Stinky
Senior Member
Posts: 1896
Loc: Whitewater, CO
Reg: 05-25-01
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02-05-23 09:39 PM - Post#2854176
I was looking at Summit, or Jegs, or both. I saw a camshaft that is used to change the firing-order. If I remember correctly, it would switch cylinders 5 & 7 in the FO. Naturally, they claim it will run stronger, smoother and be better. It was for a 350/5.7 in a Gen I or II (I think).
Anybody heard anything about this?
Edited by Stinky on 02-05-23 09:45 PM. Reason for edit: No reason given.
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 GreatNorthWoods
"8th Year" Silver Supporting Member
Posts: 1452
Age: 80
Loc: Littleton, New Hampshire,...
Reg: 03-31-02
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02-06-23 05:12 AM - Post#2854177
In response to Stinky
Haven't heard of that. I'm no engine expert but it seems that the crank would have to be changed too if you change the firing order. 
Vern
1953 Chevy Belair Sport Coupe - 355 Chevy V8, 700-R4, 4-wheel disc brakes, Ididit column, cruise/tilt,'59 Vette Steering Wheel, A/C
1930 DeSoto Business Coupe- 350 Chevy V8, Edelbrock 600, 4-wheel discs, Wire Wheels, TH400, S-10 Rear, A/C |
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 Shepherd
Valued Contributor
Posts: 2851
Loc: Lake George, NY
Reg: 11-11-15
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02-06-23 06:26 AM - Post#2854180
In response to GreatNorthWoods
That only requires the cam change from a mechanical stand point. Plenty of info online about the technique and benefits.
Edited by Shepherd on 02-06-23 06:27 AM. Reason for edit: No reason given.
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65_Impala
Very Senior Member
Posts: 4960
Reg: 12-29-02
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02-06-23 10:59 AM - Post#2854189
In response to Stinky
Lots of info online. It swaps 4 & 7. Some claim maybe a 3-5hp gain on a fairly serious engine build.
With a 90* V8 with the 90* 4-journal crank, 2 cylinders are at TDC at the same time. You can theoretically swap any of the cylinder pairs that are across from each other on the distributor cap. 1-6, 8-5, 4-7 or 3-2.
I think the theory is the cylinders at the back of the engine tend to run hotter and are more detonation prone so the swap changes it from 5-7 firing together to 4-2 firing together.
LS engines have 4-7 and 2-3 both swapped. You could get a cam to swap a LS to the small-block order so it would sound like a small block if you really wanted to.
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Tony1963
Frequent Contributor
Posts: 2074
Loc: Orlando Florida
Reg: 07-09-18
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02-06-23 01:39 PM - Post#2854193
In response to Stinky
I remember reading a Summit magazine back in the early 90s where one product talked about containing the heat in your exhaust system for better performance, then on another page there was a product to help REMOVE heat from your exhaust for better performance.
After reading that, I tossed their magazine in the trash and laugh about it to this day.
If any of this were true, don't you think that the OEM would have changed this in their design?
| People fear change because it threatens what they know, or what they claim to know. |
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65_Impala
Very Senior Member
Posts: 4960
Reg: 12-29-02
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02-07-23 07:56 AM - Post#2854212
In response to Tony1963
GM changed it when the designed the LS engines, must be something to it...
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wagonman100
Site Ambassador
Posts: 15777
Loc: Baltimore, MD
Reg: 11-27-04
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02-08-23 10:10 PM - Post#2854286
In response to 65_Impala
My buddy did the 4-7 change in his 572 and the car made more power on the dyno. Same cam specs, just the cylinder swap. It ran a bit faster at the track too.
Jay
Friends don’t let friends drive Fords.
