Muffler and exhaust quandry

More info...
http://www.borla.com/products/xr1.html
There are two product lines in the XR1 family....Sportsman and Multi-core.
Both have the same level or performance from a restriction standpoint which from my experience and testing is negligible.
when I contacted Borla to determine what the difference was (the multi-core is 2x the cost) they indicated the multi-core was constructed differently to be quieter with the same flow as the Sportsman. So if you have a serious noise issue, then the multi-core is a better solution. For me, the cheaper Sportsman does a great job.
 
Mine is like Greg's. Straight down the middle and turned down just in front of the rear subframe. I welded a strap front and rear to help it slide over anything that would snag it. G
 
Got another question -

I've got a nice big transverse space in front of rear axle where stock fuel tank was.

Nicest install would be with muffler crossways to car axis - but it takes some bends to get everything nicely positioned, probably a 90 and a 135 into the muffler and a 90 back out of the muffler. Right now I have a 90 into muffler then a sliced off turndown.

Running ~125bhp through 2.25 OD pipe, should I care about the extra restriction through the pipe bends? I'd be using mandrel bends butt-welded.

Al Seim
HP VW Scirocco 1.6
 
What about a mid-entry/exit muffler like a vette or something? you could go back through the center of the chassis and then into the muffler, or maybe two small/short 2" mufflers? I don't know if that will help or hurt- just brainstorming a little.
 
The bends wont make much of a difference. Try to position the muffler to occupy that space from the under-the-car air's perspective. Filling that big hole under the car will help.

Waste not ....

-Kyle
 
Al, but that "large" of a muffler also would weigh a ton, much more than the straight Borla or cherry bomb we're both using now.
 
Kyle -

Good input, I had not really thought about undercar airflow - the current setup is transverse but extends several inches below the floorpan at the cavity leading edge which is not optimum I'm sure. With a couple of extra bends I can tuck the muffler up into the cavity and smooth things out a bit.

Tim -

I'll definitely be watching the weight! Few of the muffler mfgrs post weight online but they presumably can give it by phone. Amazon has weights for a lot of items but I'm not sure how much to trust.

The big thing here is to accept the fact that a few more (smooth) bends won't hurt appreciably. That opens up the freedom to package neatly.

Al
 
If I am remembering correctly you want to place the muffler the same distance from the collect as the length as your primary tubes on the header. IE if the header has 36 inch primary tube length then place the muffler at 36 inches from the collect or at an even multiply of that: 72 (36*2) 144 (36*4)

I would need to find the documents again to confirm.
 
More questions -

1. Ron mentioned placing the muffler an integral number of primary pipe lengths away from the collector. Others have quoted a similar thing, except with the secondary length INCLUDING the muffler. Presuming that this is to have pressure wave reflections from the secondary (main) pipe reinforce those within the primaries, it seems to me that if the muffler is a "LOUD" straight through one it presumably passes the main pressure waves through and thus ougt to be within the nominal length. A big quiet muffler would likely be the reflection source and thus ought to be itself the "end" of the measured length. Does this make sense to anyone?

2. I had been assuming that the muffler ought to be near or at the rear of the system - but Borla's website says within 18 inches of the collector "for max power". Does that ring true with anyone?

Al Seim
HP VW Scirocco 1.6
 
Also - the Dynomax bullet muffler was about half empty of packing, the upstream half was gone, either blown out or maybe compacted into the rear half. So my lazy approach would simply be to replace it...
 
Went through the noise issue with our 16.1 948 Sprite engines. Went to Flowmaster (Nick, ext 457, [email protected]) and came up with the FLO-325408 muffler from Summit that was designed for the IRL's entry level series open wheel cars. The Flowmaster numbers said that I should have gained 2 to 3 HP at max rpm. What I actually got was an extra 5 to 800 rpm rip that I never had and better pull in the higher gears. It is a one baffle oval muffler that fits nicely under the rear of our Bugeye Sprite and allows for the preferred 8 inch pipe on the end. Pipe size is 2 1/4. Went from 111 db to 97 db.

More info.. I have a chart from a late '90s exhaust test that put the Borlas near the top and the last 2 of the 11 tested as "any straight through glass pack" and the Super Trap systems. Our muffler wasn't designed yet so don't have a recent comparison. Our pipe goes straight out the rear (thru the tunnel exhaust).

