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General Category >> Rubber Side Down! >> Evolution of a Hot Rod Part 3 - Exhaust System
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Message started by DragBikeMike on 06/06/21 at 23:52:29

Title: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/06/21 at 23:52:29

This is the third in a series of reports intended to document the results of progressive modifications to the LS650 engine.

Part 1 outlined the project, set the rules, and established the baseline performance values for a box-stock LS650. You can find Part 1 here.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1620523526

Part 2 examined the airbox. We improved performance dramatically with a few simple and inexpensive modifications. It was a lot of bang for the bucks. You can find Part 2 here.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1621150483

Part 3 takes a hard look at the exhaust system. The airbox mods allow a lot more air into the engine, now we have to make it easier for the combustion products to get out of the engine. In Part 2, we discussed how engine output is largely dependent on the amount of air that can fill the cylinder. More air pretty much equals more power (as long as you add the correct amount of fuel). It’s easy to add more fuel, but hard to add more air.

If the exhaust system isn’t up to the job, combustion products will be left behind. Those spent gasses take up room and prevent air from completely filling the cylinder. There will also be pumping losses associated with a restrictive exhaust system. As the piston rises on the exhaust stroke, a restrictive exhaust system results in higher cylinder pressure. The piston has to pump against the residual pressure. It’s a parasitic loss we could do without.

So, we want an efficient free-flowing exhaust system to get all of the combustion products out of the engine as quickly as possible. Seems to me that the logical place to start is the muffler.

What I am about to describe worked good for me. If you decide to try this stuff on your own, you assume responsibility for the outcome. If you don’t have the skills, don’t do it. If you don’t understand something, STOP and get help. Get a manual. Read up. Comply with ALL the safety requirements outlined in the manual. Make sure you know what you are doing before attempting any of this stuff.

Let’s get started.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/06/21 at 23:54:02

The go-to muffler for the Savage crowd seems to be the “Harley Dyna”. From a practical standpoint, it’s a quick & dirty solution. The term “Dyna” is sort of misleading. Most of the Harley mufflers will fit the bill (Softail, Sportster, Dyna, FX, any of the two-into-two systems). You can find them on eBay, scrounge them up at the local Harley dealer dumpster, wheel & deal at independent shops, etc. A simple Google search using “used Harley mufflers” yields pages of eBay adds ranging from as low as $29 bucks a pair to upwards of $300.

For this experiment, I will be using a stock Harley muffler of unknown pedigree. I know it’s off a Harley. I know it has a catalyst. I know it’s chrome. It has a 1.75” inlet. That’s about it.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/06/21 at 23:54:40

This is how I know it has a catalyst.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/06/21 at 23:55:17

It flows a bit better than stock. It pulled 41” H2O on the trusty, two-shopvac test bench. In contrast, the stock muffler pulled like 46.5” H2O, so I know the Dyna is less restrictive.

To keep this mod simple and inexpensive, we are going to install the Harley muffler on the stock Suzuki head pipe. That will require an adapter. I used a Nickson 1.75 ID x 1.75 OD, part number 17515. They cost a little over $3 bucks.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/06/21 at 23:56:15

But alas, it’s not that simple. There’s a kink in the plan. The adapter requires a kink, because the stock header is angled inward toward the centerline of the motorcycle.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/06/21 at 23:56:52

So, you need an adapter with a kink to properly align the muffler with the bracket.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/06/21 at 23:57:42

I’ve tried to bend these adapters. It’s very hard to do. There’s another way. Cut the adapter half-way through, bend it, then braze it. It’s easy.

