91 6 bolt timing cycle??

[scottsee]

does ayone know of a website that describes the 4g63t 4 stroke timing cycle. i know understand the cycle of a 4 stroke from reading my asc book, but it would benifical while building my 6 bolt if i knew it's exact 4 stroke timing cycle.

[EclipseRST]

1st thru 4th cylinders look like this:

While I'm assuming you are at TDC in cyl #1, the 1st cyl is on combustion/power stroke, the 2nd cyl is on the compression stroke, the 3rd cyl is on exhaust stroke and 4th cyl is on intake/gas stroke. So there for it fires in the certain cylinder each time the crank rotates 180 degrees from TDC as 1-2-4-3-1-2-4-3...

Since 1 & 4 cyl and 2 & 3 cyl are linked together there is no way to have the firing order 1-2-3-4 because when cyl 2 is on the combustion stroke, cyl 3 is going down with it. So cyl 1 & 4 move up and down at the same time/speed and cyl 2 & 3 move up and down at the same time/speed. (I put this in cause I know someone will end up asking why cant it fire 1-2-3-4)

So say you have the car at TDC in cyl #1, rotate the crank 180 degrees and you have combustion on cyl #2, rotate it another 180 degrees and you are on combustion stroke in cyl #4, rotate it another 180 degrees and you are on combustion stroke in cyl #3, then when you rotate it another 180 you are back at TDC and have combustion in cyl #1.

Sorry if that throws anyone off, its how I learned in school and I dont have a diagram for it. If you want me to go through and explain it better or if Kevin can do a better job go right ahead.

I look around for a diagram and see if I can find one somewhere on the net.

[kjewer1]

That sounds about right. I'll just add a note about the ignition system, since the topic is firing order. 1-4 and 2-3 are linked together as jake said, both are in the same position at the same time. While one is on the compression stroke, and the other is on the the exhaust stroke, both plugs will fire. Most poeple know this because you can swap the plug wires between the two paired cylinders and nothing changes. Its known as a wasted spark system, since the spark on the exhaust stroke is "wasted." This is also the reason there are only two coils on a 4 cylinder engine. Some poeple may wonder why the plug is firing on the compression/exhaust stroke and not the power/intake strokes, but remember that the plug is fired Before Top Dead Center, making the actual spark event part of the previous stroke. Just some useless info to start your day off...

[scottsee]

crap, I was curious to the 4g63’s valve timing cycle, not the 4 stroke cycle. Sorry for being vague.

The 4 stroke intake duration starts to open at 21 degrees before the piston reached TDC and remains open until it has travled 51 degrees past BDC. Then its exhaust Duration begins at 53 degrees before BDC and continues until 15 degrees after TDC which is 200 degrees of the crankshaft duration. Giving that a 36 degree overlap.

what i would like to know is what the 4g63's cycle looks like & how its timed.

[kjewer1]

Just look at the cam spec card for a HKS cam, or whatever. You can draw a diagram that looks just like the one above, except that each cam will only have its function, exhaust or intake. OVerlay them if you want to see both. Its not going to be anything special, just the actual numbers will vary from what you have above.