For those that are about to modify or have modified their 996TT and are having some questions on spark plugs, here is some advice for you. This is only my opinion and other ideas or advice is more then welcome here.

From HowStuffWorks - "The spark plug is quite simple in theory: It forces electricity to arc across a gap, just like a bolt of lightning. The electricity must be at a very high voltage in order to travel across the gap and create a good spark. Voltage at the spark plug can be anywhere from 40,000 to 100,000 volts. Spark plugs use a ceramic insert to isolate the high voltage at the electrode, ensuring that the spark happens at the tip of the electrode and not anywhere else on the plug; this insert does double-duty by helping to burn off deposits. Ceramic is a fairly poor heat conductor, so the material gets quite hot during operation. This heat helps to burn off deposits from the electrode."

On the Porsche 996TT, it is recommended to change the spark plugs every 48,000 miles. However when you are modifying your Turbo, it is common that even in low mileage cars, the plugs cannot work with the increase modification and changes in fueling. This causes the car to studder or misfire in the RPM band. Random misfire caused by a loss of spark or a weak spark may be due to fouled spark plugs or the plug gap too wide.

Here is an example of what a car reacts like with fouled plugs. You can see that when peak torque should be hitting at full boost, the car starts breaking up at 3600rpm. This extends all the way through 5300rpm substantially affecting the vehicle.





So what type of spark plug should you change to? There is stock heat range, colder heat range, NGK, Denso, Bosch, etc.

The OEM replacement plug from Denso is the K20TNR. This plug is known as a mulit-ground type. This firing tip design tends to erode the tip of the ground electrode faster than a traditional plug. Erosion at these points creates a larger gap between the center and ground electrodes causing plug misfire. With more ground electrodes you extend plug life. A multi-ground plug will not perform any better and may actually perform worse than a traditional plug. Since most are going to do an ECU flash or add some type of power modification, w eusually recommend going with an Iridium plug.

The next step up in plugs in the Denso line up is the Iridium IK20 or IK22. This Iridium plug has a higher melting point and conducts electricity better then a Platinum plug. With an OE gap of .035" the IK20 is well known for general automotive use and racing. However the premier plug that we have found most important is the Denso IK22. Because of the increased energy caused by the enhancement of power, this also increases heat. With a stock heat range plug on the modified car, the gasoline would end up pre-igniting or detonating without the need of an electric spark, creating an uncontrolled explosion that would severely damage the engine. The IK22 is a 1 step colder plug then the standard IK20. The colder spark plug has a shorter insulator nose and absorbs more combustion chamber heat. This heat travels a shorter distance and allows the plug to operate at a lower internal temperature. Running the car at higher rpm's for a longer period of time and increased power make colder plugs mandatory to eliminate plug overheating and engine damage. The colder type plug removes heat more quickly and will reduce the chance of pre-ignition detonation of the firing end.

You can see by the dyno graph below (dotted line after plugs replaced, solid line with intake), that the plugs smoothed out the power curve which brought the torque tremendously up. It is always good to make sure you have fresh plugs.



So in the end, changing your plugs out to an Iridium type may be the best solution to improve performance and driveability. We have used the Denso IK22 on our vehicles but know that there are other recommended plugs out there.

View this install DIY guide on Renntech forums here - http://www.renntech.org/forums/index.php?showtopic=3603&mode=threaded&pid=17303

 

would this spark plug work well on a supercharged 996?

 

Usually when I want to see what spark plugs are available for cars, I go to www.sparkplugs.com and enter in the make/model information. As I have just done, they do list the IK20 and IK22. As stated above, the colder IK22 is a great plug for performance cars. Having owned a supercharged 996C2 myself, you are basically pushing about the same amount of power as a stock 996TT. This is quite a bit more and the addition power would greatly benefit from a colder spark plug whether it was the Denso, a NGK, or Bosch. So to your question, you bet!

 

Thanks for the info. Always great reading from you.

