modified eng/plug suggestions

I am looking for the best spark plug for my new motor. The heads are aluminum 215 runners, the manufactuer recommends a champion c57c, The champion web site shows that as a "race" plug, with the new number c57cx, all the auto parts stores (high performance also) say they don't have that plug, and have never used it, and recommend "something else" but don't recommend something else. they also don't show any cross reference with autolite,NGK, bosch etc. Any suggestions. the motor is a 383 stoked/386 act @.40 over, holley 4150 - 750 cfm d.p. Victor intake, with hooker 1-7/8 primaries, 4" side-pipes.

This is what I get for this plug using an NGK cross reference:
NGK: R4118S-10
Thread size: 14MM
Hex size: 0.8125
Reach: 0.7500
Seat type: GASKET
NGK Electrode type: PALLADIUM
Tip Proj: No

Autolite: 2414
Bosch P/N: W07CS
Bosch STK: 7529
Champ P/N: C57C*
Denso P/N: W29ES-V
Denso STK: 4058
Motorcraft P/N: AG040
Motorcraft Stock: 67
NGK Type: MTCYC.


They also list a NGK R5671A-10 as a replacement for the C57CX which is listed as a "Hi Perf" plug.

I got this info off of a big spreadsheet found under the "NGK Cross-Reference Matrix (2.0meg)" link on http://home.att.net/~ngkaz/wsb/html/...ome.html-.html

well that helps, cause I am running a NGK R5671A - 7 not R5671A-10 , That they claim to be the cross reference. which means I am running a (hotter) plug, are they not suggesting a considerably colder plug with the "10" denotion?? (same plug, a race plug, but 3 pts colder) If so, again, this recommendation is just from the head (air flow reserch) co. they suggest this as a starting point. How significant is 3 pts. difference in a hot/cold plug as far as overall performance?? Hoe do you get the ideal plug on a compleatly modified engine??

[Jacko]

Cold plugs (racing / hi-perf) foul terribly in a street driven car.
They are expensive and you will load them up and foul them out a lot. What good is running a motor on 5-6 cylinders when there are a couple plugs that are fouling out on you?

Run a plug that burns clean, the hotter, the better.
Experiment with plugs until you find one that burns a nice light tan color. If it blisters the porcelin, you are too hot.
If its black and sooty, or wet, too cold.
By the way, that is a pretty large head @ 215.
Is the motor sharp? Volume is not as important on the street as is velocity.
I run a 190 head (Brodix) and love it.
Just wondering.

Jacko, thanks, for the input, experimenting with a few plugs is not that hard, just don't want to damange anything.

I am not sure what you mean by is the motor "sharp" I was going to go with the 200cc head, and my engine man told me with the set-up, large header primarys, (1-7/8) the intake, cam and 1.6 rockers, etc, that he would go "definetly" with the 215s, I thought he knows more than me.

[Jacko]

What I mean by "sharp" is....
Is it responsive from a start? Does it run nice and crisp at lower rpm range? Can you drive the car normally? Can you floor it at any low rpm range and get kicked in the seat of your pants?
Most "semi-pro" engine builders overkill street motors.
Your head size is typically too big. And I have seen this time and time again.
Don't forget, you don't need a business licence to be an engine builder, you don't even need an education to call yourself one.
All you need is an engine stand and some tools.
The better engine builders will always try hard to steer you away from too large of anything. Check to see how many RACES this engine builder's motors have won at the track.
That's usually a good indication of a man that knows what he is doing.

Here are the specs for your type heads:
355-406 c.i. 11.5 Minimum Flat Tappet / Roller 4000-7000 Oval Track / Bracket Race / Pro Street

Here is what I run on the street and is a good recommendation:
355-406c.i. 9.5 - 10.5 Hydraulic / Flat Tappet 6400 Maximum Street/Strip / Pro Street

Good luck to you. And hey, it's only money. You can always change them if your not happy.

Originally posted by jon79flavette
well that helps, cause I am running a NGK R5671A - 7 not R5671A-10 , That they claim to be the cross reference. which means I am running a (hotter) plug, are they not suggesting a considerably colder plug with the "10" denotion?? (same plug, a race plug, but 3 pts colder)

Actually, with NGK, the number after the "-" indicates the gap out of the box, so the R5671A - 7 and R5671A - 10 plugs are the same physical plug.

To see the number scheme for NGK plugs, go to:
http://www.ngk.com/sparkplug411.asp
Hit the last link at the bottom on the left under "Manufacturer's Numbering System".

[AKRAY4PLAY]

go to the AFR website and look under the tech support section for frequently asked questions. there will be a listing of all the alternate plugs that AFR recomends. i like the ones you have, the body of the plug is smaller resulting in more header to plug wire clearence. i do agree with Jacko on the head size, AFR 195's would be a better choice, but what you have will work with a carefully selected cam. run the NGK's and enjoy the motor, Brian