Hi

 

What would be the best Spark Plugs?

 

Spec-

 

4kc head, compression at 11:1

Electronic Ignition

Worked engine cam, overbore etc etc

 

Thanks

Should be nothing wrong with a stocko bp5ey

Should be nothing wrong with a stocko bp5ey

 

Thank you,

 

.... sorry to sound stupid and may be over complicating it, but am I right in thinking there are long reach plugs for the 4kc head, will this cause a problem now that the head has been skimmed to increase the compression. I am sure it's an obvious answer :)

You might want to go one plug colder in the heat range.

I don't think you could skim a head enough for pistons to hit the plugs. What you really should do is fit all four plugs and make sure they protrude into the combustion chamber the same amount. Use shim spacers to get them even. Then do your combustion chamber sizing to get all four chambers the same volume using those plugs, so you have 11:1 on all four cyl.

 

Parrot's right, you should try a heat range colder. If it fails when cold or at low revs you can always go back up..

Thank you guys for all your advice. As always another problem resolved here :)

Youll never hit the plug the valves will go first. Another old school trick is to face the spark to the exhaust port

Always found the twin electrde worked very well.

Thanks again, any particular brand or model of the twin electrode?

What you want to do a on a worked motor is find the correct plug to suit, the plugs trap heat to burn off deposits

so a standard plug works in a standard motor. When you increase the motors performance the combustion chamber

temperature goes up and you use a colder plug so the plug will operate at the correct temperature. Its all in the plugs trap

area, its bigger for hotter and smaller for colder, the rest of the plug is the same.

 

Hot burns off deposits, too hot breaks the plug down

Cold keeps the plug together, too cold causes fouling from deposits

 

Best to buy 2 heat ranges colder from standard using a basic cheap plug and go from cold to hot until the plug stops fouling.

Then buy your fancy electrode style plugs if you like or replace the basic ones more often.

 

The shim and facing thing may refer to spark plug indexing, where you buy a set of shims to allow all the spark plugs to face

in one direction to improve performance. The shims just allow indexing, the extra height spacing is irrelevant. May improve

by a small amount in some applications but often dismissed in lower hp builds.

 

I prefer ngk over bosch, personal thing I guess!

Edited November 30, 201411 yr by styler

Awesome, thank you for taking the time to share, great advice much appreciated

I"m running big comp on my 5k and I've never had any issues with the bp5ey. I did go with some BP6eys for a while but not really any difference.

 

It's tuned well as well.

Yeah if it doesn't foul or burn up its good to go! Running from cold to hot plugs is the safe way of finding out :)