Spark plug ponderings

[Kayla850]

I'm sticking another 3TJ 4/6 together and have just put some new plugs in it (CR9E) but I was wondering if I could use CR9EKs (twin electrode plugs) instead and whether this would have any benefit at all.

My thinking is that the extra electrode would take up a little more volume in the combustion chamber and raise the compression ever so slightly. I'm also (relatively!) sure I read somewhere about 400 racers removing the seating washers from plugs before they fitted them to give a similar effect but I can't find anything anywhere about this so it might just be my rubbish memory playing tricks on me

[Evilchicken0]

Yes you can use those plugs, a racer recomended them to me.
I'd keep the sealing washer, you want the plugs to seal to the head or you'll loose the compression.
Can you get "kit" head gaskets for this ? A kit gasket will be thinner so raising compression, otherwise skiming the head will raise compression a lot more than the volume of an electrode. You'll need to build the engine with old gaskets and measure the valve / piston gaps with plastigauge. Calc your tollerance, skim and rebuild. That's where an endoscope would be really useful to check it all.

[Kayla850]

You'll need to build the engine with old gaskets and measure the valve / piston gaps with plastigauge. Calc your tollerance, skim and rebuild. That's where an endoscope would be really useful to check it all.

I'm lazy and just couldn't be bothered to do all that, plus I'm tight so I won't pay anyone to do it either I was thinking of a cheap and quick way to pep an engine up.

[Evilchicken0]

Time > Cost > Quality

The route is more time than anything else.
You'll need to set up the valves tollerances to the min limit and assemble the top end. You already have old gaskets so really all you need is some plastigauge. Once you know the thickness of plasti subtract the gasket thickness and tollerance and that would give you the skim depth.

Or just use a stock motor

[Morespeedvicar]

Hi Kalya, could you use surface disharge plugs? That would very slighty raise the compression. Tho as Borris says only way to do it really is skim the head/barrel. I dont know what there number would be tho sorry. The volume change of the extra electrode prob wouldnt be detectable.

Cheers
Ian

[Hogdigerdy Dog]

hello again people, the summer has been one hectic week joined to the next with barely any breathing space between, but things are slowing down now

not sure you'd get any benefit (compression wise) from the EKs as the twin earth electrodes aren't actually any bigger than the single on the 9Es as the EKs stop level with the centre electrode and the 9Es go over the top



if you see what i mean

[KIYOSHI]

CR10EK, remove the sealing washer, this lowers the combustion in the chamber and raises compression slightly.

Makes 1-2bhp difference on an 80bhp+ race engine.