What fuel is best?

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John Martin

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I had a 1970 Dart with 225 slant 6 a few years ago and I was never sure what fuel to really put in it. I was using 87, 89, 93, and any mix of two and some times an octane booster. The car ended up breaking all its compression rings on one cylinder. And would never idle again.

What fuel should I use in my next Dart? It does not have hardened valve seats so I will use a lead substitute.
 
93 if you can get 94 run that the higher octane the slower it burns ,less ping... or pre ignition
 
Several factors can effect what octane to use. Ignition timing, compression ratio, piston to combustion chamber quench, carbon build up, and air inlet temperature can all cause/prevent detonation. If the motor is together then a good tune and trial and error will tell.
 
93 if you can get 94 run that the higher octane the slower it burns ,less ping... or pre ignition

It will be a totally stock 225 that was factory built. No mods. I’m surprised that even that would need 93.
 
It does not need 93. However, you asked what the best fuel is. Probably something like Cam2 118 leaded or Sonoco Supreme. Those would be "best". A stock 225 does not need "best". They are 8.1 compression at the most, regardless of what they were rated. They always blueprint out less than the rated compression ratio. Even if they didn't, 8.5:1 in no way shape form or fashion needs 93 octane fuel. You will be wasting your money. I would use 87 and run a good lead substitute and you should be fine. I also run an ethanol treatment in mine as well.
 
It does not need 93. However, you asked what the best fuel is. Probably something like Cam2 118 leaded or Sonoco Supreme. Those would be "best". A stock 225 does not need "best". They are 8.1 compression at the most, regardless of what they were rated. They always blueprint out less than the rated compression ratio. Even if they didn't, 8.5:1 in no way shape form or fashion needs 93 octane fuel. You will be wasting your money. I would use 87 and run a good lead substitute and you should be fine. I also run an ethanol treatment in mine as well.

That’s what I thought. All I’m interested in is keeping the engine from pinging and reducing wear as much as possible. If it helps that is the context of best. Best for the application: a stock, unrestored car that will be a daily driver.
 
That’s what I thought. All I’m interested in is keeping the engine from pinging and reducing wear as much as possible. If it helps that is the context of best. Best for the application: a stock, unrestored car that will be a daily driver.

In that case, I would run something like I do......a known name brand like Chevron, Shell, Amoco, something mainstream. Not Flash Foods or Achmed's magic carpet.
 
In that case, I would run something like I do......a known name brand like Chevron, Shell, Amoco, something mainstream. Not Flash Foods or Achmed's magic carpet.

I’m just trying confirm my hunch. I was told to use 89 before. If everyone would say something like BP 87 or Shell 87 or something like that, it would be good enough for me.

My personal choice would be Sunoco but there are none in my area.
 
I’m just trying confirm my hunch. I was told to use 89 before. If everyone would say something like BP 87 or Shell 87 or something like that, it would be good enough for me.

My personal choice would be Sunoco but there are none in my area.


Why are you not running hard seats? Then you have to screw with lead additives and all that crapola.

Hard seat the head and just use straight pump gas.
 
Why are you not running hard seats? Then you have to screw with lead additives and all that crapola.

Hard seat the head and just use straight pump gas.

Because I have to get the car home first. It’s a 2200 mile trip. Then I will have to get some $$ saved to do it. Engine is untouched since Chrysler put it together.
 
Aviation 100LL (low lead)...runs marvelous! No ping, lot's of zing! $3.75 a gallon here. It runs great "straight up," or you can mix it 60/40 (AV60/Mogas40) If you can get someone to sell it to you. :rolleyes:
 
I tell you man, I've built a lot of engines, but I've torn down probably three or four times as many. I've seen valve seat recession from unleaded gas on non hardened seats, but not on a large scale. IMO, they are slap not needed for a lighter car like an A body. Now, if you had a truck you were using for towing and hauling on a regular basis, then yes, I would recommend them, but IMO they are a colossal waste of money on something like a light hot rod, or even a light stock vehicle. The exhaust gas temperatures are just not hot enough. I see nothing wrong with t good lead substitute if that's what you want to run.
 
