ok did a quick search on here and didnt find anything relating to it. but I was looking at articles in the upcoming HOTROD mag and the say that by changing the firing order on a small block you can make 30 extra HP? is there any truth to this and does anyone have any detailed info on this? - TOT

heres something I found

A typical Chevy firing order is 1-8-4-3-6-5-7-2. For the vast majority of applications, this firing order works nicely and there’s probably no need to change it. But in a race application, there are various firing orders that can effectively improve power and reliability in an engine. Typically, there are seven other firing order arrangements which can be used without changing the crankshaft layout on a Chevrolet V8. These firing orders include the following:
1-8-4-2-6-5-7-3
1-8-7-2-6-5-4-3
1-8-7-3-6-5-4-2
1-5-4-3-6-8-7-2
1-5-7-3-6-8-4-2
1-5-7-2-6-8-4-3
1-5-4-2-6-8-7-3

Reher-Morrison has tested the various combinations and found some interesting results. When the firing order is revised to 1-8-7-3-6-5-4-2, you’ll find some power and reliability. Now, if you race a Pro Stock car, this is no secret since the revised order has been in vogue for some time. With the revised firing order, fuel distribution dilemmas are resolved. The engine tends to run cooler, and perhaps just as important, the engine is actually smoother. How much extra power is there? Anywhere between 8 to 10 measurable horsepower. There was once a caveat here though: The average enthusiast couldn’t easily get a cam with the revised lobe positions, but not so today. Reher-Morrison sells such a package (called Big Stick Cams) for Chevy big block/Big Chief head combinations.

Does this mean you need a custom cam? or just simple swap pug wires? if so why isnt THIS the normal firing order?

 

woah............. im down for 30 extra hp

 

ya in the one article its said 8-10 measureable HP and on there upcoming article it said 30HP so I dont know. even 8 extra HP just by switching the fireing order would be sweet.

 

A camshaft is an absolute must for this swap.

On a fuel injected car that is sequential you must also move the injector harness' around to match the firing order (and the plug wires). But if you notice this would mean that the stock computer will be lookeing for the exhaust on a few cylenders in the wrong bank. For instance swapping 4 and 7 make the O2s worthless for these 2.

Now if you made a custom set of headers that cross these primaries to feed right...lol

 

hmm swapping the injector wires wouldnt be a problem, but is the o2 sensors realy going to know that 7 didnt fire at the exact time it was supose to but later in the sequence? what if you went with a wideband?

 

Wouldnt that completly change the sound of the exaust note?

 

Yes it would, and LS1 sounds WAY different than a LT1 the firing order of an LS1 is 1-8-7-2-6-5-4-3 I dont know what changing a LT1 to 1-8-7-3-6-5-4-2 would sound like

 

You are right, but wrong on the reasoning. The LS/LT difference is the construction of the block. The LS is all aluminum and the LT is an iron block with some having alum heads.

 

Yeah, can someone explain how the O2 sensor would know whether # 7 or #2 was firing?

 

are you sure that im wrong? if firing order doesnt play a part then the ford 5.0 would sound similar to a 305tpi with dual exhaust and h-pipe. firing order has to make a huge different, when the sound wave from each cylinder travel down the exhaust tubing they bounce around inside. each "wave" from the 8 cyliders would have a different distance from thewave from the cylinder that was fired before it. its like banging on a drum. if everything was constant and you beat a drum with equal "beats" then you would have one sound but take that same drum and hit it at different intervals it would have a different sound. I dont think an aluminum bottom end would make ANY difference in exhaust sound.

 

Firing order would change sound significantly more than the material of the rotating assembly....but it is the combination of 'differences' that gives some cars their distinctive sound.

 

exactly, but back to the main point has anyone done this?? and could someone like bret make a cam without any problems?

 

I've seen a couple of big blocks, and a couple super stock class LT1's with the modified firing order, but nobody with a street car.

 

looks like im gonna have to buy the new HOTROD mag. It looks like a pretty popular thing to do on a track car.

 

The O2 doesnt "know" which cylender is firing, but it is on a bank of cylenders, and the PCM knows which O2 is on what side, if one of the swapped cylenders was running excessively lean or rich the wrong O2 would take the reading and adjust the wrong bank.

This is a non issue on a carbed car.

On OBD 1 it would be a minor problem, on OBD 2 it could cause some nice problems.