1999 Silverado Z71 4X4 extra-cab short bed
1983 Malibu Fauxmad - tubbed
1978 El Camino Kustomized
1972 Monte Carlo
1957 210 handyman wagon
1957 Nomad sport wagon
1957 Cameo Carrier |
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Tony1963
Frequent Contributor
Posts: 2074
Loc: Orlando Florida
Reg: 07-09-18
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02-09-23 04:40 AM - Post#2854291
In response to 65_Impala
Yes, there is something to it, but it has nothing to do with horsepower. GM noticed that the engine idle was smoother. Here's an article.
https://www.motortrend.com/how-to/ccrp-1109-ques ti...
And another...
https://www.onallcylinders.com/2022/12/27/chevy-sm...
| People fear change because it threatens what they know, or what they claim to know. |
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65_Impala
Very Senior Member
Posts: 4960
Reg: 12-29-02
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02-09-23 02:57 PM - Post#2854308
In response to Tony1963
Reduced crankshaft torsional vibration was the main reason GM adopted the LS engine’s 1-8-7-2-6-5-4-3 firing order (4-7/2-3 swap for SBC). According to GM engineers, computer modeling showed that the new firing order improved reluctor wheel accuracy and eased bearing loads.
Yes, the only improvement was the idle....
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Tony1963
Frequent Contributor
Posts: 2074
Loc: Orlando Florida
Reg: 07-09-18
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02-09-23 03:04 PM - Post#2854309
In response to 65_Impala
Thank you for the contribution! No, this wasn't a horsepower issue although it appears that products are being sold that paint that very picture.
| People fear change because it threatens what they know, or what they claim to know. |
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Tony1963
Frequent Contributor
Posts: 2074
Loc: Orlando Florida
Reg: 07-09-18
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02-10-23 05:43 AM - Post#2854324
In response to 65_Impala
Take a look at this - somehow the vibration and smoothness has turned into a horsepower advantage and I'm wondering where the science is to back this up?
https://www.youtube.com/watch?v=hpJAqvZe0mU
| People fear change because it threatens what they know, or what they claim to know. |
Edited by Tony1963 on 02-10-23 05:47 AM. Reason for edit: No reason given.
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65_Impala
Very Senior Member
Posts: 4960
Reg: 12-29-02
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02-10-23 01:49 PM - Post#2854350
In response to Tony1963
I don't care enough to look. If the engine isn't using power to cause torsional vibrations and there is less bearing load then there will be more power output from the crank. How much I don't care much.
There are lots of racers who do it and lots that have tested both ways and concluded it is better.
I think GM also change the firing order in the 8.1L big block engine.
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Tony1963
Frequent Contributor
Posts: 2074
Loc: Orlando Florida
Reg: 07-09-18
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02-10-23 04:03 PM - Post#2854358
In response to 65_Impala
Interesting post on this thread from a dyno owner.
https://www.racingjunk.com/forums/showthread.php?t...
| People fear change because it threatens what they know, or what they claim to know. |
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Tony1963
Frequent Contributor
Posts: 2074
Loc: Orlando Florida
Reg: 07-09-18
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02-11-23 05:16 AM - Post#2854369
In response to 65_Impala
I'm also noticing a few variations by manufacturer on their V8 engines...I wonder how each determined their firing order? It would be interesting to know.
Firing order 1-5-4-2-6-3-7-8
Firing order 1-5-4-8-6-3-7-2
Firing order 1-5-4-2-6-3-7-8
Firing order 1-8-4-3-6-5-7-2
Firing order 1-8-4-3-6-5-7-2
None of these are GM engines. However, I find it interesting that two of them use the old Chevrolet V8 firing order. Notice the first three vary 2 and 8 only.
| People fear change because it threatens what they know, or what they claim to know. |
Edited by Tony1963 on 02-11-23 05:16 AM. Reason for edit: No reason given.
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1983G20Van
Super Senior Member
Posts: 3988
Loc: Hurst, Texas, USA
Reg: 11-13-02
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02-11-23 07:14 AM - Post#2854373
In response to 65_Impala
I don't care enough to look. If the engine isn't using power to cause torsional vibrations and there is less bearing load then there will be more power output from the crank. How much I don't care much.
There are lots of racers who do it and lots that have tested both ways and concluded it is better.
