Cadmaro

My new motor is almost done and i have no clue how to choose the heat range spark plugs i need. Any one care to help?
scat/ speedpro 383 rotating assembly
11:1 compression
Lightly ported brodix ik200
TPis miniram 2
Delta Cam custom grind 243/248 @.050 .546/.558 109 LSA

Brodix website has this to say
Spark Plug Starting Points:
CHAMPION RN12YC or AUTOLITE 3924
for Pump Gas

but i wanted someone to confirm the heat range before i screw something up. Also do yall think Ive made it close to my goal of 475-500hp at the flywheel?

Joe B.

This chart may be of some help for heat range vs. compression.

LT1 w/ Trick Flow & Edelbrock 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)

**NOTE: Use chart for static compression and adjust heat range for nitrous use accordingly.

ddahlgren

Duration at WOT is the biggest deal with a dyno is rougher than at a drag strip or street car. Cam overlap as well makes a real big difference as the engine will self egr at low speeds and cool things down. There are a lot of factors and the reccomendations will be very conservative.

WW7

The chart above seems inline with what I have been told.. I have 10.25 to 1 compression and Im running NGK FR5 plugs with no problems..When I take them out they look fine.. Your running 11 to 1 so I would say go with the next heat range.. Alot of guys don't know it but the higher the compression you have, the cooler plug you want to run.. Logic would dictate just the opposite to be true.......WW

Cadmaro

So something like an AR3911 would be good to start with? According to my cam card I have 26* overlap. Does this change my spark plug choice significantly? Or am I thinking too much? What other factors are important?
Thanks for the help so far! I really appreciate it!

Zix

I run NGK BKR7E-11 plugs in my 383 (7 heat range). They are gapped almost perfect out of the box and hold up very well to my engines heat.

leesvet

exactly...

rule of thumb,
the hotter the plug the colder the exhaust, meaning more is being combusted and not discharged. Colder the plug the hotter the exhaust..

The trick is not to go TOO hot and have to deal with PING (pre-ignition from a plug that never cools off between firing) which is different than knock, or one thats so hot that you "hole" a piston from the plug tip acting like a welding electrode over the aluminum piston dome.

I always run the coldest possible plug for safety margin...if the insulator is burning clean, the exhaust is not rich, and combustion temps are not too high forcing excess EGR activation, then its all good.

Use the chart then run it and go back and pull a couple plugs to take a look. If they are the right color and you are satisfied with the tune, its good to go. The best possible heat range has a doz factors to be considered, such as normal operating range, tune, cam, exhaust, ambient temps, EGR presence, operating temps. Unless you;re running nascar its not critical to try and get that detailed. I've seen the true tuners actually run different heat ranges in different cylinders where an inner cyl might be hotter than outter cylinders...thats getting extreme.
.

Interesting to see someone wanting to do it right with a new build. I see too many folks that assume the same 'ol plug is the correct plug for the new build even though it is a different engine. They'll usually work ok but not as good as they could if they were the right heat range for that motor.

Cadmaro

Thanks for all the help! Not sure I'm extreme enough to have different plugs for different cylinders, but Id do it if there is a big enough difference in em. Guess I'll start with the "8" to see how she likes it and go from there.

WW7

Good choice... I just wanted to say that I have tried most brands of plugs and have had the best results with NGK V- Power plugs....WW

C409

....... Keep in mind that NGK plug numbers go up for colder while everyone else's go down for colder ... i.e. ... NGK TR6 is colder than TR4 ... while Champion RC9YC is colder than RC12YC ...

ugleevette

I know this is an old post but was wondering where this info was from?