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Old 03-15-2008, 08:07 PM   #1
2k2C5
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Default LS1 firing order

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.
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Old 03-15-2008, 08:09 PM   #2
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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 !

Last edited by Oldvetter; 03-15-2008 at 08:13 PM.
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Old 03-15-2008, 09:35 PM   #3
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Originally Posted by Oldvetter View Post
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 !
But new GM trucks use the same firing order?
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Old 03-15-2008, 09:47 PM   #4
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But new GM trucks use the same firing order?
I just checked and you are right, so why do the truck engines sound better than ours?
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Old 08-24-2009, 01:26 PM   #5
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Daa!!! wrong thread posting. my bad!
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Old 08-24-2009, 02:01 PM   #6
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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.
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Old 08-24-2009, 02:24 PM   #7
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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.
http://www.idavette.net/hib/ls1c.html
Very good reading on the LS1 engine.
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Old 03-15-2010, 02:25 PM   #8
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Quote:
Originally Posted by 2k2C5 View Post
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.
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.
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Old 03-15-2010, 03:33 PM   #9
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I just checked and you are right, so why do the truck engines sound better than ours?
Aren't the truck engines cast iron?
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Old 03-15-2010, 03:38 PM   #10
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Wow...this thread was started 2 years ago.....to the day.....
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Old 03-17-2010, 12:02 AM   #11
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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.
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Old 03-17-2010, 12:02 AM
 
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