I just picked up a 99 cobra a month ago and wondering if only high octane must be used, i know that it says it on the dash, but gas prices here in vegas are outrages. Would running mid grade hurt it or not. also i want to put some simple bolt ons and does anyone think that bassani x-pipe and flowmaster catback is a good combo. thanks hope to hear some replies.
Last edited by tyronbiggumsvt; 05-25-2004 at 05:11 AM.
Most likely it will ping with Vegas weather, but try it out, fill the tank and disconnect the battery for 30 minutes, that is for the EEC to relearn the fuel strategy. If it pings...high octane is the only cure.
I would fear of using any grade below 93 octane It will ping for sure no matter what you do since the 99-01 motors have close to 10:1 compression which requires a slower burning fuel. With 82 or even 87 octane fuel you will suffer from pre-ignition and or detonation. Don't worry too much, from what I read about the 4.6L mod motor, the worst thing you can do is either pop a hole in a head gasket or in a piston. The block and heads will take the punch. A slight ping is not that bad, but having your motor detonate feels like someone rear ended you or you ran into an invisible brick wall. Believe it or not, the lower grade fuels burn faster, the lower the octane the lower the flash point. 10:1 compression motors will run hotter than the usual 8:1 compression engines found in everyday cars (including the GT). If you must use lower grade fuel, then you should add some octane booster before fueling up. The cost of the additive with the lower grade fuel will cost you more or about the same with the 93 octane (depending on which stuff you get). With the fuel as it is at 93, I still add octane boost since some 93 octane fuels ping in my 01.
thanks man, i put in 89 octane once already would it ping right away or later i havent heard anything just yet, but if it does would higher octane remedy this or not. All we have here in las vegas is 91 octane , we used to have 92 but i dont know what the hell happened with that. you said all that stuff with the head gasket and pston being blown and what not happen to a modded motor.thanks snakepit
__________________
99 svt cobra
STEEDA diff bushings,HD crossmember bar
SLP "LOUD MOUTH" CATBACK
SLP X PIPE
It is probable that detonation will occur. I have had that happen already and my main concern was the integrity of the head gaskets. What occurs during detonation or pre-ignition ,which is caused by hot spots on pistons and or areas in the combustion chamber, is the creation of more than one flame front which gives it that ping sound. Depending on when the ignition takes place it can be destructive and quite disturbing. If the ignition of the fuel occurs while the piston is moving towards the top during the compressin cycle, the piston attempts to compress an expanding gas from the pre-ignition. This force is strong enough to stop the motor for a split second (have you ever stalled a manual transimssion car? it usually happens with a nasty bang or sudden jar which make you fell like you were rear ended). Just imagine that at 80MPH down the highway. This will usually occur if the car is running lean, but is more than likely something that will happen if you use the wrong fuel. With high compression motors, (10:1 or above) require retarded fuels for proper control of the flame front. Since regular grade gasoline is highly volatile it will self detonate under high compression at engine temperature (similar to a diesel engine). Not only will your engine run hotter it will run like s**t unless you use a fuel additive. At first it may work, but over time, the result of carbon deposits will ultimately cause severe detonation. What makes it worse is all of the emmision components and restrictive exhaust. Just take a look at the Ford web site or look at some vehicles at the dealerships. Most cars were designed to run on regular grade fuel typically 85-87. They also have a reduced compression ratio of 8:1 (usually less than 8.6:1). If you notice any pinging under acceleration do not push the car thinking it will go away because you may be causing damage. There are several performance additives that you could add to the tank at every fuel up. There are some that are not too expensive $3 and some cost up to $12. I have already purchased 93 octane fuel at a Mobil dealer and wound up with regular grade fuel in the tank. I suspected this after driving 10 miles from the gas station the car just bogged down and would barely move without banging or pinging. At least there were several auto parts stores within reach to get some additives. (they mix better if put in the tank first). My problem was that the carbon build up in the combustion chamber raised compression close to 12:1 (perhaps an exageration on my part) so I was having problems with just about any fuel I used. (caused by a stuck or defective EGR valve, dirty MAF, etc all which were corrected and or replaced when I cleaned out the motor with water /alcohol mist by spraying it into the throttle body in small ammounts at 1/4 throttle movement. I now have included intake cleaning, spark plug checks and vapor injection as a part of regular maintance every oil change to reduce the carbon build up. I took the car to ford with the pinging issue and carbon build up, they said I babied the car too much If they knew of my driving habits they would have changed their statement. If you do not feel confident or fear that you may cause vapor lock in the motor, ask for MotorVAC at the dealer. I was told it works well by another customer that had it done who was standing behind me at the counter.
