100 octane gas...great stuff!

On a hot 90f+ degree day my BB512i engine would often "ping" under wide open throttle using BP 93 octane gas. Over the weekend I filled her up with Citgo 100 octane racing gas at a cost of $3.65 per gallon. It cured the problem 100 percent. What else could I do to alleviate the pinging other than paying $75.00 for a tank of gas? Timing...mixture...octane booster...any recommendations?

 

Easiest fix--retard the timing ~3 degrees.
Fix that's even easier but has limited possibilities of working--go to the auto parts store and get one of any number of "combustion chamber deposit removers" to add to your gas.
You could also richen the mixture up, use octane booster all the time or tear down the engine & rebuild to remove carbon deposits/put in a thicker head gasket to lower compression, use new cams to lower effective compression, etc.

(And here when I read it I though it was gonna be someone saying "I put 100 octane in my car and it's so much faster now!")

 

I use 110 octane VP race gas in my 308 once in a while. A very happy car when I do this. I don't get the usual popping and lean misfire from the pipes like I do with the crappy 92 unleaded around here.

Higher octane will allow you to run more timing advance if you are tuning for max HP too.

 

don, won't retarding the timing reduce performance as well; as would your other more expensive suggestions such as tearing the engine down, new cams or using a thicker headgasket ? Someone else has suggested that I richen the mixture due to my recent installation of K&N air filters which they claimed may have lean out the mixture anyway. How can I tell if I have combustion chamber deposits ? And, does those cleaners really work? I have seen a fuel injection and combustion chamber cleaner from Redline but never believed those "snake oils" really worked?

 

Used to have the same problem with my BBI. Used stabil fuel stabliser and it cured the ping, seemed to free up the injectors better after storage as well. During the engine out we cleaned up the intake system fron 20 years of accumulated gunk, did the water pump and totaly rebuilt the distributor. I could not believe the difference the car is significantly faster and no pinging on 93. Apparently part of the issue is cooling, namely a good waterpump and bleeding the system properly.

 

"Yes"
As for knowing if you have deposits... unless you can get a good peek down a spark plug hole, you're mostly on your own.

 

My $.02

The following is an abbreviated version of my understanding of the relation of pinging to timing: Normally peak pressure within the cylinder occurs between 8 - 14 degrees ATDC, depending on engine design. Pinging is the simultaneous combustion (detonation) of the last ~10% of the charge due to this portion of the charge exceeding the spontaneous ignition temperature of the mixture. If you retard the timing you are lighting the mixture later and since combustion time is relatively constant for a given mixture, your peak cylinder pressure will occur a little further past TDC and therefore will not be as high (read: lower temperature) and you will have a normal burn. This loss of peak pressure will reduce your power output.

If you are running lean, the combustion temperature will also be higher. Richening up the mixture will cause the excess fuel to cool the combustion event and reduce the chance of detonation without loss of power. However, this solution doesn't work if you have cats.

I would keep running 100 octane (booster should work if you don't want to use the good stuff). If you don't have cats, a cheaper solution is 25% avgas/ 75% premium.

If you think you have carbon, then you are either not driving hard enough or out of tune. Try an "Italian style tune-up." The "snake-oils" do work but you have a lot of carbon built up, it may damage something if too big a chunk comes off at once.

I hope this was useful.

Good Luck,

Art S.

 

"Normally peak pressure within the cylinder occurs between 8 - 14 degrees ATDC"
Could you explain this further please?
"Pinging is the simultaneous combustion (detonation) of the last ~10% of the charge"

What do you mean by "the charge"?

Thanks a lot, Jerry

 

You know I have never actually heard a Ping. What does it sound like?

 

Get in somebody else's car and do as the really bad drivers do, all over Sydney, and go around a corner in top gear and then try and accelerate up a hill ... the engine will ping it's balls off.

Pinging is extremely bad for an engine and if you can hear it then you can probably bet that other, unheard pinging is also occuring and eating away at your pistons!

Have fun
Pete

 

I go around in my 82 6er in top gear up hills (and it only has like 182 hp) (used to atleast when I was too lazy to shift) with no issue that I can think of. Im still confusd. What does the sound sound like, maybe I am just missing it. :-/

 

Sorry forgot to add that your speed needs to be less than walking pace ..., and you probably need to have your mobile implanted in one ear, with your arm wrapped across your face so you cannot see and also grabbing a bit to eat at the same time.

I would love to sound the sound out for you mate ... but er, don't think you would hear me ... all I would do is make my work mates think I was even stranger ...

Pete

 

Jerry,

When the charge (air/fuel mix that is compressed in the cylinder) burns, the result is heat and gases (CO2, water vapor and others). These gasses would like to expand into a larger volume than the original charge occupied. However, since they are in a confined space - the combustion chamber - the expansion comes in the form of a pressure rise.

When you light the charge the combustion is not instantaneous, it actually burns quite slowly (in relative terms). This means you need to light it earlier in order to compensate for the slow burn rate. However, when the charge detonates, it burns instantaneously which causes vibrations, or pinging, in the chamber. These vibrations cause a lot more heat to transfer to the metal, which will eventually cause failure (a little pinging will not cause noticeable damage).

The reason for the peak pressure location being slightly after top dead center is that you want the piston to be starting its way back down the cylinder when you apply the majority of the force (pressure). My previous explanation was just to help with understanding as peak pressure location is used on the design level, not for tune ups.

Hope this helps.

Art S.

 

Art, please excuse my ignorance, but I really want to understand this completely. Are combustion and detonation 2 different things? Is there always detonation with each stroke of the piston/each time the spark plug sparks, or is detonation in itself something that you want to avoid (associated with the pinging)? Thanks a lot, Jerry.

 

Jerry,

In a four stroke engine (all Ferraris) combustion occurs every second revolution of the crank, per cylinder. Combustion is the burning of the air/fuel mixture which, in gasoline engines, is ignited with a spark. The type of combustion you want is not instantaneous but having a steady progression. Think of the movies when the bad guys pour a trail of gasoline then light the end of it, the flame travels back along the trail until it hits the dynamite and explodes. I believe the fuel burns at about the same rate in your engine as the gasoline trails in the movies.

Detonation is a form of combustion where the remaining unburned fuel explodes. As with any explosion, it’s a violent event that produces strong vibrations (shock waves?) which cause the cylinder walls to ring. This is known as pinging. Detonation is not desirable. Think of the dynamite at the end of the gasoline trail.

Does this make any sense?

Art S.

 

Yes it does Art, thank you very much!! I love understanding how and why things work. I appreciate your time and effort. Jerry.

 

I have learned that pinging comes from early, uncontrolled combustion before the spark ignites the fuel/air-mixture b/c of the heat produced by the compression in the up-stroke?

I normally use 98 octane fuel and recently changed to 100 octane. I couldn´t notice any difference in performance.

 

Jerry,

You're welcome!


AR!,

You are describing pre-ignition, which is the loss of ignition timing control due to a "hot spot". This is a much more dangerous and damaging condition than knock or pinging.

Heat is generated from compression in gasoline engines but the heat needed to cause pre-ignition is usually carried over from previous combustion events. Common "hot spots" are the spark plug tip and carbon deposits.

Regards,

Art S.