Primary size and length on SC engine

[MidTexCuda]

I finally bit the bullet (well really swallowed the whole gun) a bought a F1x rev front mount Procharger for a 400 low deck stroker build.

My plan is a 470 blow through pump gas engine street engine. My build has some gaps- mainly a short block but I do have a block I was using for mock up and want to start making the headers for the new build.
I had started making them for a 517 N/A motor but now after the new acquisition I am worried my 2" primaries will be to small. The original plan was 2" to slip on merge 3.5 to 3" pipes to Borla multi cores. The total exhaust would be about 6' long.
Now my worry is the 2" will be to small and so will the rest. Every search I have made here any other places has yielded mixed info. some say as big as you can fit to using the same size as N/A.
Any ideas?

 

[69MOPE]

Header size for max perf on a S/C motor does not matter, as long as there is no restriction. You will need to know your exhaust port square inch measurement and your tubes (inside diameter square inches) should be no smaller than the port measurement. Also 3 1/2" collectors should be OK. The collector (I.D.square inches) should be no smaller than 4X the inside of the primaries.

 

[MidTexCuda]

would that mean 4x the volume of one primary tube. example 2" tube 30" long with a volume of roughly 174.74" with a 3.5" collector at 5" long? or do you mean take the 174.74 x4= 698.96 which would require a 3.5" collector to be roughly 30" long?

 

[69MOPE]

No, lenght of tubes does not matter, only the square inches of a cross section at any one point.

 

[69MOPE]

Tube length only comes into play for scavageing. S/C motors do not care about that, they only want no step down or restriction. That is why you see zoomies on blown cars.

 

[69MOPE]

Example; if you exhaust port was perfectly square and measured 2" x 2" that means the primary inside diameter must be 4 square inches or greater, and the collector I.D. must be 16 square inches or greater, no matter what the length. The formula's for measuring oval's and round tubing can be a little tricky. You can measure completely around a odd shaped opening and use that as a circumfrance in a circle, square inch formula.

 

[MidTexCuda]

Well this kind of stinks.
My math:

stock port opening at about -2.5"

1.75 primary = 2.14 x4=8.56
1.875 primary =2.46 x4=9.89
2.00 primary =2.84 x4=11.36
2.15 primary =3.14 x4=12.56
2.25 primary =4.15 x4=16.6

3.5 collector =9.08 (use 1.75 maybe 1.875)
4.0 collector =11.95 (use 2.0)
4.5 collector =15.20 (use 2.15)
5.0 collector =18.5 (use 2.25)

does this look close?
thus meaning run a min 1-7/8" tube or 2.0" tube to maybe a 3.5 collector but preferably a 4.0 collector.

 

[69MOPE]

Well this kind of stinks. My math: stock port opening at about -2.5" 1.75 primary = 2.14 x4=8.56 1.875 primary =2.46 x4=9.89 2.00 primary =2.84 x4=11.36 2.15 primary =3.14 x4=12.56 2.25 primary =4.15 x4=16.6 3.5 collector =9.08 (use 1.75 maybe 1.875) 4.0 collector =11.95 (use 2.0) 4.5 collector =15.20 (use 2.15) 5.0 collector =18.5 (use 2.25) does this look close? thus meaning run a min 1-7/8" tube or 2.0" tube to maybe a 3.5 collector but preferably a 4.0 collector.

(A)Your exhaust port opening needs to be in square inches.
(B)The inside diameter (measured in square inches) of the primary needs to be no smaller than the port.
(C)The collector inside diameter (measured in square inches) needs to be no smaller than 4 X the primary.

C = Bx4 "or greater"
B = A "or greater"
A = You need this measurement first.

NOW MY BRaiN HURT"S.

 

[MidTexCuda]

all of those numbers are in square inches I just didn't take the time to indicate it. the tube sizes are all ID I subtracted for the 16gauge material. The 2.5 came form an average of gaskets sizes I found on line because I don't have the heads in front of me. I fudged the radiuses because I didn't want do the math on 4 corners that small. so I am thinking I have it correct.
Thanks for your help 69MOPE!