67mustang302

http://www.prosystemsracing.com/scoop040909.html

2+2GT

The 69 only offered two 302 cid engines, the F code 2V version, and the G code BOSS. The 302 2V was strictly a low-compression dished-piston transportation unit, intended to run on cheaper regular gas, and it still should. If you have pinging, check the timing, and the advance curve adjustments of the distributor. Internal distributor advance adjustments are usually screwed up.

snorulz

I agree with the first part of that statement, higher octane fuel is more resistant or patient to ignition. In other words, a higher octane fuel can wait longer for the spark before pre-detonating than a lower octane fuel.

The second part is wrong, Octane number has no effect on flame velocity in an engine.

1slow67

I tested my 200 I6 last year. I found out my I6 drives better with 87 than it does with 89 or 93.

snorulz

I can tell a difference between 87 and 93 in my car, 93 will chirp the tires shifting into second and 87 wont. I have a 69 w/ 302.

urban_cowboy

That is probably b/c of your tune. 93 is a more lean fuel than 87. Typically you need more fuel when running high octane b/c it contains more alcohol and other additives to lower the octane but they also cause a lower stoichiometric thus you need more fuel for a given volume of air. You need to tune a car (both carb and timing) for a particular fuel. You are probably running too rich with 87 and just right with 93. BA Mustan is probably tuned better for 87 and runs too lean with 93. EFI cars mask this due to EECs and O2 sensors. They are able to compensate for fuel levels (rich or lean) where carbs cannot. Like CPR said, run as low an octane as you can without detonation and jet according to that fuel.

What each engine needs depends on CR, type of heads, cam timing, ignition timing, etc. I run an aluminum head 10.5:1 CR stroker 240/246 duration cam @.05 with 93 octane. Any more compression, and I would need race gas. If I was running a 9:1 motor, I would run 87 octane both b/c of cost and lack of need for added resistance to ignition. Most any motor CAN run a higher octane, but unless you are wanting to speed the extra money, and tune the car for that fuel, you are not accomplishing anything.

CyprusMustang

im not sure whats going on, i get a foul smell from my exhaust, tried to adjust the timing and i think i got it at 14 degrees but still smells and smokes a little.

question, when i first rebuilt engine, i attempted to start car for few days but i didnt have luck, i was 180 degrees off on the dizzy, then one day i flooded it while attempting to start it and i blew the air filters off and dip stick out. question, could that have mixed some fuel in within with the oil.... my oil smells a bit. i didnt change oil yet since i only put on 250 miles. i wanted to wait until 500.

next question, with the timing light, i put a white dot on 14 (advance) and most of the time it comes spot on 14 but ever 10 seconds or so, it will come on 20 for a split sec and then back to 14...does this mean its not timed properly? does it need to be constant on 14?

67 evil eleanor

Thats because of all the "****" they put in gas these days.......

67mustang302

Higher octane fuels do burn slower. They don't simply have some arbitrary octane rating, they're all made from base fuel stocks, then specific components are added in the blending process to achieve the desired result. There's a whole array of chemicals that are added, each to achieve different effects. Some increase the fuel's flash point, so more energy is required to ignite it, some help to control burn rates for a more complete chemical reaction during combustion, some chemicals are added back in to try and increase burn rate to offset the side effect of flash point raising chemicals etc etc. Modern gasoline, and especially racing gasoline, are very complicated and sophisticated chemical blends....they're base gasoline blend with sometimes dozens of other chemicals added in(in highly controlled amounts) to alter the properties of the fuel.

They don't just "add octane" to higher octane gasoline, it doesn't work that way. "Octane rating" is actually a scale referencing iso-octane(100) and n-heptane(0), a fuel with an octane rating of 100 means that it has the same resistance to ignition/combustion/detonation as pure iso-octane, that is to say it has nearly identical combustion characteristics. But generally during the blending process the chemicals added to increase the octane rating result in a fuel that is harder to ignite and slower burning, sometimes the octane increasing chemicals are MUCH slower burning, so burn rate increasing chemicals are added in, but you have to be careful not to blend it back to a lower octane rating again while trying to speed burn rate back up. That's one reason why race fuels are so expensive, they use very expensive blending components to achieve higher octane ratings with acceptable burn rate(xylene, toluene, benzene, cyclohexane etc), and it's in very VERY controlled amounts.

Then end result is that a higher octane gasoline is not only harder to ignite(greater resistance to pre-ignition) but it also burns slower(greater resistance to flame front generated detonation). The thing is, in a high output engine that NEEDS a higher octane fuel to run maximum effort tune, the slowed combustion of the fuel is more than offset by the characteristics of the engine causing combustion rates to increase. That's why beyond the needed octane you end up losing power, since the fuel can't completely combust.

Whether a higher octane fuel is richer or leaner than a lower octane fuel is entirely dependent on the blending components. Some have higher specific gravities(more fuel molecules per cc) and as a result need less fuel volume due to increased density, so they run richer. Some have lower specific gravities and run leaner.

As for pump fuel, there's not a huge difference between 87 and 91/93, but it's enough to make a difference in some cars. And the blends between different manufacturers can be quite different.

snorulz

You are correct, my car is running rich however around here 93 is not more lean than 87. We have the 10% ethanol crap gasoline for everything less than 93. Being that ethanol has less energy content than gasoline this will be part of the difference i see. The other thing is I believe i have my timing advanced to far so it is very possible i am getting knock with 87 octane and not with 93.