DIYEFI.org Forum

I've been thinking of the pro's and cons of using fuel only as a RPM limiter, no butter fly, no idle bypass, ect. I'm sure there are good reasons for decreasing intake pressure for idle, but I don't know them off the top of my head.

I seem to recall redundant system(s) are handy for limiting power in the event an injector is stuck open. Also controlling the air is easier than controlling the fuel charge (partly Xtau issues, partly fuel metering tolerance issues).

I also seem to remember that burning lean can be harder to ignite and burning lean can cause erosion. Both leading to engine damage.

However, and humor me, if you drilled a hole down the center of a spark plug, then installed it in an engine with a center mounted spark plug, couldn't you inject fuel through the plug? Placing your charge in a tower in the center of the cyl cavity. Then when you spark, you would spark in an area with a higher concentration of fuel, (where it's not considered lean) which would then increasing the chances of combustion? As well as reducing the ping on the side walls, preventing erosion and emissions due to the extra air cushion around the charge.

I think VW does a similar thing, called GDI. Any how, I think about it because I've got a small engine with a center mounted spark plug. The plug on these engines is also quite short, making it easier to drill a hole down the center.

Thoughts?

Lowest vac = least fuel wasted idling.

As for the rest, yeah, like you said, just go and buy any modern DI stratified charge engine and be happy :-)

It works because when you ignite it's rich and won't knock, and when the flame gets past the richness, the piston is well beyond tdc and it won't knock.

The result is 13:1 compression and 91RON/86AKI gas and good performance with no knock.

However, they aren't all that reliable yet and the fuel systems run enormous pressure etc etc.

Fred.