2K14C7

Can anyone explain why GM changed the firing order of the LS1?

As most of you know the firing order of the Chevy small block had been 1-8-4-3-6-5-7-2 since the 265 ci came out in 1955. Then in 1997 and the introduction of the LS1 it was changed to 1-8-7-2-6-5-4-3.

Just wondering what benefits this change had and I also suspect that is the reason that the LS1 exhaust note doesn't sound quite like the small blocks of yesteryear.

Oldvetter

GM changed the firing order to allow them to increase the compression ratio without causing localized overheating and predetonation. I'm also told this allowed them to get away from the "reverse flow" of the C4 and it's problems with bleeding the cooling system of air.

And I hate it, the LS1 now sounds like a motorboat. GM trucks sound better than our car. Sometimes technology sucks !

Mike94ZLT1

But new GM trucks use the same firing order?

Oldvetter

I just checked and you are right, so why do the truck engines sound better than ours?

Eric D

Daa!!! wrong thread posting. my bad!

Blown427conv

I've heard that it was to even out the airflow in the intake, whereas the old school firing order would pull from 7 and 2 at nearly the same time causing a lean condition and uneven burn on other cylinders. There are cams for the old school engine that allows you to swap 2 cylinders in the firing order said to gain a small amount of power.

2KFRC5

http://www.idavette.net/hib/ls1c.html
Very good reading on the LS1 engine.

BaerMonteSS83

The reason GM did this was to take the harmonics out of the crankshaft. Due to the firing order of the past design, there was a certain amount of vibration that would come into play in the center of the crankshaft. Warren Johnson pioneered this technology in his pro-stock door slammers in the NHRA racing for years before GM finally listened to him.
As a result, you now have a much stronger lower end engine with a smoother running engine. That said, with the 6 bolt mains, we are seeing LS1 motors with cross hatching marks in the cylinder walls well over 100,000 miles. So I hope this answers the question for you and I wouldn't have known about this until noticing the firing order on a drag racer's firewall. It's very common in the drag racing seen where motors are putting out over 1,000 horsepower.

dougbfresh

Aren't the truck engines cast iron?

lucky131969

Wow...this thread was started 2 years ago.....to the day.....

Jesse Asis

This is what I heard about the firing order. The other big ignition story with Gen III is a different firing order. Gone is the time-honored 1-8-4-3-6-5-7-2 sequence. This new engine fires 1-8-7-2-6-5-4-3. The cylinders are numbered the same: left bank: 1-3-5-7 and right bank: 2-4-6-8. The reason for the new firing order is better idle stability and less vibration.

roller63

Hi Guys,

I'd like to suggest the possibly "correct" reason for the switch.

Chevy, AMC, and others, all used 1-8-4-3-6-5-7-2, because it allowed the use of an easily balanced 90-degree crankshaft. The other option was a more difficult to balance 180-degree crankshaft, present in our LS series engines. Unfortunately, the old firing order presented a problem; look at the the third, and second to last, cylinders firing; 5 and 7. Note that they are right next to each other on the engine block, and obviously, cylinder head. When five fired, its exhaust pulse was still in the exhaust manifold, creating a high-pressure zone for cylinder seven, which fired immediately afterward. This obviously reduced power, and lead to uneven heating, and wear, on the odd side of the cylinder heads. This is why headers showed such a significant increase in power over "log" type manifolds on those V-8s; they separated the exhaust pulses until much later, when the emissions from the exhaust ports had time to open up into a MUCH larger pipe, AKA the collector, which was usually twice as wide (therefore 4x the flow) of the log manifold where the pulses started off. This is also why today's LS motors only see a modest increase in power when equipped with exhaust upgrades. I've heard of guys spending $500 on shorty headers, and seeing an increase of only 5-6 hp - mainly due to this reason. Long tubes, on the other hand, allow more complex fluid phenomena to take place, including transition from laminar to turbulent flow, along with the density increase due to temperature drop occurring later, and therefore at a more opportune time to create an induced low-pressure zone at the exhaust ports than with factory manifolds. However, one point that is missed by many, is that the factory manifolds have a MUCH greater thermal inertia than SS headers, and for that reason, SS long tubes work best when wrapped with insulating material, for as much of the length of the primary as possible - the matter would be ideal if one could wrap the insulation all the way to the collector.

feeder82

Thanks for digging up a 6 year old thread

roller63

You're most welcome! I must give Google some of the credit, though! Now, since you've obviously made the excellent choice to switch to full roller-rockers, get out there under your bonnet, and wrap those stainless headers in some insulating material, and make note of the palpable increase in power, throttle response, and even some mileage! At about $10 per HP, the process is well worth it! Cheers!