I run "all gas" 87 octane, it seems to have a longer shelf life. No Alcohol blends for my Opel.

 

So you don’t run premium in it, just regular?

 

A regular GT just needs regular gas. Higher octanes are for higher compression engines to reduce knock.

That said, I used to put premium gas in my GT's for decades because I though it gave me a bit more power and gas mileage. Probably all in my mind.

If you don't have hardened exhaust seats installed in your cars, then you should consider lead additive........which I think might also give you more power, but I could be totally wrong on that.

There's a lot of debate on this subject and whether modern alternative additives are just as good as lead or better.

You should also use oil with zinc additive. ZDDP. Once again, there's a lot of debate as to whether modern oil, diesel oil, or oil additives work just as good or better.

 

Stock the Opels never had hardened exhaust seats right? Because I don’t think my engine has ever been modded before.

I run diesel oil with ZDDP.

 

I put ethanol free in mine with a lead substitute it cost a little more, However, I don't drive mine very often, so I run less of a risk of moisture absorption in my tank do to in inactivity.

 

I run the cheapest lowest grade fuel I can find in all of my Opels. I use no additives and I’m not scared of ethanol. I’ve had no issues doing this over many miles. From all of my research I’m convinced the whole unhardened valve seat debate with non-leaded fuels is just a classic example of confirmation bias.

 

I run the cheapest lowest grade fuel I can find in all of my Opels. I use no additives and I’m not scared of ethanol. I’ve had no issues doing this over many miles. From all of my research I’m convinced the whole unhardened valve seat debate with non-leaded fuels is just a classic example of confirmation bias.

Yeah that is what I have been doing and my grandpa does that in several of his cars. He does run non ethanol in his 1933 American Austin and I think his 1966 Mg Midget. But in his other old sports cars he just runs regular.

 

Here's a pic from another thread showing the pitting that happens when using unleaded fuel on unhardened valve seats. I've seen much worse pitting in pics posted here.:

 

In my opinion these erosion problems are caused by poor tuning plain and simple. The leaded fuel helped protect poor running engines.

I’ve learned over the years that you can be cruising comfortably with your Opel on the highway at 16.8:1 AFR and no signs poor tuning. Your plugs will be tan, the car will run fine, as long as the accelerator pump covers up the issue when accelerating.

But that lean of a mixture is silently heating up the valves more and more.

The fix? Richer the mixture to around 13.5:1-14:1 where it needs to be or run E10 fuel to get some of the octane boosting and cooling effect of ethanol.

 

Since we don’t have the option to fuel up with gas that contains no ethanol I have no choice. If I did I would not be using the up to 10% ethanol fuel and would go to the non ethanol gas. I’ve seen carburetors get plugged up with the fuel we get here in Ca.

I agree with the majority here, go with the lowest octane option. I’m a believer that stoic is the hottest combustion condition, if you google the subject contrary to what you might think you’ll find that the combustion temperature actually cools off as It runs leaner. As mentioned earlier, so long as it’s running smoothly and properly richened up during hard acceleration.

 

There are several ethanol treatment additives for fuel. I frequently add Stabil 360. I run the lowest octane that I can get by with. Two of my cars are lower compression and I run 87 octane. I tuned my driver to run on 89 octane. I might be able to get a little more power out of it with more timing but then I would have to up the octane.

Harold

 

Do you just run stabil to stabilize the fuel? Or are there other reasons?

 

I run "premium" 91 octane here in California. Ethanol-free fuel is incredibly difficult to find here, other than expensive race gas or leaded aviation fuel.

BUT: I have flat-top pistons and a smaller-chamber 1.5 head. Even with a modified distributor with limited mechanical advance I definitely get pre-ignition with regular fuel.

When I had the head rebuilt I had 1.9 valves and hardened exhaust seats installed. From what I can tell it's standard practice amongst machine shops here.

I also heard that California's fuel is blended to produce lower emissions, which makes it burn hotter and makes installing bronze valve guides risky. The owner of the machine shop where I had my motor rebuilt said he had a lot of heads come in with galled valves/bronze guides back in the 90's, so since then he only allowed iron guides to be installed.

To answer your question:

For a stock '73, unleaded 87 is fine. Those engines had low-compression pistons, induction-hardened seats, and a much less aggressive ignition timing curve than the pre-71 engines.

On the other hand, a bone-stock 69 19S? I would hesitate to run it on anything other than avgas without modification. I think the distributors had ~60° of mechanical advance! They were definitely designed for high-octane leaded fuel that is unavailable for the most part today.

 

I run "premium" 91 octane here in California. Ethanol-free fuel is incredibly difficult to find here, other than expensive race gas or leaded aviation fuel.

BUT: I have flat-top pistons and a smaller-chamber 1.5 head. Even with a modified distributor with limited mechanical advance I definitely get pre-ignition with regular fuel.

When I had the head rebuilt I had 1.9 valves and hardened exhaust seats installed. From what I can tell it's standard practice amongst machine shops here.

I also heard that California's fuel is blended to produce lower emissions, which makes it burn hotter and makes installing bronze valve guides risky. The owner of the machine shop where I had my motor rebuilt said he had a lot of heads come in with galled valves/bronze guides back in the 90's, so since then he only allowed iron guides to be installed.

To answer your question:

For a stock '73, unleaded 87 is fine. Those engines had low-compression pistons, induction-hardened seats, and a much less aggressive ignition timing curve than the pre-71 engines.

On the other hand, a bone-stock 69 19S? I would hesitate to run it on anything other than avgas without modification. I think the distributors had ~60° of mechanical advance! They were definitely designed for high-octane leaded fuel that is unavailable for the most part today.

