jburge01

For new motor build with a flattop L28, shaved big valve - extensively worked over E31 head, .560 lift /300 dur cam, triple weber 45's. I am only familiar with the standard NGK BP5 BP6 type plugs. Should I be looking at racing style plugs for this motor. Any special plugs used to up compression a little? I'll be running race gas.

preith

Can't remember the part # exactly, but I'm running NGK BR9ES's, which may be little hot for my motor (about 13:1), but they seem to be ok. I wanted to get BR10ES's (colder)recently, but the parts store didn't have them.

tholt29

I wouldn't spend the money on the exotic plugs... I've been running basic NGK plugs for years. THey're cheap and readily available and I've never had a plug failure yet... My motor likes the B8ES The only difference between the B series and BP series is the P signifies the "projected tip". With flat top pistons I would guess the BPs would clear and will get the spark a little further into the chamber... My 14:1 pistons just barely clear the ground tab on the B8ES. You may have to try a few different heat ranges to get it just right.

Tom

jburge01

BP9's hot! I was running BP5ES on my raggedy old L24 to keep them from carbon fouling. I'll start out with the BP7 and go from there. Thanks.

DrSideways

Actually the heat range goes cooler as the number goes up. I also am running the 8. All of the plugs and stuff are out at the shop, so I forgot the prefix. I can't run the "P" plugs as they project out into the chamber too much. They are $2.00ea. so nothing too special.

The plugs will be something that comes to your setup like the jetting does.

Alan

preith

I'm glad we had this discussion, it looks like I was a little off. I find it hard to beleive I would need anything colder than what you run Alan. But in the Electromotive's manual for the DIS, it says you can go one colder because of the high discharge. Anyway, they seem to work great for me.

DrSideways

One thing I did not mention was that cold/hot rule is for the NGK plugs. Champion goes the other way. There is a nice table covering this in the Honsowitz book.

I run the Electomotive also. A couple other things to look out for with those is not to run wide plug gaps. .028" is fine. They also tend to eat plug wires. If the engine picks up a miss, try wires. They told me a long time ago to just run the cheap wires instead of the high dollar ones. Worked so far.

Alan

jburge01

I wasn't saying BP9 is hot. Quite the opposite. Anyway, I am mainly looking for ways to up compression with trick spark plugs. Since my head is nearly setup now, I'm not shaving that. I was thinking like a dead soft copper .010" head gasket but I've heard of problems with these leaking. Custom forged pistons may be in the picture soon anyway.

preith

I was told the same, run cheap, or higher resistance wires, somewhere around 1 to 2Kohms per foot. All I could find was Taylor street which you crimp the end on, and these are of a lower value. I guess you could always by a part house elcheapo custom fit set and re-crimp the ends.

I've been running .035, and it seems to be ok, but what you say makes sense. With less resistance at the plug, the spark is less likely to short out itself on the coils or elsewhere.

DrSideways

Whoops, my mistake. I was actually referring to Phil's post and hit the wrong reply tab.

As to increasing compression using the plug.... you won't gain a bit. The projected tip plugs don't take up enough space in the chamber to make any difference.

The main thing is to get the heat range close for efficient burning. Indexing the gap under the intake valve is a nice thing to do too.

In mine and I suspect Tom's engine we have to turn the open end down to keep the ground electrode from hitting the piston. This is how it is with even a regular tip plug in the 14/1 motors.

With flat tops you should run the projected tip as cool as you can. With a 10/1 motor a 7 or 8 in hot weather should work well. In cool weather it may not want to start well with an 8.

I always have had good luck with a Nissan headgasket. When tight it goes down to almost .015" from .030". So the .010" may not get you much anyway. I do use a cooper o-ring in a groove I cut in the block. This seems to work for the 14/1 so with a flat top it should do fine.

Anyway get out and test some parts. Most of all have fun running the car.

Alan