Compression check and new iridium plugs


analogdesigner

analogdesigner

GT Owner
Mark IV Lifetime
Nov 15, 2005
951
San Clemente, CA USA
I wanted to do a compression check and change my plugs to the Denso iridium type as they have the smallest diameter electrode (0.4mm). So the compression check values are as follows (21,000 miles on odometer):

Driver side front to rear:
186
190
186
185

Pass. side front to rear:
189
189
189
190

Here is the difference between the older NGK iridium and the new Denso plugs:

Ford GT Denso vs NGK 2016-12-25.jpg

Jay
 
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Jay which plugs did you go with? It seem both NGK and Denso have two version of iridium plugs. Ones with platinum inserts on the ground electrode and those without.

I don't know the failure mode on the plugs, but in a modded engine with more boost I find the NGK TR7IX is use don't last too long maybe 2 to 3K miles before I get misfires at high rpms under boost. I took out the plug and they still looked great, but didn't work like new.
 
-ICE,

My friends that race small aircraft ended up using the Denso plugs. They are typically operating their engines at WOT >95% of time. I wasn't aware of the two types of iridium plugs and I can acquire more info this. I had problems about 10 years ago when I installed the Roush pulley kit (it increases the boost about 2 to 2.5 PSI over stock) with a slight amount of misfiring. Shadowman had recommended that I decrease the gap a slight bit, which cleared it up. This was when I had the stock plugs. I can run the iridium plugs with a 0.031" gap without any misfiring. They also have the "U-groove" ground electrode. The NGK plug in the image has about 12k miles on it and the center electrode doesn't have any wear on it. Now I drive my car fairly easy which probably helps a lot in regards to lifetime. So I just checked the NGK plug number that I was using and it's a TR6IX. What plug gap were you using? I found that a 15% decrease in gap can make a big improvement. I think that the stock ignition system is adequate for a stock setup however it begins to show its weakness at high cylinder pressures. I think that a smaller plug gap at about 0.022" to 0.025" would be better for higher boost setups.

I am still have my low boost problem which I reported on last year. My analysis is suggesting that I have a leak after the output of the supercharger. I did the compression check to make sure that I didn't have a dead cylinder. More on this problem later as I am probably going to pull the supercharger next.
Thanks, Jay
www.analogdesign.com

BlackICE said:
Jay which plugs did you go with? It seem both NGK and Denso have two version of iridium plugs. Ones with platinum inserts on the ground electrode and those without.

I don't know the failure mode on the plugs, but in a modded engine with more boost I find the NGK TR7IX is use don't last too long maybe 2 to 3K miles before I get misfires at high rpms under boost. I took out the plug and they still looked great, but didn't work like new.
Click to expand...
 
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I had no idea that Denso had such a broad selection of plug tip designs. My new plugs are the Denso IT22.
Thanks! J

BlackICE said:
More choices than I thought.

http://densoautoparts.com/spark-plug-electrode-configuration-identification
Click to expand...
 
Check out this chart:

http://www.globaldenso.com/en/products/aftermarket/plug/power/spec.html

The NGK TR7IX is the same heat range as the IT22
 
I think I have the NGK 6 in my car. I need to pull them and read them. Here's how:

http://www.ngksparkplugs.co.za/spark-plugs/
 
Heat range chart

Beach,

Yeah, you're correct as something is screwed up with the cross reference when I ordered these earlier this year. Denso's website says that it should be an IT16. The chart below shows that the IT22 is a couple of heat ranges lower which is a better direction to go. The porcelain on my NGK's look good. I will examine the plugs after a bit of driving. One thing that I should of caught is the gap on the Denso's were at an ideal 0.031" while the proper plug should be at 0.044". Thanks, Jay

Spark plug heat range.jpg



Beach-GT said:
Check out this chart:

http://www.globaldenso.com/en/products/aftermarket/plug/power/spec.html

The NGK TR7IX is the same heat range as the IT22
Click to expand...
 
More boost


Colder plug safer for detonation
Smaller gapped plug is for Spark blowout .

So for boost over 15 a colder plug and less gap is safer . I run 20 psi boost and never notice any cutting out even on older plugs at 7300 rpm with 93 octain. I have had cut out but it was a tune fuel spike not the plug. Dyno graph will show some cutout at the up top but lowing timing can also cure this. We always fight this problem with a system that has lower voltage and that is why our big prochargers needed big MSD boxes and 16 volt battery's . Spark blowout . I tune can also kill plugs .
 
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I'm running 19 pounds of boost on a Whipple Gapped at .25
 
From what I 'think' I understand about this thread is that we have some gentlemen still in the investigative stages. I went with NGK's a while ago and should probably start thinking about replacing them.

Would there be a consensus on a particular plug and gap for a stock running GT yet?

Thank you in advance.
 
Good question, but what about replacing with the factory ones for a stock GT ?
 
junior said:
Good question, but what about replacing with the factory ones for a stock GT ?
Click to expand...

Why not just use the OEM plugs gap to OEM specs?
 
I replace my NGKs at 3000 miles. They look fine but my car runs better with new plugs.

Ed
 
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