Header Primary Tube Diameter

[RussMcB]

I know this could open a can of worms, and that there is no definitive answer due to many variables, but,

Regarding header primary tube diamenter, what are the pros and cons of 1.5" vs 1 5/8"?

My engine: F1000 spec (stock internals) 2005 Kawasaki ZX10-R 1000 cc. I expect to make air box and Power Commander upgrades in the near future.

Background & additional info: I have in my possession (temporarily) a Muzzy header that has shown good HP on the dyno. It is a 4-2-1 design. My original intention was to copy its specs as much as possible while making a header that fit my chassis. Once I started measuring things, I realized that the Muzzy's primary tubes are 1.5" near the head, and then gradually expand to 1 5/8".

I anticipate that complexity will mean extra cost. If my budget doesn't allow something that elaborate, I may need to choose between those two sizes. Of course, that means the plan to copy the Muzzy and expect the same results goes out the window, but since my current header is sub par (I cobbled together something that would fit), I think there's still room for improvement. I'd also like a better header before I go to the trouble of coating it for lower engine bay temps.

Thanks for your thoughts.

[Becker Motorsports]

Russ for what its worth I contacted burns stainless for headers fabrication info and they have on line one of the most comprehensive artilces on the subject I have ever read. they also have a program that given your engine spec's and your goals [HP, Torque etc.] will tell you what the optimum sizeing should be.
regards; ernie

[cparsons]

Russ, you can get a ball park figure by using the formulas located at the bottom of the page at http://ourworld.cs.com/kellerRcng/exhaust.htm

the first formula to calculate primary length requires the RPM you want the scavenging to be at (your choice), and the degrees before BDC that the exhaust valve opens. It will calculate length
the second formula requires the length provided by the first formula (so do it first) and displacement of one cylinder. it will provide ID of primary.
using both forumulas will provide optimum length and ID of primary tubes.
primaries entering the collector should be arranged by firing order so the exhaust entering the collector is in a circular fashion and not zig-zag across the collector. (huh?) I hope that makes sense. example; R1's fire order is 1243 so primary 1 is next to primary for 2 which is next to primary 4 which is next to primary 3 which is next to primary 1 in a circular fashion like 12
34 each primary will then also partially scavenge the next primary by sending small vacuum wave up it prior to firing. scavenging of cylinder is done by the calculations above.

the pic i can't do has numbers 1 and 2 directly above 3 and 4, in that order

collectors and first stage of exhaust should be cone shaped, same length as primary + 2"(if I got that part right from another source which I can't remember to give credit to)

final stage of exhaust (optional) length best determined by dyno for torque.

But definitely get an expert opinion, I could be wrong. This in NOT my field of expertise.

[dereklola]

I'd be interested to hear if anyone finds the answers reasonable.

I just tried it for my vintage engines (Indy Lights and 2L BDG) and came up with about 3/4" primaries! I don't think so!!

[Daryl DeArman]

I'd be interested to hear if anyone finds the answers reasonable.

I just tried it for my vintage engines (Indy Lights and 2L BDG) and came up with about 3/4" primaries! I don't think so!!

Length seems very reasonable. Something wrong with the calculator on the diameter. I have a formula somewhere for the same things--I am thinking their answer might be the radius....I'll plug in the same numbers to a formula I have and see what it spits out.

[Rennie Clayton]

I'd be interested to hear if anyone finds the answers reasonable.

I just tried it for my vintage engines (Indy Lights and 2L BDG) and came up with about 3/4" primaries! I don't think so!!

When inputting the primary length that it asks for, be sure to include the decimal point. I.e., "18.000" instead of just "18".


Cheers,
Rennie

[dereklola]

When inputting the primary length that it asks for, be sure to include the decimal point. I.e., "18.000" instead of just "18".
Cheers,
Rennie

Why are these young guys so smart?

So what did the formula assume when I inputted "18" - obviously not "18.0"

[Rennie Clayton]

Why are these young guys so smart?

So what did the formula assume when I inputted "18" - obviously not "18.0"

They ran into an esoteric programming SNAFU here that is specific to the programming language they are using. Long story short, if they'd bothered to convert the value you type in to a number, they wouldn't have this problem. In the meantime, as long as you include the decimal point, the "automatic" number conversion they are using will interpret things correctly.