The adapters are aluminized. The aluminum must be removed in the area you intend to braze. See the aluminum on the grinding stone. For this job, stones don’t work. They load up with aluminum.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/06/21 at 23:58:16

Use a carbide burr. Remove the thin coating of aluminum in the area you intend to cut & braze.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/06/21 at 23:58:53

Then slice through the adapter with a hack saw. A muffler expander works great for holding the adapter. Only cut half-way through.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/06/21 at 23:59:22

Like this.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:00:02

Blunt the cutting tip of a small chisel. This one is a ¼” chisel.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:00:38

Use a small hammer and the blunt chisel to fold the edge of the cut like this.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:01:20

Use the muffler expander to hold the adapter. Insert a short section of exhaust pipe in the other end.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:02:18

Bend the adapter. Do a rough fitup. If necessary, bend more until everything lines up. It will look like this when you are ready to braze. See how the saw cut closed.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:02:58

This map gas torch works fine. They’re cheap. Most shade tree mechanics have one of these in their tool chest.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:03:31

Braze it up.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:04:14

The 1.75” OD side of the adapter fits into the Harley muffler. The 1.75” ID side of the adapter goes over the header pipe. The adapter will be loose on the pipe. Make a sleeve to fill in the gap. Take a short section of 1.75” OD exhaust pipe and cut though it with a hack saw.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:04:43

Slip the sleeve over the header pipe until it hits the shoulder. Position the cut in the sleeve facing down. Fill in the cut with silicone sealant. Permatex Ultra Grey can handle the heat. Then assemble the muffler and adapter onto the header pipe and sleeve. This shows the sleeve on the pipe with a bead of sealant in the cut, ready for assembly. The picture was taken from underneath the exhaust system.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:05:37

The muffler has a built-in mount slot. A 5/16” bolt fits in the slot.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:06:21

The bolt goes through one of the mount grommets in the muffler bracket. This shows what it looks like from underneath the muffler. A match made in heaven. It couldn’t be any easier.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:07:19

The finished installation looks OK. A little VHT paint will doll it up. It would be better with a nice heat shield, but for this test, I’m good to go.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:08:28

Let’s do a review of the current modifications before we start testing.

The airbox cover has been removed to supply more air to the engine. The stock air filter element is installed, and the carburetor has been rejetted. We have installed a #55 pilot jet and a #150 main jet. The slide needle has been raised .047” by replacing the .110” plastic spacer with a .063” plastic spacer. I refer to this needle position as +.05”, meaning it is .05” higher than the stock position.

We have replaced the stock muffler with the Dyna muffler. The stock header pipe has been retained.

Let’s fire it up.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:10:57

I did a noise test with the NIOSH app. Noise levels at 1300/3000/4000 rpm are 61/74/78 dB. I was surprised. I thought it would increase more than 1 dB @ 4000 rpm. It sounds good, much better than stock. It has a nice low-frequency thump, and it’s quiet.

A few laps around the block felt good. It seemed to have more punch and the jetting was close. Time for test & tune.

Best performance was achieved with a 152.5 main jet and the slide needle raised an additional .033”. I will refer to the needle position as +.08, meaning it is .08” higher than the stock position. I raised the needle because it had a lean surge at high-speed cruise.

Acceleration tests showed a significant improvement.

Second Gear 4K to 7K: 3.70 seconds Improvement: 0.62 seconds

Third Gear 4K to 6.5K: 7.56 seconds Improvement: 0.48 seconds

Fifth Gear 3.5K to 5K: 6.91 seconds Improvement: 0.87 seconds

Fifth Gear 3.5K to 5.5K: 11.64 seconds Improvement: 1.98 seconds

Now, it will pull all the way to 5800 rpm in fifth gear, where before, with just the airbox mods, it would not pull past 5700 rpm. The less restrictive muffler is helping a bit. The 5th gear pass simulation feels great. Most Savage owners would be satisfied with this level of performance.

Fuel mileage went down a bit. I averaged 53 mpg over several tanks of gas. Fuel economy dropped 2 mpg. That’s fine with me. The improvement in performance is worth 2 mpg. Chalk one up for the +.08” needle position.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:12:58

We now have a vastly improved induction system and a moderately improved exhaust system. The modifications are simple and inexpensive. Everything that has been modified can be restored to the stock condition. No internal engine work has been performed.

What happens if we amp up the exhaust flow a little bit. Let’s see if that crazy exhaust fitting works. The one I posted back in 2019. That would be this old post.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1554878768

The special fitting mockup was good for about 4% more flow on the test bench. I had never tried it on the motorcycle. Now was a good time to test one.

