Spark plugs on a 4.6 gt
07-19-2010, 08:42 PM
#1
Thread Starter
Join Date: Jun 2009
Location: ca
Posts: 11
Spark plugs on a 4.6 gt
Sup guys!
I just picked up my beautiful 1998 convertible mustang GT. This car is like new inside and out! The color is like tomato red i forgot what is called. Black leather inside and the top is just in new condition. It also comes with the glass window on the back. It has 50,000 miles on it and it is a 5 speed.
My current weekend car is a 2004 srt-4 with a 50 trim kit tuned on e85 and meth. So the mustang is going to be my daily driver.
Mods that were on the car when i bought it
DSP 91 tune
flow master exhaust
steeda short shifter with mach 1 shifter
k&n intake
ford c springs
eiback spacers in the back with stock 17" wheels with 245's all around
Alpine deck
I like to change the spark plugs on it and want to know what spark plugs should i use? I am not going to mod the car at all! This is going to be my cruiser and daily driver. With the mods that i have what would be a good spark plug to use?
The shocks are blown on it also. i just ordered kyb agx from tirerack so i will be installing them next day or so.
I just picked up my beautiful 1998 convertible mustang GT. This car is like new inside and out! The color is like tomato red i forgot what is called. Black leather inside and the top is just in new condition. It also comes with the glass window on the back. It has 50,000 miles on it and it is a 5 speed.
My current weekend car is a 2004 srt-4 with a 50 trim kit tuned on e85 and meth. So the mustang is going to be my daily driver.
Mods that were on the car when i bought it
DSP 91 tune
flow master exhaust
steeda short shifter with mach 1 shifter
k&n intake
ford c springs
eiback spacers in the back with stock 17" wheels with 245's all around
Alpine deck
I like to change the spark plugs on it and want to know what spark plugs should i use? I am not going to mod the car at all! This is going to be my cruiser and daily driver. With the mods that i have what would be a good spark plug to use?
The shocks are blown on it also. i just ordered kyb agx from tirerack so i will be installing them next day or so.
07-20-2010, 01:26 PM
#2
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
Just use the OEM Motorcraft AWSF-32PP double platinums, or an equivalent double platinum plug from one of the other manufacturers. You need to use double platinum plugs on your '98 because of the wasted spark ignition system.
07-20-2010, 04:09 PM
#3
2nd Gear Member
Join Date: May 2010
Location: mississippi
Posts: 386
What do you mean by wasted spark ignition system?
07-20-2010, 04:50 PM
#5
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
In a wasted spark Electronic Distributor-less Ignition System (EDIS) pairs of spark plugs are wired in series with each ignition coil (connected through the head), and therefore fire at the same time--one on a cylinder that is at the top of the compression stroke, the other on a cylinder that is at the top of an exhaust stroke.
The one that fires on the compression stroke ignites the air/fuel mixture and makes power, the one that fires on the exhaust stroke does nothing--I.e. it is "wasted".
The advantage for automotive engineers is that only 1/2 the number of coils is needed. On your car the two coil packs each contain two separate ignition coils, four coils in total to fire eight cylinders.
Because of this however the direction of the current flow though each plug in the pair is reversed relative to the other--this is why the double platinum plugs are required¹.
Here's a schematic of a wasted spark system (this is from my Miata days, on your car it's plugs #1 and #6 that fire simultaneously):
When electrons flow across a spark gap they carry a bit of the electrode material with them, and as electrons flow from negative to positive (Faraday got it wrong) which ever is the negative electrode needs to be made of a material resistant to that sort of erosion--platinum, iridium, and some other "precious" metals fit that bill.
In the diagram above the electron flow in the #1 plug is from right to left, from the side electrode to the center electrode--this calls for a precious metal side electrode. One the lower (#4) plug the flow is reversed and a precious metal center electrode is needed.
Since it makes no sense in the after market to stock two types of single platinum plugs, and it being unlikely that anyone would get them in the right holes anyway, all that are available are double platinum plugs that can be used on either side of the wasted plug configuration.
That's why you need to buy double platinum (iridium or whatever) plugs for your car...
-------------------------------------------
¹ - The OEM plugs are actually single platinum, with four having a precious metal center electrodes and four having precious metal side electrodes--this saves money on the production line. It probably only saves $4 per car, but if you're making 250,000 cars that adds up to real money...
The one that fires on the compression stroke ignites the air/fuel mixture and makes power, the one that fires on the exhaust stroke does nothing--I.e. it is "wasted".
The advantage for automotive engineers is that only 1/2 the number of coils is needed. On your car the two coil packs each contain two separate ignition coils, four coils in total to fire eight cylinders.
Because of this however the direction of the current flow though each plug in the pair is reversed relative to the other--this is why the double platinum plugs are required¹.
Here's a schematic of a wasted spark system (this is from my Miata days, on your car it's plugs #1 and #6 that fire simultaneously):
When electrons flow across a spark gap they carry a bit of the electrode material with them, and as electrons flow from negative to positive (Faraday got it wrong) which ever is the negative electrode needs to be made of a material resistant to that sort of erosion--platinum, iridium, and some other "precious" metals fit that bill.
In the diagram above the electron flow in the #1 plug is from right to left, from the side electrode to the center electrode--this calls for a precious metal side electrode. One the lower (#4) plug the flow is reversed and a precious metal center electrode is needed.
Since it makes no sense in the after market to stock two types of single platinum plugs, and it being unlikely that anyone would get them in the right holes anyway, all that are available are double platinum plugs that can be used on either side of the wasted plug configuration.
That's why you need to buy double platinum (iridium or whatever) plugs for your car...
-------------------------------------------
¹ - The OEM plugs are actually single platinum, with four having a precious metal center electrodes and four having precious metal side electrodes--this saves money on the production line. It probably only saves $4 per car, but if you're making 250,000 cars that adds up to real money...
Last edited by cliffyk; 07-20-2010 at 05:16 PM.
07-20-2010, 05:44 PM
#8
TECH SAVANT
Join Date: Dec 2006
Location: Saint Augustine, FL
Posts: 10,938
This of course only applies to the '96-'98 cars.
The '99-'04 models use the COPs which are all negative firing, as is the #4 plug in the diagram--I.e. they only need a precious metal center electrode.
Plug firing events are usually displayed inverted, here's a non-inverted trace showing the negative going ionisation pulse and firing event, of the #5 plug on my '03, and showing the triple-strike firing pattern used at idle and low RPMs:
Note that the COP plugs fires the plug three times in 4ms, and that the firing voltages are nearly identical! This illustrates that the cop is capable of firing the plug every 1.33ms.
That would be the equivalent of the engine running a little over 11,000 rpm...
The '99-'04 models use the COPs which are all negative firing, as is the #4 plug in the diagram--I.e. they only need a precious metal center electrode.
Plug firing events are usually displayed inverted, here's a non-inverted trace showing the negative going ionisation pulse and firing event, of the #5 plug on my '03, and showing the triple-strike firing pattern used at idle and low RPMs:
Note that the COP plugs fires the plug three times in 4ms, and that the firing voltages are nearly identical! This illustrates that the cop is capable of firing the plug every 1.33ms.
That would be the equivalent of the engine running a little over 11,000 rpm...
Last edited by cliffyk; 07-20-2010 at 06:06 PM.
