there are 3 thing neede to do this, cam swap, ignition, and injector. i know lunati makes a cam for a sbc to change the #4 and #7 firing.
would there be any gains in this? i belive lunati claimed a gain with their cam, but not sure how much

 

I really can't see how changing the firing order would make any difference in power.

It would, however, most likely make the engine sound different, whether that be better or worse.

 

Fairly scientific testing by many different people have shown a mixed bag of results with the firing order swap. However, gm swapped two pairs of cylinders in the firing order when they made the ls1's, so maybe there is something to it.

 

The cam firing order swap that companies make for the small and big block chevys are from the standard old 18436572 to a 18726543. The firing order of the LSx engines just happens to be 18726543. The same as the updated sbc!!! The benefits they listed for the revised firing order was basically crankshaft harmonics due to the old firing order. Some say its easier on the crank, other say you can get more rpm out of it, call it whatever you want, no real usable horsepower from it, just seems to help parts last.

 

Actually, the fo swap cams that I have seen for gen1 sbc motors only swapped 4-7, not 2-3.

 

thats what i thought. i thought lunati claimed a gain with their cam though.

 

From what I understand, it is also used because the cylinders would fire so much close to each other time wise that they would suck air/fuel from the other one. I also heard that it puts more stress on the crank.

 

I'm talking with little real world experience here, but there's a member on this site with a quote in their sig that says something to the effect of:

"[Some auto magazine] just swapped the firing order of a SBC to that of an LS1 and gained 15hp..... God I love my LS1"

Seems like maybe there might be something to it?

 

Ok, my bad, they do only swap the 4 and 7. chalk it up to not double checking....

 

4-7 swap is a common thing with aftermarket cams. Comp, Lunati, etc all do it.

 

Reading more about this, I found engine builders claim only slight gains in power on smaller displacement engines. The crankshaft harmonics are improved, meaning lower stress levels internally for LSx engines than older SBC engines. This might also help to improve NVH in newer trucks and SUV's that share the same arcitechture.

In larger engines where you are swinging longer strokes and heavier rods and pistons around is where the gains were made. Basically, less twisting of the crank from the smoother firing order (power used twisting the crank is flywheel power lost).

I'll have to see if I can find that reference....

 

I can see this as a possibility, but only minimal amounts of power. I can see it being beneficial in say nascar, where every little bit helps, but in a street driven vehicle, the gains are probably unnoticable.

 

rehermorrison.com

 

I agree 100%. Anyone who would switch just the the firing order for 2-5 hp on anything less than an all-out-race engine is barking up the wrong tree.

By the time you get to the firing order looking for power, there are probably dozens of other tricks out there that would net you better results. I'd guess that 2/3 of street driven cars do not have the optimum combination of parts anyway, and you really should have that nailed down before you start splitting hairs to find power.

 

Well, here's my input. Firing order changes idle charachteristics. You notice how the LS1 idles fairly smooth compared to an older SBC? I mean if you put the types of cams and cylinder heads on an old SBC, it would be idling a lot rougher than the LS1's.

If you do a firing change, you only need to swap the firing of the coils. You cannot change the fuel injectors because they have no idea what is going on and if you are running closed loop, you will mess the O2 sensors up.

 

You can move the "fight" to another corner but you can't get rid of it. So instead of a 5-7 succession, you'll get a 1-3, 2-4, or 6-8.

 

I guess I dont understand how changing the firing order would mess the o2's up. I can't see that being a problem, they do nothing but monitor the amount of oxygen in the exhaust. they dont refence to the engine for anything else.


Or maybe I dont understand your statement.....

Another question....can you input what you want for a firing order into the tuning programs? Still waiting on my efilive, so I havent messed with that yet.
Otherwise, you would have to actually swap connections for the injectors to deal with the firing order change....

 

You'd think they could just make it:

1-2-3-4-5-6-7-8

But i guess that would require a flat-plane crank, wouldn't it?






Someone do it!

 

It won't mess up as long as you don't change the firing order on the injectors.

No, you cannot just change the firing order in the programs. You have to do it manually at the connector. But remember, if you are trying to diagnose a problem with the misfire graph, you will have to make sure you remember that the cylinders are swapped and the one giving the misfire code may not be that right cylinder.

 

Can you explain how it would mess up the o2 if you did change the firing order of the injectors? Granted you would be doing this along with the cam and ciol change as well. I could easily see how changing that would cause probs if you changed nothing else!!!