Classic Mustangs List Archive

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Mail From: Keven D. Coates (email redacted)

I tried a very scientific experiment yesterday. I cut two Dr. Pepper
(breakfast of champions!) cans in half and put them over the end of both of my
tailpipes, held on by hose clamps. Then I put a 1" round hole in each. This
provides restriction and thus, should quiet my booming exhaust.

It was much quieter! I guess I am not really suprised by this, but my 2.5"
exhaust system has always been so resonant. Inside the car I measured 84 db (A
weighted) under light acceleration between 1500-2000 rpm. With my ridicolously
low gears of 2.79, my car stays in this range under light throttle all the
time, unless I get above about 50 mph. 84 db isn't really that loud, but it
does tend to stop conversation. Plus, it really resonates. It has two Cherry
bomb mufflers on it still (soon to be replaced, possibly by Dynomax
Ultra-flos:-)). You don't hear the exhaust pulses, just a booming about about
250 hz. It is very annoying. It sounds good at full throttle, but I don't
drive that way as often as I would like in Houston traffic.

I mean really, with two 1" holes, it wasn't as quiet as an LTD or anything, but
it wasn't as much restriction either. I figure most non-performance V8 cars
have a single 1.75 exhaust, if that. If I put in two 1" holes in my exhaust,
that translates to the equivalent of a single 1.6" pipe. This would be
slightly less restriction than a 1.75" exhaust and a quiet muffler (I'm
guessing). This is how Supertrapp mufflers work with their removable plates.

Also, it didn't seem to harm performance much below about 3000 rpm. It was
kind of hard to tell, because the car sounded so different I didn't know
whether I was accelerating as fast or not.

It was interesting. I think people should do this once in a while. I heard
things I normally don't (like anything besides the exhaust!). Like squeeks and
rattles that may tell me more about my car and what I need to fix before it
leaves me stranded.

This means that I can use butterfly valves in the tailpipes to change the
volume of my car. I can partially close them when I need to carry on an easy
conversation with my wife, or I can open them totally when I need performance
or loudness for any reason. I could use vacuum motors to control them with a
switch on the dash!

Now I just need to design a non-rattling butterfly valve for the tailpipes...

Merry Christmas!

Later,
Keven Coates
'68 straight stang!

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Mail From: Max Watson (email redacted)

>Now I just need to design a non-rattling butterfly valve for the tailpipes...

Hey Kevin,

Nology Engineering (nology.com) designed this thing called TREX
(totally regulated exhaust) which is a spring loaded valve installed in the
exhaust system. It responds to the pressure, and opens accordingly. I've
got some literature from them, in which they claim the TREX will maintain a
negative pressure wave at any RPM. They also claim their engineers found a
substantial low to mid-range torque gain. The idle is supposed to be more
stable with lower emissions due to the elimination of blow back. Most
important to you, they say engine noise at idle and low rpm is reduced
dramatically.

Problem with Nology is their stuff is $$$. I think you'de need two of
these things as well. Might want to call them and find out anyway. Their
number is 619-578-4688.

Max

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Mail From: Lev Lvovsky (email redacted)

isn't this a wrong concept though? I thought of this too a while ago,
but when you thikn about it, its working on the same principle as a
pressure regulator...it takes pressure to open the things up, so in
effect, you're not coming away with much in the way of back-pressure
reduction....active mufflers are fine, 'cus they open under their own
power, but this seems like it would simply make a bigger hole, but at the
cost of increasing the back pressure at the same time. either way,
you're not getting them opened for free. I could be wrong...


On Fri, 13 Dec 1996, Max Watson wrote:

> >Now I just need to design a non-rattling butterfly valve for the tailpipes...
>
> Hey Kevin,
>
> Nology Engineering (nology.com) designed this thing called TREX
> (totally regulated exhaust) which is a spring loaded valve installed in the
> exhaust system. It responds to the pressure, and opens accordingly. I've
> got some literature from them, in which they claim the TREX will maintain a
> negative pressure wave at any RPM. They also claim their engineers found a
> substantial low to mid-range torque gain. The idle is supposed to be more
> stable with lower emissions due to the elimination of blow back. Most
> important to you, they say engine noise at idle and low rpm is reduced
> dramatically.
>
> Problem with Nology is their stuff is $$$. I think you'de need two of
> these things as well. Might want to call them and find out anyway. Their
> number is 619-578-4688.
>
> Max
>
>
>

|URL: www.smartlink.net/~levl289/ = Lev Lvovsky
|FTP: ftp.smartlink.net/pub/users/lev
|Most cherished possesion: '66 Ford Mustang (modified)
|"There is no race with a franchise on misery"--MR. KFI AM 640
|Q:"What do you think about American Culture?"
|A:"I think it's a good Idea."

This read-only message was archived from a public mail list.
Mail From: Keven D. Coates (email redacted)


> From: Lev Lvovsky <(email redacted)>, on 12/14/96 2:11 AM:
> isn't this a wrong concept though? I thought of this too a while ago,
> but when you thikn about it, its working on the same principle as a
> pressure regulator...it takes pressure to open the things up, so in
> effect, you're not coming away with much in the way of back-pressure
> reduction....

I totally agree, but the idea they are working on is that in some situations,
there is good use for backpressure. For instance, in a car like mine that is
optimized for 3500 rpm and higher, you don't get as much low rpm torque for a
few reasons. One of the biggest ones is the cam.

The high rpm cams have longer intake/exhaust valve overlap. At high rpms this
is great for power, but at low rpms you end up sucking some air/fuel out the
exhaust. A limited amount of backpressure will stop so much air/fuel from
flowing out the exhaust, and create slightly more pressure in the cylinder.
This will improve low/mid rpm torque, emmissions, and fuel mileage at the
expense of high rpm power, unless the restriction is removed at higher rpms. I
have heard that Ferrari and others have experimented with this approach.

Nology is talking about a pressure regulator to regulate backpressure, which
may increase low/mid rpm torque depending on what cam/etc. combination you
have, but unless that backpressure is removed at higher rpms, though, you are
right, it will reduce peak horsepower (unless your exhaust is way too large for
your application).

I may try a variant of the pressure regulator idea, just to see what the
effects are at low/mid rpm. Of course, I would have to have a system to remove
the backpressure at higher rpms. No use spending all that money on an engine,
and then limiting it!

Interesting stuff! Merry Christmas!

Best Regards,
Keven Coates
Texas Instruments...Dang it's cold here! Down to 44 Degrees! ;-)

This read-only message was archived from a public mail list.
Mail From: Sammy (email redacted)

> Texas Instruments...Dang it's cold here! Down to 44 Degrees! ;-)

Hummm... is 4 here, and I was thinking that was rather warm.
-srw

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