'Home Brew' BJaBusa custom exhaust

Well my 'Home Brew' BJaBusa (adapted from a Suzuki 1300 Hayabusa) custom exhaust is done. Total cost was under $70US (and could have been under $40US), but it did take quite a bit of work.

The exhaust is only slightly louder than stock, gives a great boost to acceleration, adds torque, (and the primary two things I wanted to accomplish) is less then half the weight and eliminates the cat converter and it's related heat.

To do this I studied many motorcycle stock exhausts for something I could mod for use on the Silver Wing. On my prior SWing I had installed a GPR exhaust can made for the scooter. I did not like the radically upswept profile and so cut and welded the inlet at a more normal angle, then made a new mount strap. That could be seen in the forum's prior main photo. The GPR was super light, looked good but was louder then desired and had too little back pressure as it was straight through design.

I had also owned Leo Vince exhaust on 2 other scooters and very much like them. But being an incorrigible tight-a**, and habitual DIY-hacker-repurposer, I wanted to use something I could get cheap. It also had to look good, perform well, be lighter, eliminate the cat convertor, and have adequate back pressure / tone similar to Leo Vince (due to additional baffling compared to the more straight through exhausts like the GPR).

For this project I settled upon using the right side exhaust can from a 2008 Suzuki Hayabusa. The reasons it worked well are:
1. The Hayabusa is 4-cylinder, 1300cc, ~150hp and the exhaust exits into 2 cans.
2. Though fairly quiet, each can is designed to handle half of the engine -- 650cc at 75hp. So each can handles the exhaust pressure pulses of 2 high rev cylinders, similar to a SWing engine.
3. The 'Busa exhaust exits from four cylinders, then two cylinders funnel together on each side into a cat convertor, then exit into an exhaust can, one on each side. Basically a 4 into 2 system. Since the exhaust cans are behind the cat, it is a separate unit and the cat did not have to be used. The SWing cat is integral to the exhaust can and cannot be separated (without radical surgery).
4. Stock SWing exhaust is about ~20lbs weight, modified 'Busa can and connector pipe is under 10lbs.
5. Steel casing and integral cat on the SWing retains considerable heat (good for muffler cooking lunch). 'Busa exhaust can is dual layer aluminum and dissipates heat well. Exterior remains cool enough to not need a guard.
6. The back pressure is enough that there is no backfiring and very little deceleration pop. If I disabled the PAIR system (no longer needed as there is no cat) there would be no pop.
7. It looks damn cool!

The results are excellent! It has a nice little growl at idle and initial crack of the throttle, but is no louder than stock in riding. Just like the past use of the GPR exhaust, I can feel the difference fom removing +10lbs of dead weight from the far rear of the scooter. Performance is better than I initially thought. The engine revs quicker and more freely. Acceleration is considerably improved and torque is great. It was an absolute pleasure to ride on the Rockin' the Rockies tour. In a roll-on from about 20mph, it out accelerates my buddies stock, well tuned Suzuki V-Strom 650 (both he, and the bike, are lighter).

The 26gm Dr. Pulley sliders, and opened up air box, lowered the 60mph cruising rpm by about 300-400rpm. This I had done a few months back. The 'BJaBusa exhaust lowered another 400-500rpm. Since I live in the mountains, climbing is important --  the acceleration and torque improvement makes the elevations much more fun and capable. It feels like I may be getting better MPG, but I ride 'briskly' and have not checked.

The process took quite a bit of cutting/welding/fabrication to the 'Busa inlet pipe. As the inlet pipe bolts to the can via a 3 bolt flange (see the pics), the can needed no mod other than a 1/4 hole drilled in the hanger mount.

Unless you have some fabrication experience and have cheap access to MIG or TIG welding, this is probably not practical. I am very pleased with the results, appearance and (particularly) the cost.

The finished exhaust with the modded stainless steel guard in place.


The modified flange inlet with the modded stainless steel guard removed.


A pic of a 'Busa that the exhaust can could have come from.

"The 'BJaBusa exhaust lowered another 400-500rpm. "

Can someone explain how that is possible.

