Author Topic: Free-flowing Silencer query (Read 13255 times)

JVS · **on:** April 27, 2013, 03:56:25 am

Hey all,

For the past 9000km, I've had the EFI Silencer from Hitchcocks and it has been running wonderfully. For a change, I bought the Silman Short Bottle silencer from India and received it yesterday. What I have noticed is that this Silman silencer is completely hollow, no baffles.

So, I just did a test fit of the silencer on my B5 just to hear the sound. I must admit it brought a huge smile on my face. It has a very deeper thump to it and one can hear the idle from 30-40m away clearly. It sounds wonderful. Something like this http://www.youtube.com/watch?v=R7yAcbzdlqY but still not on the same calibre as a CI. But it's amazing.

My question is regarding appropriate back pressure. Considering the stock header pipe has two catalytic converters? is it a good idea to run this Silman short bottle for the awesome sound but at the cost of back pressure? Am I looking at long term damage of the valve seats/short life and potential failure of the engine? Ace.Cafe, considering that you have been working on the CIs and now the UCE, what is your take on this?

Any input will be greatly appreciated! Thanks!

Singh_Chicago · **Reply #1 on:** April 27, 2013, 04:56:23 am

JVS,
Everyone in India buys and runs hollow pipe, I was in India two months ago and bought Silman shortbottle with baffles, the shop guy had hard time finding one with baffles. I asked the mechanics working in enfield dealership in India, they said dont worry nothing will happen to engine with hollow pipe. I am pretty sure the loudness will be higher with hollow pipe but I am very happy with Silman short bottle with baffles. Rest the forum experts will guide more.

Bulletman · **Reply #2 on:** April 27, 2013, 05:04:54 am

Quote from: JVS on April 27, 2013, 03:56:25 am

Hey all,

For the past 9000km, I've had the EFI Silencer from Hitchcocks and it has been running wonderfully. For a change, I bought the Silman Short Bottle silencer from India and received it yesterday. What I have noticed is that this Silman silencer is completely hollow, no baffles.

So, I just did a test fit of the silencer on my B5 just to hear the sound. I must admit it brought a huge smile on my face. It has a very deeper thump to it and one can hear the idle from 30-40m away clearly. It sounds wonderful. Something like this http://www.youtube.com/watch?v=R7yAcbzdlqY but still not on the same calibre as a CI. But it's amazing.

My question is regarding appropriate back pressure. Considering the stock header pipe has two catalytic converters? is it a good idea to run this Silman short bottle for the awesome sound but at the cost of back pressure? Am I looking at long term damage of the valve seats/short life and potential failure of the engine? Ace.Cafe, considering that you have been working on the CIs and now the UCE, what is your take on this?

Any input will be greatly appreciated! Thanks!

Wow JVS, that sounds really awesome... I'm sure Ace and other members will come up with a flurry of Input...If all goes well I would like to add the same to my C5 2011 bullet.
Cheers

Arizoni · **Reply #3 on:** April 27, 2013, 05:49:12 am

I'm not sure how big the flurry will be.

When it comes to the fuel injected UCE's I haven't seen enough data around to say what the effects of using a straight thru silencer will do to the engine.
Just how much the ECU can adjust for the leaner fuel mixture that is often associated with straight thru exhaust systems is unknown.

What material the exhaust valve and its valve seat are made from is unknown so its resistance to extreme temperatures caused by lean fuel/air mixtures is unknown.

We know that a straight thru silencer on a older designed carbureted engine can burn the exhaust valve and a noticeable part of an impending problem is backfiring during deceleration but we don't know how long the new UCE engines can tolerate it.

Singh_Chicago · **Reply #4 on:** April 27, 2013, 06:09:06 am

Arizoni,
What is the reason for backfiring during decel ? I do get one or two pops in my 30 mile commute with baffeled silencer (I kinda love it). Isn't the open exhst pipe good for reducing the pumping loses due to less restriction and will also keep the engine cool.

JVS · **Reply #5 on:** April 27, 2013, 06:42:50 am

Thanks Singh_Chicago and Arizoni.

