Dansk pre-muffler questions

[Decolliber]

I am still mulling over whether to buy a Dansk pre-muffler from Pelican. I recall various past threads where people reported negative consequences from a pre-muffler (eg, loss of power, backfiring or popping noises). For example, this thread:
Euro pre-muffler backfire problems

Since there was a large group buy a while ago, I wonder if some of the people who bought one (and especially those who put one on a Carrera) could report back on how they like it. Specifically:
Any bad results (popping, backfire, loss of power)?
Noticeable power increase?

The existing bolts are M8x40 (and I would have to dremel them off as they are just blobs of rust). Would I be correct in assuming that the same size bolt will work for the Dansk, or are the flanges thicker?

I just don't want to be one of those who goes to all the expense and trouble and then hates the result and removes it.

[JeremyD]

I just did this with a dansk premuffler and dansk SS single in and dual out.

I followed it up with a Steve W chip.

Pluses - much stronger low and mid range - better exhaust sound
Easier reving

Minus -
Smells a little - the exhaust that is - a little more sulfer smelling.

DEFINITELY worth while - makes my car perform more like the 3.6 C2 I had.

[Steve W]

If I remember in that thread, BigBartGuy mentioned that he had a backfiring problem even with the stock exhaust and cat. The premuffler just made it more apparent. So I wouldn't say premufflers will cause backfiring. Bypass pipes would most likely cause exhaust popping on deceleration though. Backfiring is usually caused by unburned fuel going into the exhaust. Usually this is due to a lean condition somewhere in the fuel curve caused by either a lack of fuel or an air leak as in the intake system. The overlean fuel mixture is not enough to be ignited by the spark plug in the cylinder, so it goes out as raw fuel into the exhaust. A couple more cycles like that and eventually the fuel in the exhaust will ignite from the next exhaust port cycle.

Installing a premuffler though basically changes your car to the European exhaust configuration, which is freer flowing and would run leaner than it should with the stock U.S. chip. So is best optimized in conjunction with a chip with the fuel curves for the European exhaust. For example, most guys who have had some light exhaust popping on deceleration after putting on sport mufflers and bypass pipes, reported the lack of the popping after replacing their stock chip with an appropriately programmed one.

[Decolliber]

[i]Installing a premuffler though basically changes your car to the European exhaust configuration, which is freer flowing and would run leaner than it should with the stock U.S. chip. So is best optimized in conjunction with a chip with the fuel curves for the European exhaust. [/B]

But I assume that this problem could also be solved by making the mixture a bit richer with the pre-muffler?

[Steve W]

Yes you could, but you shouldn't be getting any backfiring or loss of power with a premuffler at all if your car was running properly. You will get a 8 hp gain at the top end, but just not the full benefit of power in the midrange at full throttle without the additional fuel. I posted two dyno comparisons here from an 87, before and after with just a stock chip if you want to take a look.

[greglepore]

I was part of the group buy. Installed the premuff with a Flowmaster 1x1, so I can't speak to the premuff directly. I do notice a "burble" -not a backfire, but sort of a pop-pop, but not that sharp, on overrun, or when decending a hill against engine load. I also occasionally get a sharp backfire when shifting at high rpm at or near WOT, allieviated by not rapidly closing the throttle when lifting to shift. I suspect it may be related to the DME shutting off the injectors with the throttle closed at high rpm, causing a leanout.

[Randy Webb]

The best pre-muffler is a turbocharger.

[carreradpt]

I was part of the group buy and am absolutely pleased with the premuffler. I love the performance feel and the sound. It took about 2+30 min to install. Used PB blaster and all the 13mm nuts and bolts (9) were removed quite easily (95K on an 85). No need for heat just a couple of taps and a turn to the right before going left. I was impressed. I had purchased an O2 sensor a while back to install when I got around to it so just left the original on the old cat. The new one came with the wires and the rubber grommet. Used the recommended ((Thanks Dickster) american sized stainless bolts 5/16" x 1.5" and silicone bronzed nuts and lockwashers. though I did not need a 2" another 1.5 would have worked on the Carrera. Used anti-seize on all and it went together just fine. I have since installed a Dansk 1-1 sport muffler and Steve W chip. The car runs fantastic no backfires or any other issue.

[BER]

John,

I was also part of the group-buy. I installed the Dansk Pre-Muffler (w/O2 bung) along with a Dansk 1-1 Sport muffler (same as Dan T.) on my '84 Carrera. I used new hardware (stainless bolts and nuts, washers) and new gaskets. I used the same size hardware as came off the car...the Dansk pre-muffler did not require any special hardware. I also have a custom Steve W. chip.

After the install, I readjusted my idle mixture using a Gunson CO meter. I set my idle CO at 3.2%.

The car runs fantastic! A lot more responsivness in the low and mid-ranges; very strong from 5k up to the redline (6800). No popping or burbles, just a deep throaty sound.

I highly recommend the Dansk pre-muffler, along with a sport muffler and custom chip (check the archieves for a lot of good information on Steve W.'s chips). My car is exempt from emissions testing, so I don't have to mess with installing a cat every year or two.

I don't think you will be disappointed if you make this upgrade.

Bruce