A chunk of scrap tubing and a 1.25” washer.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:13:38

Hack away and braze one together.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:14:14

Fit the pipe just right.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:14:49

And it fit the port too.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:15:14

After a full day of test & tune it was evident that my brilliant exhaust fitting was a dismal failure. It ran fine. You really couldn’t tell much difference seat-o-da-pants. But the stopwatch always tells the real story. It was measurably slower, not a lot but slower is slower. It’s a flop. I will update that old post to let folks know it doesn’t work. If any of you try it and have better results, by all means tell us your story.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:15:59

How about a better muffler, one that is way less restrictive?

A quick trip to the auto parts store for a 2”OD x 1.75” ID adapter, a little work with the hack saw and map gas torch, and voila, we have a new high-flow muffler hangin off the stock header pipe.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:17:50

The LCGP muffler flows a lot better than the Dyna muffler. It pulled a meager 31.5 inches H2O on the trusty two-shopvac test bench. You can find the details on the LCGP muffler in this old post.

http://suzukisavage.com/cgi-bin/YaBB.pl?num=1609379913

Can the modified induction system keep up with this hi-flow beauty?

I did a noise test with the NIOSH app. Noise levels at 1300/3000/4000 rpm are 64/77/79 dB. It’s about 3 dB louder than the Dyna at low rpm, but only 1 dB louder at 4000 rpm. Certainly acceptable. It sounds good, much better than stock, a little better than the Dyna. It has a cool low-frequency thump, and it’s reasonably quiet.

A few laps around the block felt OK. It was rideable but seemed a bit on the lean side. Time for test & tune.

Best performance was achieved with a 152.5 main jet and a compound slide needle still at +.08. You really can’t raise the slide needle more than .08” because you get to the point where it will exit the needle jet at WOT. I have run it at +.12 but it’s erratic, you can’t repeat test results. I was able to eliminate the lean condition by sanding a compound taper into the needle. It works OK. This shows the details on the taper.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:19:48

Again, acceleration tests showed a significant improvement.

Second Gear 4K to 7K: 3.59 seconds Improvement: 0.11 seconds

Third Gear 4K to 6.5K: 6.76 seconds Improvement: 0.80 seconds

Fifth Gear 3.5K to 5K: 6.15 seconds Improvement: 0.76 seconds

Fifth Gear 3.5K to 5.5K: 9.61 seconds Improvement: 2.03 seconds

It still maxes out at 5800 rpm in fifth gear, but it gets there a lot faster. The low restriction muffler is helping a lot. The 5th gear pass simulation is excellent. The sound is sweet.

Fuel mileage went up significantly. I averaged 65 mpg over several tanks of gas. Since the jetting is richer, I have to assume that the improved fuel economy is the result of reduced pumping loss (i.e less back pressure).

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:20:25

Now seemed like a logical time to groom the induction system a bit. Up to this point, the financial investment has been as low as reasonably achievable. What if we sprung a few bucks for a good low restriction air filter element? It’s easy to install but costs a lot. Is a K&N filter element worth the price? Stock on top, K&N SU-6595 on bottom.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:21:00

It’s a simple matter to pop in the K&N. It fits perfect. One screw and your good to go.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:22:55

A few laps around the block felt OK. Time for test & tune.

Best performance was achieved with a 155 main jet and the compound slide needle still at +.08.

Acceleration tests showed a measurable improvement. Are these gains worth the entry fee of $50 bucks? That’s up to you. As more modifications are added, the stock paper element may not be up to the job.

Second Gear 4K to 7K: 3.55 seconds Improvement: 0.04 seconds

Third Gear 4K to 6.5K: 6.53 seconds Improvement: 0.23 seconds

Fifth Gear 3.5K to 5K: 5.72 seconds Improvement: 0.43 seconds

Fifth Gear 3.5K to 5.5K: 9.19 seconds Improvement: 0.42 seconds

It still maxes out at 5800 rpm in fifth gear, but it gets there a lot faster. It’s the first setup to exceed 7000 rpm in 3rd gear, it pulled 7100 rpm. The low restriction muffler is working well with the low restriction air filter. The 5th gear pull feels great. Carburetion is clean. No afterfire. Considering that its 100% bolt on and completely reversible, I think this is a great setup for the average Savage aficionado.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:23:39

Since this part of the project is focused on the exhaust system, we might as well look at the header pipe.

