| Author | Message | ||
     Redscuell |
I've measured the difference between the front and rear headers, and come up with 11". The purpose of my post is not to take issue with them being different; my query: I'm confident enough in my measurement for my purposes, but wonder if anyone here has ACCURATE measurements of the lengths of the two pipes on the 09? Perhaps the 08 is the same. Cheers. | ||
| Stormy |
Fill em with water, use the radius to convert back to a effective length, only way I know of to measure without a supercomputer. | ||
| Redscuell |
Thanks for that stormy; I've made my measurements with the engine and pipes 'in situ' and I'm not planning on removing either just to get a more accurate measurement such as you suggest. But I'll bet there are some here who have! And I'm hoping they'll share. | ||
| Badlionsfan |
Someone here has the free spirits full system. Maybe they could water test the stock headers. Someone mentioned having the fmf full system too. There should be a few stock headers laying around. | ||
| Blower1 |
If someone have a extra pair of stock headers, i´m interested to buy one. About header lengths, the rear header is about two times longer than the front header. Calculated "optimal" header length is ( depending of calculation program ) something between 24" and 26". | ||
| Redscuell |
"the rear header is about two times longer than the front header" I was hoping for something more accurate than that! Even my roughish measurements say the rear is less than 2x the front: 26" rear, 15.5" front, and I don't reckon I'm off by more than 1/2"!! But someone PROVE me wrong, so that when I equalise the header lengths, I can be 'spot on'. Cheers. | ||
| Redscuell |
Here's a wild idea: Buell / H-D could actually PROVIDE this information (or any other factory information that's requested on this Board)! Oh, that's right, I forgot: no one at H-D actually cares any longer, about how paying Buell customers are faring. | ||
| 1_mike |
A collector will help equalize the system, but only up to about a four inch difference. This works with V-6 and V-8 engines. I have no doubt that it's VERY close to the same with a twin. Mike | ||
| Oddball |
I don't know if it applies to exhaust headers but exhaust vents (dryers) lose maximum available length with every turn. If that holds true for headers than maybe the bends in the front header equals a longer tube through increased resistance? Also what of the timing of pulses like used with v8's for scavenging? Think differences in length could be for that purpose? Maybe those are stupid questions/ideas, I don't know. | ||
| Bob_thompson |
I agree with what you have said Oddball and also what 1_mike has said and will add: A collector just might have MORE of an effect on a V twin. Also extra bends in a head pipe can be offset by using a little larger diameter pipe but not too large as to loose velocity, or in our case two head pipes of smaller diameter per cylinder. And I agree with you said, that timing impulses do play a part in head pipe length for scavenging especially with a collector. Much of this exhaust tuning though is what you want your engine to do, i.e.: all out H.P. at top rpm's or a well rounded torque curve throughout the rpm range. I prefer the latter for the street. Racers will differ. Just my take FWIW. And the only stupid question is the one not asked! Good info guys. Bob | ||
| Torquaholic |
I have a spare set of '08 headers in my closet. Is there something I can do with them that will help? | ||
| D_adams |
Torquaholic, cap the ends of both, fill with water, pour out into a graduated cylinder, record the amount for each and post the numbers. Beyond that, it's just math to figure out the length. If you have a Ratio-Rite, it would help for accuracy. Needs to be as close as possible in the smallest measurement you can get, ie; in cc's if you can, like 1000 cc's for the rear, 800 cc's for the front. | ||
| 1_mike |
Along with this perceived perfect header....ponder this. There IS NO such thing..! You take the parameters of the engine to start the figuring, diameter, length, step or no step, standard collector, merge collector, where to put the first collector (the twin primary tubes)...etc. NOW...you screw up all the math you just went thru because you need to figure out just what RPM areas you spend most of the time in....! Where do you what the torque curve to be...how to shift it around the power curve and return the bestest power for what you normally do. You do this by...changing the diameter of the different tubes, the length of the tubes, the style of collector(s)... Unless you are a drag racer...with a very small power and RPM band..ALL headers are a great compromise. Mike (Message edited by 1_mike on December 02, 2009) | ||
| Fast1075 |
Just to toss in another variable...don't forget that the distance between the back side of the valve and the port face is part of the exhaust lenght also. | ||
| D_adams |
Fast1075 - sure, but both heads are equal in dimensions from the valve face to the port exit from the head. I think he's just looking for a semi-accurate measurement of the headers only. | ||
