 gallons of 93 octane pump gas. Anyone have any info or ideas?

~ Cow

Your question/s have been asked and studied by thousands of racer's for the past fifty+ years that I know, and had experience with.
Since automobile leaded gas was phased out fifteen year ago it's un-available in this country. I figure you are talking AVGAS.
I could get pretty deep technically in the pro/cons of leaded/unleaded, and high octane fuels but the question is: What type of engine or need do you have for anything with a higher than 93 octane fuel?
General Aviation AVGAS is 100 octane low lead.
Just a thought: If you would mix at a ratio of 1gal. (100 octane) :10 gals.(93 octane) what kind of 'boost' would you expect out of less than 1 octane difference...

[UnexplodedCow]

Well, how are you getting that less than 1 octane difference? Oh, and I was thinking of using 110 octane leaded fuel, known around here as "super blue" unless I'm wrong about the octane rating. Anyway, how can you define octane boost? Any specific formula for it?

[UnexplodedCow]

Oh, and the need you asked about...is a high compression 1.9....I was expecting 210 psi out of it, but I'm expecting 230 now. Max for the engine to handle is 250....so I was assuming I might need something better than 93...wasn't sure, though. Besides, the gas around here comes from Ashland, and is loaded with rust and debris.

[A. Souphound]

Originally Posted by UnexplodedCow

Anyway, how can you define octane boost? Any specific formula for it?

"Well, how are you getting that less than 1 octane difference? "

For comparision purposes I used:
100 Octane (Avgas) - 93 octane pump gas = 7 octane/ 1/10 (ratio of 1/10 mix) = .7 octane.
Injecting the larger numbers: 110-93=17/1/10=1.7 octane.

Conclusion:Basically, the expections would be less than the difference in grades at the pump. The "boost" (increased performance) you would get would be negligible unless you had a suitabily modified engine that could take advantage of the higher octane fuel.

[ZX2000]

or... [(100oct*1gal) + (93oct*10gal)] / 11gal = 93.636363 octane...

little simpler equation...

[A. Souphound]

Originally Posted by UnexplodedCow

..I was expecting 210 psi out of it, but I'm expecting 230 now. Max for the engine to handle is 250....so I was assuming I might need something better than 93...wasn't sure, though. Besides, the gas around here comes from Ashland, and is loaded with rust and debris.

"Oh, and the need you asked about...is a high compression 1.9.."

Unless you have modified your engines bore and stroke, the compression ratio is probably 9:1 - 9.6:1. Not considered high compression.
I'm not sure about the significance of the PSI readings or how you arrived at them. I suspect you are mixing 'compression readings' with "compression ratio"
I also suspect you have milled the head.....reducing the 'squish' height and increasing the compression. If this assumption is correct, be sure and check the 'squish' height, there isn't much to play with, and you could destroy your engine.

[UnexplodedCow]

The squish height is fine. I ran the engine before with the same head. The stock compression ratio is 9:1, but the bore has been changed from an 82mm to an 83mm. Stroke remains the same. I had to bore the engine out that much to take care of a gouge in the #1 cylinder wall, at the top. And the compression I arrived at came from the engine before I tore it down. I used a compression gauge, and ran a standard compression test on the engine. It also had a leaky head gasket (hadn't been torqued down properly). I had replaced the rings in the engine, but when I was working on cleaning the head, I had left my dad to ream the ridges in the block (he'd worked on literally hundreds of escorts several years before), and couldn't see, so he accidentally gouged the cylinder wall. I didn't know (didn't bother to check his work), and I ran the car. It had 155 psi in all cylinders. I was shocked since it had higher compression with the original rings. But I ran the engine for 1300 miles with no problems, aside from the cylinder leaking oil like the devil. Blowby was horrible, so I tore the engine down, and discovered the gouge. So now it is remachined, bored, crank was polished, and I'm estimating that I'll have that 210 psi again. I might not, but I'm expecting it.
And the compression ratio isn't a key to knowing an engine's compression. The ratio is just the difference between the volume below and above the cylinder. And yes, the head has been milled, thus increasing the compression ratio and compression. And there is a limit to milling the head where it won't affect the safety of the engine.....i.e. the engine won't be damaged when running.

[A. Souphound]

You narrative has confirmed my suspicion of your mixing 'Compression testing' with 'Compression Ratio'
'Compression Testing' is in simple terms: a leak test.
'Compression Ratio' in simple terms is the volume above the piston at bottom-dead-center (BDC) divided by the volume above the piston at top-dead-center (TDC): C.R. = V1 / V2.
'Compression Ratio' is affected anytime there is a change in volume. In summarizing your narrative you have a stock engine bored approx. .040" oversize, and a milled head within the normal limits.
These are within the normal engine re-build guidelines, and the necessity for higher octane fuels is not necessary.