Twin Fire v6?

[99BlueSuperSix]

<blockquote>quote:</font><hr>Originally posted by John_D.:
A four stroke is still a four stroke. The cylinder can only fire and produce power on the compression stroke. There is no way to get the cylinder to fire more often than that. If you fire two cylinders at once, then you open up a gap in the overall engine revolutions where no cylinder is firing. Because instead of having the firing spread out equally across the degrees of revolution, the firing is being bunched up in pairs.

Imagine a 2 cylinder engine, for example.

Normal firing sequence:

Cylinder 1 fires on its compression stroke, while cylinder 2 is on the exhaust/intake stroke. Cylinder 2 fires while cylinder 1 is on its exhaust/intake stroke.
For every revolution of the crank, one cylinder is firing.

Double firing sequence:

Cylinder 1 and cylinder 2 fire.
Then both cylinders go through their exhaust/intake cycle at the same time, while nothing is firing.
On one revolution of the crank, both cylinders fire. On the next revolution of the crank, no cylinder fires. It is probably smoother, since opposing pistons can fire simultaneously.

But no more power, since no more filling/firing is taking place per rpm. 2 firings per 2 revolutions is the same as one firing per 1 revolution in the standard example.

The double fire is counteracted by the double dead time.<hr></blockquote>

not necessarily, because when cyl 1 fires, it turns the crank 180degrees then cyl2 fires to turn it the other 180. if they fired at the same time (assuming you had a cam that would open the intake valves on both cyls at the same time at they would both be on the downward intake stroke at the same time, then compress at the same time, you would definetely break a rod or the crank or a bearing cap or one of the other many moving parts down in there.

[Clint Porter]

[QUOTE]Originally posted by John_D.:
"A four stroke is still a four stroke. The cylinder can only fire and produce power on the compression stroke. There is no way to get the cylinder to fire more often than that. If you fire two cylinders at once, then you open up a gap in the overall engine revolutions where no cylinder is firing. Because instead of having the firing spread out equally across the degrees of revolution, the firing is being bunched up in pairs."


Your statment would be true on a 2cyl engine, but there are 6cyl's, this means there are three 2 cyl groups, these other groups fill in the dead time you explained on your 2cyl example

And wether 1 cyl or 2 cyl turn the crank, its still gona get turned.With a 1 fire at a time, each cyl is going to turn the crank 60 degrees to make the 1 compleate engine cycle. Now with twop cylinders firing each group will turn the crank 120 degrees to compleate the engine cycle. Now since you have 2 cyl's turning the crank at the same time, your theoreticly going to make almost twice the power and put twice the strain on the crank shaft... am I right?

[thebigwaldo]

Does anyone know what the other pistons are doing when #1 is on it's compression stroke?

If another just happens to be on the exaust stroke, then it's just a matter of cam timing to have the valves closed for a compression stroke.

Then you gotta get the comp to fire the plug and shoot some fuel in...and bang, we got a dual crank motor.

Or so it seems....

[black34v6]

ill throw my .02 in here if anyone cares to read it.

im reading all these posts, and im asking myself why youd wanna do this - i mean, im sure you have your reasons...

to answer your query, yea you could fire two pistons at the same time, youd need a matched crank/cam to do the job, and a custom program to go with it. would not necessarily put anymore strain on the crank than it does already. the crank is already setup to absorb explosion force from the cylinder and convert it into torque.

i dont see where there would be added strain.

fyi for 3.4L nuts (and for those of you misinformed) - Fin/Tiago are correct, firing order for the 3.4L OHV in any form is 1-2-3-4-5-6.

HOWEVER. Toast is also correct. the reason for the grouping of ignition coils, is that, on the firing area of the crank for cylinder 1, the opposite cylinder on the coil (what he says is 6, i dont remember the pairing so im just gonna be general) also fires a weaker charge at the same time. hence the reason MSD took so long to come up with a stupid DIS box for us.

dont believe it? ask MSD. ask GM too. its a wierd setup. in effect, it does sort of "twin fire" the engine, but not to make power on both cylinders, the first one (say cyl 1) fires to make power, the second (say cyl 6) fires to clean up the unburnt mix before it exits the cylinder (or something like that) -- regardless of why, both ign. coils fire..one with a slightly weaker charge. so -- yur both right.

Clint -- back to your question, if you wanted to do that, two cylinders IN LINE would have to fire. if you fired two cylinders opposite bank from each other, you'd just push the crank out of the block. i.e. - fire cylinder 1+3 at the same time, and you deliver more force down to push the crank. meaning that you would end up with two cylinders out of balance..(firing 1/3 would leave 5 to fire by itself, and firing 2/4 would leave 6 to fire by itself...your best bet would be this firing order: 1/24/35/6 : which would possibly balance the engine a little better) which would basically give you a twin fire engine (now i see why this could work on a v8, still dont see how it works on a viper tho) on two sets of cylidners (2/4 or 4/6 and 1/3 or 3/5) or you do a triple fire engine and fire all three cylinders at the same time.. which would be the only way to cover all of them. hrm. complicated. i think ill stick to making power the old fashioned way. but if you wanna talk bout this more, feel free to im me. ill be home after 8 probably. look for camwire.

