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Discussion Starter #1
When getting headers made, how important is the order of the primary tubes in the collector. I think its refered to as header clocking?

Build will be an NA SBC. 421". Around 900hp at 8000.
 

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It is supposed to be done to match the firing order of you engine :rolleyes: If you can figure that one out.
 

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As close as I can figure , it should go around in a circle with the firing order . Not cross over side to side but in a circle .
 

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Any idea what the distribution should be on the header with a C firing firing order .. 4/7 and 2/3 swap ??

Thanks
 

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How about this , use a clock for reference as in 12 , 3 , 6 and 9 oclock . 18436572 firing order , 1357 and 8462 following around the clock as in 1 @ 12 , 3 @ 3 , 5 @ 6 and 7 @ 9 oclock . Swapped order : 18726543 , 1753 and 8264 .
 

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Discussion Starter #6
But is it important? what could you gain compared to headers made to fit a car with no concern for primary clocking?
 

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If two cylinders on the same bank fire sequentially (i.e. 8 & 4; 5 & 7 on a stock firing order), then the tubes from those cylinders should be across from each other in the collector, not next to each other. Not sure that it makes much difference though, in my opinion.
 

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My primaries are clocked. Is there anything in it? Well that is the question isn't it....
 

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If two cylinders on the same bank fire sequentially (i.e. 8 & 4; 5 & 7 on a stock firing order), then the tubes from those cylinders should be across from each other in the collector, not next to each other. Not sure that it makes much difference though, in my opinion.

That makes sense in a merge collector. Some say using the Ford Flathead firing order in this manner will see some scavenge efficiency gains. The Chevy dual swap becomes a Flathead firing order. Net gain.
 

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Firing Order is most important with Tri-Y headers and 4-2-1 style collectors. The 'Y' where the pipes merge is the issue. You don't want two pulses trying to travel through the merge at about the same time. You want them spaced out as much as you can. When building this type of header, or adding these collectors... it is paramount to construct them with the firing order in mind.

For standard headers, from what you read, the pulses are supposed to fire in a circle. This is not a bad idea, but not as critical as when building a merge type header.
 

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If it makes no difference, why not do it anyway whilst building the headers,? Then if it does make a difference it's already done
 

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I'm Picking up a set of headers, their 2" came off a 67 fb, I'm gonna use them in my 74 fb. I've cut my cross member out quite a bit and am using motor n mid plates so i'm hoping they'll fit without too
much tweaking, they also have 4,2,1 merge collectors on. How much would it hurt these collectors possible gains with full exhaust on as that's what i run, but i plan on making it possible to drop off the full 3.5 X for next season to see if any gains are possible
 

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I'm Picking up a set of headers, their 2" came off a 67 fb, I'm gonna use them in my 74 fb. I've cut my cross member out quite a bit and am using motor n mid plates so i'm hoping they'll fit without too
much tweaking, they also have 4,2,1 merge collectors on. How much would it hurt these collectors possible gains with full exhaust on as that's what i run, but i plan on making it possible to drop off the full 3.5 X for next season to see if any gains are possible
Main thing is to study the firing order, and clock the collectors accordingly. You don't want two pulses trying to go through the 'Y' at nearly the same time. If the two cylinders fire one right after the other, it could hurt power. Try to pair cylinders that fire opposite each other as much as possible.

I installed a set of 4-2-1 collectors decades ago, and ended up with one horizontal and one rotated 90 degrees. Seemed to work fine. I welded header rings to the ends of them, and ran them with a 3" exhaust.

Hooker use to sell some really pretty ones with nice, smooth Y's... Flowmaster also made them, but they weren't as smooth. I'm pretty sure the Hookers have been discontinued, but haven't checked on the Flows for a while.
 

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Main thing is to study the firing order, and clock the collectors accordingly. You don't want two pulses trying to go through the 'Y' at nearly the same time. If the two cylinders fire one right after the other, it could hurt power. Try to pair cylinders that fire opposite each other as much as possible.

I installed a set of 4-2-1 collectors decades ago, and ended up with one horizontal and one rotated 90 degrees. Seemed to work fine. I welded header rings to the ends of them, and ran them with a 3" exhaust.

Hooker use to sell some really pretty ones with nice, smooth Y's... Flowmaster also made them, but they weren't as smooth. I'm pretty sure the Hookers have been discontinued, but haven't checked on the Flows for a while.
I've got the LS firing order in my Pontiac and these headers are clocked with the traditional firing order as the tubes haven't been moved around, The guy them with the merge collectors on already and he ran them that way.
 

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How about this , use a clock for reference as in 12 , 3 , 6 and 9 oclock . 18436572 firing order , 1357 and 8462 following around the clock as in 1 @ 12 , 3 @ 3 , 5 @ 6 and 7 @ 9 oclock . Swapped order : 18726543 , 1753 and 8264 .
Picked up the headers today, Drivers side is 1753, passenger is 8624, So i'd have to change those two pipes in the passenger collector correct, Or is it not as important to fire in a circle since these have merge collectors
 
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