Can firing order be changed
03-07-2010, 01:53 PM
#1
Melting Slicks
Thread Starter
Can firing order be changed
Can the 18436572 firing order to be changed for the ignition on our small block engines? If so I wonder how the engine would sound.
03-07-2010, 02:09 PM
#2
Le Mans Master
03-07-2010, 02:19 PM
#3
Comp Cams offers 4&7 firing-order swap cams. The ones they list tend to be for oval track/drag race purposes, such as 12-823-14, but to my understanding they can custom grind just about anything.
It sounds like this.
http://www.youtube.com/watch?v=R578A9_kXOE
V-P's car in above link also has 180 degree headers.
It sounds like this.
http://www.youtube.com/watch?v=R578A9_kXOE
V-P's car in above link also has 180 degree headers.
03-07-2010, 10:30 PM
#5
Pro
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As expressed by others you have to change the cam to change the firing order. Your options are to swap 4 and 7 and to swap 2 and 3. As allready stated the 4,7 swap is prety common. Less common is the 4,7 and 2,3 swap. The advantage of the latter is suposidly less stress on the crank and lower harmonics. The GM LS engins use the 4,7 and 2,3 swap firing order. The 433 BB in the "blown 65 sound clip" in my signature is a 4,7 swap and 565 in the "565 chasis dyno video" is a 4,7 and 2,3 swap (same as LS engines).
03-07-2010, 10:52 PM
#6
Le Mans Master
FWIW, I'll be going with a 4/7 swap (1-8-7-3-6-5-4-2) custom grind from Comp on the BB I currently have in the works myself, however, it's more for the crank's sake than for any potential performance gain.
TheFinn is correct about CompCams doing nearly any custom grind you desire. If you don't see the cam you're looking for on their main menu, check with them directly to see if they have a suitable core that will fit your needs. (As ZL1powr has noted, you'll more likely be able to do a 4/7 than a 4/7 + 2/3.) That said, I suggest sticking with lobes already in their library and, tho one might well tweak the LSA and/or advance, in the case of dual pattern cams to stay with lobe combinations typically used together.
TheFinn is correct about CompCams doing nearly any custom grind you desire. If you don't see the cam you're looking for on their main menu, check with them directly to see if they have a suitable core that will fit your needs. (As ZL1powr has noted, you'll more likely be able to do a 4/7 than a 4/7 + 2/3.) That said, I suggest sticking with lobes already in their library and, tho one might well tweak the LSA and/or advance, in the case of dual pattern cams to stay with lobe combinations typically used together.
Last edited by TheSkunkWorks; 03-07-2010 at 10:54 PM.
03-07-2010, 11:27 PM
#7
Instructor
It will not sound different. No matter the firing order 1 firing pulse every 90 deg crankshaft rotation. Like the other guys said, the only practical reason to do this is for crankshaft longevity. GM changed the firing order in later engines to reduce crankshaft torsional stresses.
03-08-2010, 01:14 PM
#8
Le Mans Master
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It will not sound different. No matter the firing order 1 firing pulse every 90 deg crankshaft rotation. Like the other guys said, the only practical reason to do this is for crankshaft longevity. GM changed the firing order in later engines to reduce crankshaft torsional stresses.
Regional circle track rules prohibit 4/7 swap cams. Some of the more experienced tech guys (track inspectors) can & have identified likely cam cheat suspects via exhaust note. Corroboration usually achieved as simply as taking a look at distributor cap & the order plug wires are arranged in. Protest monies ($teardown$) will verify; seldom occurs 'though 'cuz it's lots cheaper to simply accept being tossed as DNF. Yes, with open exhausts, a savvy tech guy can hear the difference.
True, there're "cheater caps" too that re-arrange wire order ... but those are known too ... & one peek beneath it & it's definately over.
*everything on internet's suspect; including the very words I just wrote.
03-08-2010, 01:37 PM
#10
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I'm running a 4-7 swap in my latest engine (407), and you can hear the difference - no question about it. It doesn't sound like a SBC anymore. I'm also running a single plane intake and I used 28 pulls on the dyno to fine-tune and optimize everything from cam timing, ignition timing, intake plenum volume, to carb sizing and jetting.
Lars
Lars
03-08-2010, 01:58 PM
#11
To my old and untrained ears the swapped firing order-engines sound like they are more busy ie. less lumpy boat anchor like. And I like it.
With these swapped firing orders in a street engine what do you get? Numbers about the same? Rev easier? Tq move up or down rpm scale?
With these swapped firing orders in a street engine what do you get? Numbers about the same? Rev easier? Tq move up or down rpm scale?
03-08-2010, 06:35 PM
#13
Melting Slicks
Thread Starter
FWIW, I'll be going with a 4/7 swap (1-8-7-3-6-5-4-2) custom grind from Comp on the BB I currently have in the works myself, however, it's more for the crank's sake than for any potential performance gain.
TheFinn is correct about CompCams doing nearly any custom grind you desire. If you don't see the cam you're looking for on their main menu, check with them directly to see if they have a suitable core that will fit your needs. (As ZL1powr has noted, you'll more likely be able to do a 4/7 than a 4/7 + 2/3.) That said, I suggest sticking with lobes already in their library and, tho one might well tweak the LSA and/or advance, in the case of dual pattern cams to stay with lobe combinations typically used together.
