DragBikeMike
Serious Thumper
Offline
SuzukiSavage.com Rocks!
Posts: 4284
Honolulu
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Very interesting comments.
Batz, I can't comment on the negative pressure wave. I just don't know enough about the acoustics involved, and I personally am of the opinion that the acoustic wave pretty much only pertains to open exhaust systems. I can't fully explain why I feel that way, but my gut tells me that if you are dumping this big pile of hot, expanding gas into a can with a bunch of teeny weeny holes, and baffles, and attenuators, the acoustic wave is toast. You need an abrupt change in diameter and pressure to create the acoustic wave. All we are getting when the gas enters the muffler is sudden stoppage. I'm sure that there is a science to all this, and folks with proper credentials have it all figured out, but a shade tree mechanic like me doesn't have the skills or the means to figure it out. So I have to keep my plans grounded in concepts that are more easily adapted to the shade tree stuff. For instance, exhaust systems that are significantly less restrictive rather than "tuned".
Regarding your comment about removing material from 3&9 o-clock positions, all I can say is that I've been reading a lot over the last few months. Pretty much everything I see from the so called experts says you want to increase the radius on the long side to improve the angle of attack, and only smooth the short side radius. The experts seem to agree that you don't want to remove a lot of material from the short radius because the port volume increases too much and the gas velocity is adversely affected. What makes this particular discussion interesting is that all the literature I am referring to deals with the roof and floor of the port, not the sides. But I also must add that the experts rarely discuss the exhaust port, they generally talk to the intake. The huge differential pressure across the exhaust sort of makes it a non-problem, at least up to a point.
Your comment regarding the converging condition being "bad news" is interesting. I agree that its a bad design, but I consider it sort of good news since it should be easy to remedy. Just gotta be prudent with the grinder.
Lancer, I like your question about the header pipe. Every piece of literature I have read and every formula I have tried indicate that the stock header is grossly undersize. But on the same topic, I can find formulas that indicate that a 1.75" ID pipe would be ideal, and others that indicate 1.5" ID is the cat's meow. To complicate the problem, the user of the formula has to come up with the rpm that he or she is shooting for. That simple question becomes very difficult to answer. You might think you want max torque somewhere around 4000 rpm only to find out you miss that low end punch. And then of course that formula stuff is theoretical. I can tell you this, I installed a MAC header that has a 1.79" ID. That seemed to me to be way bigger than necessary, so before I bolted the header up, I shoved an 18" section of flexible exhaust pipe down it's throat. The flex pipe has a 1.5" diameter ID, but its sort of corrugated. The corrugation feature makes the problem complicated since it adds an unknown that the formulas don't address. The bike feels great with that set-up, and I've had to drastically increase the jet sizes (usually a good indication). But honestly, its seat-o-da-pants. That seat-o-da-pants stuff has bit me in the butt on more than one occasion. I believe Rutley is running a 1.75" ID header with a 97mm setup, and he seems to like it a lot (Yo, Rutley, I apologize in advance if I got the numbers wrong). So a trip to the dyno is in order. But I just can't justify paying for dyno time every time I make a small change. So the next time I get some dyno data, it will represent a number of changes, and as such, will be impossible to correlate to any one mod.
Regarding smoothing out the sharp edges and opening the outer ring, my opinion is that sounds reasonable and proper. It seems logical. I will probably do it unless I find some good reason not to do it. Smoothing the sharp edges and getting rid of things that upset laminar flow are non-threatening modifications, there is little risk of screwing up the head. Opening that port exit has some risk but it simply seems too logical. It makes no sense to neck it down like that. I will most likely enlarge it to match my final header pipe ID.
Now I have a question for you. As I recall, you are located out in Henry, Oklahoma. As far as I know, that's hot-rod country. You got wide open spaces and plenty of opportunity for the WOT stuff. I've heard a rumor or two that you have a pretty swift Savage, and of course you have lots of experience with this beast, and what seems to be the inside track on performance parts. What size header do you run? Have you tried several size headers, and if so, why did you choose your current header size?
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