Hi snorulz,

thats a fantastic read, so thanks for that. I find the story with the pipeline/refinery very interesting.
Still I don't get in how my statement about what octane is and what a knock sensor does is wrong. You basically say the same ?!
at the same time i fully agree that octane numbers are not a measure of burning velocity, but I do believe like Mark states that different octane numbers burn at different speed.
I am not a fuel expert but I know a bit about explosives and different mixtures decide between detonation and deflagration. i have a hard time believing that the 87% iso-octane and 13% heptane mixture will burn at same speed as the 100% iso-octane. If that makes a difference to the car I don't know :-]

Kalli

 

Kalli,

You said that higher octane fuels are harder to burn, that is not the case in an engine. The spark plug will be able to burn the fuel just as well with 87 octane as with 94 octane.

Everything else you said i agree with completely.

I will have to pull my notes tonight about the velocity, i don't remember exactly why but i believe it has to do with the turbulence in the cylinder. I will look into this, it may take a couple days since i may also have to pull the book out since i didn't take the best notes.

I know with my car there is a noticeable difference when i run 93 instead of 87. The cars is stronger but i have my timing advanced quite a bit. If he switched to 87 fuel, his HC's at idle will either stay the same or increase if the engine starts to knock.

My whole point in all of this is the 94 octane is not his problem and it is not a problem to run it in his car. You do not need high compression or anything like that. If he is getting any gains from it i do not know but it wont hurt anything. Worst case is it could be a waste of money.

I had heard once that regular fuel had a higher octane number when our cars were made. Can anyone prove or disprove this? I am just curious and don't have a clue if it is true or not.

 

Would be interesting to know if you find reference.
for the higher octane in the past I can vouch for it but only for Germany as this is where I lived my first 30 years ;-)
we had two types of petrol:
Super (98 octane) and Normal which was 95. But i have no recollection on when that actually stopped. I have a feeling it was around the same time they removed lead from it.

Kalli

 

SO as not to completely hijack this thread, I will comment on both topics.

sno:

Facinating post. Thanks for taking the time to share that. The results have been different for me, though.

I have a rebuilt stock 302 4bbl. I burn discount (Arco) 87 octane. The timing is advanced 16°, and there's no ping or knock. Idle speed is 850 rpm. I do 50-50 city/freeway driving and get a steady 15 MPG.

I don't know if anyone has similar results, but it could be because CA has unique emissions laws. Attitives to minimize hydrocarbons have to be added by law in my state, so maybe that's why the discount gas here burns smoothly. I'm guessing.

kurupt:

As far as passing a smog test in BC, if you can adjust the carb to its leanest (without the engine cutting out) and you still don't pass, you might need to install a cat converter for the duration of the test.

In CA, cars built before 1974 don't have to get smogged. My car has never had to take this test. I don't know if it is the law here, but if you don't pass, you don't pay for the test. Check if this rule applies to where you got smogged to insure that the place wasn't just trying to sell you a cat.

CP

 

Ok sno, after doing some research, I concede. Interesting that I've never heard it stated this way, though.

Carlos, the gas here is crap. They oxygenate it with ethanol (as opposed to the old hazardous MTBE) so that it burns cleaner, not smoother. Winter blend gases are worse. My car probably drops a full mpg during the winter.

I don't see how/why you're running 16* advance on a 'stock' rebuild, though. That's too much even for my aggressive cam. To be getting away with that, you'd have to have really low compression or a cam with a lot of lobe separation. That, or the outer ring on your balancer may have slipped.

And as far as not paying if you don't pass, that's a sometimes-used smog station gimmick. That has nothing to do with CA smog laws. Most worthwhile shops will charge you no matter what.

 

carlos, i don't understand what you are saying about your results to me. Are you just saying you can pass emissions with 87 octane gas?

 

I would like to toss a wrench into this conversion for the fun of it . From what I understand, to achieve higher octane ratings, the gas company puts additives in. What fuel has a high octane rating? Alcohol. Alcohol is a leaner fuel (takes more fuel per air volume). So by adding alcohol to gasoline wouldn't you think you are making a leaner fuel?

So...would using 93 octane cause you to have a little less unburned fuel than 87 octane given the same tune?

 

kurupt

Too rich is possible.

So is a lean misfire, possibly due to a vacuum leak.

The approach that generally worked when I had to run a carbureted car through NJ emissions testing was to "lean it and retard it". Try taking a few degrees out of your static timing. Or if your vacuum advance uses manifold vacuum rather than ported vacuum, pull and plug the distributor end of the vac advance hose.

I imagine that CO is also checked.


Norm

 

I can relate. I live near Vancouver and failed that same test, not one but twice. I soon realized my spark plug to piston one was very loosely on, I was down to 7 cylinders when taking the test haha. I put it back on tightly and passed the test.