Well, my very unscientific explanation would be.....
The exhaust (and other mods) allows the engine to be more efficient and thus produce more power. That added power allows the engine to work less to accomplish the same thing. 60mph is the point I used for my before, and after, comparison. My observation is that from stock, to now the engine rpm is about 700-1000 less at 60mph.

This is not specific to my custom exhaust. Any good aftermarket performance exhaust, that is tuned correctly, should have the effect of increasing power. Other scooters, bikes, cars, etc will respond best by addressing the most power restrictive aspect of the engine/drivetrain. On the Silver Wing (in my experience) the exhaust is EXTREMELY restrictive. The airbox (at my elevations) would be next.

On my V-Strom 1000 (sold) I used a device called a Teka box to tune the fuel injection while riding. On this bike it is well documented that a FI retune does wonders. The exhaust remained stock and the airbox was opened up. The retune increased mpg by 3, made the bike much smoother and eliminated the low speed stutter. So by addressing the worst/most restrictive aspect of the bike's performance, there were great improvements.

Again, this is only my unscientific 'seat-of-the-pants' observations.

I put a LeoVince performance muffler on my Swing. The rpm at cruising at 100 kph was exactly the same with the stock muffler. The only rpm reducing mod I have seen was the installation of Dr. Pulley sliders. They directly affect the variator's drive ratio. The shape of the stepped slider allows the sheaves to be pressed tighter together, forcing the belt even farther out towards the circumference of the sheaves, thus reducing the drive ratio.
I don't think a few hp gain could possibly lower cruising rpm by 700 to 1000 rpm.

I'll be waiting for Chris Olson's engineering dissection of this one.

bigbird wrote:

I'll be waiting for Chris Olson's engineering dissection of this one.

I do not know if that was meant to be constructive or not. But basically, I have to agree. In order to change engine rpm at a given road speed you have to change gear ratio in the transmission. To my knowledge there is no way an exhaust modification can have any effect on transmission gear ratio.

I may have posed this question previously, but here it is again: Won't reducing the back pressure as well as opening up the air filter, cause the engine to run lean? And if so then isn't there a significant risk of burning a hole in a piston.

Unless you are running a custom fuel map via a dyno'd Power Commander how can you correct for that lean mixture?

Tim

Cosmic_Jumper wrote:

I may have posed this question previously, but here it is again: Won't reducing the back pressure as well as opening up the air filter, cause the engine to run lean?

It depends. With a throttled engine at partial throttle conditions the position of the throttle valve determines how much air mass is admitted to the cylinders, not exhaust or intake restriction. So the air/fuel ratio does not change at partial throttle.

At wide open throttle (like a typical dyno run or for brief periods on the hiway) then you will need to remap the max injector duration to richen the mixture a bit.

ScooterBJ wrote:

The modified flange inlet with the modded stainless steel guard removed.

So is that the Honda clamp welded to a large flat 'washer' which, in turn, is welded to the 'Busa flange? Are the 'washer' and flange stainless?

Tim

OK, maybe I am not doing a good job of explaining so here is a try using a generic example.

- A vehicle's engine puts out 100 horsepower at 5000rpm. It goes 75mph at 3500rpm.

- You modify that engine and it now puts out 100 horsepower at 3500 rpm and 135 horsepower at 5000rpm.

- The vehicle now requires only 2500rpm to be at 75mph. 3500rpm provides 100mph.

I am just using basic principles of 'hotrodding. The project was a gamble (as are most of my projects) as I did not know the results of the exhaust being adapted -- I was 'guestimating'. The plan was lighter weight and less heat buildup. Extra performance would be a bonus. I also understood that if the back pressure was off, or the engine's exhaust pulses were a bad match to the baffle design, the engine could lose power. But that did not happen and my gamble paid off well.

Sorry to hear Leo Vince for Silver Wing does not provide much improved performance. I had decent results using the 4Road on a Kymco 250 and Majesty, years back. Perhaps the standards to be European street legal limits the performance capability. However, they are lighter, well made and look good. Many USA sold aftermarket performance exhausts will state something like "for off highway use only" as they do not meet sound or emissions standards. The ones that would meet standards may not improve performance much.

