Changing the Firing Order

[01bonne]

I was watching an old episode of Horsepower and they changed the firing order of the pistons on a SBC. Doing so gave them about 25 or so more horses. How plausible would this be with our 3800's?

[Allmachtige]

I was watching an old episode of Horsepower and they changed the firing order of the pistons on a SBC. Doing so gave them about 25 or so more horses. How plausible would this be with our 3800's?

It isn't plausible. The PCM would require an entire custom reburn involving "stuff" I cannot comprehend.

There would be no gain. The engine was designed to fire in its current order.

[Greyhare]

You would need to have a custom cam grind.
You would also need to find out why it works on the SBC then, see if the same effect is possible on the 3800.

IMHO more trouble than it is worth for something that may or may not work.

[01bonne]

Ok, it was just a random thought during my chem final

[Jrs3800]

Lets look at it this way... I may be very wrong but its a theroy...

A Small Block Chevy uses a Common shared journal, The Buick 3.8 Later years, and the 3800 all years use a split pin crankshaft

[00Beast]

It doesn't change the ignition timing of anything. What it does is changes when the valves open up for those cylinders, changing the velocity of air somehow, and making it work better. It only works on V8's that have that firing order. It wouldn't work on a 3800.

[BonneMe]

IIRC there's a second firing pattern that can be used OE on SBCs, and it really doesn't gain much, but some find it balances better. HRM was on it a few times when I subscribed to it. it was the #4 and 7 IIRC. I certainly don't remember 25hp gains in the articles.

The 3800 can't change it, you could swap wires on the same ignition coil since it is a waste spark system, but that's not changing firing order.

[clm2112]

It doesn't change the ignition timing of anything. What it does is changes when the valves open up for those cylinders, changing the velocity of air somehow, and making it work better. It only works on V8's that have that firing order. It wouldn't work on a 3800.

Yep. Think of airflow more like flowing water..it has mass and get it moving in a particular direction it then has momentum. The trick of altering the firing order (and thus which cylinders are drawing air on the intake stroke) gets air in the plenum moving in a direction and feeding two cylinders near each other with less effort..like free supercharging. Only works with short runner, open plenum manifolds. Long runners and classic dual plane manifolds defeat the purpose.

Now. In my opinion... *ALL* Performance TV Shows and Magazines should come with disclaimers and subtitles: Little tidbits like "This is complete BS, but sounds neat, so we are going to shovel it at you anyways", "Hey, did we tell ya that the people who make this garbage paid us lots of money", etc, etc.

Ok, that said, there is a theoretical change in the 3800's firing order that would produce a huge change in it's characteristics. It's called a "BIG BANG" motor. The way it works, you take the pair of cylinders that are at TDC and fire them together by changing the cam timing.

If you look at the coil packs on your motor, you see the pairs of cylinders at TDC on opposite strokes...when the coil fires, one cylinder is at TDC on the compression stroke, the other in at TDC on the exhaust stroke. Alter the cam so that BOTH cylinders are at TDC on the compression stroke.

What you end up with is a fake 3 cylinder motor...with HUGE torque peaks every time a pair of cylinders fire. But you also get long pauses between those firings.

It's done quite often on motorcycle engines...make a motor with 2 cylinders behave like a motor with one big piston.

Now, there are some serious issues with doing this.

The first, and biggest, is the strength of the crankshaft. Firing two cylinders at once is probably going to snap the stock crank like a "mister salty" pretzel. You are asking it to absorb a lot of energy in a very short time frame. Yes, the total energy being pumped through the crank at any given rpm is the same as before, but the pulses are stacked on top of each other, instead of being evenly spread out. (That is the whole purpose of doing Big Bang motors, getting those huge torque pulses.)

Second, it would never balance right...or should I say, there probably isn't any practical way of balancing the motor without a flywheel the size of tire hanging off the back. You just have to live with the banging around under the hood.

Last, that I can think of off the top of my head, is the controls: It's going to drive the PCM bonkers. You could probably alter both the cam and crank sensors to trick the PCM into thinking you are running at 1/2 actual engine RPM...it's not smart enough to actually see which cylinders actually fired. But with it knocking and banging away in there, it's going to have issues.

So, well, file the idea under "Stupid Human Car Tricks" and work on the bread and butter of performance (i.e.how to cram more air & fuel into it.)

[dirtracr95]

IIRC there's a second firing pattern that can be used OE on SBCs, and it really doesn't gain much, but some find it balances better. HRM was on it a few times when I subscribed to it. it was the #4 and 7 IIRC. I certainly don't remember 25hp gains in the articles.

The 3800 can't change it, you could swap wires on the same ignition coil since it is a waste spark system, but that's not changing firing order.

yea it is a 4/7 swap and it does gain 25-30hp on the SBC athough you cant do it on the corvettes because it already has it. It has something to do with how efficient the engine takes air in. I will have to ask my friend who has done it. Horsepower TV did it to one of there cars and gained in the 25-30 hp range on the dyno

[SSEIYAA95]

I believe it was done on the older 3.8 Buick Turbo engines. I'll have to look back at the GN pages.