online170

This is a little "out there" but i thought maybe id ask anyway.

Recently my car developed some "knocking" issues. I blamed it on the lack of tuning in the holley carb, with the cold changing weather. However, both my bro, and my freind's car are behaving unusually similar.

We always fill up 91 octane shell, because it seems to be the only place not having the 10% ethanol mixed in. Shell gas has always run good for us, sunoco works too, but they have the 10% ethanol.

Anyway, last week, we all went racing, and our cars ran great. They ran even smoother after the track, because they hadnt been run WOT in a while.

When our tanks ran out, we all got about 30 more liters of gas, and now all our cars are knocking and dieseling when shut off. I was screwing around with my timing a bit, so i didnt catch on, but turns out all our cars knock at the same revs, and they all diesel. They all feel a little low on power, and hesitate a bit as well in the same pattern.

Anyone else noticing the same thing within the last 2 weeks around Ottawa, or maybe Ontario??? Maybe its the gas.

F-BIRD'88

If you had filled up and used Sunoco 94 consistanly you would not have that problem. A high performance motor needs more than 91 octane.
The small difference in cost of the 94 is more than made up by avoiding costly engine damage from allowing your motor to detonate and ping using crap gas.
(Decent, consistant) gas ( that yes you pay a few cents/liter more for) is much cheaper than pistons and rings and bearings.
We won't even get into machine work labour and time (yours).

What is the beef with the 10% ethanol blend?

George

It sure as hell wouldn't be surprised if some places where selling regular has premium.

On the other hand it could just be bad gas from what ever station you all went to.

Either way, run some 94 through it and see if the knocking goes away.

BtownZ28

94 octane? whats that? 91 is the highest they sell in my neighborhood. Consider yourselves lucky.

6speedIROC

iTrader: (3)

I run 91 on 11.2:1. 'hi-perf' doesn't need 94, depends on your setup.
I was told that NO premium fuels (91oct) have any ethanol in them.

online170

Ive been using 91 sunoco or shell for the entire life of the car, ive never had a problem before. This just happened in the last 2 weeks. I thought it was because i was messing with my timing a bit, but the other two cars havent been touched, and they are experiencing the same knocking in the exact same places.

Shell gas is far from crap, they have their own supplier, and its one of the better fuels ive put in my car. When i first bought my bird, i tried all the stations, and sunoco and shell were noticeably better (smoother running) than anything else (petro, pioneer, esso, etc...) Sunoco's supplier is MacEwen, and Shell is its own supplier i think. Most of the other guys use Stinson Fuels.

I was told that sunoco 94 is acheived with additives. He complained about residue in fuel lines, but i have yet to experience that myself so i cant say. I only use 94 if im going to the track, and i feel like doing a little tuning.

My beef with ethanol?
10% more fuel required with a blended fuel, for the same amount of air as without. 25% less power. I didnt beleive this at first, but next time you go on a long trip try it.

(Ottawa to Toronto is a good example in my freind's F-150 5.4 triton v8), we towed a U-haul trailer from Ottawa, to Oshawa along the 401, filled up at a shell station to start. Dropped off the mustang we were towing and the trailer, and filled up at some regular station with blended fuel (Ultramar i think), and we got better mileage while towing.

Theres also talk about how the fuel is harmful to the engine gaskets, and valves. Similar to the leaded and unleaded situation. But any info saying it ISNT harmful to your vehicle, is on government sites. Any info saying it IS harmful, is hear say. Neither provide any evidence, so i dont know. Ill assume the worst till i can prove otherwise.

SBlackfoot

Funny, I filled up with premium at a Pioneer in Hamilton one evening. The next morning, about 10 kms later it damn near left me stranded on the QEW. Missing like crazy, stalling, etc... I've been checking everything I can think of before draining all sixty liters (only 30 were from that fill up) and trying gas from a different station. No luck so far.

Eric2ndGen

Haven't been around much last little while, but:

Gasoline blend specifications change 4 times every year. While the octane is supposed to remain the same- other components of the mix do not.

The most significant change (which would have occurred on September 21) for people is the Reid Vapour Pressure index. This indicates the evaporative quality of the gasoline. The lower the rating, the slower the gasoline evaporates at a specified temperature. The higher the rating, the faster it evaporates at the same temperature. The idea is that by increasing the vapour pressures specs, the gas will evaporate/blend with air better at lower ambient temperatures.

Here's the problem- this was all well and good when all cars ran carburetors and had to start on cold mornings, but is less significant with fuel injection which forces fuel vaporization more so than does a carb. Once an engine is up to operating temperature, the point at which the fuel evaporates when cold is almost entirely irrelevant. So, when you mileage goes down the toilet in the winter vs. the summer, it is not purely because of "colder weather" it is, in large part, as a result of higher RVP ratings allowing the gas to evaporate and burn off faster- mileage drops and power drops as well (although power drop is hard to notice as more fuel gets blended with the air due to the colder ambient temperature, but it still burns off much more rapidly).

So, near the end of September the specs on gas change (for the worse as far as I'm concerned) and this can cause issues- especially for people with carburetors and a very precise tune set-up. I'm not saying this is the only issue in this case, but it will be a significant contributor to the problems mentioned.

online170

Eric, thanks for the post.

I was aware that the blend specs change through the year, but i didnt know in depth like the info you provided. I also neglected to take that into account. But the time frame youre mentioning lines up with the probs were experiencing.

All three cars have a fairly precise tune, that was played with within a degree of timing, and 1 jet size on the carb to achieve for example.

For the time being we switched to "stiffer" springs on the distributor's weight advance, which seems to bring the advance in slower and limits it a bit as well. Seems to be helping, but not a cure.

All cars are now parked for the winter, so we'll have to wait and see how they behave in the spring. This is the first time in a long time, each of us has had our cars out regularly past October, so its a new experience.

Will update in about 6 mnths and see if the prob goes away.