to clarify header od dyno results

travelguy

Turbocharged
Joined
Aug 13, 2006
Messages
743
Location
Costa Mesa, CA
this is what 1.75 vs 2.0 od tubes looks like on a dyno..red(run 425) is 1.75 blue (run430) is 2.0.. there seems to be a lot of bigger is better out there but well hey i built both and these are the results.. no i havent built a 1.625 in this "cr" style.. dont think i will cuz im about done with it. this does show what od does on a stock bike. ive never seen a carp dyno comparing 1.75 vs 2.0 in their design so im not sure what they are basing their od on.. what i have found is as you increase od above 1.625 you will start loosing torque in the 0-3k range for a nominal gain in hp at rev limit kick in area. but hey make up your own minds. all my builds have baffles in them.. for me running a baffless system is not an option and if you heard one in person i seriously doubt you would run it on your bike either even if you pick up 1 or 2 hp.



this is the above "crish" design vs equal length in 1.75 (green run 422)
 
Close enough I couldn't tell the difference riding it Sam,
but the smaller ones sure look the best from what I can tell.
Bout done with mine?
Ready for me to shoot your money to you yet?
You just say when buddy, I'm sittin' on Go here.
If they're not quit done yet, I understand,
you can't rush perfection, and I'm not trying to.
Just wanted you to know I'm ready on my end..
 
They will be worth the wait, I know I had a lot of coments from people about the looks And The Finnish of them and as Mitch has himself noted they make the Staintunes sound even better at one stage while cruising along at 160klm/h (100mph) they sounded so magnificent I would have like to be able to record the sound it was orgasmic, friggin unreal...better stop I'm getting a woody!!
 
Hey Laz,

Scuse the dumbarse question but what is OD? I am assuming d is diameter but I always refer to things as ID for Internal Diameter. Anyhow, my question is have you ever tinkered with 2-3 inch ID headers?

I need to learn about this as am about to spend $$$ on a custom build and would love to hear your opinion first. Secondly is this subject a matter of split opinion amongst people that actually know what they are talking about, unlike myself that really doesn't have the foggiest when it comes to back pressure and airflow science.
 

OD = outside diametre
 
triple

pont, blue line is 2"od which is 1 7/8 id.. most headers are built using .065 or 1/8 thick wall tube..

as far as larger than 2 od no i havent.. to give you an idea what you are asking about : here is the math behind a 1400hp v8 motor.. and they used 2"od primarys with a 4" beyond collector... im just curious where you guys get this idea that bigger is better.. any and i mean anyone who builds motors or exhaust for a living in the real boy clubs of nascar etc would laugh at a 200-240 hp 3 cylnder with 3"od primarys.. their 1400hp v8 means a 2" will support 175hp per primary.. if and i mean if you are pulling a true 240 hp that is 80hp / primary

but hey if your guys says so build it and see how it runs it's only money

------------------------------------------------------------

An engine requires about 2.2 CFM per horsepower, and exhaust gas flows about 115 CFM per square inch.

Assuming 1,400 hp / 2 (since there are two exhaust pipes) means we have 700 hp per exhaust pipe. Multiply that by 2.2 cfm / horsepower and we see we need 1,440 cfm. Divide that by 115 cfm / square inch, and we need 12.5 square inches of pipe area. The area of a 4-inch round pipe is equal to (pi r (squared) = 3.14 x 2 (squared) = 12.6 square inches. So a 4-inch exhaust is just barely big enough to support 1,400 hp.


As an aside, 1,400 hp means each primary tube in the header needs to support 1400 / 8 hp = 175 hp. Doing the same calculation 175 x 2.2 / 115 = 3.3 square inches. The area of a 2-inch tube is 3.1 square inches
 
I had it @ 140hp per header wants 2.68sq"
with 2"od (1.75id) gives 2.7sq"
Thats why I think 2" headers will work well on my motor.
Plus look the dogs doodas.
 


Ohhhh, thanks for clarifying that for me, LOL, now I get it????? Brother you are talking to a bloke who has just bought my 7th set of screw drivers and all the f__kers are left handed, cant seem to get them to work correctly - if you know what I mean,

Now, on a serious note, I gather you think going too big is wrong? or is it just not necessary??? Not doubting you brother, just need it broken down to 3 words (kinda) I gather you are suggesting 1 7/8 ID is the optimum for my bike... I believe my rear wheel HP will be a very real 210-220hp I certainly am not expecting 240 as trying to keep it streetable..
 
rocket

pont, think of the od like a blow gun.. part of what you are doing with header design is the velocity of the escaping gas.. your aborigines dont use a large diameter tube.. they use a small diameter one.

there's a lot more to this stuff.. it has to do with sound waves etc and things like the radius and number of turns that are in the tubes.. length of the primarys.. choke point diameter of the collector. the convergent angle and consequent length of the collector... ete etc.

paul runs my original predators which are 1 5/8 od on his supercharged bike and pulls 295 hp

the problem with me advising you on this is all my testing has been on a "stock" bike. my way of design is say what you want but build it and run it and see what happens. from my above results if it were me i would be running a 1.75 od set up on a built motor for the best "overall" power band but that is my opinion based on what my results have been building shall we say numerous designs with varying specs. some here have taken the power band into different relms and need to lose torque to better use the power.. that is another discussion and there are ways to do that also but i wouldnt say it applys to you.
 
gotta tell ya les those headers make me stop and stare at them every time i walk by.. they really look , shall we say, aggressive.
 
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