Bob
 
Al Seim":sejqpihs said:
More questions -

1. Ron mentioned placing the muffler an integral number of primary pipe lengths away from the collector. Others have quoted a similar thing, except with the secondary length INCLUDING the muffler. Presuming that this is to have pressure wave reflections from the secondary (main) pipe reinforce those within the primaries, it seems to me that if the muffler is a "LOUD" straight through one it presumably passes the main pressure waves through and thus ougt to be within the nominal length. A big quiet muffler would likely be the reflection source and thus ought to be itself the "end" of the measured length. Does this make sense to anyone?
Click to expand...

Agree.

Reflections occur due to an expansion of area.

Even a straight "loud" muffler will dampen the reflected pressure wave - thus ultimately reducing how strong it as as it enters back into the cylinder at its tuned length to some degree.

In conversations I've had with a serious exhaust builder (NHRA, NASCAR, Le Mans, IMSA, WoO Championships to his name), he'll laugh if you mentioned the chambered mufflers. The consensus is to stick the muffler as far away from the engine as possible. He also mentions anyone seeing gains with mufflers usually mean their exhaust wasn't tuned correctly and is usually a symptom of too large of a collector/tailpipe or a wrong exhaust cam timing. "There is no such thing as too little back pressure".

The Spec Miata guys tried the muffler "diffuser" trick - that racer got away with it once (the Runoffs).

To put 2.25" tailpipe into perspective - the same builder uses a 2.25" choke (choke merge collector) on each bank of 590bhp (8200rpm redline) small block Ford road racing engines - so 295hp through that 2.25" choke.

The principle that is at work in a merged collector is this. The smaller the choke the longer it takes for
atmospheric pressure to equalize into the back door of a given engine. It protects your power curve the
same way as shorter cam timing and longer primary tubes. Just slipping a collector on with a smaller
choke will usually show more power at the bottom of the curve. (which Joe points out)..
The secret is that you can now shorten your header which is how you can make more power upstairs.
Header length is always relative to rpm band but also the size of the choke. Most headers have to be
long because the collectors are so large. The longer tubes keep the reflected wave "back" at the lowest
point on the power band that the engine has to pull from. Change the collector choke and shorten the
tubes and you will see the power. If you can't shorten the tubes, do not blame the collector, and if you
need shorter headers, call me...
Click to expand...

Something to get you thinking and maybe how you can make a muffler work for you (in lieu of using a choke merged collector).
 
All our tracks are taking sound from the left, the same as yours.
I've had no problems running the exhaust out the right side by the pump. It gets pretty hot here in the summer, too. I DID install a heat shield above the pump of course. Also I have a quick release setup on the exhaust pipe in case I have to get in there. I don't run any muffler and sound is not an issue any longer.
 
If you are weight and cost conscious, exit on the side opposite the sound measuring device. Use a down turn on the exit. Make up a set of pipes that will allow you to test, using your old muffler. I would think you may not even need the muffler.

Mounting the exhaust exit under the car is possibly creating chassis/sheet metal acoustic resonance that may increase the overall decibel level reading. Not all of the noise emanating from the car is created by the exhaust note... Think of the sound level of a large marching band type drum is much higher than the effort being put into beating the drum.

I found that rolling beads into the interior sheet metal of a tube frame car reduced the noise level. There was no "stock" sheet metal on the car. And, the beads made the metal panels more rigid, with less accoustic resonance.

Also found that with a 650 hp V8 Chevy, GT1, I could meet the sound requirements with a simple turn down on each side pipe exhaust, left & right side. I had invested in some other mufflers for the car, but found the simple downturns required less maintence and carried le$$ weight.
 
In case anyone is interested -

I wound up switching from a left exit, with turndown, using a (half blown out) Dynomax 24234 bullet. Was right at 102-103 dBA, measured on left at Summit Point. Before getting blown out it was almost that high.

Went to a rear exit, no turndown, using a Dynomax 24244 (cylindrical not bullet even though Dynomax lists as a bullet, and an inch bigger OD) and was astounded to be at 90 dBA at same track.

Data indicates no significant power change. System maybe 4 pounds heavier due to longer pipe. Mufflers almost same weight.

Someone clued me in that the "dead volume" (the part packed with glass fiber) of the muffler was key. This muffler weighs and costs about the same as the bullets but being a cylinder not a drawn bullet, and being an inch bigger on OD, has several times the internal dead volume of my first one.

So three changes - new muffler, different muffler, different exit. But HUGE loudness reduction as measured. I do highly recommend the Dynomax 24244 as a good, cheap, relatively light race muffler.

BTW, the pics of this muffler on Summit and Amazon are correct, JEGs and Dynomax incorrectly show it as a drawn bullet.
 
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