Cosmic_Jumper wrote:

Won't reducing the back pressure as well as opening up the air filter, cause the engine to run lean? And if so then isn't there a significant risk of burning a hole in a piston.

Unless you are running a custom fuel map via a dyno'd Power Commander how can you correct for that lean mixture?

If you have an '08 or newer Swing; no worries. The O2 sensor will signal the ECU to adjust the fuel delivery according to the new demands of the engine.

For an '07 or earlier, yes, it will run lean.

ScooterBJ wrote:

OK, maybe I am not doing a good job of explaining so here is a try using a generic example.

- A vehicle's engine puts out 100 horsepower at 5000rpm. It goes 75mph at 3500rpm.

- You modify that engine and it now puts out 100 horsepower at 3500 rpm and 135 horsepower at 5000rpm.

- The vehicle now requires only 2500rpm to be at 75mph. 3500rpm provides 100mph.

Sorry to hear Leo Vince for Silver Wing does not provide much improved performance.

Your logic is illogical. The amount of horsepower available is inconsequential. It's all about the gearing. Horsepower does not change the gear ratio. Gear ratio determines rpm, unless a torque converter or clutch slippage is involved.

Regarding the LeoVince performance. I cannot judge by the seat of my pants how much, if any performance is added by my straight through muffler. All I know is that it saves over 10 lbs, does not get hot like the cat equipped stock muffler, sounds good to me, and gives the aural impression of increased power and performance. Without a 1/4 mile time ticket or a dyno printout, your guess is as good as mine.

Cosmic_Jumper wrote:

So is that the Honda clamp welded to a large flat 'washer' which, in turn, is welded to the 'Busa flange? Are the 'washer' and flange stainless?
Tim

Hi Tim. It is the sleeve, inner sleeve gasket and clamp off the end of a stock SWing muffler. I did not want to screw up my stock one (as I didn't know if this would work) so I bought a dented one with a busted guard. Turns out, the inner tube of the 'Busa inlet is the same inside diameter as the SWing sleeve, so I could've made the sleeve, used the existing clamp and bought a new sleeve gasket.

The large diameter stainless steel outer tune, which was cut away and not used, was turned into an exhaust tip for my GMC pickup (but did not improve it's performance).
 [/quote]

ScooterBJ wrote:

OK, maybe I am not doing a good job of explaining so here is a try using a generic example.

- A vehicle's engine puts out 100 horsepower at 5000rpm. It goes 75mph at 3500rpm.

- You modify that engine and it now puts out 100 horsepower at 3500 rpm and 135 horsepower at 5000rpm.

- The vehicle now requires only 2500rpm to be at 75mph. 3500rpm provides 100mph.

I'm a little confused.  Are you saying your results are theoretical or measured?

bigbird covered this about as well as can possibly be done.  You cannot see any rpm change at a given road speed because of increase in power potential.  You need to change the gear ratio to do that.

In reference to the exhaust modification, I can add a little.  Considering a single cylinder, it fires once then the crankshaft turns 1.5 revolutions before it fires again.  The energy stored in either the flywheel and/or engine rotating mass continues to do work, including scavenging and recharging the cylinder.  The energy used during the exhaust stroke to scavenge, and during the intake stroke to recharge is called pumping losses.

Assuming the stock exhaust is restrictive (I don't know this), if you open it up to be more free-flowing, you will realize less pumping loss.  So the potential exists to see an increase in fuel mileage (and peak power) by using a more free-flowing exhaust system.

bigbird wrote:

Your logic is illogical...........

It is starting sound a bit personal. I cannot present this any more plainly. But I do hope it gets the crap analyzed and debated out of it. Hell, put up a poll and get votes. I will have a blast reading the back and forth, but have no need to further rationalize my results -- results I know as I did the work and I ride the scoot.

Mods are made to make oneself happy and everyone has their own opinion, that's why you see different mods on different bikes. We do what makes us happy not what makes someone else happy. If we wanted to make others happy we would ride Harleys and dress in black leather costumes and run straight pipes.    And of course loud pipes save lives not safty gear  

model28a wrote:

and dress in black leather costumes

With fringes and chrome studs.