The stock header pipe is double wall. The inside diameter is small for a 40 cubic inch engine. On the left is a 1.3” ID stock header pipe compared to a 1.79” ID Mac header pipe on the right.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:24:14

This shows the outlet side of the two header pipes.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:25:08

IMO, the stock header is too small while the Mac header is too big. The perfect size should be about 1.62” ID. How much difference do these header pipes make? Let’s find out. We know that the current setup with a stock header pipe runs really good. If we install the Mac header with the LCGP muffler we can compare the two and see which one runs better.

Off with the stock header and on with the Mac. The switcheroo took about 30 minutes. No more special kinked adapter for this installation. The muffler just slips right onto that big pipe.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:27:31

A few laps around the block felt OK. Seat-o-da-pants there was no difference. No audible difference. Time for test & tune.

Best performance was achieved with a 155 main jet and the compound slide needle still at +.08.

Acceleration tests showed a measurable improvement in 2nd and 3rd gear, and a measurable slowdown in 5th. We’re talkin almost no change. Certainly nothing the average bear can feel.

Second Gear 4K to 7K: 3.45 seconds Change: 0.10 seconds faster

Third Gear 4K to 6.5K: 6.38 seconds Change: 0.15 seconds faster

Fifth Gear 3.5K to 5K: 5.90 seconds Change: 0.18 seconds slower

Fifth Gear 3.5K to 5.5K: 9.33 seconds Change: 0.14 seconds slower

It maxed out at 6000 rpm in fifth gear, a 200-rpm increase. It pulled 7200 rpm in 3rd gear, a 100-rpm increase. Based on the acceleration times, it’s obvious that the larger header improves the high rpm portion of the power band, while the smaller header favors the low rpm portion. I suspect that the larger header will work much better as things get amped up. Once I start throwing in cams, larger carbs, and some porting, the larger header will start to pull away from the stock header. We shall see.

For this setup, the stock header seems to work better in the range of operation where most of us ride. Only the most discerning individuals, those with a calibrated butt dyno, will be able to tell the difference. So why shell out hard-earned cash for the big header if you don’t plan on taking your bike to the next level. The stock header works fine. Me, I gotta have the big one.

Title: Re: Evolution of a Hot Rod Part 3 - Exhaust System
Post by DragBikeMike on 06/07/21 at 00:30:15

This completes the exhaust system portion of the project. I may revisit the exhaust system as the project moves forward. Let’s take a look at the results so far.

We have improved the overall performance of the motorcycle. Carburetion is better. Throttle response has been improved. Fuel economy is up by 8 mpg. Afterfire and backfiring have been eliminated. Audible noise has increased a modest amount, but the quality of the exhaust note is more pleasing to the ear. All-out 3rd gear acceleration has improved by 3.95 seconds, and 5th gear passing acceleration has improved by 3.75 seconds (13.24 seconds if you run it all the way up to 5500 rpm). It really is like a different motorcycle.

I think that’s pretty good for such a small investment in time and money. Most of us could accomplish these modifications for under $200 bucks.

Next, I want to move on to the carburetor. The stock carburetor’s fuel delivery is grossly restricted by the stock needle. Even with the compound taper, it’s tough to maintain a safe air/fuel ratio. As I mentioned in Part 2, simple measurements and calculations show that the stock needle limits the maximum main jet to about a #155. Jets larger than #155 don’t have much effect on the air/fuel ratio at higher rpm. If I want to amp up the air flow through the engine, I will need a better carburetor, or at least figure out a better way to set up the stock carb. It’s tough when there isn’t a full selection of readily available parts for tuning.

At this point, I have done 105 WOT acceleration pulls to dial in the different combinations. The old girl is holdin up good. No leaks. No ugly noises. Not using any oil. Zero oil accumulating in the airbox. It’s a solid motor.

I hope some of you find this project informative and can use the data I collect to help make decisions on your own project. If you have suggestions or comments on my test methods, post a reply so we can discuss. As mentioned earlier, if you have a particular component or modification that you would like to see included, let me know and we can collaborate.

Best regards, Mike