question about factory headers
 

As I just installed new exhaust gaskets im not too keen on the idea of taking off my headers until this winter but I have a question if anyone can answer.

on another post I mentioned how I was thinking of making my own single shorty/gp style can for my bike on top of a full performance rebuild of the engine.

Does anyone know if the headers are equal length from the exhaust ports to where they meet or should I design my own headers for this venture?

or if anyone thinks this would be detrimental to performance Im also considering dual shorty/gp style pipes but thats only if I make my own headers which would be true dual with crossover.

No, they are not equal lenght, they are tuned length... Basically they match the speed of the exhaust flow to make the pulses not interfere... It's a lot of math...

It's been discussed in the other thread, and most likely you will loose top-end with a single, but perhaps gain low-end torque... It should be possible to make it work without losses, but that takes a lot of math, or a lot of trial and error...

well then heres a question... I was informed of the reason for difference in jetting front to back being the temp differences...

I will be doing a stage 1 high compression rebuild on the bike this winter along with some other things...

how does using equal length+longer velocity stacks change jetting front to back and does it make the jet settings closer to equal front to back?

if in fact it does make jetting closer to equal then wouldnt my sh benefit from headers that meet up closer to equal length (proportionately)...

and yes I am talking about making my own headers for my exhaust and Im not scared of trial and error

Well... you are confusing yourself, mixing 3 different things together... Sure they are related, but not neccesarily in that way...

One the reason for the different jetting is amongst other things temps (the front getting more cool air), but not exclusively...

The reason for the different length stacks is that a short stack is good at high RPM's, and a long stack is good at low RPM's (Some never bikes have a variable stack)... And making them out of ABS plastic which is cheap, light but not neccesarily that precise in flow characteristics, the best option to get reliable operation over a wide range is to make them staggered... And yeah, combined with the temp and jetting difference it makes sense to orient them as they are...

That was stock... Now, if you swap the velocity stacks to the billet ones, they are not taller than the stock one's... They are about equal with the tall one, but take a bit more space in the airbox due to the lip of the flared inlet... They have a much more precise shape since they are CNC milled alu instead of molded ABS, creating an airflow that is roughly equal to both the short and tall stack at each respective RPM range, and better in the midrange... The result is that instead of one carb being at near optimum and one a bit off at all times, meeting at a roughly even setting in the midrange, you get both close (or atleast closer) to optimum at all times... But no, the jetting isn't affected much in terms of balance between the front and back, all the other effects like different temps remains the same...

But the reason for the "staggered" headers are a complete different scenario... The pistons aren't firing at the same time, it's a V-twin... Meaning that even if you make the headers the same length, you won't get the exhaust gas coming out at the same time... As it is stock, it's supposed to time the pulses, so that you get the best possible exhaust evacuation... Meaning the correct backpressure at the correct time, and the correct flow at the correct time... Not that easy...

Now, the stock header is probably far from ideal, and if you do the research you can probably improve on it, a lot of full systems have proven that... But I doubt you will manage that with just trial and error... It will take a significant amount of math, to understand the flow of gasses, and a lot of reading about the theories about exhausts... I haven't interested myself in it too much, enough to know I prefer to buy a proven exhaust instead of making one...


If you want to improve on the design, take a good look at the proven designs, like the M4, Yoshi's or Moriwaki...

well tweety you are have an amazing amount of information and have always been a great help on the forum, and I now understand how those systems differentiate from eachother as well as effect eachother...

I know you said you havent interested yourself in completely understanding exhaust flow but it seems you may have enough information to help me with this one(hopefully) last question..

if the "proven performance" headers are designed to maximize exhaust flow and reduce scavenging so as the exhaust pulses are not fighting eachother, what would/could I gain or lose in terms of power with a dual exhaust no crossover but having the ability to adjust backpressure for each cylinder?

obviously adjusted and tuned using a dyno and using header wrap to keep gasses hot in the headers to increase velocity.

Well, the proven designs have a crossover in some form, so I think that it's probably beneficial... The ability to adjust backpressure is probably a good idea for a testrig, but I see no use for it on the final product...

But then again, I know how this stuff works only as far as it helps me understand the whole, and how it affects other things I have tuned on bikes... And I have done a lot more calculations of gasflow than I care to remember way back in time, so I get the basics, but not good enough to know if a design is good, bad, or whatever...

ok well heres what Ive been "designing" in my head... custom made headers with crossover similar to factory but done much cleaner to improve exhaust flow..

from the crossover 2 pipes to a custom made single shorty on the right side (dual inlet/dual outlet) and either change the diameter of the pipe that would normally go to the left in order to emulate proportionally the factory backpressure or make that pipe only adjustable for back pressure...

do you think Im on the right track here?

BTW besides my soon stage 1 motor build I want to drop as much weight as possible (just in case you were wondering why I dont want 2 cans) and have a build that wont take too much effort to go from stage 1 to stage 2 in the future.

I know your probably sick of talking about exhaust theory by now but as always I do appreciate the help and knowledge, especially from someone as experienced as you are when it comes to this engine.