FWIW, when you type in "18", for some reason it is seeing "180" when it tries to automatically convert it to a number - probably some hidden end-of-line character.

Sorry for the programming threadjack, resume the header diameter discussion.


Cheers,
Rennie

[dereklola]

Thx Rennie

Not exactly the same but somewhat like ordering a 45deg hose end and getting a 135deg - doh! Don't ask how I know.

[RussMcB]

Pictures of the Muzzy.

At first, I didn't notice the gradual increase from 1.5" to 1 5/8". It's subtle.

The increase after the last collector is more obvious.

[Art Smith]

Russ-

having opened the "can of worms", it's my sense your question is a good deal more complicated than primary/secondary diameter and length. besides which stock engine you have and where it makes power (or what rpm you want to tune to), if you want something done right the number one constrainst to what's possible is the space available in your car!!

leaving only a 1/2" clearance, what is the shape and dimensions of the space your car currently has available for an exhaust system? what, if anything, are you willing to move to make space for a correctly designed exhaust (ie: horsepower/torque)?? what is the diameter (or H x W) of the exhaust port at the interface to the exhaust system?

included as an example is a printout of a solid model of an exhaust for a Honda 18C done in ~2001 for a drag race application. front wheel drive (bottom), an oversized radiator (front), and the proximity of the wheel well (left & right) left very little room to work. all that said, the hardest part was 2.000" OD tubing (bend radius) and the design rpm (length). notice it's a 4:1 design with the firing order feature explained above. there wasn't room for a 4:2:1 design.................. stepped diameter tubing increases the length of the primaries for any given design rpm.............. lack of space/length can force you to less than optimum collector designs (4:1 AND 4:2:1) and that should be one of your top concerns needing to turn everything 90 degrees................... flip the image left-to-right with your graphics program if you're having trouble with the front left wheel well design and how it relates to your situation.

I'd recommend thinking of stainless steel tubing wrapped with silica insulation to address your engine compartment concerns; lighter and much better control of the internal surface of your tubes. after all, it's the inside of the tubes that make horsepower; the rest of the material is structure!!

Art
artesmith@earthlink.net

[carnut169]

Just curious....

Anyone have any data that shows the difference between an optimized design for a given application/ engine/ space vs. a "generic" exhaust (S&S, or whoever) that fits and is of decent quality but not specifically designed for that car?

Are we talking about 10hp or a 10th of an hp?

Its an interesting proposition as I'd hate to spend what it would take to bdesign and build a custom stainless exhaust for an engine that will be outdated and replaced in 2-4 years anyway. I recently ordered a Peter-D stainless header/ collector (I believe they get it from S&S) that I'm sure I will have to slightly alter to fit my application but at $460 its not breaking the bank.

The wizzy Stohr headers that I wanted were just a bit out of reach (just like the rest of the car) at $1400.

Wonder what I'm giving up?

Stohr unit:



Peter-D

[Art Smith]

Sean-

it's my sense that a disposable exhaust system will provide affordable disposable performance. since that's not likely what you want to hear, here's a single public domain research data point (there's more if you look) for consideration:
"Performance Tuning in Theory & Practice - Four Strokes" by A. Graham Bell
Haynes Publishing Group Sparkford, Yeovil, Somerset BA22 7JJ, England 1991
p.118 ....... In fact I have found on the dyno, using cams of up to 290 degrees
duration and 70 degrees overlap, that headers 10% 'out of tune' resulted in a power
decrease of not more than 3% on the same motor with 'in tune' headers. However,
I have also determined that once the valve overlap increased to 100 degrees-130
degrees the tuned length became very critical, to the point that a slightly out of tune
header dropped power 10-12%."
my own work on 1600 and 2-liter Fords suggests the low overlap number is probably slightly understated. given the collectors in the pictures in the book and the fact the bulk of the author's work was done at or below 7500rpm it's also my sense (ie: I have NO back-to-back dyno data for high overlap engines) the high overlap numbers are understated.

for perspective, assuming a population of approximately 180hp engines and high overlap cams, my calculator suggests there's more performance difference potential with a properly designed/tested exhaust system than between all the manufactor's published performance numbers!!! the current GCR says exhausts are unrestricted. at the end of the day it comes down to a cost versus performance trade.........


Art
artesmith@earthlink.net