sar

iTrader: (1)

I have read that some people cut the grommets off of their spark plugs to allow for greater compression and closer spark.

I realize the gained compression is relatively low, but does anybody know if this does any good or is it just an unreasonable risk?

Do you do it and what effect have you noticed?

gildardo

Head of it to. Its supose to bring the plug closer to the chanber for better spark or something like that, don't quote me thow....



Gil

White_FC

All measurements are approximate...

Washer = 0.1cm
spark plug = 1cm

you will decrease the size of your combustion chamber by ....

around 6cc´s.... if that...

so.. not much at all...
This also doesn´t change the compression per se, because its 6cc´s smaller at BDC and TDC aswell...

so no good.

As for it bringing it closer to the combustion chamber.. well it may help, but theres plenty of high HP 13bs without this done to them..

Syonyk

Actually, the change at BDC & TDC is made more significant by the silly thing called compression.

Using some sloppy math here (because it's early, and I don't feel like looking up the exact numbers):

Engine displacement: 1300 cc/eccentric shaft rotation
~= 650cc/chamber

Using a compression ratio of 9.0:1 means that the chamber volume at TDC is 72.2 cc

Recomputing with a BDC volume of 650-6 (644) and a TDC volume of 66.2 (72.2 - 6) gives a compression ratio of 9.73:1

So, White_FC, I'm going to have to disagree with you about it not being significant. I'd say in increase in compression ratio of .7 is actually fairly significant, given that the difference between rotors is in that range as well.

Also, getting the plugs closer to the chamber can't hurt combustion efficiency at all - less space for oil to get swept into.

-=Russ=-

Syonyk

IGNORE THE PREVIOUS POST

My math was fine. The 6cc number coming in was completely junk.

1cm diameter plugs = 0.5cm radius plugs, for a surface area of 0.25*pi, or 0.785cm^2/plug. Two plugs, though the trailing one has such a small hole that it may not contribute much, gives a total area of 1.57cm^2. Using 0.2cm as the displacement gained by cutting the grommet off (seems to be about right), this gives us a displacement change of 0.31cc.

Now, *redoing* my math with this number, (650 - 0.31) / (72.2 - 0.31) = 9.03:1

Not huge, but still possibly worth a little bit.

-=Russ=-

sar

iTrader: (1)

Wow syonyk, thanks for the sweet math skills. Hmm, so with my s5 NA 9.7 compression it would bump me up to 9.744, i suppose that could be like 2 hp.

Its a really good point that with spark plugs closer to chamber the oil will stay closer to the rotating.

Does any rebuilder etc have an extra housing to take a pic of stock and after grommet removal to see the difference and to double check to make sure that it is apex seal safe or to see what other effects this could have.

I suppose with a .04 compression difference this could be like a 1hp mod, why doesnt everybody do it and why does ngk put the grommet on?

trainwreck517

iTrader: (1)

I suppose the gromment is there to add pressure to the plug.. kind of like a lock washer.. so it won't vibrate loose.

White_FC

Wow yeah im going to have to 100% agree with you on that one... dunno what I was thinking..

anyway the actual dia. = 13mm

so yeah, still two poofteents of **** all if you ask me.
Carbon build up on the rotor would probably account for more of an increase..