Hi guys. I had a couple questions about spark plugs. First of all, let me tell you about the background of the situation. Over the last year or so I've been datalogging in tts datamaster. When I'd look at the dyno curves generated, the hp would drop off above 4400 or 4600 rpm or so. That's where the hp would peak. There are no inlet or exhaust restrictions and I have cnc ported lt4 heads. In addition, I have a crane hi 6 ignition and crane coil. I had a feeling that I was getting spark blowout since the hp curve didn't keep climbing like a centrifugally supercharged car should. I had a t trim on there.

Today I pulled the plug and all the plugs look like they're pretty black (like the car is running rich). I thought that was okay since it's better then seeing white specs on the electrodes. What did catch my eye was the the majority of the plugs were now at approximately .041 or .042. If I recall correctly, I tried to gap them between .030 and .034 when I installed them.

I do have a few questions.

1. Does the gap open up over time as miles are racked up?
2. On 7 of the plugs, they say champion "rs12 pyp". On the 8th plug, it says "rs12 eyp". What gives? What does it mean?

Also, I got the car running briefly with the ysi(I need longer plug wires so I don't burn things up before I run the car on the street). In anticipation of high boost (15-20lbs), what plug would you suggest and what is the part number that fits my lt4 heads. I know I've posted this before and I got a couple great suggestions, but I never got the part numbers.

The big gap on these plugs somewhat answered why my hp is dropping off above 4500. The wierd thing is that never did it feel like a rev limiter or anything like that. It'd still pull to 6000 although not as strong as it should
.

Also, I have to take the smog test. Will plugs 2 ranges colder increase my nox at all or any of the other emissions? If so, I'll toss some stock plugs in for now and toss the blower plugs in after I pass smog.

Thanks to all in advance!

 

Hi Russ,

Yes the plugs will erode over time, if they were platinums it could be possible that the platinum "puck" may have come off thus increasing your gap.

I'm at about 11.5 pounds of boost with my "T" trim, I'm running NGK Iridiums BKREIX's but these are GASKET not the taper fit like on your LT4 heads. So you would need to cross reference for the taper plugs.

I would say that with that much boost you would probably want to go at least one step colder that you are now... Atlot will depend on what boost you actually get too...

Are you sure your AFR is good above the 4500 mark? Maybe you are running too rich if you are not seeing knock... or possibly you are running to much water injection?

I'm at 18 gph and i have mine injection kick in at about 3 pounds..

MO

 

Yeah, i really need to pickup a wideband.....

I'll probably call ngk tommorrow and get the part number on those plugs. I've heard a lot of good things about them. I'm going to try to really push tuesday and wednesday to get everything together and running. I only have to work until 2 on Tuesday.

 

hmm... their part number reference guide is a little confusing... based on my situations, it looks like it'd want to look for plugs TR6-1-IX, series BREFIX.

http://www.ngksparkplugs.com/docs/te...tnumberkey.pdf

I'm trying to find some iridium plugs that fit my lt4 heads and are colder than stock. The ones gapped at .031" from the factory would be perfect....

 

The 6 is one heat range colder than stock. I don't think you can get into a colder plug without getting into NGK's race plug line. Emissions wise the only thing you need to be aware of is the chance of fouling if you're too rich with the colder plugs.

 

Sorry guys, I totally messed up on that part number...


Mine are: BKR7EIX but these are gasket not taper fits...

Sorry for the typo... I ran these plugs and passed emmissions...

I want to say the taper type are TR7's

MO

 

Here's what NGK said....

Hello,

For this application witht hat much boost pressure I would suggest
trying a TR7IX stock# 3690 This plug is two heat ranges cooler than the
stock recommended plug and will come gapped out of the box at .039" I
would not recommend gapping the plug up or down more than about .008"
as
the relationship between the center firing and ground electrodes can
become distorted and can cause poor performance and also misfires.

Typically with an iridium fine wire type plug you will be able to run
a
slightly larger gap than you would with a standard nickel plug because
they require less initial voltage to be able to fire the plug. I would
try first gapping the plug to about .040" as a starting point as the
factory gap for this vehicle is around .055-.060" I believe. A good
"old
school" rule of thumb is to close the gap around .004" for every 70 hp
that is added. Hope this helps, thank you.

Best regards,


Brandon Peeler

Technical Support Representative

Aftermarket Division

NGK Spark Plugs (U.S.A.), INC.

46929 Magellan Dr.

Wixom, MI 48393

Bpeeler@ngksparkplugs.com

 

wow, $9.19 a plug....

 

Yeah not cheap, as I thought the TR7's....

I'm at .039

 

That's what I installed them at. Out of the box they're supposed to be at .039 but I actually found them to be a little tighter then that; approximately .037-.038. I figure if they'll sucessfully fire at .003 or .004 more than a regular plug, I should be fine. I was figuring that it would be the equvalent of regular plugs at .034 or so... Either way it's tighter than my old plugs so I'm on the right track.