So sence im swapping headers im gonna change plugs & wires & idk which plugs to go with the NGX TR55IX or the Denso IT16 & yes there both Iridium plugs which is what oem was, so which is better??

 

NGK and Denso are the same company, but just be sure to go to a colder heat range from stock, and the NGK equivalent of the Denso plug you have there is a TR6IX, which is a colder range than the TR55IX. You can run a colder plug with iridium than copper without fouling, i'm running TR7's, looking to go to TR8's, remember with plugs, if you go too cold, you have to replace the plugs and nothing else, if you go too hot you have to replace most of the engine. the colder plug you run the more heat gets pulled from the combustion chamber to the head, meaning you can run more timing without predetonation and make more power assuming you can tune the car.

when you put headers on you have to drop to a colder range or you may melt down the strap on the plug, found this out the hard way on my first engine when i threw headers on, ended up having to go 3 ranges colder to get the plugs to not melt

 

Hi `Mike, they are both ranked great plugs.
My grandfather used NGX in his Corvette & he always does his homework b-4 he invest...
I think you should just flip a coin `if you can't decide


Spark Plug Heat Range - Where do I start?

LS1 Stock and AFR
Thread – 14mm
Reach - .708”
Socket – 5/8 hex
Seat - Taper
Stock Heat Range: 5
Gap: .060
Plug: NGK TR55 (stock number 3951); NGK TR55IX (stock number 7164); Autolite 764; Denso IT-16 (stock number 5325)

Nitrous (one step colder)
Heat Range: 6
Gap: .035 - .038
Plug: NGK TR6 (stock number 4177); NGK TR6IX (stock number 3689); Autolite 103; Denso IT-20 (stock number 5326)

Nitrous (two steps colder)
Heat Range: 7
Gap: Consult
Plug: NGK BR7EF (stock number 3346); NGK TR7IX (stock number 3690); Autolite AR94; Denso IT22 (stock number 5327)

Nitrous (two and a half steps colder)
Heat Range: 8
Gap: Consult
Plug: NGK R5724-8 (stock number 7317); NGK TR8IX (part number 3691); Denso IT-24 (stock number 5328)

Nitrous (three steps colder)
Heat Range: 9
Gap: Consult
Plug: NGK R5724-9 (stock number 7891); Autolite AR93; Denso IT-27

Nitrous (four steps colder)
Heat Range: 10
Gap: Consult
Plug: NGK R5724-10 (stock number 7993); Autolite AR92


LS1 w/ Edelbrock and Dart Heads
Thread – 14mm
Reach – 3/4”
Socket – 5/8 hex
Seat – Gasket

Stock – MFG Recommendations: approx under 9:1 compression
Heat Range: 4
Gap: Consult ignition mfg.
Plug: NGK FR4 (stock number 5155); NGK BKR5EIX (stock number 6341); Autolite 3926; Champion RC12YC (stock number 71); Denso IK16 (stock number 5303)

MFG Recommendations: approx 10.5:1 compression
Heat Range: 5
Gap: Consult ignition mfg.
Plug: NGK FR5 (stock number 7373); Autolite AR3924 (Racing Plug); Autolite 3924; Champion RC9YC (stock number 2075); Denso K20PR-U (stock number 3145); Denso IK20 (stock number 5304)

MFG Recommendations: approx 11:1 compression
Heat Range: 8
Gap: Consult ignition mfg.
Plug: NGK R5672A-8 (stock number 7173); Autolite AR3911; Champion C63YC (stock number 796); Denso IQ24 (stock number 5314)

MFG Recommendations: approx 12:1 compression
Heat Range: 9
Gap: Consult ignition mfg.
Plug: NGK R5672A-9 (stock number 7405); Autolite AR3910; Champion C61YC (stock number 785); Denso IQ27 (stock number 5315)

MFG Recommendations: approx 13:1 compression
Heat Range: 9 - 10
Gap: Consult ignition mfg.
Plug: NGK R5671A-9 (stock number 5238); Autolite AR3933; Champion C59CX (stock number 296); Denso IK27 (stock number 5312)

MFG Recommendations: approx 14:1 compression
Heat Range: 10
Gap: Consult ignition mfg.
Plug: NGK R5671A-10 (stock number 5820); Autolite AR3932; Champion C57CX (stock number 295); Denso IK-31 (stock number 5321)

 

Do o need to drop a heat rang with headers & a stock ls2 head swap?

 

what will the compression be at? i don't know the LS line like i do the 3800's


i've always seen people go 1 colder for every level of compression raised (like going from 8-9 comp), and one colder for headers as well, a colder thermostat will help the plugs do their secondary job even better.



and i will say again, err to the side of being too cold, the very worst that will happen is a fouled plug and you'll have to buy a range warmer.
if you start too hot, you will destroy the heads, bearings, and pistons

 

Its 10.5:1 i believe, & ill go 160* tstat when i swap tb so prob wouldnt be bad to go one colder

 

`Mike,
To be safe (?), I'd check a GTO Forum & see what others with same/similar setups are doing...Good Luck

http://www.ls1gto.com/