straight pipe exhaust

anyone run there bike without the baffles?

i once had a 76 kz900 that had megaphone pipes. no baffles. i thought the bike sounded cool but the cops didn't like it much if i goosed the throttle. HEHEHE. it had a deep rumbling VROOM VROOM.

was wondering what the xj650 might sound like.

jcwhitney has some clearance sidecut slash mufflers for $12.49 i'm thinking about ordering. but running straight pipe in the meantime. by cutting the backs out and pulling the baffles.

one muffler has a crack and the other muffle blew a hole. i'm thinking the mufflers are plugged and i certainly don't want to be blowing holes in the headers.

 

Sounds AWESOME! I have some sportster take offs that have the baffles removed and it sounds great! Go for it!!

 

Just remember that if you eliminate the back pressure completely then your bike will have a tendancy to run lean. So take into consideration that you may have to re-jet to richen up your fuel/air mixture!

 

i've got replacement mufflers coming. see how the bike runs. before i rejet it. if i can't get better freeway speed. then i'm selling the thing. LOL.

the one muffler i'm trying to get off with a hole in it. has TONS of shit falling out.

 

Agreed! My bike does run lean. Any ideas on what type of jets to use??

 

My bike had an old Mac 4-1 exhaust on it with no baffle and just the plate with the whole in it at the tip of the muffler for back pressure and it sounds and runs awesome.

 

Not sure what size to suggest, only that it should be bigger than stock. I'm sure someone with a 650 can give you a ball park size to move up to. Also maybe the needle settings. Are you running the stock air filter? Or k&N or pods? So many things can affect the tuning.
Fill in your bio a bit more, location etc. you never know, an experienced board member may live near and can lend a hand or suggest a decent honest shop nearby if you are not up to tackling it on your own.
We just had a carb clinic in London today, I went for social reasons only, but I left early and I think 4 or 5 bikes had been set up before I left.
Maybe WesleyJN can help, I just noticed in his sig that he has a 650....Wes???? any suggestions?

 

When I was bobbing my 550 I decided to run straight pipes and was contemplating this very question. I found a link to a page that explained how to keep the back pressures while running pipes. I gave it a try and the bike seems to run better than with the holey exhaust I had left on it.

dragpipes

Heck of a lot easier than re-jetting. Hope this helps

 

i'm actually toying with the idea of welding the muffler backs to the pipe. and grinding down so the pipe has no extended edges. and it looks halfway professional. AND hopefully reduces the noise.

it be nice to ride this weekend. but hopefully my new muffs get here before friday as i've got a big arse ride planned for the upcoming weekend.

$35 for exhaust pipes and adapaters. $35 WITH shippping for some clearance sidecuts from jcwhitney. supposedly comes with reducer and reversible mount brackets.

 

i got a set of the side discharge mufflers from JC Whitney and put them on my XJ550 this weekend. They look and sound great. I had to customize the mounting bracket on the left side to make it into a center stand rest. The set i got have removable baffles.

Before I put these on I had stock mufflers that the PO cut out the baffles. It sounded good at low rpm but could not take the screaming going down the highway. These still gave me the rumble at low rpm and greatly reduced the screaming at highway speed.

 

those are the ones i ordered. $12.49 a peace.

 

just to clear up "BACK PRESSURE" a bit, here is an extremely well written explanation about exhaust function, and the back pressure myth. i take no credit for this, but see no need to write it in my own words.

Backpressure: The myth and why it's wrong.

I. Introduction

One of the most misunderstood concepts in exhaust theory is backpressure. People love to talk about backpressure on message boards with no real understanding of what it is and what it's consequences are. I'm sure many of you have heard or read the phrase "Engines need backpressure" when discussing exhaust upgrades. That phrase is in fact completely inaccurate and a wholly misguided notion.

II. Some basic exhaust theory

Your exhaust system is designed to evacuate gases from the combustion chamber quickly and efficently. Exhaust gases are not produced in a smooth stream; exhaust gases originate in pulses. A 4 cylinder motor will have 4 distinct pulses per complete engine cycle, a 6 cylinder has 6 pules and so on. The more pulses that are produced, the more continuous the exhaust flow. Backpressure can be loosely defined as the resistance to positive flow - in this case, the resistance to positive flow of the exhaust stream.

III. Backpressure and velocity

Some people operate under the misguided notion that wider pipes are more effective at clearing the combustion chamber than narrower pipes. It's not hard to see how this misconception is appealing - wider pipes have the capability to flow more than narrower pipes. So if they have the ability to flow more, why isn't "wider is better" a good rule of thumb for exhaust upgrading? In a word - VELOCITY. I'm sure that all of you have at one time used a garden hose w/o a spray nozzle on it. If you let the water just run unrestricted out of the house it flows at a rather slow rate. However, if you take your finger and cover part of the opening, the water will flow out at a much much faster rate.

