Pre-muffler vs bypass pipe

[Decolliber]

Thinking of Spring projects. Noticed that Pelican's price for the Dansk pre-muffler has gone up to $400. The Fabspeed pre-muffler is only $250. Pelican also has bypass pipe for $130.
What would be reason(s) to pay more for a pre-muffler instead of just a cheaper by-pass pipe?

[SRISER]

Less resonation and a bit quieter. Fabspeed is a nice unit.

[v9ff]

The bypass pipe is just that... a straight pipe which is much louder than the pre-muffler. The pre-muffler is also a straight pipe but it has a resonator as an inner wall. The pre-muffler is the way to go... unless you're finanacially challenged then the bypass pipe will work just fine.

[Wil Ferch]

The straight pipe is reported to make little or no additional hp. The factory Euro pre-muffler has a shape and internal geometry to make about 6 more hp. Dansk and Fabspeed follow the factory design.
---Wil Ferch

[1987C1]

I have the bypass pipe with a stock muffler - did not change the
sound very much and you save weight over the pre-muffler.
Still a very quiet car but sounds a little better now.

[1987C1]

Originally posted by Wil Ferch
The straight pipe is reported to make little or no additional hp. The factory Euro pre-muffler has a shape and internal geometry to make about 6 more hp. Dansk and Fabspeed follow the factory design.
---Wil Ferch

Dosn't the straight pipe follow the shape and geometry of the
pre-muffler. I don't see why the straight pipe would be any
different than the pre-muffler - should have better flow?

[KFC911]

Originally posted by 1987C1
I don't see why the straight pipe would be any
different than the pre-muffler - should have better flow?

What Wil said...

[Wil Ferch]

It might be similar to "expansion chambers" used in two stroke racing motorcycles...there isn't all that much "obvious" on how *those* things are shaped to produce hp, too !
Similarly, I recall Pano articles on how Porsche designed a particular "curve" in the 944 exhaust system....that did not have identical cross sectional area throughout, because the mass of gass hugged the outside curve more than the inside....a different ( engineered) shape was required.
Finaly, Bruce Anderson mentions similar gains / no gains in his performance book ..related to a straight pipe vs. proper pre-muffler.
--Wil Ferch

[cyprusx]

From previous posts... Even the premuffler is a straight pipe with a shroud. No difference in HP what-so-ever. Can I prove it? Nope. Can you? Nope. Unless you spend the time and money to specifically test the differences. It makes sense that the bypass may be louder but come on... Your pipes leading to the bypass/premuff aren't baffling the sound at all. In the end, it depends on your muffler.

[1987C1]

Looks like why the pre-muffler is better than the straight pipe is a mystery. I have never seen any tests done on this except the note in Bruce's Performance book (is it correct? what tests were done?)
I have never understood why an "expansion chamber" would help performance or seen this on any other cars or in any aftermarket designs. I must have a lot to learn.

[dickster]

Even the premuffler is a straight pipe with a shroud. No difference in HP what-so-ever. Can I prove it? Nope. Can you? Nope. Unless you spend the time and money to specifically test the differences. It makes sense that the bypass may be louder but come on... Your pipes leading to the bypass/premuff aren't baffling the sound at all. In the end, it depends on your muffler.

not quite true.

at last dyno figures for 1986 3.2 with dansk premuffler/sport 2 out muffler

[Wil Ferch]

The point of all this is that people like BA have a close relationship with Jerry Woods and Co...and those guys see a lot of different configurations.
BA is quiter clear that empirical evidence shows no hp gain with a "simple" straight pipe, but does indeed add 6 hp or so with the Porsche-designed premuffler. Are you asking me if I have proof? I personally didn't run a dyno on this set up but I defer to BA not giving false info based on his numerous observations and publications. Dicksters runs seem to colloborate that. The Pano article I mention is also "real" and shows the mass flow distribution vs. cross sectional area...and how Porsche designed a particularly egg-shaped "curve" to compensate. So... there *is* some science involved here.
--Wil Ferch

[cyprusx]

I thought that if you looked through each of them, they both appear to be straight pipes. Is this not true? The only differences reported previously would be the large shroud or lack thereof for a bypass pipe. I am no expert but this continues to be a ambiguous and controversial subject which implies that we still don't know one way or the other. If they both are essentially straight pipes, then how can they perform differently? I purchased a bursh bypass pipe from our host (arrived all scratched up which pisses me off) and have not put it on yet. It will be installed winthin the next week or so... So if there are some facts around this and I can shell out another $150 for additional factual improvement, I would seriously consider it. However, I personnally have doubts about any noticiable differences between one straight pipe vs. another straight pipe with a shroud. The main benefit that I am after is a more aggressive tone with my stock muffler and hopefully a cooler running machine...

