i was just wondering if there is some kinda formula to figure you primary lenght and dia.on a n/a header any help is appriciated.

 

There are design books, plus http://www.headersbyed.com and http://www.burnsstainless.com will both figure the specs for you, for a small price. It's all driven by what you plan the engine to do, horsepower and rpm.

 

burns will do it for i think $40 but dont quote me on that! you will need all the schematics of your motor for them to do it. on their site they have a form to fill out. i would make sure you can provide all the info for this sheet before even contacting them.

 

there are several units you can work with. you would basically need the speed of the air travel.

but there is the highest positive pressure that comes out right as the exhaust valve opens, so that number would be +- 1700 ft/sec i think. but then you have the mean air speed travel which is like 250 ft/sec.

then you would need the exhaust valve opening in crank degrees (time) and then divided by the engine rpm you want to emphasize. that would probably give you the ideal primary length for your engine combo.

let's say skunk2 stage 2 cam Hi lobe.

int open - 37 BTDC
exh closing - 21 ATDC
exh opening - 61 BBDC
int closing - 49 ABDC

So i would ask do you time the whole exh valve opening (262 degrees)
Or exh valve opening right before the intake opening (204 exhaust degrees)
Or that medium 61 BBDC + 180 Degrees to TDC = 241 degrees

 

This is what I use


_________
ID = \/ cc x 2.1, where
_________
(P+3)x2

ID = Primary tube inside diameter, CC = Cubic centimeter displacement of one cylinder, and P = Primary tube length



Here's an example: ID = V500
_____ ______
(34.4 +3)x 25 = 500x2.1
______
935 ID=1.53


You then pick the appropriate outside diameter primary tubing with a wall thickness to give you an ID close to the calculation. Example: 18 gage 1 5/8" OD tubing has a wall thickness of .049" and an ID of 1.527", which is pretty close to our 1.53" calculation.




Modified by RMF at 10:10 AM 11/8/2005


Modified by RMF at 1:42 AM 11/12/2005

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RMF &raquo;</TD></TR><TR><TD CLASS="quote">This is what I use

_________
ID = \/ cc x 2.1, where
_________
(P+3)x2

ID = Primary tube inside diameter, CC = Cubic centimeter displacement of one cylinder, and P = Primary tube length

__________ _____

Here's an example: ID = \/ 500 = \/ 500 x 2.1 ID = 1.53"

(34.4+3) x 25 935



You then pick the appropriate outside diameter primary tubing with a wall thickness to give you an ID close to the calculation. Example: 18 gage 1 5/8" OD tubing has a wall thickness of .049" and an ID of 1.527", which is pretty close to our 1.53" calculation.
Modified by RMF at 10:10 AM 11/8/2005</TD></TR></TABLE>

damn Randy. A true enthusiast in my book. I don't care what HT says about ya, your alright...

Not all shady like those other discrete, threatened dousche bags who own Hondas.

 

randy always appears to be forthcoming with information to HELP other people.

i think he actually realizes that some guy isnt gonna steal BASIC ideas that help a beginner out and start copying him lol...

everyone else is so damn secretive

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RMF &raquo;</TD></TR><TR><TD CLASS="quote">This is what I use


_________
ID = \/ cc x 2.1, where
_________
(P+3)x2

ID = Primary tube inside diameter, CC = Cubic centimeter displacement of one cylinder, and P = Primary tube length

__________ _____

Here's an example: ID = \/ 500 = \/ 500 x 2.1 ID = 1.53"

(34.4+3) x 25 935



You then pick the appropriate outside diameter primary tubing with a wall thickness to give you an ID close to the calculation. Example: 18 gage 1 5/8" OD tubing has a wall thickness of .049" and an ID of 1.527", which is pretty close to our 1.53" calculation.




Modified by RMF at 10:10 AM 11/8/2005</TD></TR></TABLE>
ya what he said!!!!!!!!!!!!!!!!!

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RMF &raquo;</TD></TR><TR><TD CLASS="quote">Here's an example: ID = \/ 500 = \/ 500 x 2.1 ID = 1.53"

(34.4+3) x 25 935

</TD></TR></TABLE>

Maybe it's just me, but those numbers don't work. 500*2.1 = 1050, 500/1050 = 1.123. Can you clarify, or is there a wrong number in there?