ScooterBJ wrote:

bigbird wrote:

Your logic is illogical...........

It is starting sound a bit personal.

As they used to say on Dragnet, "just the facts". You keep trying to sell your belief that horsepower lowers rpm. I'm not buying. Caveat emptor.

model28a wrote:

Mods are made to make oneself happy and everyone has their own opinion, that's why you see different mods on different bikes. We do what makes us happy not what makes someone else happy.

Indeed true. But I must say for the sake of other readers that see this and say, "wow - that's exactly what I been looking for" that the claim of what it does defies long established laws of automotive engineering (or motorcycle engineering, if you will).

So it probably wouldn't hurt to provide a disclaimer stating something to the effect that there may be mysterious forces at work in the particular 'Busa muffler can used. And the results might not be able to be duplicated with a different muffler can.

bigbird wrote:

You keep trying to sell your belief that horsepower lowers rpm. I'm not buying. Caveat emptor.

Man, you guys are gems! I'm not trying to 'sell' anything, just providing my results. Hey, don't believe my observations of power improvement. But you might have to admit I came up with a decent looking, lightweight exhaust, without a cat converter, at a fraction of the cost of an aftermarket exhaust. But allow me to set this straight:

*DISCLAIMER*

1. It should be noted the creator of this exhaust application is bordering upon insanity, may be drinking snake oil and due to living in Colorado, could be legally stoned.

2. Individual power results will vary. This Hayabusa exhaust application utilizes tiny Suzuki elves that shovel the exhaust through at high speed. Due to the unreliable nature of Suzuki elves, their age, physical condition, general humorless attitude, habit of taking frequent smoke breaks and affinity to over-think situations, may affect results.

3. Rather than attempting to replicate this exhaust application it is recommended to spend $400 on an aftermarket exhaust which provides a comparable weight savings and the sensation of a power increase, opposed to an actual increase.

I think you may have missed my point. There was a thread on the forum not too long ago where one of the folks was looking for a way to reduce engine rpm at road speed. This is normally going to involve changing something in the transmission, or maybe fitting a larger rear tire. Changing the exhaust system, in my experience, has nothing to do with this.

There are other benefits to changing the exhaust. But you said in your first post on this:
The 26gm Dr. Pulley sliders, and opened up air box, lowered the 60mph cruising rpm by about 300-400rpm. This I had done a few months back. The 'BJaBusa exhaust lowered another 400-500rpm.

We are failing to understand how the muffler reduced the engine rpm. Your explanation of it makes no sense. That is all.

ScooterBJ wrote:

But you might have to admit I came up with a decent looking, lightweight exhaust, without a cat converter, at a fraction of the cost of an aftermarket exhaust.

Absolutely. Kudos to you.

I agree too that it's a nice idea for a low cost aftermarket exhaust system. It seems I saw that one of the admins here provided some dyno slips that included a run with aftermarket exhaust both with and without remapping the injection. It seems that changing the exhaust system is probably the single most effective performance enhancement you can make, assuming it is legal in your state. Usually it isn't legal. The aftermarket manufacturers for Harley-Davidson go to great lengths to supply dyno and emissions data for Harleys so they still meet EPA for the year of manufacture and it can be (legally) done at a Harley dealer. The noise is another issue and I've heard of a few Harley guys getting ticketed for that. For the most part local and county cops seem to not bother with them. State boys will though if you happen to catch one in the wrong mood.

Chris Olson wrote:

 It seems that changing the exhaust system is probably the single most effective performance enhancement you can make, assuming it is legal in your state.  Usually it isn't legal.  

Surprisingly, up here in my neck of the woods, it's legal to modify one's exhaust system. We do not have any emissions testing, but if a motor vehicle is to be sold, it must pass a regulated and enforced safety compliance inspection. There is no problem with an exhaust system, even one specified by the manufacturer as "for off road use only", passing our safety inspection. An unsafe muffler would be one that is rusted through, or improperly anchored or attached. A safe muffler could have all the baffles drilled out, could be hellaciously loud, yet still be safe.

