Plug choice and gap 402
Thread Starter
Racer
Joined: May 2012
Posts: 427
Likes: 10
From: Texas
Plug choice and gap 402
Im looking for some input on a spark plug and gapping. I’m looking at a NGK TR55 and TR6, I’m running a LS2 NA 402, 11.4 :1, healthy cam should be around 625 crank hp. Plan on running 93 octane, in Texas.
Thanks Rich
Thanks Rich
Racer
Joined: Jul 2018
Posts: 289
Likes: 33
From: Virginia Beach
Team Owner
Joined: Mar 1999
Posts: 22,025
Likes: 192
From: At the beach in little Rhody
TR6. The TR55 is a hotter plug (1st 5) and the gap is large (2nd 5). The TR6 is one range colder (recommended by NGK for every 100 hp added over stock) with a smaller gap. I am running TR6 in my setup.
Last edited by vettenuts; Dec 8, 2018 at 03:46 PM.
Race Director
Joined: Apr 2017
Posts: 10,247
Likes: 888
From: Hickory NC
2025 C5 of the Year Finalist - Modified
2022 C5 of the Year Finalist - Modified
2020 C5 of the Year Finalist - Modified
St. Jude Donor '17 thru '26
Hi Rich:
Same as vettenuts, I use the TR6 in my head/cam/intake car (about the same CR as yours). Talking with a few performance engine builders in the area they also recommend the TR6 for modded LS engines.
Cheers, Larry
Edit: Noticed I forgot to address your question about gap. Currently running .040 which is the NGK out of the box setting, and also corresponds to GM's 40 setting for ACDelco plugs. I know some are experimenting with everything from .038-.045 but I'm good at 40, for now.
Also I use the GM spec 11 ft/lb torque.
Best wishes with your 402!
Same as vettenuts, I use the TR6 in my head/cam/intake car (about the same CR as yours). Talking with a few performance engine builders in the area they also recommend the TR6 for modded LS engines.
Cheers, Larry
Edit: Noticed I forgot to address your question about gap. Currently running .040 which is the NGK out of the box setting, and also corresponds to GM's 40 setting for ACDelco plugs. I know some are experimenting with everything from .038-.045 but I'm good at 40, for now.
Also I use the GM spec 11 ft/lb torque.
Best wishes with your 402!
Last edited by Route99; Dec 9, 2018 at 07:55 PM. Reason: Added comment
Drifting
Joined: Aug 2000
Posts: 1,601
Likes: 52
From: Jefferson City MO
I have almost the exact same setup 4 squared chamber, Trickflows, big cam, high compression and other stuff. Went with TR55, but gap was too big. Car runs best at .038 to .040 and when narrowing the gap on TR55's, the electrode became shrouded. As mentioned, TR5 or TR6 works the best.
Now question for you, you able to get that monster to hook?
Now question for you, you able to get that monster to hook?
Last edited by Andrew; Dec 11, 2018 at 08:31 PM.
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
GM changed the reccomended plug gap on a LS engine from .060 to now ,040---So that is what we run them at--no issues
As far as TR55 vs TR6---- The TR6 is one heat range colder made to get rid of heat better at high RPM's--However IF your car is used on the street mostly The TR6 will have a tendency to foul---The hotter TR55 will clean up better and have a less tendancy to foul while normal street driving-----We only use TR6 plugs on boosted engines or on highly modded N/A engines that are ran typically over 5000 RPM's most of the time--
As far as TR55 vs TR6---- The TR6 is one heat range colder made to get rid of heat better at high RPM's--However IF your car is used on the street mostly The TR6 will have a tendency to foul---The hotter TR55 will clean up better and have a less tendancy to foul while normal street driving-----We only use TR6 plugs on boosted engines or on highly modded N/A engines that are ran typically over 5000 RPM's most of the time--
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Le Mans Master
Joined: Jul 2010
Posts: 6,021
Likes: 727
wow 600ish. Just my personal opinion you might be disappointed. If I remember correctly there was a member that build a 440 was only around high 600ish. Wow I would be surprise but you never know.
