Just Bought Some 100LL Av Gas From Our Local Airport

[Jeffrey S.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

I go to the small airport in Troy. It is across Coolidge Hwy from the Home Depot store.

[Ronald L.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

Exactly what I figured as its only a few miles from you.

[Lawrence S.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

Paid $5.62 per gallon over the weekend for LL 100 octane. I believe I was incorrect at $6.02 per gallon in my previous post.

[Tim S.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

I bought 30 gallons late last week @ 5.79 gal here in north central WI

[Stephen G.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

$ 5.60 in Central NJ

[Dennis D.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

$ 5.60 in Central NJ

Which airport?

[Stephen G.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

Which airport?

Central NJ 47N Manville, NJ

[Rocco S.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

I live in the Shennandoah Valley in western Virginia and have a small air strip down the road. The strip is mostly used for sky diving. Yesterday I went there with a 5 gallon gas can and was able to buy 100LL (low lead) fuel for $5.49/gallon. It is a self-serve pump and open to the public. They even told me I could pump directly into my car. Great news and very convinent. I plan to try mixing 50/50 with standard 93 octane gas. My 67 is an L79 with 11:1 compression and I currently use an octane booster with 93 octane. At $5.49/gallon the cost will be about the same.

[Ronald L.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

why bother with the goofy fake stuff and alcohol??? send me a prepaid shipper I'll give you what I have left unused on the shelf for 30 years.

The AV gas has a required shelf life that fuel stabilizers cannot beat


alcohol fuel is NO GOOD after 90 days, and its no good for any part of your fuel system

I used to test this stuff at oeM

[Duke W.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

I live in the Shennandoah Valley in western Virginia and have a small air strip down the road. The strip is mostly used for sky diving. Yesterday I went there with a 5 gallon gas can and was able to buy 100LL (low lead) fuel for $5.49/gallon. It is a self-serve pump and open to the public. They even told me I could pump directly into my car. Great news and very convinent. I plan to try mixing 50/50 with standard 93 octane gas. My 67 is an L79 with 11:1 compression and I currently use an octane booster with 93 octane. At $5.49/gallon the cost will be about the same.

Your L-79 should run detonation free on 93 PON E10, especially with the lazy OE spark advance map that doesn't bring in full centrifugal until 5000 RPM and will likely run detonation free if it's all in at 3000.

GM advertised compression ratios were very optimistic and your "11:!" was likely closer to 10.5 than 11 as built by Flint, and if it was every rebuilt it was likely done with lower compression. Has it ever been rebuilt? Measure head gasket thickness. If it's thicker than .018" it's been rebuild and compression is likely no more than 10:1.

Today's 93 PON has about the same detonation resistance as 97-98 RON premium from the sixties. Contrary to myth sixties vintage premiums were not all 100 RON. If fact, octane numbers were not posted and fuel blenders only blended enough octane to minimize customer detonation complaints and winter and high altitude blends had and have, today, lower octane that near sea level summer blends.

"Octane boosters" are mostly worthless. Their "points" are 0.1 not 1.0.

It's your money, but if you run an octane test you may find that you can even run something less than 93 PON.

Duke

[Rocco S.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

Duke,

Thank you for your prompt response. It looks like I need to do more to determine the current timing situation.

To add some additional information, the car is a low mileage (56K) all original 1967 L79. with M21 and 3.70 Posi. If it matters it has factory AC. It has the original Holley 3810. The engine has never been apart so I assume it still has the steel head gaskets. When I acquired the car about 9 years it had been parked since 1974. I took all precaustions before its first start-up. That included removing the distributor to prime the oil system, carb rebuild, new fuel pump and cleaning the fuel tank and flushing the fuel line. While the distributor was out, it was disassembled, checked for wear, lubricated and re-assembled. The original weights and springs were retained. The orignal VAC was checked with a Mightyvac and showed no leaks. I believe, at the time I checked the number on the VAC and determined it was the original unit.

I will re-check the VAC number and report back if not original. I have the static timing set about two degrees less than book since I had pinging under certain driving conditions, like pulling up a slight hill at moderate speeds. Reducing the static timing helped somewhat. The octain boost seemed to eliminate the slight pinging.

I just acquired a Snap-On digital advance timing light and hope to get accurate timing readings. The engine idles fine at about 700RPM so I don't think the mechanical advance is activated at idle, but will confirm that.