Stage 1 and Stage 2 engines are complete different animals and require a different crankshaft and cams (and also oil pan for a true Stage 2 set up)....... so there is no "easy" way to go from one to the other...... ;)

Yeah... Not at all similar... A Stage 2 engine isn't really suited for street riding that much, and going from one to the other isn't an easy swap... A Stage 2 engine more or less requires a large bore full system... So the system made for a Stage 1 might not be ideal later...


Seriously, the weight of one alu/cf can vs two isn't a substantial weight loss, in terms of how the bike could be lightened, it's rather marginal... And the cost and effort of making your own exhaust is by far counterproductive if you weight it against swapping out suspension components giving both weight loss and performance improvements, and swapping wheels for lower inertia...

I know I'm speaking to a wall, I can recognise a "pet project" when I see one... And I'm wired the same way, stubborn is a good word... ;) But it needs to be said, you can loose far more weight in other ways, with proven gains, for less money and effort... My bike is substantially lighter than it was when I started, with far sturdier components...

In terms of what I know about exhaust, well I think I have said most of it... ;)

Only thing would be to make one more or less the way you want it, with a variable restriction in it, for both pipes, and then put the bike on the dyno and test it... I'd make that out of the cheapest available pipe in the correct diameter, just crudely slap it together... Then once you know if you get gains, and how to get them, have a good welder redo the same thing in Ti... That's what I'd do if I was going to do a system myself... But then again, I have the equipment to do both welding and dyno testing myself...

And it's unlikely I will ever need to since I happen to own two full systems for a VTR, one of which is the very rare Stage 2 Moriwaki system, that needs a modified oilpickup... The other being the equally hard to find M4 full system... So I think I'm good on the exhaust front... ;)

ok ok... i understand im going overboard for nothing more then personal achievement... but I believe I understand enough about exhaust now to be able to make a system that does offer performance gains(idle-redline) and weight savings...

As for "pet project"... yes I am like you and many other people on this forum who are very stubborn and determined and have no lack of effort or ability to take in new knowledge to make a project work and not completely kick myself in the ass..(i have no problem starting over from scratch)

My SH has been my main form of transportation rain or shine(8-9 months out of the year) for 5 years this month actually... all other vehicles borrowed... which is why I will be making the full exhaust myself (mandrel bends/welds/muffler) so if I cant get the project done by the end of the winter I can slap my current exhaust back on and not worry about it.

As for the stage 2 motor, I appologize greatly for not having done my research, I didnt realize it was a little more complex then I thought... (might have to buy another SH for that one:p)

as for other performance gains elsewhere Ive been messing around with the rear shock(and contemplating a JD F4I shock) as well as I already have racetech fork springs to install with new seals and fluid and will be getting gold valves this winter.. bracing the swing arm is soon to come as well as new rear rotor and pads... front brake mods are still mulling around my head (theres many options)... when I have my SH apart this winter everything that doesnt need to be there will be removed for weight savings(unless removing them is detrimental to performance... samco hoses are coming this winter my stock ones are soft and it will help with coolant flow and cosmetics...

Ive also been reading up on making carbon fiber parts to aid in rigidity and save weight but that may be a project for another year...

and finally, what we've really been discussing the straight through muffler(dual inlet/dual outlet) I could make different size inserts for both outlets in order to change backpressure either seperately or together... and from the sounds of it you think this is feasable and could give me performance gains all the way through redline of course if I spend a good amount of time on the dyno.

Yeah, it's feasible... But that aint saying much... ;)

None the less, good luck, and I sincerely hope you document this adventure because like with all things VTR, I'm curious as hell... The only reason I ended up not doing it, was that I lucked into getting those exhausts...

will do...

and yea im not that lucky and with a baby on the way finances wont let me purchase (if I could find) a full exhaust system like that... fabricating an exhaust over time and building an engine, buying parts here and there over time is a little more financially doable...

Tweety,
What exhaust are you currently running...the M4?

Were all waiting for tweety to measure out all the bends and diameter of the M4 system so we can replicate it. :)

+1 on that,been thinking of replicating a system.
would love to get full measurements of all the top systems.

Yep, M4 is on the bike... And since I'm playing with a lot of other stuff, anyone waiting for measurements is going to have to wait a while... sorry... ;)

BTW, after having looked at that thing for a while now, I'm actually pretty sure that it's goinng to be nigh on incomprehensible to understand those measurements anyway... The pipe keeps shifting diameter every 2-3 inches and the bends looks more like a snake, so I actually havent got a clue what to reference...

buy this book first
 

i read this book before i made my rear header and single exhaust. i would have screwed it up otherwise. it explains what backpressure really is and that it is usually a misnomer, how scavenging works and its relation to header design and firing order/angle. there are many useful equations in there, mainly the darcy weisbach equation for turbulent gas flow.

Darcy

Amazon.com: Scientific Design of Exhaust and Intake Systems (Engineering and Performance) (9780837603094): Philip H Smith, John C Morrison: Books