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Discussion Starter · #1 ·
Ok this might be a dumb question but, I just want to verify this with you guys.

ok the standard firing order of a sbc is 1, 8, 4, 3, 6, 5, 7 , 2.
The ones that are 180 degrees apart are 1-6, 8-5, 4-7, and 3-2.

in a 4-7 swap and or a 3-2 swap, do the cylinders that are 180 degrees apart still the same as the standard firing order? it looks like it to me.

I am getting a set of headers and this is kind of a big deal seeing that I am spending 1300 on the set... stahl btw.

Help would be great.:thumbup:
 

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You have to have the right Cam To do a 7/4 swap.. The new firing order would be 1, 8, 7, 3, 6, 5, 4 , 2 ,As far as I know about it..
 

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The firing order is determined by the camshaft. Obviously, you set ignition timing on #1, on the compression stroke, just before TDC.
The second cylinder in the firing order has the camshaft lobes 45 CAMSHAFT degrees "retarded" from the lobes for #1, because the second cylinder fires 90 CRANKSHAFT degrees after #1.
The third cylinder in the firing order has the camshaft lobes 90 CAMSHAFT degrees "retarded" from the lobes for #1, because the second cylinder fires 180 CRANKSHAFT degrees after #1.
The fourth cylinder in the firing order has the camshaft lobes 135 CAMSHAFT degrees "retarded" from the lobes for #1, because the fourth cylinder fires 270 CRANKSHAFT degrees after #1.
The fifth cylinder in the firing order has the camshaft lobes 180 CAMSHAFT degrees "retarded" from the lobes for #1, because the fifth cylinder fires 360 CRANKSHAFT degrees after #1.
For the rest of the cylinders, add 45 degrees to the rotation of the camshaft, and 90 degrees for the rotation of the crankshaft
I hope you can see the pattern for the rest of the cylinders.
These numbers work on a 90 degree V-8
 

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Discussion Starter · #6 ·
Yes we got the tube size correct. and the length etc. and i know how the swaps work. I just need to make sure that those are still 180 degrees apart. The tubes are going to be connected. I'm doing a 360 degree header.
 

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Discussion Starter · #7 · (Edited)
these firing orders are used by some v-8 race cars
1-5-4-8-6-3-7-2 4-------------8 3-------------7 2-------------6 1---

BMW 134 Judd V8 - Georg Plasa - 40. Trierer Bergrennen 2011 - YouTube
Their crank is different I don't think that would work for me. i am going with the ls firing order. The only reason I am doing it is for stress on the crank. I understand the huge cost difference. Reliability finishes the race.

I just verified that is a 180 degree crankshaft they use in the KV675. The firing order patterns for 180 crank dont work with cross plane.
 

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Ok this might be a dumb question but, I just want to verify this with you guys.

ok the standard firing order of a sbc is 1, 8, 4, 3, 6, 5, 7 , 2.
The ones that are 180 degrees apart are 1-6, 8-5, 4-7, and 3-2.

in a 4-7 swap and or a 3-2 swap, do the cylinders that are 180 degrees apart still the same as the standard firing order? it looks like it to me.

I am getting a set of headers and this is kind of a big deal seeing that I am spending 1300 on the set... stahl btw.

Help would be great.:thumbup:
AFAIK as long as you don't use standard order tri-Y/4 Into 2 Into 1 headers w/the 4-7 swap cam you'll be OK.
 

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Discussion Starter · #10 ·
Jere shahl 360 header,probably 1 3/4 pipe for a low/medium horse power 327
not using a tri y from what I understand
Him and edd headerman and travis knowlton all agree 1 and 5/8s is what I need. We should be any where from 480-560ish hp. the design was for hp over all. its a 7500ish rpm engine. we will see what it actually does on the dyno.
 

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Him and edd headerman and travis knowlton all agree 1 and 5/8s is what I need. We should be any where from 480-560ish hp. the design was for hp over all. its a 7500ish rpm engine. we will see what it actually does on the dyno.
I'm a little surprised that for a 560 hp 327 the primaries aren't at least stepped or 1-3/4 but then I'm no fluid dynamicist.

What are the power peak rpm for 480 and 560 hp?
 

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Discussion Starter · #13 ·
I'm a little surprised that for a 560 hp 327 the primaries aren't at least stepped or 1-3/4 but then I'm no fluid dynamicist.

What are the power peak rpm for 480 and 560 hp?
The problem with that is we really wont know for sure until its on the dyno. They can quote 7200rpm or 7500rpm or 7800rpm but its going to be (around) there if you follow me. there are too many other factors that can make a difference. like the degree of the cam. I just trust that the guys who have been doing this for so many years no their shiz-

They were saying too big is about as bad as going too small. I don't really want a lot of tq because my car weighs less than my civic- but you have to have some tq to get hp.
 

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Pretty fancy stuff there Mark.:thumbup::thumbup:
That's why they pay me the big... ah hell, you know better! :D

Richard, what do you make of the size of the primaries on this deal? I remember you used your software to show the output using bigger long tube headers was close to the 1-5/8 headers, and this was on a milder build than a 500-plus hp/ 7500 rpm engine.
 

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The problem with that is we really wont know for sure until its on the dyno. They can quote 7200rpm or 7500rpm or 7800rpm but its going to be (around) there if you follow me. there are too many other factors that can make a difference. like the degree of the cam. I just trust that the guys who have been doing this for so many years no their shiz-

They were saying too big is about as bad as going too small. I don't really want a lot of tq because my car weighs less than my civic- but you have to have some tq to get hp.
The thing is, smaller primaries will help torque more than hp. This is almost an oversimplification, but I'm sure you get the gist. This isn't a dig at you- I'm just trying to understand the expert's advice is all.
 

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That's why they pay me the big... ah hell, you know better! :D

Richard, what do you make of the size of the primaries on this deal? I remember you used your software to show the output using bigger long tube headers was close to the 1-5/8 headers, and this was on a milder build than a 500-plus hp/ 7500 rpm engine.
Mark, you know that I'm no scientist, I'm just an old hot rodder sittin' on a stump with a pencil and paper. The things that I don't know or don't understand scientifically, I try to figure out with common sense and what seems real to me.

When I was doing the sims, I found that the breakover for primary tube size was around 6000 r's on a 383 or larger motor. A 350 at 6000 would still make max power with 1 5/8" primaries, but a 383 at 6000 made a little better power with 1 3/4" primaries.

Here's how I would try to figure out what you're thinkin'. Let's say that a 383 at 6000 passes 665 CFM uncorrected for efficiency. We might conclude that somewhere around 665 would be the breakover point for larger primaries, since they make more power on a sim. Now, a 331 buzzed to 7600 would pass 728 CFM uncorrected, so it would seem logical to me to use a larger primary tube for more power at the top.
I might be full of it, but that's how it looks to me, sittin here on this stump.:thumbup:
 

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Thanks for the input Richard. I see no flaws in your "stump logic". :thumbup:

I'm tryin to get my head around the recommendation from experts for a small primary, and in this application it just doesn't seem to jibe w/what I thought I knew. Makes me wonder all the more about what I'm missing here.
 

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Discussion Starter · #18 ·
You are generally correct. I still need tq to make hp though. Everything else on the setup is for hp. This is the ONE thing that isnt. F, i'm running a single plane
 

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thinking something like 750 plus CFM a/f management system,255 ish @ 050 timing on the intake,maybe 260 ish exhaust solid roller(probably 108 square). 280 plus CFM intake volume heads with 75% plus exhaust ratio. Jeres headers 11:1
rocker shafts a must
 
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