Bad Girl

I am wondering who has the best plug for 700hp and up blown motors. I am running 32 degree lock timing with 8 psi at 5800 rpm.
Currently running NGK R5671 A - heat range 8 for their plug. Resistor plug

any input ??

Hydrocruiser

For a supercharged engine you want to use a copper plug.

DO NOT USE platinum or iridium.

This is to make the electrode run hotter (it has nothing to do with the heat range, that's totally different).

This helps to burn the carbon deposits off.

I think the plug you have listed has a solid copper core..just check to be sure. Porsche' wrote a service bulletin for their Carrera Turbo and in it says copper rules for boosted engines.

Strip Poker 388

iTrader: (6)

I ran the R5674-8's in mine.

isnt the 71 a not projected tip?

KNOT-RIGHT

I like the NGK myself

5673-8 Plug is cold. This is what I use in cast iron head
10lbs boost intercooled. Timing locked at 32.
I wouldnt use a projected tip.

I find it easy to read the NGK,s due to the nickel finish.
I like to see the Electrode half colored.
and a 3/4 to full ring of soot on the last thread.
Insulators will turn a reddish tan due to the additives in the fuel.

I have a nice link refering to plug reading let me find it.

Gerry

KNOT-RIGHT

http://www.maxracesoftware.com/spark_plugs.htm

Here.

mv35

what is the correct way to jet primarys and secondarys evenly.871 blowers, merlin heads 510 c.i. ,850 demons at 8 to 10 lbs boost ,timing at 30 degrees,5500 to 5800 rpms.im running mr43t now.what plug would be best for me with this set up?

joe900sc

I run 5671a-7 in KE 800s 6lbs boost at 5800.

KNOT-RIGHT

Lean cylinders are 2 and 7. As stated use a NGK they have a
finish that is easy to read. Without Pyrometers and or o2
sensors it is tough. Remember "Lean is mean" Go a
a little fatter.

If I remember I have mine staggered in my Demon 850,s.
I spent a couple of days on the water tunning. I also marked throttles just before the secondarys open and did a motor shut down to get a mid range plug reading.
Dont forget to check wide open aswell. With twins you can shut one down without getting swomped.

Are your Power valves boost referenced?

Wilks

NGK reccomends R5673-8 in supercharged Mercury motors all the way to the 800sc. The 900sc changes to a 5671-9. The 71 has 1/4" longer reach.

Bad Girl

Thanks for the feedback. reading the plug isnt the problem. I was looking for the majority plug that seems to pop up in motors more often than any other in this HP range. I run the NGK R5671-8 in Aluminum heads recommended by the motor buider (Pfaff) but also I am in Ohio where water temps are typically cooler than CA. Instead of running the -8 I may decide to go one plug hotter to a -7.
Thanks again