Drifting
Joined: Aug 2000
Posts: 1,601
Likes: 52
From: Jefferson City MO
I would not be surprised. My build is very similar and the car has laid down well over 500 rwhp on a Mustang Dyno, that is known to be stingy (my stock z06 with Vararam, LTs and tune did 362 on the same dyno and conditions). This places the crank HP over 600. The nice part is over 500 rwtq from 3k rpm up. As mentioned above, the hard part is making the tires stick. The torque comes in hard and very fast!
Last edited by Andrew; Dec 12, 2018 at 03:58 PM.
Thread Starter
Racer
Joined: May 2012
Posts: 427
Likes: 10
From: Texas
I have almost the exact same setup 4 squared chamber, Trickflows, big cam, high compression and other stuff. Went with TR55, but gap was too big. Car runs best at .038 to .040 and when narrowing the gap on TR55's, the electrode became shrouded. As mentioned, TR5 or TR6 works the best.
Now question for you, you able to get that monster to hook?
Now question for you, you able to get that monster to hook?
just called NGK and they recommended a TR7ix part number 3690, I’ve not seen that one before.. haven’t broken it in yet and done final tune so no answer yet in Hookin..
Drifting
Joined: Aug 2000
Posts: 1,601
Likes: 52
From: Jefferson City MO
Thread Starter
Racer
Joined: May 2012
Posts: 427
Likes: 10
From: Texas
no nitrous or FI, not going with tat plug they recommended, staying with copper.. guessing TR6 or 5, waiting to see what my tuner has to say..
Drifting
Joined: Aug 2000
Posts: 1,601
Likes: 52
From: Jefferson City MO
I have used both. The TR5 is cleaner but the TR6 is more consistent. Good and bad either way. Since I use the car infrequently, leaned toward more consistency and just change out the plugs more often.
Le Mans Master
Joined: Jul 2010
Posts: 6,021
Likes: 727
I would not be surprised. My build is very similar and the car has laid down well over 500 rwhp on a Mustang Dyno, that is known to be stingy (my stock z06 with Vararam, LTs and tune did 362 on the same dyno and conditions). This places the crank HP over 600. The nice part is over 500 rwtq from 3k rpm up. As mentioned above, the hard part is making the tires stick. The torque comes in hard and very fast!
Le Mans Master
Joined: Aug 2005
Posts: 5,375
Likes: 328
From: CA.
St. Jude Donor '13-'14-'15
Just some old school knowledge on how we used to read plugs however still relevant on todays computer controlled cars
To read the AFR ratio or fueling we would want the color on the center electrode to be about 1/4 inch from the bottom of the porcelain--and the color should be a tan/brownish color
As far as timing goes to read this correctly you must have a new set of plugs and run them at WOT for a few blasts and then shut it down----- On NGK plus you can eaisly read new plugs as the cadium plating burns off cleanly
Perfect timing would be when the "color change" occurs just at the bend of the strap--If the color change occurs further down towards the tip it does not have enough timing If the color change occurs further down towards the threads then you have Too much timing--
To read the AFR ratio or fueling we would want the color on the center electrode to be about 1/4 inch from the bottom of the porcelain--and the color should be a tan/brownish color
As far as timing goes to read this correctly you must have a new set of plugs and run them at WOT for a few blasts and then shut it down----- On NGK plus you can eaisly read new plugs as the cadium plating burns off cleanly
Perfect timing would be when the "color change" occurs just at the bend of the strap--If the color change occurs further down towards the tip it does not have enough timing If the color change occurs further down towards the threads then you have Too much timing--
Acct Suspended APR 2026 by request
Joined: Dec 2010
Posts: 10,367
Likes: 1,272
2020 Corvette of the Year Finalist (performance mods)
C5 of Year Winner (performance mods) 2019
fwiw I ran the tr6 up to around 800rw and they did fine but started giving me problems higher than that so I switched to br7ef's which are the same heat range as the tr7ix, I see no need to go to that heat range in your case