Spark Plug Recommendation?

[Cal Tonsley]

Interested in getting your recommendations on where to start for spark plugs to suit my 410 - 360 + .040 4” stroke, -16.9cc dish pistons 10.5:1 with ported Edelbrock RPM heads and hyd roller 238/246 @ .050” on 108. Will be street use to 6000 rpm max and running sequential fuel injection with timing control through MSD 6

 

[BrianT]

I am running a very similar combo in my 408 and my builder used NGK BKR7E plugs.

Edit: Welcome to FABO!

 

[Steven190]

I am using NGK R5671A-7 #4091

 

[jimjimjimmy]

it depends on your engine but I would start with a champion rc9yc and go hotter if need be .
in champion the higher the number the hotter the plug .

 

[Krooser]

What reach are those plugs?

 

[72Dart6pack]

E3 plugs! Dude they are awesome!

 

[RustyRatRod]

It's impossible to give a plug recommendation here, because we don't have head details. What's the plug hole depth? It is a tapered seat or does it take a metal gasket? You posted the wrong side of the head for spark plug questions.

All that said, As for heat range, I would use something dead on top of the stock 68-71 340 heat range......with whatever the heck kind of plug that head takes.

 

[Cal Tonsley]

Thanks and apologies Rusty, I should have been more specific, as mentioned the heads are Edelbrock Performer RPM 60775’s which are designed to use a 14mm x 3/4 reach, gasket seat, spark plug. Regardless, as you’ve guessed, I was really just interested in getting an idea where to start as far as heat range goes.[/QUOTE]

 

[yellow rose]

What reach are those plugs?

3/4 reach with a 5/8 hex

 

[RustyRatRod]

I was sorta figurin that and because your compression is right on top of the early 340, start with the heat range for the stock 340. That should actually be very close.

 

[famous bob]

I was sorta figurin that and because your compression is right on top of the early 340, start with the heat range for the stock 340. That should actually be very close.

QUESTION for RRR , what is the diff. between ngk 6 heat range plugs , one sells for 1.95 , and the other for 2.95 ? both have the same electrode package . ????????? Figured you`d know .

 

[RustyRatRod]

QUESTION for RRR , what is the diff. between ngk 6 heat range plugs , one sells for 1.95 , and the other for 2.95 ? both have the same electrode package . ????????? Figured you`d know .

I bet the 2.95 one is the Nickle plated version.

 

[pittsburghracer]

AR22 Autolite

 

[Dicer]

Got tired of jumping around trying to find the correct plug on the 340. I went back to the shop manual and found they used Champion N-9Y, got a set from eBay. I really needed a base line to start from, if not, one heat range higher...until it works.

 

[crackedback]

I'd start with an NGK FR5 and adjust from there if necessary.

 

[RustyRatRod]

Got tired of jumping around trying to find the correct plug on the 340. I went back to the shop manual and found they used Champion N-9Y, got a set from eBay. I really needed a base line to start from, if not, one heat range higher...until it works.

View attachment 1715145078

If you are going a heat range hotter because of more compression, you are going the wrong way.

 

[leblanc]

Your best bet is would be a good copper core plug and I would go at least 1 or 2 levels hotter depending on your coil output. Your best bet might be to ask (google) a NGK or Champion expert. Giving them a call is usually better.

 

[yellow rose]

You could have used the C9Y (actually RC9YC is the number) as it's the same plug it just doesn't have that clumsy 13/16 hex on it.

 

[Dicer]

If you are going a heat range hotter because of more compression, you are going the wrong way.

Yes you are right! I love my ole girl, she's a Swinger, and she likes to drink. If she carbons the plugs, I'll treated her with something more spicy.....bless her mopar heart. LOL

 

[famous bob]

If you are going a heat range hotter
^^^^^^^^ because of more compression, you are going the wrong way.

Only 10.3 C.R. , started w/ ngk 7`s, trying to clean it up a bit by adjusting timing, mixture, and plugs, "all done on the handheld". I have used most of the other plugs in the above posts in other cars, I like ngk plgs.

 

[KnuckleDuster]

You could have used the C9Y (actually RC9YC is the number) as it's the same plug it just doesn't have that clumsy 13/16 hex on it.

Edelbrocks REQUIRE a 5/8" hex. 13/16 will not go in.

 

[lomchivok]

Mine is a 408 with 10.3ish compression and Indy LAX Heads from Brian. Milled to 59cc's W/202...160 valves. my cam is a hughes SER3438ALN-10 110/106. Was running NGK-ZFR6F-11
Had detonation and run on issues. Monkeyed around with initial/all in, vacuum advance can timing and run 92 E10 trying to get it to go away to no avail. I messed with the Fitech AFR settings to see if that would do anything...but no (not using timing control). Started at 18* initial with 35* all in. got all the way down to 12*... power was down and it still pinged and ran on. Finally the light bulb came on figuring that the plugs must be the problem and they were. went to the NGK-ZFR7F-11...1 step colder. I'm back up to 18* initial now with no more ping and no more run on.

 

[famous bob]

Edelbrocks REQUIRE a 5/8" hex. 13/16 will not go in.

Surely u jest !

 

[famous bob]

Mine is a 408 with 10.3ish compression and Indy LAX Heads from Brian. Milled to 59cc's W/202...160 valves. my cam is a hughes SER3438ALN-10 110/106. Was running NGK-ZFR6F-11
Had detonation and run on issues. Monkeyed around with initial/all in, vacuum advance can timing and run 92 E10 trying to get it to go away to no avail. I messed with the Fitech AFR settings to see if that would do anything...but no (not using timing control). Started at 18* initial with 35* all in. got all the way down to 12*... power was down and it still pinged and ran on. Finally the light bulb came on figuring that the plugs must be the problem and they were. went to the NGK-ZFR7F-11...1 step colder. I'm back up to 18* initial now with no more ping and no more run on.

I`m at 21 initial, 34 all in at 3400, 44 total for cruising , w/ a 1200 cfm throttle body, running about 3 hairs rich , the reason for the I step hotter plugs. running 91 octane real gas. (STILL LAWNMOWER GAS !)

 

[lomchivok]

I`m at 21 initial, 34 all in at 3400, 44 total for cruising , w/ a 1200 cfm throttle body, running about 3 hairs rich , the reason for the I step hotter plugs. running 91 octane real gas. (STILL LAWNMOWER GAS !)

When I was having the detonation issues I tried running the 92 clear I can get here locally. That seemed to make it ping more than 92 E10...but I did see an increase in mileage from 11 to 12.5 mpg.