The Enfield dealership response gives me confidence, yet as Arizoni has mentioned, we are not really sure about the UCE behaviour with the hollow pipes. I went for a 50km trip with the Silman Short Bottle, and yes, it is way louder than the EFI silencer, but at the same time I have noticed that the bike accelerates a lot quicker. More air flow etc

It might take time to get used to the sound, but at lower RPMs it is a nice thump. Open throttle and it is like 5 or 10 lions roaring amplified by a factor of 2 or so lol. Still scared about the damage to the valves, after the trip I may have weakened the valve seats? I don't know. I might just put the EFI silencer back on to be on the safe side $:-\$

hillntx · **Reply #6 on:** April 27, 2013, 11:10:50 am

What if you just took the baffle out of the end of your EFI silencer? Wouldn't it sound basically the same?

JVS · **Reply #7 on:** April 27, 2013, 11:30:05 am

Quote from: hillntx on April 27, 2013, 11:10:50 am

What if you just took the baffle out of the end of your EFI silencer? Wouldn't it sound basically the same?

Nope. I've been riding without the mechanised baffle from the EFI Silencer for a long time. It is loud, but not on the same level as the free-flowing one. It is not a deep thump, but it is still very decent. The EFI silencer has packing/baffle/mesh inside it and comes with the mechanised baffle that we can remove. So, even without the mechanised baffle, the EFI silencer is not a straight through pipe.

BRADEY · **Reply #8 on:** April 27, 2013, 01:13:28 pm

Could anybody in their leisure time
post the innards of the EFI silencer by Hitchcock.

ace.cafe · **Reply #9 on:** April 27, 2013, 01:37:10 pm

Basically, it comes down to the flexibility of the mapping on the EFI system in the ECU. If the EFI can adjust for the leaner mixture created by the change to the exhaust system, then it will do fine. If not, then problems can result.

Regarding "back pressure", there is nothing good about "back pressure". We always want as little of that as possible. However, the ability to adjust the mixture for the conditions presented by lower restriction is paramount to the success of the modification.

If you find that the EFI system cannot tolerate the change to a hollow exhaust and runs too lean, you can add that little "Baffle tube" that bolts in to the tail pipe, to help it out. I have used that before, and it does affect the mixture towards a richer direction to a certain degree. Or, you could put a "lollipop" in the end of the tailpipe, if you prefer. It will be a little bit quieter, and it might be enough restriction to bring you to a point where the EFI can handle it.

barenekd · **Reply #10 on:** April 27, 2013, 08:32:41 pm

The popping in the exhaust is caused by the lean mixture in the cylinder when you roll the throttle off. This mixture still lights when the plug fires, butthe lean mixture burns more slowly that a proper one, so it still goes out the exhaust valve afire. That is the fairly light popping. The big bangs occur when the little fire lights a big one from residual mixture still in the pipe. wit a properly designed exhaust system, or one with a lot of baffles, the sonic waves bouncing back and forth in the pipe will tend to hold or push the fire back into the combustion chamber, preventing the racket. This is part of the tuning of exhausts which basically says that long pipes will work in low RPM sections and shorter pipes work better at higher RPM. The sonic pulses match the opening of the exhaust port. If you look at old comp Gold Stars you will note that the scramblers have a much longer pipe than the road racers. It's to match the waves with the engine speed range you want to use.
Bare

JVS · **Reply #11 on:** April 28, 2013, 02:13:00 am

Thanks ace.

I may check the spark plug etc to see how lean/rich it is running. If it is too lean, I might adjust the TPS voltage to make it a tad richer. But for now, I have put the EFI silencer back on and will probably test the Silman again next week.

wildbill · **Reply #12 on:** April 28, 2013, 12:11:16 pm

Craig McClure · **Reply #13 on:** April 28, 2013, 06:09:31 pm

I have a new old stock british 1960's upswept cocktail shaker on my 2010 G5 Deluxe, & it works fine. There is only a shower drain type baffle in the muffler, my headpipe has not shown any aditional blueing in the year I've owned it. Even with throttle, it is not as annoying as many Harleys.

JVS · **Reply #14 on:** April 29, 2013, 10:59:10 am

Update

Honestly people, I will not recommend a short-bottle/long-bottle free-flow exhaust. Not sure about other free-flow silencers. The cocktail shaker exhaust sounds very good from the videos I've seen.