I think GM also change the firing order in the 8.1L big block engine.
I changed 1 of my 8.1L engines to the normal old big block firing order with a GM 454/502 HO cam.
I have not noticed a huge difference in bearing wear between a SBC and LS.
The only way I feel swapping around the firing order would help would be on a engine that had a single plane intak manifold and a carb.
I also know if I were to change the firing order on either of my vans they would lose power.
| 1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals |
Edited by 1983G20Van on 02-11-23 07:15 AM. Reason for edit: No reason given.
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1983G20Van
Super Senior Member
Posts: 3988
Loc: Hurst, Texas, USA
Reg: 11-13-02
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02-11-23 07:16 AM - Post#2854374
In response to 65_Impala
I don't care enough to look. If the engine isn't using power to cause torsional vibrations and there is less bearing load then there will be more power output from the crank. How much I don't care much.
There are lots of racers who do it and lots that have tested both ways and concluded it is better.
I think GM also change the firing order in the 8.1L big block engine.
I changed 1 of my 8.1L engines to the normal old big block firing order with a GM 454/502 HO cam.
I have not noticed a huge difference in bearing wear between a SBC and LS.
The only way I feel swapping around the firing order would help would be on a engine that had a single plane intak manifold and a carb.
| 1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals |
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Tony1963
Frequent Contributor
Posts: 2074
Loc: Orlando Florida
Reg: 07-09-18
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02-12-23 08:51 AM - Post#2854405
In response to 1983G20Van
I asked my neighbor about this - he's a design engineer.
The GM technical guide on the redesign of the engine made sense to him. He gave me an explanation of how energy pulses can cause a certain amount of harmonic vibration and that is likely why GM changed the firing order. This was done in an era of RVH (roughness, vibration and harshness) in an effort to make vehicles as smooth and quiet as possible.
I asked about the amount of horsepower that might be lost to torsional vibrations and he indicated that it wouldn't be enough to spin the engine one time. He said it would actually be more torque than horsepower lost to the vibration and that we're talking 1/100ths of a foot lb or less.
| People fear change because it threatens what they know, or what they claim to know. |
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1983G20Van
Super Senior Member
Posts: 3988
Loc: Hurst, Texas, USA
Reg: 11-13-02
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02-12-23 11:01 AM - Post#2854414
In response to Tony1963
I asked my neighbor about this - he's a design engineer.
The GM technical guide on the redesign of the engine made sense to him. He gave me an explanation of how energy pulses can cause a certain amount of harmonic vibration and that is likely why GM changed the firing order. This was done in an era of RVH (roughness, vibration and harshness) in an effort to make vehicles as smooth and quiet as possible.
I asked about the amount of horsepower that might be lost to torsional vibrations and he indicated that it wouldn't be enough to spin the engine one time. He said it would actually be more torque than horsepower lost to the vibration and that we're talking 1/100ths of a foot lb or less.
I have had numerous examples of both SBC and LS engines apart that are over 200K miles. Could not tell a difference in bearing wear. The L31 350 had OE bearings that looked practically new in it.
| 1983 G20 Van, 350 TPI, Ported 906 Vortecs, Edelbrock 3817 Base, ASM oversize runners. Reed Custom Roller cam, 700r4, 12 bolt with 3.08 gears, Doug Thorley Tri-Y headers, true duals |
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Tony1963
Frequent Contributor
Posts: 2074
Loc: Orlando Florida
Reg: 07-09-18
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02-12-23 11:56 AM - Post#2854416
In response to 1983G20Van
Yes, I understand and agree with you. There was not enough to justify a change to the original small block's design, but when you are designing an engine from a blank sheet of paper, why not make the change?
| People fear change because it threatens what they know, or what they claim to know. |
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IgnitionMan
Valued Contributor
Posts: 4028
Reg: 04-15-05
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02-20-23 12:03 PM - Post#2854793
In response to Stinky
Six of one on one side, half a dozen on the other side.
Time, and money waster, no joy.
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