'87 Why is the Euro pre-muffler better than a cat. elliminator pipe?

[movin]

I still don't get it. After phyiscally seeing both I don't see how the Euro Pre-muffler could be a greater benefit, especially when you are still using the stock muffler. Clearly, the straight pipe of the cat. elliminator will out-flow the Euro Pre-muffler (Glaspack). Everyone says the Carrera's exhaust system is too restrictive, right?

[dickster]

LOL - this subject never ends. hours of endless amusement!

it is something to do with back pressure, and how it works to benefit carrera's (exhaust pulses etc).

i can't say they are better but the point is, they work.

[Steve W]

I don't think a true Europremuffler is a glasspack. It is more of a resonance chamber with a lightly perforated tube within a can just a little larger than the tube. Look for premufflers in this design. But besides the benefit of more power of a premuffler over a straight pipe is that the premuffler will not really make the car louder from that of stock with a cat. Replacing the cat with just a straight pipe will create more exhaust noise that is not necessarly a more pleasant note.

[Bill Verburg]

The problem with the stock 75-94 exhaust is not so much restriction(altough there is at least 1 major choke point where the right side bank crosses under the case) as just a poor design to try to take advantage of acoustic effects that are used to extract exhaust gases from the combustion chamber.
The shape of the tubing internally can enhance or degrade what little effect there is. The interior shape of the euro pre muffler apparantly enhances the flow. This effect was measured on the dyno.

A properly designed exhaust will have equal length primary tubes, longer for street use shorter for track use, sized to allow unrestricted flow at max revs, but no larger. Larger will only allow reversion to take place diluting the fresh intake charge. Smaller will increase backpressure causing the exhaust gas to pile up in the tube as revs increase. In general smaller(to a point) is better for low revs, bigger(to a point) is better for high revs. The primaries need to dump into a collector, again the shape and size of the transition is important to the efficiency of the exhaust as is the collector length. Putting a muffler on all of this tends to obliterate the scavanging signal, but not entirely. It does damp the effects a lot. For max effect, albeit in a very narrow rev band properly shaped extraction cones will be attached to the collector. Take a look at any 4 stroke racing bike from the pre muffled days. You will see the double cone that maximised the acoustic scavanging effect. Of course for street use this will not work.

[jfitzoz]

Can anybody please tell me, in layman's terms, why Bruce Anderson and some Pelican-heads recommend a Euro-pre muffler?

Thanks,

JFITZOZ

[1Gunner]

Just a hunch, but the euro on quick inspection "looks like" a catalytic converter and therefore pass a visual emission test.

I have a straight pipe on my 87 Cab, and no way will it pass a visual emission test. But it does sound the way I expect a 911 to sound!!!!!
Not like the choked chicken sounds some folks seem to prefer coming from there stockers
And I say that in an honest and purely subjective way....

[gr8fl4porsche]

1 Gunner,

Other than the nice sound - did the straight pipe and anything to the 'seat of the pants' feel. While I realize that many so called performance improvements do not add to the total hp or torque, it seems that changing the torgue curve can be beneficial for street driving.

[turn6]

All this talk of pre-mufflers vs cat bypass pipes...why can't you just gut a cat? Externally a cat has the expansion chamber shape somewhat similar to a premuffler and it will definitely pass a visual. anybody btdt? Tia.

[Steve W]

If you gut a cat, then you pretty much have destroyed it when you need it. In cars where I have gutted cats, I have found they to be more restrictive than a straight pipe. These were on other European cars where the cat cores are identical in design and manufacture to those found on the Porsches - ceramic honeycomb. The restriction is not so much the core as it is the shape of the can. The taper of the entry of the cat shell is too sharp, slowing the velocity of the exhaust gasses. If this taper were cut off and replaced with a new shape made longer and more gradual, it would actually flow pretty well. Empty cat shells also produce wierd noises which sound a lot like an exhaust leak occuring inside a metal can. A euro premuffler is much smaller in volume and contains a lightly perforated tube into a outer expansion chamber. The design flows as well as a straight pipe without the nasty exhaust resonance. One thing I have done though is gut a cat, cut it in half and weld in a stainless perforated pipe, and stuff the outer chamber with steel wool. It looks like a cat, flows like a open pipe, and is as quiet as stock. Works really well - especially on turbocharged cars I have.

[1Gunner]

gr8fl4porsche,

In a word, yes. It pulls harder in mid and upper rpm range. I've run my 87 for 7 years, first stock, then added a Borla pipe, then a K&N powerflow, and now with the cat pipe. In simple terms, anytime you help the engine breath better, it will reward you.
The pipe also sounds aggressive without being loud and obnoxious. But sound is purely subjective. Like music, one man's melody is just fingernails on a chalk board to another

I did install last fall, then remove last week, a chip. Other than increase fuel consumption, make it idle lousy, and backfire so loud that pedestrians would cower, it was a great investment...