Fordnatics List Archive

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

Chuck mentioned:
> If the spacer had any effect at all on the intake's resonant RPM, it
>would probably drop somewhat, because the runners are just that much
>longer. I suspect any changes in the torque curve would be barely
>measurable.
................................................................
Chuck's comment reminds me of a question that has been puzzling me
for some time:

Is there any relationship between the acoustic properties of intake
(or exhaust) systems and their performance?

One could also ask questions like should one tune a system to give
a standing wave at XXXX Hz? Or NOT to give a standing wave at that
frequency? Or could one cross-tune two ports by putting
oscillators/speakers in each of them and then listening to how changing the
tubing affects the final sound? Or maybe, for the computer-literate, to
simulate such a system?

I started to think about this after monkeying around with the
throttle linkages on my '84 Plymouth police cruiser (Yeah, I know it's not
a Ford, but my Ford has a 2 VV carburetor and no primary-secondary linkages
to hit with my big pair of pliers). The results surprised me...
1) The secondaries no longer open fully. They're only about 80%
open at WOT.
2) When I enter freeways at WOT and hit abut 50 mph, I get the most
amazing trumpet blast of music from under the hood. The whole passenger
compartment vibrates as if it were in the horn of a giant trombone.

What have other Fordnatics found over the years?

Best regards,
George

This read-only message was archived from a public mail list.
Mail From: chucko (Chuck Fry)

Date: Thu, 1 Sep 1994 11:28:40 -0800
From: (email redacted) (George Chang)

Is there any relationship between the acoustic properties of intake
(or exhaust) systems and their performance?

There is a direct relationship between acoustic properties and
performance. Engine designers deliberately tune resonant frequencies of
intake and exhaust pipes to move the torque and RPM peaks of an engine
around. Whole books have been written on the topic.

As far as I know, though, the properties of a column of intake charge
(or exhaust gas) are not a one-to-one match with those of ordinary air
at room temperature. This makes it difficult to accurately predict the
resonant RPM of a tuned intake (exhaust) system, though there are rules
of thumb that let you get close.

For a couple of concrete examples: One of the reasons the fuel-injected
5.0 is so much fun is that its intake manifold has been tuned to give a
massive torque peak in the range of 3000 - 3500 RPM. And the injector
stacks on a sprint car engine are set up to peak in the neighborhood of
7000 RPM. The "calliope stacks" on some '60s CanAm cars were intended
to provide two separate torque peaks, the net effect being one broader
peak.

Likewise, long-tube 4-into-1 headers would be even more effective at
scavenging at a particular RPM if the four exhaust pulses per side were
evenly spaced. You'll occasionally see race cars with 180 degree
headers built specifically for this purpose (each collector takes tubes
from *both* sides of the engine, a real plumber's nightmare), and you
can tell them by their distinctive buzzing exhaust note.

As for the trumpeting Plymouth cop car, I don't have a clue...
-- Chuck

This read-only message was archived from a public mail list.
Mail From: "Fontana Peter" <(email redacted)>


> When I enter freeways at WOT and hit abut 50 mph, I get the most
> amazing trumpet blast of music from under the hood. The whole passenger
> compartment vibrates as if it were in the horn of a giant trombone.
Wow George - music?! Is sounds more like vibrations from something
trying to self destruct - are you sure you're not ready to chuck
something (sorry Chuck)?

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

Hi Everyone,
I am sorry to post this so generally, but somehow I can't get
it in to the rockwell.com system. SD wrote a very funny parody of car
history about my trumpeting Plymouth, and I tried to email a reply
directly. But my message bounced back to me.
This isn't really a Ford story, but it may help to explain why
so many police fleets chose the Crown Victorias over the Diplomats in
the '80s. And, yes, there is another consideration. The local cabbies
tell me that they prefer Crown Victorias because they have SMALLER turning
radii than do the little Diplomats. With a Crown Vic it's easier to
make an illegal U-turn to pick up passengers.
...........................................................................
SD wrote:
...........You have an extremely rare bird. You have unknowingly
stumbled on to one of a few "Trumpeter Plymouths"...limited production
............. 7 were police cruisers, and the
remaining two ..... were given to the U.S. government...
................................................................
Hi SD,
Actually you were much closer to the truth than you may have
imagined! I got the car at a government auction in '89. It was 5 years
old and had only 20,000 miles on it. From service print-outs, I gather
that it was bashed in a small accident, but that only took the car out
of service for a week or so. For some reason the federal marshalls
just didn't want to put mileage on the car.
I think that the reason they avoided it was that it was that the
car was the wimpiest police cruiser in the fleet. When I got it, the car
had less power than my civilian Crown Victorias or Gran Fury. Even after
fiddling with timing and throttle linkages, it is no racehorse.
There is another strange thing about the car. It has a 3.55 rear
end. All the CHP and local police Gran Furies/Diplomats have 2.72 rear
ends.
I don't know what's going on, but I wish that I could get either
better mileage or better performance out of this tub! But I do my best
to cope... I let my wife drive the tub, and I drive my Crown Victoria
police cruiser :-).

Best regards,
George

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


> Date: Thu, 1 Sep 1994 11:43:13 -0700
> From: Chuck Fry <(email redacted)>
>

You guys knew I would have to say something :-)!

>Likewise, long-tube 4-into-1 headers would be even more effective at
>scavenging at a particular RPM if the four exhaust pulses per side were
>evenly spaced. You'll occasionally see race cars with 180 degree
>headers built specifically for this purpose (each collector takes tubes
>from *both* sides of the engine, a real plumber's nightmare), and you
>can tell them by their distinctive buzzing exhaust note.

There are two camps on this, and I am not part of the above. The effect
of exhaust pulses from one cylinder to another in the collector have
negligible effect. I think it is quite comical (and stupid) to run
exhaust from one side to the other. You gain absolutely nothing,
ruin the most important primary scavenge pulse by dragging it over to
the other side, increase the heat in the engine compartment in places
you least want it, and in a serious race car you end up with high
weight where you least want it. Collectors and crossovers are simply
convenient acoustic expansion devices. If rules and space allowed,
I would run one pipe per cylinder from the head to the atmosphere,
never connecting with another cylinder.


-- Dan

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


> Date: Thu, 1 Sep 1994 11:28:40 -0800
> From: George Chang <(email redacted)>
>

> One could also ask questions like should one tune a system to give
>a standing wave at XXXX Hz? Or NOT to give a standing wave at that
>frequency? Or could one cross-tune two ports by putting
>oscillators/speakers in each of them and then listening to how changing the
>tubing affects the final sound? Or maybe, for the computer-literate, to
>simulate such a system?

I have two different simulators that run on a computer ($$$ in software),
which we use as a guideline and then fine tune on a dyno. They are both
very involved models, and tuning the system is not trivial. You have to
consider everything from one end to the other. Intake plenums, runners,
volumes, valve area, cam timing, ignition timing, temperature of the
intake and exhaust, air/fuel ratio, compression ratio, etc. The simulators
are a good guess, since they don't consider combustion chamber efficiency,
coatings, or fuel variations (at least the ones I have).

A couple things to remember. One is the interdependency of the entire
engine components. If you change the cam, you probably have to change
the A/F vs. RPM curve, ignition vs. RPM curve, and the intake/exhaust
tuning. There is only one "right" header for a given application, and
you probably need to build it. A second thing to remember is that only
a fool will tune for big peak numbers. We always race against people
with higher peak numbers, but when you look at the graph there is nothing
on either side. It's the _area_ under the torque/HP curve where you
run that is important, once the absolute numbers are competitive.


-- Dan