bajaman

Hard to see in this pic, but why do the trailing spark plug holes have such a small little orifice in them, as opposed to the full diameter, wide-open port of the leading plugs?

dgeesaman

iTrader: (7)

My guess is to reduce compression losses as the apex seal sweeps over it. The trailing plugs are basically there for 'cleanup' ignition, and so the smaller exposure is not a big deal.

Dave

Kento

I'd agree with that theory. If you look at the animation on Rotary Engine Illustrated's site, you can see that the trailing portion of the power "stroke" occurs right as the apex seal goes over the trailing plug hole.

neit_jnf

iTrader: (17)

There's a pressure difference between adjacent chambers, intake vs compression. When the apex seal goes over the trailing spark plug hole there's a compression leak so the hole diameter is smaller to minimize this leak.

At the leading spark plug position both adjacent chambers have the same pressure when the apex seal crosses it. Since the pressures are the same there's not a compression leak so the hole is full sized.

cewrx7r1

iTrader: (2)

The winner of the correct answer!!!!!!!!!!!!!!!!!!!!!!

bajaman

Excellent information guys, thanks!

dgeesaman

iTrader: (7)

Hmm, that's basically the same thing, except I didn't talk about the rotor position issue.

Dave

SAMIboarder

iTrader: (2)

when people run all 9's, do they fit right in the leading holes w/ no problem then?

YoshiFD3S

iTrader: (19)

I'm interested in knowing that myself.

I've got 4 brand new NGK 9's that I've been meaning to put in, along with some thick thick Taylor Pro spark plug wires.

TwinTurbo_SE7EN

9's fit in the leading hole with no problem.