my 944 is TOO LOUD!!!

[cwiert]

hey...
I bought this car (1988 944 NA) a few weeks ago and have been having fun with it. a couple issues here and there, but overall, seems pretty solid. the thing i hate the most about it, though, is the exhaust. it's so freakin' loud. not sure what kind it is, i think it's some sort of stright pipe/glass pack, something or other. what i do know, is that' it's brand new. new Cat converter, and new stainless pipes all the way to the new (loud) muffler. The pipes are 3" in and out of the muffler. I want to swap the muffler for something else that's quieter. But I don't think the OEM 944 muffler is 3". Plus its like $250 or more, and I don't want to spend that kind of money. Will any muffler do that's 3" in and out? Or if I find a used cheaper 944 muffler that's 2.5" (or whatever it is), can I just get adapters, or will that create back presure issues.
Any cheap, low cost suggestions to get my car quieter will be greatly appreciated. Here's a pic of the current setup...

[John_AZ]

The OEM Porsche muffler and pipe is stainless and even in CT the rust should be minimal on a good used setup. I would try an autoparts wrecking yard or keep looking for a car being parted out. Shipping cost would be expensive. Another excellent place to get a setup is from George at www.944ecology.com. He is a knowledgeable member and he is located in your close? area.

I have a stock setup on the '88 924S and a nice upgraded sound on the '87-I call it the "humble rumble"

GL
John_AZ
1988 924S + 1987 924S

[911paige]

hey i don't know about them too much but i could say that the 3 inch is used on the turbo that's the muffler i like i think they sell them on ebay i have a borla 21/2 with a nice tip on it if you would like to trade. the system you have is almost like not having a muffler at all kind of a straight thru pipe .... but it is nice.

[Tervuren]

If you lived clsoer to me I'd swap exhausts in a heart beat. Mine's so quiet when the secondary fan is on you hear it over the motor. Someday I plan to go hogwild the other way with a full 3" lindsey exhaust, just can't drive it that way past the neighbors in the wee hours.

[Dantilla]

A 3" is not optimal for a street-driven NA.

My race car has a 3", and while it improves flow at sustained high RPMs, there is a big loss of low-end torque. This was immediately noticeable as soon as we put the race exhaust on. The car will be far more fun to drive with a 2.5 diameter exhaust.

The car used to be driven on the street often, but with the 3" exhaust, it became too noisy. I found myself constantly trying to keep the rpms low, with less throttle to keep the noise, both inside and outside the car, down.

I no longer even license the car for the street. I just trailer it to the track.

[cwiert]

Originally Posted by Dantilla

A 3" is not optimal for a street-driven NA.

My race car has a 3", and while it improves flow at sustained high RPMs, there is a big loss of low-end torque. The car will be far more fun to drive with a 2.5 diameter exhaust.

That's interesting. Why would there be a loss of low-end torque?
Yeah, it's just too loud for me. I have 2 young kids. And when they are sleeping, I can't even take the car out cause my wife will yell that I'll wake them up.
So if I bought a muffle with a 2.5" in and out, then I can just swap it? I know I'll need an adapter since the pipe coming from the cat is 3". I don't want to replace that entire pipe.

[speedracing944]

I bought a whole stock system from the exhaust manifold back for $65 shipped. It was in good shape. Try posting a WTB ad on the 944 parts board. You may get a bite.

Speedy

[legion]

George (944Ecology-in NY) and John (APartAbove-in OH) are both excellent sources and both are relatively close to you.

[Tervuren]

Originally Posted by cwiert

That's interesting. Why would there be a loss of low-end torque?
Yeah, it's just too loud for me. I have 2 young kids. And when they are sleeping, I can't even take the car out cause my wife will yell that I'll wake them up.
So if I bought a muffle with a 2.5" in and out, then I can just swap it? I know I'll need an adapter since the pipe coming from the cat is 3". I don't want to replace that entire pipe.

Pulse length of the exhaust, each time it fires you have a low pressure wave behind it, the larger the pipe with the same flow, the shorter the wave, if they space out too far, the pulse behind can't use the tow of the pulse in front. ooo-ooo-ooo might be the spacing on the smaller exhaust, larger, its O---O---O, the big spaces are less efficient. Higher RPM reduces the spaces, so at race RPM it has more flow.

