trying different spark plug

[hickskateboarder]

we changed the plugs in my brothers 88 jeep wrangler 4.2 I6 the other day, and it is a lot longer than the stock blaster plug. this got me thinking. the combustion chamber is about 7/8 of an inch deep from where the ground electrode is on the spark plug to the bottom of the head (where the piston would be at tdc) so i thought, what if we put the plug in with longer reach, therefore igniting at more towards the center of the air/fuel mixture instead of at the top? the flame front could then expand outward in all directions instead of just down, giving quicker combustion and more power.

so i tried it. it seemed meant to be b/c the threads are the same size. the jeep plug is like 3/8 of an inch longer, if i remember correctly. i didn't measure, just what i can remember from lookin at them side by side. after a rip thru the yard it seemed to run good and maybe pull harder top end, i can pull it up in 6th gear on this little bump in my yard, which i couldn't do before....

so i went on a ride with a friend, and that seemed to confirm that it pulls better up top. going up thru this one field where there is a figure 8 track, she would run flat and sometimes bog if i got it in 5th gear goin up the hill, but now pulls the whole way.

my only worry is that with it igniting closer to the piston it just might get the piston too hot and burn a hole in it, which would suck. but it ran fine beatin on it for an hour or 2, and she needs rebuilt anyhow, so i'll let you know what the piston looks like when i get around to tearing it down again. try to get some pics up soon of the plugs too.

until then, let me know ur thoughts.

 

[hickskateboarder]

plug pics

these arent pics of the exact 2 plugs i used, they are off the internet but the same kind of plugs. the jeep one is obviously the 2nd pic. you can see the center electrode sticks out much farther.

 

[ruthless_one3k]

by taking up more room in the head it would also raise compression and that could give a little bit of power. but just remember the top of the piston isn't flat so it sticks up into the dome a little bit so be careful not to cause mechanical damage

 

[cirame1]

mayb we r getting at sumthin here... i wonder how far it sticks down i may hit the piston under high rev? so possibly a longer spark plug could raise a lil compression and by sparking closer isnt that basically advancing the timing a lil?

 

[quam]

no i don't think you could say that it advances timing.....also, i would think that displacing a little more volume inside the head would DEcrease compression....
and even if you're not hitting the plug w/ the piston (it wouldn't matter if you were in high revs or not) now, if you did a proper p&p w/ good headwork it prob would hit then.
we'll see though! def post up pix and results after you tear her down. how many hours do you think you can get in before the tear down?

 

[FLOTEK]

without going into a longwinded explanation for why you shouldnt do this, i will just give you a warning your about to end up with a 3/8" diameter hole on the top of your piston if you keep running that plug

 

[hickskateboarder]

hahaha when i saw on the main page that the last reply was from flotek, i was like uh oh here it comes. lol. but as for clearance, there should still be about 1/4 to 3/8 between the top of the piston and the plug.

and guam, if you take up more area in the cumbustion chamber, you decrease the size of the combustion chamber, which means ur cramming everything into a tighter area, increasing compression.

so flotek, what kinda gap do i need between the piston and plug? would it really be that much hotter at the center of the piston? i would think after beatin on it like that it would've melted by now if it was that detrimental, although it has been cool outside....

 

[tjscott]

yep, plugs are sold in different heat ranges, meaning longer and shorter. theres a reason the heat range is reccomended for you blaster

 

[FLOTEK]

i realize theres still some space there but less trapped volume a concentrated heat source and spark close to the piston crown top is asking for *detonation* ,this is trouble brewing especially on pump gas as it will burn at a much faster rate and create more heat than high octane race blends if yo uwant more compression machine the head and do it right ..trust me theres a valid reason they recommend a NGK B8ES and not any old automotive plug found at walmart

 

[Superjet11]

You are making one giant hotspot in the combustion chamber.

 

[98blaster+4]

is there any difference in a bR8es plug as opposed to the b8es????

 

[pportera]

is there any difference in a bR8es plug as opposed to the b8es????

Yes the R stands for resistor.

 

[ruthless_one3k]

You are making one giant hotspot in the combustion chamber.

yeah, hot spots are bad umkay=))

 

[hickskateboarder]

WOW

well i tore it down to do a little more porting and headwork, the piston looked fine, the bottom side of the dome is a little more brown than it was before when running the ngk, but not by much. i put the ngk back in for safety sake cause i milled the head some more when i was playin with the squishband and combustion chamber.