Anyhow, just did a few runs with the Silman Short Bottle on. Firstly dad rode the bike and I tried to hear the sound properly, and then I rode the bike and dad had a listen to it. At lower RPMs, it is a great thump, awesome Bullet sound. Till a steady 50km/hr is bearable. As soon as we give it a bit of throttle or higher RPMs, it gets very loud and blatty. Instead of thump, all you hear is phat phat phat. Any amount of moderate-high acceleration releases an obnoxious sound. And at higher speeds I can predict it will be very annoying to the rider and of course other people. No respect for Bullet. I even tried the removable baffle from the EFI silencer in the free-flow one. With that, all you hear is air coming out the exhaust in a rhythmatic note - fuss fuss fuss.

I will easily switch back to the EFI Silencer without the removable baffle. It is not too loud and not too quiet - just decent enough. I don't have the Silman Short Bottle with baffles, but after listening to the video Singh_Chicago posted, I think it is decent. Any short bottle with some kind of baffling, i.e. perforated tube or glasswool type of material should be okay.

We can still run the free-flow, but it all depends on the person. If you like very loud and blatty sound from your Bullet, then go for it. Otherwise, as long as you prefer a decent thump throughout the rev range, please choose some type of restricted silencer. The EFI silencer does a great job. Yes it does get a bit blatty at higher RPMs, but not too bad at all. Maybe we can drill a few larger holes in the perforated tube of the EFI to make it more louder, but I think it is okay as it is.

wildbill · **Reply #15 on:** April 29, 2013, 02:06:52 pm

i plan on doing a 200 klm plus trip tomorrow. do 100klm with the efi muffler's baffle out and the rest of the trip with it back in.
should give me a good idea what one works best for me

barenekd · **Reply #16 on:** April 29, 2013, 07:27:45 pm

The EFI has a great sound at any speed. The noise level is very middle of the pack as far as decibels go. Cops don't give you a second look at any speed, unless they are looking at you for a particular "any speed". You can still here it from about a block away puttering down the local neighborhood, but it's such a pleasant thump, it doesn't arouse animosity. Most of the people don't even look around as your thump by. By far, the best sounding pipe I've heard, all things considered.
Bare

Gypsyjon · **Reply #17 on:** April 30, 2013, 03:10:15 am

Goldstar!

wildbill · **Reply #18 on:** April 30, 2013, 08:42:22 am

did the 240klm run today - ran without and then with the baffle.
baffle out - pretty loud and ran ok - baffle in - still sounds good and appears to pulls the hill better.
conclusion - baffle stays

wildbill · **Reply #19 on:** May 01, 2013, 01:50:33 pm

forgot to mention. with the efi muffler and baffle out i experienced quite a bit of loud backfiring on throttle off.
a couple of times almost like a shotgun.

blaisecardoz · **Reply #20 on:** May 05, 2013, 08:16:26 am

https://www.youtube.com/watch?v=TydiR0_UnXE

mattsz · **Reply #21 on:** May 05, 2013, 12:32:38 pm

Wow, what a lot of silencer threads all in a row! Somebody must have posted to each one. I wish there was a link to a video of an Indore Silencer installation in one of them though.

Wildbill - that must be a pic of your EFI silencer, yes? Mine just arrived, but it's hard for me to tell what's inside. It's got a removable baffle in the tail end, held in place by a nut and locking washer:

When I hold it up, or shine my flashlight in this case, and look through it, light shows through clearly (no flash used for this pic):

When I look in the tail end, I can't see anything through the baffle, but through the input end I can see a tube inside, roughly the same diameter as the end pipes, perforated with small holes. I can also see the perforated screen shown in your pic:

What makes this thing a "silencer"? Is there some kind of packing material around the inner tube? Aside from that permanent perforated disc and the removable baffle, it seems like it should be like a straight pipe. How's it work?

And, are most people running this thing using the baffle? I want a thumpier note, and a little more umph than stock would be nice; I'm prepared to live with a bit more noise, but loud definitely isn't what I'm after. Of course, I'm going to try it with and without the baffle, but what has been your experience?