valve tickling noise reduction

[MMBRAZIL]

Hi, I drove my car today with 50/50 aviation/premium gas on my car. I noticed the car is iddling and running smoother. And I had a little valve tickling ( nothing compared to the 75 911 ) that disapeared. Could the valve noise be cause my car was running lean ( here we have 25% of alcohol mixed to the non aviation gasoline)?

I felt the car is running "happier" with this gas mixture.

[kang]

Hmmm, there could be more than one thing going on here. First, of course, would be the increase in octane from the aviation gas. What octane is your premium? And you’re saying that the premium has 25% alcohol? That’s a lot. In the states I think it’s something like 5 to 10%, and even that is a lot. Alcohol has a lot less energy per unit volume than gas. I think we can conclude that the “happier” and “smoother” feeling is from a combination of increased octane and less alcohol.

Do you run fuel system cleaners (Techron, etc) on a semi-regular basis? If not, there could be some reduction in fuel system and combustion chamber deposits going on here, due to the aviation gas. I don’t know what detergent properties or additives aviation gas has. Sometimes when my car feels better for whatever reason, my right foot tends to get a bit heavier, if you know what I mean. This leads to an Italian tune-up effect, which creates a self-fulfilling prophecy, so to speak. Some of that could be going on. The smoother running has caused you to run the car harder, which burns off the carbon in the combustion chambers, which leads to even smoother running.

As for the valve ticking, hmmm, that’s a bit tougher. Does the aviation gas have lead in it? If it does, you’ll ruin your cat (you knew that, right?), but I don’t know if that is an issue where you are. If the aviation gas has lead in it, the lead could be lubricating the valves. That’s what the function of lead is. It was added deliberately to lube the valves.

On the other hand, it could just be a function of increased timing due to higher octane. Are you sure the valve tick you heard was not a ping? Cars can sound funny if you retard the timing too much. What model car? 964, 993, 996? If you have hydraulic lifters (993, 996), and one was going bad (ticking), I doubt a change in fuel would fix it. I suppose it is remotely possible that the aviation fuel has caused fuel contamination in the oil, which could clean out a dirty lifter, but this is highly unlikely. Do you get lifter clatter on startup?

[MMBRAZIL]

Hi kang,
I use a special gasoline called podium, its the same Petrobras delivers to Williams F1 team. But it has 25% alcohol for local markets. Most premiums gasoline in Brasil have aditives. I am not sure the PODIUM has. If I am not mistakem PODIUM has 98-100.
The valve noise was not ping. its constant even in iddling.
You are right, my right foot got heavier. But I don´t beleive it was carbon deposits, cause the noise reduced a couple of minutes after I started the motor.

I beleive with the alcohol, the car might run leaner, thats why I
decided to mix avi gas. Could a lean mixture cause the valve noise?

And definetly the car looks like it hade some REDBULL.

[kang]

I’ve never heard of alcohol causing a car to run lean, but then again I’ve never heard of 25% alcohol either. The ECU keeps the A/F ratio pretty accurate, even with alcohol in there. Did you look at your plugs? Did they indicate lean? And I also don’t know how lean running could cause valve noise. I don’t see the connection there.

[MMBRAZIL]

I´ll investigate this further.....and keep it posted.