I read in several of your posts where you refer to the "Two-Inch Rule" but could not find your seminar. Could you send me a link for this seminar as I think it would help me understand more on this subject?

It would be great if I could eliminate the use of any fuel additive and still enjoy driving the car at its peak performance. I do have an NOS Delco VAC, Part # 11162361, which I believe is correct for the L79. Can you confirm is this is correct?

ThankYou,
Rocco

[Rich G.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

[QUOTE=Ronald Lovelace (50931);953092]why bother with the goofy fake stuff and alcohol??? send me a prepaid shipper I'll give you what I have left unused on the shelf for 30 years.

The AV gas has a required shelf life that fuel stabilizers cannot beat



i agree. I run straight 100LL in my 66 L79 and also in my Corvair (which is almost an airplane engine). Those of us who have lower compression aircraft engines designed (in 1937) to run on 80 octane sometimes experience lead fouling of the plugs. To combat this TCP is an FAA approved additive to help scavenge the lead. Also we have learned to aggressively lean to keep EGT up. Airplanes have mixture controls in the cockpit. I have not had lead fouling in either the airplane or the cars. The recommended dose of TCP is 30 mL per 10 gallons, so one can goes a long way.

[Duke W.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

Open the following thread, which is second to the last in the "sticky section", and scroll down the first "tuning and timing" subject and open the link.

https://www.forums.ncrs.org/showthre...tion-Documents

The following thread describes a "blueprint overhaul" of a L-79 distributor and how to optimize the spark advance map. The VAC is too aggressive and the centrifugal is too lazy.

https://www.forums.ncrs.org/showthre...print-overhaul

It's easy to measure the head gasket thickness at the corners of the head block interface with feeler gages If the gasket is OE you should be able to see the corner of the gasket and it has a small hole. Better to be sure since it's so easy rather than assuming what it is.

Duke

[Duke W.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

An OE L-79 VAC would be stamped 236 16. 236 is the last three digits of the GM long part number and 16 is the max crankshaft advance. All original GM VACs have this ID scheme. It provides max advance at 8" and above. I'm not familiar with the part number you quoted. Measure the vacuum required to begin pulling the pin and the vacuum to pull it to the limit and report.

With an OE cam typical L-79 idle behavior is 14-15" @ 750. A 12" VAC meets the Two-Inch Rule, and I recommend a 12" B26 as a replacement. The NAPA/Echlin part number is VC1765, and this can be cross referenced to any name brand replacement, including "Delco" All are made by Standard Motor Products... same part, just a different box and marketing channel.

Since there have been a lot of reports that some VACs don't meet spec, I highly recommend all to purchase locally and check with a vacuum pump that it meets spec before accepting the part.

Since the OE centrifugal is 30 degrees you need 6-10 initial to achieve the optimum 36-40 WOT advance. 93 PON should operate detonation free at least at the low end of this range, and it's okay to go as low as 4. The tuning seminar also explains how to "drive around" detonation, if detonation is experienced in the most severe test like lugging up hill at low revs.

Duke

[Rocco S.]

Re: Just Bought Some 100LL Av Gas From Our Local Airport

Duke,

Thank you for the prompt replies and links to your seminar and additional information. I want to offer some additional information on my situation. Due to inclimate weather I have not been able to confirm Idle vacuum readings, static timing or max timing. I will try to get these soon and report back. In the meantime here's what I have determined.

1. The installed VAC is marked "MS", "236" and "16". It appears to be original and working properly.

2. The NOS unit I have is Delco #1116236. I appologize for the typo where I added a "1" to the end of the number originally reported. I confirmed this part # is correct for a 1967 L79 based on a dealer parts book under Group 2.410.This is also known as Delco "1316A" which I found in a 1970 Delco Parts Book. The unit is also marked "MS" "236" and "16".

3. A bench test of the NOS unit with a Mightyvac confirms the advance starts at about 4 inches and finishes at about 7-8 inches.

4. My car has Transistor Ignition.

5. The head gaskets are indeed original and measure about 0.018 inches.

6. I have a pair of "gold" Mr. Gasket advance springs I could easily install.

It would seem that the original 236 VAC meets your "Two-Inch Rule" since it starts and finishes well below the Idle vacuum of about 15 (from memory) which I will confirm. I'm thinking that just changing the advance springs to the "gold" ones may eliminate the slight pinging problem. Or should I also change the VAC to a NAPA B26 unit?

I really appreciate your expertise and very technical responses.

Rocco