-Russell

[toast]

<blockquote>quote:</font><hr>Originally posted by Fin:


The 3.4L V6's correct firing order is 1-2-3-4-5-6.<hr></blockquote>

My bad [img]redface.gif[/img] I always thought they where the same untill i i looked it up and sure enough i was wrong. I guess i will shut up now. :(

Oh by the way Scott, what did i eat? :D

[John_D.]

<blockquote>quote:</font><hr>Originally posted by Clint Porter:
Your statment would be true on a 2cyl engine, but there are 6cyl's, this means there are three 2 cyl groups, these other groups fill in the dead time you explained on your 2cyl example

And wether 1 cyl or 2 cyl turn the crank, its still gona get turned.With a 1 fire at a time, each cyl is going to turn the crank 60 degrees to make the 1 compleate engine cycle. Now with twop cylinders firing each group will turn the crank 120 degrees to compleate the engine cycle. Now since you have 2 cyl's turning the crank at the same time, your theoreticly going to make almost twice the power and put twice the strain on the crank shaft... am I right?<hr></blockquote>

Not exactly...
Let's take a 6 cylinder for example, using a 1-2-3-4-5-6 sequence.

And let's say each cylinder fires at 60 degree intervals. (because it's a 4 stroke, I believe it is actually at 120 degree intervals, but let's just say 60 for this example).

Normal:
--1--2--3--4--5--6
-60-60-60-60-60-60 = 360 degrees, 1 full rotation

Twin Fire:
1/2-xxx-3/4-xxx-5/6-xxx
60--60--60--60--60--60 = 360 degrees, 1 full rotation
The xxx's are where no cylinders are firing.

When you pull one cylinder ahead, it leaves a gap. At first glance, you might think the other cylinders could come in and close the gap, but they can't, because they still have to wait for a full rotation. If you did pull them in, then all the xxx's would be at the last half of the rotation.

Otherwise, you would have to figure out how to fit some extra strokes into one crankshaft revolution.

Also, the theory that is flying around about the purpose of multiple coils, and two cylinders per coil, to fire one more time to clean up emissions, is not quite right either. There is no varying spark strength either. The coil has no concept of which cylinder is supposed to be firing, it just shoots voltage out to both plugs.

Multiple coils are used to provide a stronger spark, especially at high rpms. It takes time for a coil to build a charge back up after firing. If you spread that across multiple coils, then each one has more recovery time, and you get a stronger spark.

One coil per cylinder is overkill. So to save space, money, etc, it is reasonable to drive two cylinders off one coil. As long as they are opposite each other in firing sequence and stroke, it doesn't hurt to have them on the same coil, it's just a wasted spark to one of the cylinders.

Motorcyles have been using this technology for a long time. I don't know how far back it goes, but I have a 1978 which uses it, so it's at least 24-25 years old. Four cylinders, two coils, two wires coming out of each coil. (in fact I just put a pair of yellow accel coils on it last year, st the same time I converted it from dual points to electronic ignition.)

[93v6firebird]

<blockquote>quote:</font><hr>Originally posted by Clint Porter:


Your statment would be true on a 2cyl engine, but there are 6cyl's, this means there are three 2 cyl groups, these other groups fill in the dead time you explained on your 2cyl example

And wether 1 cyl or 2 cyl turn the crank, its still gona get turned.With a 1 fire at a time, each cyl is going to turn the crank 60 degrees to make the 1 compleate engine cycle. Now with twop cylinders firing each group will turn the crank 120 degrees to compleate the engine cycle. Now since you have 2 cyl's turning the crank at the same time, your theoreticly going to make almost twice the power and put twice the strain on the crank shaft... am I right?<hr></blockquote>

My logic tells me that youd either have double the dead time, or double the RPMs. which would strain the entire engine beyond belief. It would heat it up so much I imagine some of the metal would actually get soft... I dont think this is at all possible

[DJ-BurN]

<blockquote>quote:</font><hr>Originally posted by John_D.:


Twin Fire:
1/2-xxx-3/4-xxx-5/6-xxx
60--60--60--60--60--60 = 360 degrees, 1 full rotation
The xxx's are where no cylinders are firing.
<hr></blockquote>

So, by this theory, if you were to use a twin fire 12 cyl. engine it would fill in the gap(s)? Ok . . . who wants to be the first to try this on a 12 cyl.? :D

[Scalpel4]

I tell you know, I wouldn't dare try this with the 3.4L V6. Had my engine replaced last year, cost me almost as much as an engine swap to a 350, but that's beside the point. Anyways, my friend spoke to the supplier about this engine, and GM only made them for a few years because they're prone to throwing and snapping rods when stock. When I replaced mine, decided to get stronger rods, and beefed up the compression to 12.5. Now I get about 30-40% more power than before just from that. If you want more power out of your 3.4, try doing this first before adding even after market components, just in case, since once you lose this engine you're better off buying a wrecked Z28 and upgrading everything.