| Fast1075 |
Sorry...right you are...Where i was going with that was if someone is doing a "from scratch" design and wanted a total lenght to work with rather than an "in addition to" lenght. | ||
| Redscuell |
Torque, there IS something you could do to help. Although I DO like the volumetric method on offer, it's more than I personally would ask you to do. My measurements, WITH THE MOTOR AND HEADERS IN THE BIKE, from the header flange where it meets the head, to the final edge of the outlet gasket, are 26" rear, 15.5" front. If you would, measure your pipes? I know that the 08 and 09 pipes are different, but I'm thinking that the differences are restricted to being O2 sensor location? Of course you would want to NOT measure along the inside or outside of each curve; instead you would measure along the centreline of the SIDE of a curve. Yes, I know that the individual pipes from each valve are not the same length. One could measure both ways and average? Cheers. | ||
| Torquaholic |
I haven't gotten out the string and attempted to measure the headers yet. Between each header, there is a clear difference in length of both the main tubes and the individual smaller primaries stemming from the exhaust flange. I brought the headers to work today and just finished taping/filling them with water, emptying into a 2000ml graduated cylinder. I drained and filled twice to see the numbers repeat, made sure I moved them around enough to release all air bubbles in the tubes before topping off and measuring. The rear header, the longer one, holds 880ml. The front header holds 540-550ml. The cylinder was marked by 20ml increments. If I had to guess, the header holds 545ml, as it was just below halfway between 540 and 560ml. These measurements were made from a stock set of 2008 headers. the 02's were removed and the bungs taped at the surface, so they might account for 5ml of volume, but the ratio of front to rear header volume is the same since I had both set up the same way. Hope that helps for now. I'll try to get some rough estimates of the individual and total tube lengths for you some time this weekend. That'll be tricky though, given the irregularity of the bends on these tubes. I may have to take an average of three sides to give a rough length with respect to the bends.... We'll see. More to come. --Kevin | ||
| Torquaholic |
also, as I posted on another thread before: In case you haven't been able to get the measurements. I ran a quick set of measurements on the spare headers I have. ID of the header inlet at the exhaust port: 28mm, roughly 1.125"(x2) OD of the header inlet at the exhaust port: 31mm, roughly 1.25" (x2) ID of the larger primary: 1 11/16", roughly 43mm OD of the larger primary: 1.75", roughly 45mm wall thickness of the larger primary tube seems to be spot on at 1mm thick. I don't know what gauge that converts to. these measurements are the same for each header. I don't know if that helps anyone. That's what I just came up with, using a cheap manual Vernier Caliper. --Kevin | ||
| Redscuell |
Thanks so much, torque, you have done the Board a great service. Your volume measurements of 545/880 indicate that the front header is 62% by volume of the rear; my external measurements of the two showed 26"/15.5", which indicates the front is 60% of the rear; so my method was, as we say here, 'a bloody good guess'. Cheers. For any who would say, 'why bother' equalising the header lengths -- I would say, 'because it's there'. | ||
| Torquaholic |
Red, indeed it looks like your measurements were very close. Good work. A quick volume calculation with an ID of the pipe measuring 43mm tells me the front header would need to be extended an additional 9.084", or 23.07cm to be equal to the rear header. Anyone care to confirm that calculation? (Message edited by torquaholic on December 05, 2009) | ||
| Bob_thompson |
I'm trying hard here guys to understand just how the volume would be "directly" involved in the flow characteristics of a given pipe. It would seem you would also have to involve the diameters, bends, friction variances of small vs larger pipes, material, etc. I DO believe volume is important but everything else has to work in harmony with the end product. Good job calculating though guys. The dyno tells the final story whether in torque or top end H.P. of the finished pipe/muffler combination. Just my take, FWIW. | ||
| 46champ |
Could the difference in header length be a way of adjusting the exhaust flow pulse to equal out time wise when it reaches the collector, considering the timing difference because of the uneven firing impulse by the configuration of the engine. | ||
| D_adams |
Anony, we need some input here. It doesn't have to be detailed engineering specs or anything, just a general explanation for the different length headers. Inquiring minds want to know. | ||
| Torquaholic |