I'm not sure what states in the US mandate emissions testing to get registration on a vehicle.  But in Wisconsin here it is broken down into several "jurisdictions" where it is required to be certified every two years.

They have been cracking down on diesel pickups lately.  State Patrol has been stopping them just because they see it's a diesel, and conducting roadside inspections.  It was popular to pull out the DPF and eliminate the DEF injection system - until a few guys started getting caught and got hung with $10,000 fines for tampering with a vehicle emissions system.

So at least in the US I would recommend checking before doing something like removing the cat on a '08 and later.

Edit:
I just checked the US laws on this. Anyone convicted of tampering with a vehicle emissions system is subject to a minimum fine of $2,500 at the federal level (EPA Enforcement Division) and additional state and local fines.

Aftermarket components can be installed provided evidence of federally approved testing for that component exists, and the results of the testing show that it does not alter the emissions of the vehicle as it was certified for the year of manufacture.

The exhaust system, regardless of whether or not it has a cat, is considered part of the vehicle's emissions system, since it was certified with the exhaust system on it. California has gone as far as to require sound emissions certification for any bike built after Jan 2013
http://ultimatemotorcycling.com/new-california-motorcycle-exhaust-law/

So I would again caution folks to check before doing anything to the exhaust on your bike. The days of "it's easier to ask for forgiveness than permission" are over when it comes to tampering with vehicle emissions systems, including on motorcycles.

When over 70% of the Harleys are using straight pipes I hardly think that a Silverwing with a muffler is going to be noticed as an affront to the environment and ticketed.

FWIW the Silverwing exhaust (at least on my '03) doesn't have an automotive-type catalytic. Instead it has a very narrow passage within the muffler which causes the exhaust gasses to become super hot and cook off any pollutants -for the lack of a better term. The reason the muffler is so heavy is because it is made from very heavy gauge steel and is double walled with a layer on insulation between so that it can handle the heat. My 2¢

Tim

Cosmic_Jumper wrote:

When over 70% of the Harleys are using straight pipes I hardly think that a Silverwing with a muffler is going to be noticed as an affront to the environment and ticketed.

There are some jurisdictions in various states that require periodic emissions testing to even get registration for your vehicle. Most of the time simply changing the exhaust on an older bike or car without a catalyst is not going to change anything. But it will definitely change it on one with a catalyst. Removing a catalyst from a vehicle OEM equipped and EPA certified with one is illegal. It used to be illegal only for professional technicians or shops. But the current law goes after individual owners who have tampered with the emissions system.

This only applies to the US. Don't know what the laws are in other countries. DMV has info on their website on what states have mandatory testing, and what is required. And, for instance, in Wisconsin motorcycles and mopeds are exempt, while vehicles required to be tested are tested on a dyno with a sniffer. On the other side of the coin, in Washington D.C nothing is exempt unless it was manufactured before 1968 or certified as a "zero emissions vehicle".
http://www.dmv.org/smog-check.php

Just saying that it's probably not a good idea to advocate illegal modifications on a vehicle on an internet forum with the advice that "you probably won't get caught".

Chris Olson wrote:

<>...in Washington D.C nothing is exempt unless it was manufactured before 1968 or certified as a "zero emissions vehicle".
http://www.dmv.org/smog-check.php

Damn, and here I was going to nominate BJ as Senator at Large from the High Country to represent our scootering interests in Washington. I guess it would be disingenuous to expect him to do so while using a government Chevy.

Hey, what about those parade horses in DC, don't they have some rather obnoxious emissions?

Tim

Cosmic_Jumper wrote:

Damn, and here I was going to nominate BJ as Senator at Large from the High Country to represent our scootering interests in Washington......

Thanks for the thought, Tim, but no politics for me. I (apparently) have a hard enough time explaining simple concepts, much less national-scooter-affairs. It would push me to shoot myself!

Holy Thread Revival Batman.

Would anyone have the photos of this modification?
Or has anyone else done similar?
Thanks.