[BGCarrera32]

The premufflers usually have a glass pack surrounding the inner pipe, which cuts resonance. The Fabspeed unit has a perforated inner wall surrounded by...I'd say 1/4" thick wrap of glass fiber and finally the outer shell. There may be a slight difference in horsepower using the premuffler with the revised chamber shape. Kinda like how you can tune the powerband of a go-kart engine by making the tailpipe longer or shorter. O.k., bad anaolgy maybe but similar in principal. The inner pipe on the Fabspeed is larger in diameter than the 2 pipes that make the 90 which feed into it. Gets back to cross sectional area again...

[dickster]

rick,

it is different. check out muffler construction, some are straight through and some not. it deosnt mean the straight thru' design offers nothing over a pipe alone!

what you are after (noise) you will get with the bypass.

[Wil Ferch]

Rick / cyprusx:
What's the problem? Are you insisting that a straight pipe of "X" diameter...is exactly the same thing as a pre-muffler that happens to have a perforated sheet at "X" diameter surrounded by a void space "can" ??? ...because you can similarly "see through" them the same way lengthwise?? Too simple!

The two indeed ARE different...and why do you say it continues to be "ambiguous and controversial"? Maybe I'm defending BA in this case more than I should, but he's seen hundreds of racing and "tuned" engines...with empirical ( i.e...tested, real world) differences....so why question that ? Zero hp for test pipe...5-6 hp for premuffler chambered design. Maybe you can contact him directly ( BrucePor@aol.com...the last time I looked) ??

--Wil Ferch

[cyprusx]

No problem... Just a friendly discussion which has occured many times in the past. I scanned this board for information surrounding this topic before deciding to purchase the bursh. Unfortunately for me, I couldn't draw any conclusions based on previous discussions. I indeed thought that the diameter of the pipes were the same and do not recall any perforation in the posts that I had read until this discussion. What is the goal of these things anyway. If the goal is increase flow to the muffler would it matter? Not be more controversial, just would like to understand . I have no problem with returning the Bursh and purchasing the Fabspeed. At the time, a couple of weeks ago, I couldn't find enough information to drive me towards spending more money on a premuffler over a bypass pipe. This thread is making me lean towards the premuffler but do not want to throw away money unnecessarily. It sure looks good but you really can't see it anyway when installed.

For those that had or tried the Bursh and then upgraded, could you chime in here?

[Wil Ferch]

Rick:
That's OK.....maybe we didn't talk about your own expectations in this regard.
Straight pipe is OK for less weight, better sound, "maybe" better performance ( but likely not).
Euro pre-muffler has the same advantages as straight pipe, but in addition also gives a small hp increase...if that's what you want.

Wil Ferch

[KTL]

Rick,

If you decide to go the Fabspeed route, make sure to ask the guy on the phone if they fixed their fitment issue. Awhile back some buyers had problems with their premufflers being seriously crooked (not readily apparent until installing the part) which made for some very bad flange mating issues.

I have a Fabspeed and mine fits pretty good. Nice part. Took awhile to get it and a few phone calls were not too helpful in narrowing down when I could expect to get the part. I think it took over a month? Can't remember. I do remember that I was considering a call to cancel the order and then it showed up on my doorstep that day.

Here's the discussion that comes to mind:

Fabspeed Premuffler Fitment Issues

Not trying to knock Fabspeed as I think their part is pretty nice. Just that they've had some fitment and customer issues on occasion.

[BGCarrera32]

The Fabspeeds have been corrected. Nice parts, o.k. welds. Plenty strong I'm sure. Their customer service is kinda poor mainly because I think its 1 or 2 guys their and they probably are pretty busy. Worth the headache IMO because the Dansk is way overpriced.

-BG