Ok...that makes sense. You're just trying to get it home.

Yes. My last Dart only made it 88,000 miles before it ran so bad I stopped driving it. That’s low for a slant six.

I want to make sure I give the new car the best chance I can give it.
 
So the things that may cause it to ping on the trip will be carbon buildup on the residue and too much timing.
The most likely scenarios for timing a little bit more advanced are a) someone set the initial too high b) springs have slightly stretched.
I wouldn't worry about either really. Start with a with a name brand mid octane fuel, and if you hear a slight ping or rattle at part throttle loads (uphills), then back off the throttle a hair and next fuel up use a higher octane. If no ping, you can try a regular (87 AKI) next fuel up.

Sunoco's main east coast facility for high octane pump gas is out of commission since the fire. I don't know what they've been doing but it seems to me their retail prices for higher octane are reflecting that shortage. Just my limited observation. Conoco and some others don't seem to be effected.
 
As mentioned above. You should be fine on 93 for the trip. As said above, if it pings, something is mis-adjusted. Check the idle w a vacuum gauge, maybe a compression test. If it was all good, I wouldn't hesitate to drive a stocker across the country.

If it's high mileage, you could try the old water trick - dribble water down the carb, as much as it will take without stalling, while holding the throttle around 2200-2700 or higher. Should be fully warmed up first. It will pop and miss, but also steam the carbon out a bit. This can be a tricky, or risky procedure if you've never done it before.
 
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The trip is from Oregon to Illinois. I plan to do some work on the car before setting out.

Carb rebuild
Spark Plugs
Cap
Rotor
Condenser
Air filter
Oil change
Valve adjustment
Timing

I expect to have to advance and retard timing according to altitude and I will try 93 as well to avoid any issues caused from high-altitudes.
 
The trip is from Oregon to Illinois. I plan to do some work on the car before setting out.

Carb rebuild
Spark Plugs
Cap
Rotor
Condenser
Air filter
Oil change
Valve adjustment
Timing

I expect to have to advance and retard timing according to altitude and I will try 93 as well to avoid any issues caused from high-altitudes.
I'd run it, or at least check things before replacing, exception of the spark plugs.
And depending on its situation, best oil change is usually with the oil warm. Judge whether that's wise when you see it.
I'd bring a couple of condensors and points, but new ones are a crap shoot. If the old ones good - run 'em.
Timing: Bring a light, a tach, golf tee (and a rag). If its the original distributor, set it to factory initial. That will be close. You can make small adjustments if you find its needed while driving. Don't see any reason to use 93 octane. Its not cleaner, it doesn't have more energy, and it costs more.
 
I'd run it, or at least check things before replacing, exception of the spark plugs.
And depending on its situation, best oil change is usually with the oil warm. Judge whether that's wise when you see it.
I'd bring a couple of condensors and points, but new ones are a crap shoot. If the old ones good - run 'em.
Timing: Bring a light, a tach, golf tee (and a rag). If its the original distributor, set it to factory initial. That will be close. You can make small adjustments if you find its needed while driving. Don't see any reason to use 93 octane. Its not cleaner, it doesn't have more energy, and it costs more.

I’m fully aware that 93 octane is not higher energy, and more expensive. With the trip going through the Rockies and being almost a mile above sea level it may need to be used if I can’t adjust any pinging out with timing.
 
I agree running uphill will definately heat soak the engine and so make it more likely to ping if there is too much timing at that rpm and load.
The only vehicle I've had that I recall having a different timing for high altitude is my '85 Grnd Wagoneer. Initial is advanced another 5 to 6* for high altitude.
So doesnt seem like knock was the concern - and that's on a vehicle where the owner's manual advises that high octane fuel may be needed.

That's why I'd try out the first few hundred miles on mid grade like 89 or 91 AKI. Then you'll have a better idea of what it can tolerate. If you can get 93 as you start into the long climbs, great. But if you use something less to evaluate with, you'll have a cushion when the going gets steep or only 91 or 92 is available.
 
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