TheFinn is correct about CompCams doing nearly any custom grind you desire. If you don't see the cam you're looking for on their main menu, check with them directly to see if they have a suitable core that will fit your needs. (As ZL1powr has noted, you'll more likely be able to do a 4/7 than a 4/7 + 2/3.) That said, I suggest sticking with lobes already in their library and, tho one might well tweak the LSA and/or advance, in the case of dual pattern cams to stay with lobe combinations typically used together.
03-08-2010, 06:48 PM
#14
Instructor
While theory suggests 4/7 swap shouldn't sound different, practice has shown otherwise.
Regional circle track rules prohibit 4/7 swap cams. Some of the more experienced tech guys (track inspectors) can & have identified likely cam cheat suspects via exhaust note. Corroboration usually achieved as simply as taking a look at distributor cap & the order plug wires are arranged in. Protest monies ($teardown$) will verify; seldom occurs 'though 'cuz it's lots cheaper to simply accept being tossed as DNF. Yes, with open exhausts, a savvy tech guy can hear the difference.
True, there're "cheater caps" too that re-arrange wire order ... but those are known too ... & one peek beneath it & it's definately over.
*everything on internet's suspect; including the very words I just wrote.
Regional circle track rules prohibit 4/7 swap cams. Some of the more experienced tech guys (track inspectors) can & have identified likely cam cheat suspects via exhaust note. Corroboration usually achieved as simply as taking a look at distributor cap & the order plug wires are arranged in. Protest monies ($teardown$) will verify; seldom occurs 'though 'cuz it's lots cheaper to simply accept being tossed as DNF. Yes, with open exhausts, a savvy tech guy can hear the difference.
True, there're "cheater caps" too that re-arrange wire order ... but those are known too ... & one peek beneath it & it's definately over.
*everything on internet's suspect; including the very words I just wrote.
Steve
03-08-2010, 07:39 PM
#15
Le Mans Master
They've simply rearranging a few cam lobes and re-ordered when the plugs fire...
03-08-2010, 08:56 PM
#16
Team Owner
The short answer for the 'casual' driver with a Chevy engine is "No". The firing order is a design feature and is dependent on the lobe positions of the cam. As mentioned, if a 4-7 swap cam is installed, then the normal #4 and #7 wire positions in the distributor cap are reversed.
And, yes, you can rewire the distributor so that the engine will run backwards...but you would have to reverse the idle timing to the "retarded" side of TDC ; but it wouldn't do much for the torque converter in an automatic tranny.
[A novel little 'factoid' that has no useful purpose for anyone on this Forum.]
And, yes, you can rewire the distributor so that the engine will run backwards...but you would have to reverse the idle timing to the "retarded" side of TDC ; but it wouldn't do much for the torque converter in an automatic tranny.
[A novel little 'factoid' that has no useful purpose for anyone on this Forum.]
03-09-2010, 07:07 AM
#17
Drifting
Firing orders
G'day,
I don't have any experience with 4/7 swaps, but one reason I have seen quoted is to do away with having two adjacent cylinders firing sequentially. In the case of a SB1, these two are 5 & 7. If you swap the firing order from 18436572 to 18736542, you then have 2 & 4 running sequentially, so what have you gained?
All V8 engines have one thing in common, the centre four cylinders fire for 360 degrees of crankshaft rotation, then the outer four fire for the remaining 360. (Or the other way around
) Doesn't matter if it's a Chev, Ford, Buick or Holden, they all do this. The only exception would be an engine fitted with a single plane crankshaft, where each bank runs like a four cylinder engine with equal 90 degree firings along each side. Trouble is, they vibrate like crazy though, unless a lot of money is spent on balancing it.
For the street, I wouldn't bother with a 4/7 swap as you would be hard pressed to notice any gain, although I bow to the Lord Lars and accept that the exhaust note would be different. I would rather spend the money on a 180 degree header system and then you would REALLY notice the different exhaust note. And probably some neddies too!
Just my 02c worth.
Regards from Down Under
aussiejohn
I don't have any experience with 4/7 swaps, but one reason I have seen quoted is to do away with having two adjacent cylinders firing sequentially. In the case of a SB1, these two are 5 & 7. If you swap the firing order from 18436572 to 18736542, you then have 2 & 4 running sequentially, so what have you gained?
All V8 engines have one thing in common, the centre four cylinders fire for 360 degrees of crankshaft rotation, then the outer four fire for the remaining 360. (Or the other way around
) Doesn't matter if it's a Chev, Ford, Buick or Holden, they all do this. The only exception would be an engine fitted with a single plane crankshaft, where each bank runs like a four cylinder engine with equal 90 degree firings along each side. Trouble is, they vibrate like crazy though, unless a lot of money is spent on balancing it.For the street, I wouldn't bother with a 4/7 swap as you would be hard pressed to notice any gain, although I bow to the Lord Lars and accept that the exhaust note would be different. I would rather spend the money on a 180 degree header system and then you would REALLY notice the different exhaust note. And probably some neddies too!
Just my 02c worth.
Regards from Down Under
aussiejohn
04-07-2010, 12:44 PM
#18
Safety Car
Here's what stock firing order look like:
George
George
