Baldy

Ok, I've heard a lot about advancing the timing, in pretty much any vehicle. What exactly does this mean? How's it work, and how does it improve perfomance? What's bad about it, that it isn't done to all vehicles?

UniqueTII

It makes pre-ignition more likely...that's the bad.

I'm not 100% sure about the good, so I'll leave that up to somebody else.

Baldy

so, when you advance the timing, are you making the spark plugs spark sooner?

UniqueTII

Yeah...unless I'm an id10t, which is possible.

j9fd3s

i think its simplest to think about it in a piston engine, the piston come up on the compression stroke, hits top dead centre (tdc)*, and goes down on the power stroke. you want the maximum impact from the fuel/air mixture ignition just as the piston is starting to move down, the problem is that the fuel air mix takes time to burn, so if you fire the sprk plug at tdc you wont get the maximum "push" on the piston until its some way down the cylinder already. the solution is to advance the spark in relation to the piston/rotating assembly, or fire the plug before tdc (btdc). another issue is that the fuel air mix takes a certain amount it time to burn*, yet the engine can speed up. so at higher rpms you need to fire the plug sooner than you would at idle.



mike



*tdc on a rotary is when the rotor face is closest to the spark plugs



*the burn time is dependent on the octane of the gas, air fuel ratio, temps, and pressures in the chambers, thusly there isnt a "right" timing thats good for everyone

Baldy

cool, thanks. That made a lot of sense. Why aren't engines timed that way from the factory? Too much risk on their part?

UniqueTII

They are timed with caution because people treat their cars like crap. Manufacturers don't know what octane of gas will be run, how old spark plugs would be, the condition of the cooling system, etc... Most cars run a little richer than they have to because of these factors too.

j9fd3s

yeah ed's right, they have no idea if you're gonna run the thing on rocket fuel or tequila.



mike

Baldy

quit putting ideas in my head!

j9fd3s

we've tried the tequilia its exactly the same as back to the future part 3



mike