Spark Plugs, Timing, and more

[Anthony @ LG Motorsports]

This is something that popped up a number of weeks ago and blew up into a big thread about spark plugs, so let's look at this a bit deeper because honestly a stock LS7/LS9 plug is not always the answer.


This is nothing new for us, but I thought I would show you how to possibly correct some issues with your own car when you are upgrading and modifying the engine. Especially when increasing HP and cylinder pressure it is important to go with a colder spark plug in almost every case to protect your engine from harmful detonation.


...THE TEST...
No big build, high compression, stupid timing table setup here....STOCK GM parts and tune.

These same things listed below are there to help you figure out what is right for your car and your build.



Test car....2008 C6 Z06 Corvette LS7
Stock plugs
Stock timing table
93 octane pump Dallas fuel
40k street driven miles.

This car developed a bit of audible knock, so HP Tuners was used to log the car to see exactly where the knock was going on and to what degree.
LOG FILE

Make note that we have knock across the board, not just at the top of the RPM range and it is happening not only under WOT but also at throttle tip in (noted by now far down the cylinder fill it goes)

To make a quick test we mixed 5 gallons of 104 octane fuel in the mix to see if it was mechanical or possibly fuel/timing related (remember this car still has the stock timing table and spark plugs in it)
LOG FILE WITH RACE GAS MIX

Here you can see that the knock is still there but greatly reduced from stock. Again still throughout the board but not as much in the lower ranges.


STOCK GM PLUG BEING REMOVED

Notice the detonation marks (bits of black)


Back ground checks...
Air/Fuel ratio checks out and is similar to any other stock car, reaching almost 11.4:1 when the car goes into cat over temp. So it is not running lean.

All plugs look the same, injectors check out and the car has plenty of fuel pressure.

02 sensors check out, and are functioning properly.

So now the question....what to do?

1. You can modify the tune and remove timing, which is also going to pull HP as well. Whats the point of having a fast car then?
2. Run race gas full time...sorry $7/gallon for a daily driver isn't fun
3. Run a colder plug to reduce spark knock.


In this case we are going to go slightly colder on the spark plug to a NGK TR6iX plug to hopefully reduce the amount of knock.


At this point the car has no audible knock, and feels much stronger in the mid range, which is probably due to the lack of 4-6 degrees of timing being removed.


Tomorrow I will follow up with a plug removed for inspection, and also a data log of the same drive conditions to see if we have in fact removed all of the knock from the car with no fuel or tune changes.


Stay tuned for final results tomorrow.





Some follow up reading
http://ngksparkplugs.com/tech_suppor...lugs/index.asp

http://www.ngk.com/sparkplug411.asp?...osch%29&mfid=1

http://www.summitracing.com/expertad...ug-Heat-Range/

[BlackM6RS/SS]

Good read

[cody.freeman1]

Can't wait to read your updates tomorrow!

[TornadoSS]

Nice info! Subscribed!

[Aries240SS]

Great info Anthony!
Makes me want to go log mine this weekend and check...

[Anthony @ LG Motorsports]

Now one thing I did not do.

Dyno the car. I wouldn't dyno a customer car nor my own car with that much knock retard...so we can not see HP figures before and after but I can tell you the car's reaction is light years different.

[Higgs Boson]

i agree that the stock high octane map is too aggressive for e10 pump gas. gm calibrates using a spec fuel which is ethanol free. this is exactly why the low octane map is so low. there is plenty of learning room for the ECM to learn down the knock to a safe area in between the high and low maps.

yes, it is true that running a colder plug will cool the combustion process and thereby reduce preignition. the only issue I have run into is on a street car, daily driver, the colder plugs can load up at idle and create minor drivability issues. sometimes they can be cleared up but sometimes not. I mean, if the easy answer is running a step colder plug, why doesn't it come from the factory that way?

what do you think, Anthony?

[ss/rs-matt]

[BLACK10]

we also prefer NGK tr6's on most of our builds. great info, thanks!

[K32 Camaro]

Originally Posted by Higgs Boson

i agree that the stock high octane map is too aggressive for e10 pump gas. gm calibrates using a spec fuel which is ethanol free. this is exactly why the low octane map is so low. there is plenty of learning room for the ECM to learn down the knock to a safe area in between the high and low maps.

yes, it is true that running a colder plug will cool the combustion process and thereby reduce preignition. the only issue I have run into is on a street car, daily driver, the colder plugs can load up at idle and create minor drivability issues. sometimes they can be cleared up but sometimes not. I mean, if the easy answer is running a step colder plug, why doesn't it come from the factory that way?

what do you think, Anthony?

What are these drivability issues?

[Higgs Boson]

Originally Posted by K32 Camaro

What are these drivability issues?

just anything related to a fouled or fouling plug. nothing one would ever notice in a hard driven weekend car or race car but something noticeable if you have to wait on thousands of other cars to start moving.....

there are a lot of mods that work great for our toys that may not be ideal for our appliances. all depends on what you do with your car.

[Anthony @ LG Motorsports]

Originally Posted by Higgs Boson

i agree that the stock high octane map is too aggressive for e10 pump gas. gm calibrates using a spec fuel which is ethanol free. this is exactly why the low octane map is so low. there is plenty of learning room for the ECM to learn down the knock to a safe area in between the high and low maps.

yes, it is true that running a colder plug will cool the combustion process and thereby reduce preignition. the only issue I have run into is on a street car, daily driver, the colder plugs can load up at idle and create minor drivability issues. sometimes they can be cleared up but sometimes not. I mean, if the easy answer is running a step colder plug, why doesn't it come from the factory that way?

what do you think, Anthony?

I have never ran into an issue of going this minor of a change in plug heat range on a street car. We will check the plugs in 20k miles and see.

You may...find that by doing this to a 100% stock car could effect emissions output on the car and cause it to rise. Remember also the factory has to not only meet HP and reliability issues but also a very strict emissions regulation, along with that saying the plugs in the stock car will last for 100,000 miles.

Would I possibly suggest this for your 80 year old grandmother that drives the car? No..but chances are she isn't heavy enough into the throttle to ever see knock to begin with.

Same goes for things like engine oil though...sure the factory puts 5w30 in the engines. Would I run a full weekend open track weekend on that in 110 degree heat? NO, not unless I like changing bearings and crankshafts.

[Anthony @ LG Motorsports]

Originally Posted by Higgs Boson

there are a lot of mods that work great for our toys that may not be ideal for our appliances. all depends on what you do with your car.

Exactly.....listen to what the car tells you that it wants.

Fact of it goes, for those of us hot rodding the cars...a stock plug be it a stock LS3 heat range or even a LS7/LS9 plug can be far to hot for even mild modifications.

[ss/rs-matt]

So what is the heat range of the stock plug? If I wanted to get a colder plug, how do I know its colder?