As for the Bassani X pipe and flowmasters, any increase in exhaust scavaging (reduced back pressure) will help with performance effeciency and fuel milage. Let me know if the 89 octane fuel gives you any problems. I am curious if it does. If you intend to use fuel additives, avoid the nitro-methane stuff until you are sure there is no pre-ignition, especially if you are running octane levels below 101. More than likely the detonation will not be so violent as to cause any major damage, but with power additives like nitro methane (which I have added once but in small ammount) or NOS the ping will more than likely pop a hole in a piston. I have read several articles on pre-ignition, detonation, carbon build up, etc so I could solve the carbon issues I had. So far I have corrected the problems and I don't feel the ping anymore Believe it or not, the 4.6L is one of the esiest ford motors to work on.
yeah so far on the 89 octane no pinging yet. is it suppose to be real loud or barley any sound. i'm really worried now i want to burn this crap out my tank now and run 91 in it now, now its in the back of my head that it might happen hopefully not and i could get away this time. so i'll try the octane booster now to clear it up for then on my next refuel i'll put in good ole 91. its weird we only have 87,89,and 91 here and seems every one else has 93, or other grades. well thanks alot snakepit for your help.
__________________
99 svt cobra
STEEDA diff bushings,HD crossmember bar
SLP "LOUD MOUTH" CATBACK
SLP X PIPE
pinging will not be real loud unless you have detonation (which by the way does not sound like a backfire). Some will say it sounds like marbles in the motor rolling around. If you are not pinging on 89 octane that is good. Most of the fuels will list the octane rating by a specified method. In PA they call it the RH+2 whatever that means. Some may list an entirely differnt means so the octane may be lower in other areas. What makes the fuel crapy over here is that it is oxygenated fuel (close to winter grade gasoline) which tends to ping (Mobil, Texaco, Shell, and Sunnoco). I found the BP or Hess gas to work the best (I used to think they were the crapy fuels - not any more).
i have put 89 in my car for a month at a time and i never had any problems, you do notice a lack of response and power, burning the good stuff just makes you engine really happy, but i have had NO problems with the lower grade fuel, lucky for me 93 octane is only five cents more per gallon in my town!
fuel for 99 cobra 
It will ping for sure no matter what you do since the 99-01 motors have close to 10:1 compression which requires a slower burning fuel. With 82 or even 87 octane fuel you will suffer from pre-ignition and or detonation. Don't worry too much, from what I read about the 4.6L mod motor, the worst thing you can do is either pop a hole in a head gasket or in a piston. The block and heads will take the punch. A slight ping is not that bad, but having your motor detonate feels like someone rear ended you or you ran into an invisible brick wall. 
Believe it or not, the lower grade fuels burn faster, the lower the octane the lower the flash point. 10:1 compression motors will run hotter than the usual 8:1 compression engines found in everyday cars (including the GT). If you must use lower grade fuel, then you should add some octane booster before fueling up. The cost of the additive with the lower grade fuel will cost you more or about the same with the 93 octane (depending on which stuff you get). With the fuel as it is at 93, I still add octane boost since some 93 octane fuels ping in my 01.
If they knew of my driving habits they would have changed their statement. If you do not feel confident or fear that you may cause vapor lock in the motor, ask for MotorVAC at the dealer. I was told it works well by another customer that had it done who was standing behind me at the counter.