 

good info dan!!

 

You don't need to change to a colder range unless you are spraying. Stock plugs work just fine in high hp 996/7.

 

i have some denso dp 22's im going to give a whirl when i change the ic's... ill keep u posted the outcome

 

We run a step colder in all our modified cars. From EVO's to STI's, the plugs are the first thing to change. Stock heat range is exceptable, but a 1 step colder is much better for firing.

Quote from this site http://www.ngk.com/charglossary.asp?kw=Heat+range

"An unaltered engine will run within the optimum operating range straight from the manufacturer, but if you make modifications such as a turbo, supercharger, increase compression, timing changes, use of alternate racing fuels, or sustained use of nitrous oxide, these can alter the plug tip temperature and may necessitate a colder plug. A rule of thumb is, one heat range colder per modification or one heat range colder for every 75–100hp you increase. In identical spark plug types, the difference from one full heat range to the next is the ability to remove 70°C to 100°C from the combustion chamber."

 

dan
k24 car
chipped
red lined everyday

what is my best bet ?

 

Steve - good question as this is a pretty normal setup for most here. I run the Denso IK22 in my cars. The car in the dyno plots from the 1st post is exactly that same setup as you have. I feel the IK22 from Denso is good. The Iridium 1 step colder lasts a long time and is perfect for that additional power. I am not sure who tuned your car, but you may also want to consult with them. Some recommend the Bosch and some the NGK.

 

These engines are turbocharged from the factory, so factoring a turbocharger and the appropriate step colder into the appropriate heat range has already been done so by the factory. A colder range is necessary with Nitrous, however on a stock 996tt engine the step colder will not play a factor as much as fresh plugs will. In most applications a copper plug that is changed frequently will work as well as anything, however the complexity of changing spark plugs in our engines requires a plug with a tip that is designed to be more durable.

It will also be very tough to tell a difference in plug heat range or plug indexing without the use of an engine dyno. Using a controlled cell takes out the external variables and will show more of the 2-3hp gains that can be associated with plugs. We've done this on some of our racing engines where a range must be determined (stock plugs do not work with twin injector, methanol setups with over 50lbs of boost). We've had great luck with both NGK and Denso brands with most engine combinations.

 

Well said ONELOVE.

Todd at Proto recommends these copper plugs to his clients I know. We have always used the NGK 1 step colder in our factory turboed EVOs and STIs running GT35R kits. These cars usually make around 500awhp and benefit from the 1 step colder. The Denso IK22 we came across when we first started with our 996TT 3 years ago and has served us well. I am sure the other options out there are good too and can be debated. Its hard to compare a Flashed 996TT to a methanol Supra though. When we built our D1 Drift 240SX, it required several different trial and error plug changes. So I know the feeling that this statement is not for all cars. I think people here are looking for what they can change in their almost stock car to benefit them.

 

Simply put in a stock/flashed or K24/18G car running on pump gasoline, the factory replacement plug or your choice will be fine (I as well prefer the Densos in this particular application). A step colder isn't going to hurt, but I don't know that it is something that will be noticeable or even needed on any car still using factory sized injectors. If you're Markski or any others trying to go 9s, the plug range colder is likely an well chosen option, but frequently changing your plugs will be a necessity at that point.

I would say a good rule of thumb would be to replace the plugs anytime you are easily able to, if you're upgrading to a K24/18G setup, or have the clutch being swapped, it's a great time to install some fresh plugs.

 

I agree with your statement. If your at the mileage needed, change your plugs. If you have done a turbo upgrade, change you plugs.

 

I just got some of the denso IK22's from Dan, installed them, and am very happy with them. My old plugs (Bosch ldc) didn't actually look that bad, but I noticed the car runs smoother with the new plugs. Of course, anytime fresh plugs are installed you are likely to see some improvement, but for just a few bucks extra per plug, I figured why not go with the irridium IK22's, and I'm glad I did.