TheSamba.com :: View topic - An exhaust system that delivers performance, yet is quiet?

Mon Apr 29, 2024 1:25 pm

G'day, all. I've got a question that may seem somewhat odd to most motor-heads.

When I acquired my most recent 914-4, a car that seems to have a mild performance cam in it to complement its twin dual-Weber 40IDFs, the car also had a modified exhaust system (that I am tempted to identify as a 'MONZA-type' set-up).

It has, understandably, scads of BHP horsepower for a formerly 1.8 liter powerplant, an engine that a Porsche mechanic recently opined "probably generates at least about 100+ BHP, as it now exists."

All well and good, but as someone with Austrian maternal roots and a strong sense of Germanic engineering horse-sense, the noise it generates is almost embarrassing. I'd hate to have my local PCA cohorts think I'm trying to impress anyone with my car! In fact, I'd much rather have a moderately powerful powerplant but one that is far quieter. The existing exhaust is a 4-into-2 type but the mufflers it has (a la the Monza configuration) seem to do little to quieten it down for daily street use.

My question for the forum is therefore this: What sort of exhaust system should I consider adding that won't significantly lower power output yet still reduce the existing loud ambient noise level my car produces? Or is such a dual-objective simply not feasible?

I'd be interested in any comments forum-regulars have to make on this subject. [I should noter that my car no longer has the OEM Porsche 914-4 stock heat-exchangers (with its 4-into-2 exhaust ducting), hence no passenger heating capability as it now exists.] Thanks. See image of the car's current exhaust system below, if that is useful.

Tue Apr 30, 2024 9:41 am

install 2.0 heat exchangers and a factor replica muffler and be all set. The sestup was factory designed to cause the most horsepower for the 2.0 engine

Tue Apr 30, 2024 12:18 pm

[email protected] wrote: install 2.0 heat exchangers and a factor replica muffler and be all set. The setup was factory designed to cause the most horsepower for the 2.0 engine

Thanks for that suggestion, George. Makes sense. I've always been a big fan of 'stock setups' for exactly that reason (the engineers optimised for maximal performance and operation) and normally am not big on enthusiast modified setups (such as mine), but I 'inherited' the car, hence the system in place on it that I want to replace with a quieter system. [Cockpit heat is a necessity, too; A/C is definitely not (IMO)]. Cheers, Windisch.

Wed Jan 01, 2025 1:11 pm

The pipework lasts quite well, but the mufflers are often cheap steel and rot internally becoming loud.
Just replacing the silencers with known quality US made straight through ones will last and be quite quiet. (Less eyewatering price if you don't want to easily spend a couple of grand upwards).
Magnaflow and borla for example. These may be very quiet at first but after a break in period it will increase slightly.
Try angling bolt on tips differing directions.
Ensuring the exit is long-past end of the bumper helps.
The oe style exhausts often achieved a legally required Db by using a baffled or chambered style muffler, performance was secondary .
Excess back pressure on this type creates heat in the heads and reduces performance. BAS Germany used to have a system with two mufflers in line, one after another. Usually with straight through silencers this dealt with noise adequately.
There is always a compromise between noise and performance if there is limited space.

Wed Jan 01, 2025 1:41 pm

Backtotheeightiesagain wrote: The pipework lasts quite well, but the mufflers are often cheap steel and rot internally becoming loud.
Just replacing the silencers with known quality US made straight through ones will last and be quite quiet. (Less eyewatering price if you don't want to easily spend a couple of grand upwards).
Magnaflow and borla for example. These may be very quiet at first but after a break in period it will increase slightly.
Try angling bolt on tips differing directions.
Ensuring the exit is long-past end of the bumper helps.
The oe style exhausts often achieved a legally required Db by using a baffled or chambered style muffler, performance was secondary .
Excess back pressure on this type creates heat in the heads and reduces performance. BAS Germany used to have a system with two mufflers in line, one after another. Usually with straight through silencers this dealt with noise adequately.
There is always a compromise between noise and performance if there is limited space.

Very useful information...thanks. I am such an unknowledgeable naif when it comes to the technical aspects of back-pressure/heating effects as they relate to car exhaust systems. I've gradually gotten more comfortable with the sound output of my present system (dB-wise) since I suspect that a slight upper freq. hearing loss makes me more sensitive to noise than someone who is younger, but I'm going to mull this all over and give some further thought to the situation. I agree largely with George that a 2.0 liter spec OEM exhaust system, with heat exchangers, might be a good idea, since cockpit heating is nice to have, but since I drive my car mostly when it is warmer (and not at all whenever it's damp or raining (older 914s DO NOT like rust and neither do I), it's not absolutely necessary at this time. Your suggestions are appreciated; I'll mull everything over and see what seems best. Good rainy-day project!