[cwiert]

Originally Posted by Tervuren

Pulse length of the exhaust, each time it fires you have a low pressure wave behind it, the larger the pipe with the same flow, the shorter the wave, if they space out too far, the pulse behind can't use the tow of the pulse in front. ooo-ooo-ooo might be the spacing on the smaller exhaust, larger, its O---O---O, the big spaces are less efficient. Higher RPM reduces the spaces, so at race RPM it has more flow.

hmm... so just replacing the muffler wouldn't help the low end torque? in order to get a little more torque, i'd have to replace the entire 3" pipe, right?

[Dantilla]

A larger diameter pipe has a slower velocity of exhaust gasses flowing through it.

Think of exhaust pulses as ping-pong balls travelling down a pipe. There is a high pressure area in front of the ball, and a low pressure area behind. We can use the low pressure area to help evacuate exhaust from the cylinder, and with a bit of valve timing overlap, help suck the fresh charge of fuel/air mixture into the cylinder. Ideally, we want a low pressure area behind the exhaust valve when it opens. This can be truely optimized for a short range of RPMs, and a highly-tuned exhaust can have flat spots in the torque curve where we end up with a high-pressure zone where we don't want it.

Now if we put our ping-pong balls into a large-diameter pipe, they all slow down, and we loose the high and low pressure areas that we found so useful.

Exhaust design is really part science, part art. It can be optimized for one small rpm range (3" for racing), or compromised for a wide range of rpms without dead spots. A street car uses a wide range of rpms, and should have the exhaust designed for that use.

To oversimplify, a smaller exhaust will provide the proper volocity for low RPMs (torque), while a large exhaust will provide the proper volocity only at high RPMs (peak horsepower rating).

[HondaDustR]

Good explanation! I always wondered just exactly how it works on a 4 cycle engine. It's practically like a 2 cycle tuned exhaust, just on a less dramatic scale.

[9:44 Dismissile]

I'm still curious as to where I can find a straight through 2.5 muffler to add some more growl to my 944? any ideas?

[cwiert]

Originally Posted by 9:44 Dismissle

I'm still curious as to where I can find a straight through 2.5 muffler to add some more growl to my 944? any ideas?

I just bought a stock cat back exhaust off a 944 turbo that i'm gonna be installing in a few days. I'm gonna cut off my 3" GHL Performance Cat-Back and try to sell it. It's nearly brand new...probably less than a 100 miles on it. The PO installed it and I don't like it... it scares my kids! To much Growl
Wanna buy it?

[thekidd]

I think the 3'' exaust on any N/A is way too big. 2.5'' the biggest that you should go on the N/A, and 3'' is the biggest on the Turbos and S2s (someone say something if I am way off on this, just trying to think back at what others have said. You start loosing back pressure if the exaust is too big.

[Dave L]

Originally Posted by 9:44 Dismissle

I'm still curious as to where I can find a straight through 2.5 muffler to add some more growl to my 944? any ideas?

Any "performance" place should be able to get them. I got a 2.5 straight through muffler. I think it is a Vibrant, it was dirt cheap, a little louder than stock.

[Dantilla]

Originally Posted by thekidd

You start loosing back pressure if the exaust is too big.

Loosing back pressure is good. Loosing velocity is bad.

[SuperXRAY]

Tuning a 2-cycle with exhaust is modifying back-pressure and, most importantly on 2-cycles, scavenging. I'm not sure scavenging is that necessary on a 4-cycle.

[lovemy924S]

i'll trade ya my stock system! lol, i'm gonna need a 3 inch for the v8 swap i'm doing...

[944Spec_bound]

I know almost nothing about exhaust technology, let me get that out of the way.

But it looks like you have a 3.5" tip on that system. Did you look into finding a silencer that fits in the tip, the kind that's secured with set screws?

Mine's way too quiet at the track, I can't hear it through my helmet, but I wouldn't want to drive around town with a track exhaust either.

So, at the risk of sounding like an idiot....I've been playing with the idea of making an adjustable exhaust like they have for motorcycles (I think it's called the Jeckyl and Hyde exhaust). I've seen different kinds, some even work like a valve and have an electric servo wired to a knob so it's adjustable on the fly. I assume that in addition to decibles, it would be a backpressure/velocity adjustment also, and therefore you could fine tune your torque up or down the rpm range?