On my 69 GT it has a 1973 Engine with a 1969 Distributor. I have always wondered if that makes it run different.

 

Do you just run stabil to stabilize the fuel? Or are there other reasons?

We run Stabil 100% of the time because it is very difficult to find ethanol free gas in the octane we need to prevent pinging. When we don't run stabil, we get some gumming/clogging on the idle jet that is closest to the engine. After about 2 or 3 months, it gets a nice little sticky varnish on that jet (hot side of carb) and performance is impacted. With stabil or ethanol free gas, the jet does not clog.

We use Stabil or ethanol free gas on every car in the collection. Note - gas has a "shelf life" and it is shortened considerably with ethanol which impacts combustibility. Since it may take a few months to use up a full tank, the Stabil is critical to extending the life.

 

We run Stabil 100% of the time because it is very difficult to find ethanol free gas in the octane we need to prevent pinging. When we don't run stabil, we get some gumming/clogging on the idle jet that is closest to the engine. After about 2 or 3 months, it gets a nice little sticky varnish on that jet (hot side of carb) and performance is impacted. With stabil or ethanol free gas, the jet does not clog.

We use Stabil or ethanol free gas on every car in the collection. Note - gas has a "shelf life" and it is shortened considerably with ethanol which impacts combustibility. Since it may take a few months to use up a full tank, the Stabil is critical to extending the life.

That is interesting. I will have to try stabile out more. Especially since winter is coming and the will be sitting for a couple months. I will definitely try that out!

 

I’m using “rec” gasoline which is 100% gas 90 octane. Regular gas seemed to all vaporize when the car sat overnight so it would have long crank times for a cold start.
There’s no need for high octane gas with the low compression of my Manta.

 

My car seems to start really good. I haven’t really had any vapor problems.

 

My car seems to start really good. I haven’t really had any vapor problems.

I run airplane mogas. I go to the local airport and get no alcohol 91 octane. Usually has a credit card dispenser at most airports. Plus, my car is not a typical daily driver, so the added cost is marginal. I guess you could get additive for your fuel to boost it more, but don't know if that would be worth it. Its pricey fuel, but worth it, cause ethanol fuel causes destruction, and thats expensive too. I have high compression motor and sniper EFI that I am still figuring out. If you have a not updated Opel motor, 100LL at the airport may be an option, about the same price as aviation mogas.

 

Unless you have a high compression engine you are wasting money on 91 octane fuel for your car.

 

Ethanol free regular with sta-bil.

 

Ok Guys So My grandpa and I just run the cheap 87 octane regular gas in my 69 GT. He thinks we should probably start running 93 premium in it. What do you guys run? Do you guys run non ethanol? The non ethanol around here is 90-91 octane. Or do you guys run octane booster? We have a lot of different stuff we sell at O'Reilly's. There is Lucas that makes it go up 3 octane numbers. And then we have the more expensive Vp racing stuff that can raise it like 8 numbers. Also have you guys noticed an increase in gas mileage in certain fuels? I am just curious. I need gas in it anyway. Also the specs on it are: 1973 Engine with lower compression, Weber 32/36, header and full 2 inch exhaust, automatic trans, and it is pretty worn out. And then I have a 1973 GT that has a refreshed 1973 Engine that has very good compression(basically a brand new engine), Weber 32/36, header, It will get a full 2 inch exhaust, 4 speed, and that car isn’t worth out. And the engine is still out of it yet. What are your thoughts and ideas. Thanks Sam Edit: Do you guys think we need leaded additives? My co worked says I should run it in my Opel. He has a lot of experience and say leaded fuel would be better for my Opel. But I don’t think that Opels really need that.

If it's a carbureted brand new engine you need to run non-ethanol gas or it will destroy the cam. Also you should probably run 20/50 with the zinc additive

 

How will ethanol gas destroy the cam?

 

A regular GT just needs regular gas. Higher octanes are for higher compression engines to reduce knock. That said, I used to put premium gas in my GT's for decades because I though it gave me a bit more power and gas mileage. Probably all in my mind. If you don't have hardened exhaust seats installed in your cars, then you should consider lead additive........which I think might also give you more power, but I could be totally wrong on that. There's a lot of debate on this subject and whether modern alternative additives are just as good as lead or better. You should also use oil with zinc additive. ZDDP. Once again, there's a lot of debate as to whether modern oil, diesel oil, or oil additives work just as good or better.

Yes, zinc additive in oil to protect camshaft and lifters. Modern engines use roller lifters so they don’t need zinc, zinc fowls catalytic converters after lots of miles. No need for lead additive because of low stress and low mileage utilization of antique cars. Use only non-ethanol gasoline due to protection of steel gas tank and “rubber” parts and carburetor from the effects of ethanol.

 

I run 89 (they don't have 87 here) in my stock engine (+weber, electronic ign, and 2" exhaust) 73 manta. It's not super worn, but I found that it runs best with about 16 deg of initial advance and 36 total. Has a lot more power than the stock timing with no ping or knock. I discovered it needed a lot more initial timing after watching UTG on youtube where he said to just give the distributor a twist until the throttle response was snappy.

 

It won’t.

 

Higher octane fuel is only needed with high compression or forced induction engines. Higher octane rating delay fuel ignition from heat being created in the cylinder prior to the spark being firing (detonation). 87 octane is all that’s needed. Wasting money running the higher octane. You should use a top tier fuel supplier. Not all 87 octane fuels are equal. Google top tier fuel stations to enlighten yourself on quality fuel stations.

 

I am running shell right now. They seem to be a pretty good brand. And I use my uncle’s rewards so I get like 10-15 cents off each gallon of gas.