The astute exhaust designer knows that you must balance flow capacity with velocity. You want the exhaust gases to exit the chamber and speed along at the highest velocity possible - you want a FAST exhaust stream. If you have two exhaust pulses of equal volume, one in a 2" pipe and one in a 3" pipe, the pulse in the 2" pipe will be traveling considerably FASTER than the pulse in the 3" pipe. While it is true that the narrower the pipe, the higher the velocity of the exiting gases, you want make sure the pipe is wide enough so that there is as little backpressure as possible while maintaining suitable exhaust gas velocity. Backpressure in it's most extreme form can lead to reversion of the exhaust stream - that is to say the exhaust flows backwards, which is not good. The trick is to have a pipe that that is as narrow as possible while having as close to zero backpressure as possible at the RPM range you want your power band to be located at. Exhaust pipe diameters are best suited to a particular RPM range. A smaller pipe diameter will produce higher exhaust velocities at a lower RPM but create unacceptably high amounts of backpressure at high rpm. Thus if your powerband is located 2-3000 RPM you'd want a narrower pipe than if your powerband is located at 8-9000RPM.

Many engineers try to work around the RPM specific nature of pipe diameters by using setups that are capable of creating a similar effect as a change in pipe diameter on the fly. The most advanced is Ferrari's which consists of two exhaust paths after the header - at low RPM only one path is open to maintain exhaust velocity, but as RPM climbs and exhaust volume increases, the second path is opened to curb backpressure - since there is greater exhaust volume there is no loss in flow velocity. BMW and Nissan use a simpler and less effective method - there is a single exhaust path to the muffler; the muffler has two paths; one path is closed at low RPM but both are open at high RPM.

IV. So how did this myth come to be?

I often wonder how the myth "Engines need backpressure" came to be. Mostly I believe it is a misunderstanding of what is going on with the exhaust stream as pipe diameters change. For instance, someone with a civic decides he's going to uprade his exhaust with a 3" diameter piping. Once it's installed the owner notices that he seems to have lost a good bit of power throughout the powerband. He makes the connections in the following manner: "My wider exhaust eliminated all backpressure but I lost power, therefore the motor must need some backpressure in order to make power." What he did not realize is that he killed off all his flow velocity by using such a ridiculously wide pipe. It would have been possible for him to achieve close to zero backpressure with a much narrower pipe - in that way he would not have lost all his flow velocity.

V. So why is exhaust velocity so important?

The faster an exhaust pulse moves, the better it can scavenge out all of the spent gasses during valve overlap. The guiding principles of exhaust pulse scavenging are a bit beyond the scope of this doc but the general idea is a fast moving pulse creates a low pressure area behind it. This low pressure area acts as a vacuum and draws along the air behind it. A similar example would be a vehicle traveling at a high rate of speed on a dusty road. There is a low pressure area immediately behind the moving vehicle - dust particles get sucked into this low pressure area causing it to collect on the back of the vehicle. This effect is most noticeable on vans and hatchbacks which tend to create large trailing low pressure areas - giving rise to the numerous "wash me please" messages written in the thickly collected dust on the rear door(s).

 

Correct me if I'm misunderstanding, but in essence you get a better exhaust pulse using a smaller straight pipe than a baffled large one?

I always wondered why my cousin put such small annoying straight pipes on his Triumph. He always boasted he got more HP on the dyno with the narrow straight pipes. People still talk about that little purple Triumph smoking big bikes at the Harley races. Sounded like hell coming at you with a purple paint job. But man that bike flew and ran like a top.

 

that story was my theory at first too. but your going to find that most people will declare that the myth is indeed true.

why do you lose horse power?????
if you've gotten rid of the backpressure????
becuase your not getting as complete a burn by discarding the backpressure. thus, the theory of running richer jets. to allow more fuel into the cylinders so the spark has more to burn in order to maintain the horsepower rating. it also helps to keep the cylinders cooler. as your running hotter with a greater chance of burning up the exhaust valves.

discard the backpressure---you don't get a complete burn--- which also means a lean misfiring condition----thus the running hotter causing valve burnup.

you need backpressure. for maximum horsepower and fuel efficiency.

running richer jets might help to maintain the horsepower but it also decreases the fuel mileage.

would love to hear these thoughts from a dyno expert. they would know more about this theory since that's there expertise.

 

vedalkin- you are correct. your cousin had matched the exhaust to the engine and the powerband that he wanted out of it.

snowwy- its not a theory, its proven, simple first level physics. as you requested....this writeup comes from a dyno expert! if you would like to argue it, contact eddie sisneros on thumpertalk (www.thumpertalk.com). he was the first one to get a suzuki Z400 engine to cross the 60hp mark. he has also built and tuned many other high horsepower machines in the bike/atv/sled world.

 

i'm not saying it's not impossible to increase power. but there's more work involved then just exhaust m ods.


all i'm saying is there are also other experts that would disagree about the fact the backpressure is indeed needed. without it. you lose power becuase your running lean. so you need richer jets. and we all know what richer jets do to gas mileage.

you have to be an expert to know what your doing. and for most of us. we don't have that t ype of knowledge of the equipment to do such a tuning job.

 

i would urge you to TRY to find an expert (a real world successful expert, not self proclaimed) who would disagree with that writeup.

the major point for this thread should be, don't put exhaust throttle plates (backpressure) in your straight pipe in an attempt to avoid rejetting. if you dont want to rejet, dont alter your engine. if you want a strong low-mid powerband, dont put on 3" straight pipes. if you want to win a race, dont put on a pea-shooter.

even a look at most stock exhaust systems will reveal that there is still a very clear flow path for exhaust, often it is tight to promote exhaust gas velocity at lower rpms but it is not restrictive nor does it create backpressure (for its intended usable rpm range).