Change in Firing Order

[scottc]

Heard about this for big block engines and it give more hp. Any details? What do you have to do to do this? Cam change, crank?

Thanks,
Scott

[PatriYacht]

Cam change and switch a couple of wires. Supposedly it evens out the mixture between some of the cylinders. Worth a few hp mostly in the upper rpms. If it's a new build, why not, it doesn't cost much. I wouldn't tear down a good motor to do it.

[Airpacker]

I assume you are talking about BBC's.
Lots of 4 / 7 swaps done. 18436572 becomes 18736542.
Latest is a double swap. I am running this order on my motor . 18726543. Better harmonics and less loading on the main bearings. More even fuel distribution.
Change cam, rearrange plug wires, remember the new firing order. Simple as that.

[scottc]

Any of these changes shown on a dyno? What hp or tourque changes?

[Trim'd Up]

I am running the 4/7 3/2 swap in my latest motor. It is the LS1/ 496 firing order. Simple to do, but I had to keep looking at the firing order after years of stock chevy. Bob Madera cut my cam and I think it cost me $25 for the swap. Main benefit is like Airpacker said, easier on the crank. Maybe good fr 10hp under 6000. A little more if you spin the chit out of it. It does sound a little different though. If your having a cam cut, why not, but don't waste the time or money otherwise.

[Steve Miklos]

I am running the 4/7 3/2 swap in my latest motor. It is the LS1/ 496 firing order. Simple to do, but I had to keep looking at the firing order after years of stock chevy. Bob Madera cut my cam and I think it cost me $25 for the swap. Main benefit is like Airpacker said, easier on the crank. Maybe good fr 10hp under 6000. A little more if you spin the chit out of it. It does sound a little different though. If your having a cam cut, why not, but don't waste the time or money otherwise.

I feel it makes a wider torque curve also.
Steve

[BenPerfected]

We build from scratch and still didn't do it....seemed like tripping over mouse turds.

[cubicinches]

We build from scratch and still didn't do it....seemed like tripping over mouse turds.

I agree... Much to do about nothing.

[BUIZILLA]

have you ever heard a lobe swap on a SBC at 7500 rpm???

there is no sweeter music to be heard... makes more power, smoother, and rev's like a mutha fvcker..

[Airpacker]

I agree... Much to do about nothing.

There are reasons GM went to this firing order. Here's a quick read for ya


Excerpts from a Q&A discussion about camshaft firing order swap between Billy Godbold, COMP Cams lead cam designer, and Mike Mavrigian, editor of Precision Engine magazine. Look for a more indepth discussion of this topic in the pages of Precision Engine magazine.


1. A typical 4 & 7 FOS (firing order swap) seems to be fairly common today. Why is this firing order change beneficial?

There are three basic issues that engine builders or developers try to address through a firing order change. Here are three considerations:

A) Hot spots in the head and block – With a common pin V8 crankshaft, it is impossible to eliminate having adjacent cylinders (paired next to each other) fire subsequent to one another in the sequence (which we call a hot spot). While this is unavoidable on a four counterweighted throw crankshaft, you do have some choice as to which pair(s) fire together. The 4 & 7 firing order moves that hot spot from the 5 & 7 cylinders up to the 4 & 2 cylinders which is more desirable as the front pair of cylinders are easier to keep cool with a front mounted water pump.

B) Main bearing issues – Most engine builders see better bearing life and less scuffing indicators with the 4 & 7 swap camshaft. In the case of the LS firing order (which utilizes the 4 & 7 swap plus an additional 2 & 3 swap), there may be a bearing life benefit. Again, we are talking about pairs of rods firing together, keeping the force of the adjacent crank main bearings in the same pin. Moving this “hot spot” to the back of the engine seems to be a good idea because the drive train is much better able to dampening these forces in this case rather than with a small mass on the front of the crankshaft. When we consider the power that can be gained with lighter weight, lower viscosity oils, bearing life becomes not only question of durability, but of power as well.

C) Fuel distribution – Changing the firing order is one of the best ways to change the cylinder-to-cylinder fuel and air distribution in the engine. Just like the forces experienced by the bottom end with hot spots where cylinders fire together next to each other, when this occurs with an engine, the same happens in the manifold with ports that are next to each other. This creates a very dynamic system in the manifold plenum where pressure waves of air (and also fuel in a wet manifold) are moving from the front to the back and side-to-side. Changing the firing order definitely changes how the ports interact.

[Offshoredrillin]

I am running the 4/7 3/2 swap in my latest motor. It is the LS1/ 496 firing order. Simple to do, but I had to keep looking at the firing order after years of stock chevy. Bob Madera cut my cam and I think it cost me $25 for the swap. Main benefit is like Airpacker said, easier on the crank. Maybe good fr 10hp under 6000. A little more if you spin the chit out of it. It does sound a little different though. If your having a cam cut, why not, but don't waste the time or money otherwise.

bingo, same thing in mine, evened them out and they sound great, depending on set up its worth a good 30 top end hp. there is a cam already out there for it.