Bob, I'm no expert and I know you have done a good bit of homework in exhaust theory as well, having come up with your own exhaust setup. you're certainly correct in your assertion that volume isn't everything. Given that both headers use the exact same size pipes, I'm just using the header volume to determine how much shorter the front is than the rear. The main reason I think an equal length header setup would be beneficial is merely for exhaust pulse timing and how having an equal length would, in my head, be beneficial with regards to evenly distributing the exhaust flow.. Evenly spacing the exhaust pulses by having even length headers should allow the positive pressure wave coming out of one header to effectively create a negative pressure (suction) in the adjacent header when they meet at the Y-pipe, thereby increasing exhaust velocity and efficiency, as well as smoothing out the flow... instead of having two pulses dump on top of each other, followed by a empty period until the next double pulse comes along in an uneven setup like we have. I know there's a lot more to it than that, so if anyone anyone sees it differently than me, please explain your thoughts. Thanks. --Kevin | ||
| Anakist |
Torquaholic: It is a V Twin. The cylinders are offset by 72deg so the equal length headers would be a bit less than half (72/180) a turn out of phase. Your theory works perfectly for a parallel engine, but IMHO there needs to be an adjustment for the fact that the cylinders are 72deg out of phase anyway. James | ||
| Blower1 |
The cylinder offset is 72deg, so the firing impulses are 432deg and 288deg. If simplifying header lengths 432/288 = 1.5, so the other header should be 50% longer. BUT if looking Ducati v-twin engined superbike race headers, they are both equal length.I believe that the Ducati race department has put some hours to create the best possible exhaust system in their bikes. | ||
| Redscuell |
I've enjoyed this exchange; the most civil series of postings I've seen on the Board for a very long time; and the posts involve critical thinking, rather than critics. "volume calculation with an ID of the pipe measuring 43mm tells me the front header would need to be extended an additional 9.084"". My own formula, not using your volumes but assuming that I needed to adjust at least one of my rough measurements to bring the ratio into accord with your 62%, indicates I would add about 10". I don't know if that's right, because my method has to assume that at least one of my "string" measurements is correct; but I also expect that a 1" delta from "ideal" won't matter if a 9-10" delta doesn't. I am going to do more than add length to the tubing; and when the entire mod is completed next week (have to hurry, Australian businesses tend to close up in the weeks before and after Xmas) I'll post up pics/dyno. I have a NEW 09 'N' muffler as a backup in case I screw up the old one with my mods. (Message edited by redscuell on December 08, 2009) | ||
| Torquaholic |
Stemming from thoughts about this thread, I decided to email a race exhaust's technical department. Here's a bit of the conversation to share with you all: My question to you exhaust experts is: how does the fact that the engine is a 72 degree v-twin affect header length? ...Not much. It is not a 180 or 90 degree engine. Any engine is affected by length. Too short no inertial or torque...too long and wasted heat energy and or timing of reversion. One of the other guys involved in the discussion had this to say, "The cylinder offset is 72deg, so the firing impulses are 432deg and 288deg. If simplifying header lengths 432/288 = 1.5, so the other header should be 50% longer. Is that necessarily true? No. Looking at race team V-twins, I see that Ducati race bikes have equal length headers. ...Ducati is 90 degree engine. Pulses are symmetrical You mentioned having a V-twin at either 180 or 90 degrees would result in symmetrical exhaust pulses. Does that mean an equal length primary set is really only beneficial in a symmetrical-pulse engine setup? ...No. It is just more benefit in equally spaces firing pulses. Reversion arrives at compromise situations...one can be longer than the other. the 1125 is a 4-valve motor. does that affect headers any? ...4 valve engines breathe very well but have large valve curtain area. Big mistake is to make too large a primary tube. We use 1 3/4" primary tubes on 1100/1150/1200 BMWs but they could have been 1 5/8" (40 mm). Can you give me some general ideas on how you would design an exhaust for this engine? ...Merge collector, narrow angle, knife edge internal, no positive uphill steps. No stepped header. Primaries in the mid 20" to maximum 28" range. Collector diameter up two 1/8" steps from primary tube size ( 1 5/8 to 1 7/8 or/ 1 3/4 to 2"). Secondary tube length 12" to 17" ( 1 7/8 to 2") ...beyond 17" doesn't do diddly, just routing. Low back-pressure muffler. Just thought I'd share some interesting bits of tech for those of you still reading this thread. Take it how you will; I'm not saying this is the final word in the matter just because I contacted an "expert". BTW, I too have enjoyed this thread. --Kevin | ||
| Bob_thompson |
Great job Kevin, getting info directly from the "horses mouth" Best info yet and as Reds said, the best exchange of ideas yet. Thanks much guys. Bob |
