Fordnatics List Archive

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Mail From: "Fontana Peter" <(email redacted)>

> I had one other question that I forgot to put into my
> original post. What does a cross-over do to an exhaust system? I've seen
them
> mainly on cars but am curious as to their function and application.

Their purpose is to equalize pressure between sides of the exhaust system.
The basic layout of the crank/cam (one cylinder fires at a time) tells us
that when there's a pulse in one side of the exhaust, there won't be one in
the other.

The major benefit of a crossover are mainly an increase in lower end torque.
Some minor benefits can be reduced "harshness" in the exhaust sound at the
tailpipes, a small increase in power in the upper ranges, and a small
increase in MPG.

HotRod magazine occasionally runs a piece on how to determine where the
optimum place is to put a crossover. I've found that the most inconvenient
place is usually where it likes to be - right under the middle of the tranny.
A couple more things: use the same diameter pipe for the xover are the rest
of the system, and be sure the openings in the main pipes where the xover
piece connects are close to the ID of the xover.

If you really want to talk crossovers, give Pro-Motorsports a call at (801)
571-6097. They sell an "X" shaped set of pipes to replace the traditional
"H" - they have big claims for it. Sounds good, but it seemed a little
pricey.

Good luck.

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Mail From: Dan Malek <(email redacted)>



Wow...Exhaust. My love and hate :-)......

> Date: 6 Jan 1995 08:08:41 -0500
> From: Fontana Peter <(email redacted)>
>
>> I had one other question that I forgot to put into my
>> original post. What does a cross-over do to an exhaust system? I've seen
>them
>> mainly on cars but am curious as to their function and application.

>Their purpose is to equalize pressure between sides of the exhaust system.
>The basic layout of the crank/cam (one cylinder fires at a time) tells us
>that when there's a pulse in one side of the exhaust, there won't be one in
>the other.

It has nothing to do with pressure, but since you mentioned "pulse",
I will say you are pointed in the right direction.

>The major benefit of a crossover are mainly an increase in lower end torque.
>Some minor benefits can be reduced "harshness" in the exhaust sound at the
>tailpipes, a small increase in power in the upper ranges, and a small
>increase in MPG.

Well, the benefits depend upon the rest of the engine, and an incorrectly
placed or sized crossover can actually decrease performance.

>HotRod magazine occasionally runs a piece on how to determine where the
>optimum place is to put a crossover. I've found that the most inconvenient
>place is usually where it likes to be - right under the middle of the tranny.
> A couple more things: use the same diameter pipe for the xover are the rest
>of the system, and be sure the openings in the main pipes where the xover
>piece connects are close to the ID of the xover.

Since I have hundreds of hours of dyno time to prove otherwise, I will
disagree. I am sure there is an engine configuration that will prove
me otherwise (and I am willing to listen), but on the several I have done
the crossover always goes right at the collector, as close to the end of
the individual primary tapers as possible. It is the same diameter as
the collector. The tail pipes should not be further restricted in size.
If you are running 2" tail pipes, get a 2" collector, don't be doing this
3" collector restricted down to 2" tail pipe stuff.

>If you really want to talk crossovers, give Pro-Motorsports a call at (801)
>571-6097. They sell an "X" shaped set of pipes to replace the traditional
>"H" - they have big claims for it. Sounds good, but it seemed a little
>pricey.

I have never talked to them, but I will assume the best. They will
probably tell you how important it is to "tie" one bank of a V8 to the
other :-). Get some dyno test results and engine configurations that
prove this.....and then call me since I have never been able to prove
this.

I continuously talk to a few of the most knowledgeable "wave action"
folks in the performance industry, and have invested lots of time
and money in simulators and dyno testing. Everything is pretty well
understood until you get to the crossover. I have not found anyone
that can simulate it, and no one can explain why they work. The only
answer is that with a dyno, you can find the right place to add one,
that will give you the benefit you are trying to achieve. This is
also very dependent upon engine configuration, all of the way back to
where the air first enters an engine.


-- Dan

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Mail From: (email redacted) (Scott Griffith, Sun Microsystems Lumpyware)

On Jan 6, Peter Fontana wrote:

> Some minor benefits can be reduced "harshness" in the exhaust sound at the
> tailpipes...

Actually, for some of us this minor benefit is very important. Out
here in California, we have a lot of fine, wealthy folks who have
moved in next door to our racetracks, and who bitch endlessly (and
very effectively!) about the noise we make. For example, if we run at
Laguna Seca, the sound level limit enforced by the Monterey County
officials has been reduced to 92dB(A)@50ft. This is in fact quieter
than many _highways_, if there are semis or Harleys with race pipes
going by... In any case, we consider outselves lucky to get a weekend
at a facility that allows 103dB(A). Of all the roadracing facilities
out here, only Willow Sprigs still allows open exhausts, and it's only
a matter of time for them as well.

Living in this environment, we've found that a well done balance tube
is good for a solid 3-6dB(A) reduction in sound pressure levels at the
meter, in the absence of any other changes. I'm aware that this
doesn't apply to most folks at most racing venues. But if you're
scrambling to make the sound limit at your local facility (and,
unfortunately, sooner or later you'll probably have to!), the
importance of this can't be overemphasized.

Just for your amusement, here are some representative numbers from our
Laguna Seca experience. A 5.0L Mustang with stock exhaust and a stock
state of tune peaks right at 86dB(A), a slightly warmed-over 5.0 with
shorties, 2.5" offroad H-pipe, and 2-chamber Flowmasters will hit
94dB(A), and a race-prepped 289 in an early Mustang with a serious
cam, real headers, balance tube, and straight side-dump pipes is good
for about 107dB(A).... And so is a Harley with race pipes. A Cosworth
DFV in slightly detuned race trim (in an '82 Williams F1 car) is good
for 119dB(A), and a current Indycar with a Cosworth HB is good for all
of 97 dB(A).

-skod

- --
Scott Griffith, Sun Microsystems Lumpyware
expatriate SCCA New England Region Flagging/Communications worker
(and driver, of anything that turns both right and left,
and can pass tech...) Return Path : (email redacted)

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

>
> very effectively!) about the noise we make. For example, if we run at
> Laguna Seca, the sound level limit enforced by the Monterey County
> officials has been reduced to 92dB(A)@50ft. This is in fact quieter

> -skod

Is this rule enforced during the Historics? Last time I attended
(a couple of years ago), there were some pretty loud cars on the
track.

Roland

This read-only message was archived from a public mail list.
Mail From: (email redacted) (Scott Griffith, Sun Microsystems Lumpyware)

On Jan 6, Roland Dudley wrote:

[Re: the 92dB(A) sound limit at Laguna Seca]
> Is this rule enforced during the Historics? Last time I attended
> (a couple of years ago), there were some pretty loud cars on the
> track.

No. At Laguna, there are 5 "waiver weekends" per year that are run
with no sound limits, as permitted by the track's contract with the
county. These are reserved for the big money making events, which last
year were IMSA, IndyCar, the Historics, the PreHistorics, and the FIM
US Grand Prix. These are the big money making events for SCRAMP, the
charitable organization that runs the track. Additionally, there are
12 "103dB" weekends provided for in the contract, which are dedicated
for SCCA and AMA regional and national races, and testing dates for
the major pro series. And even those dates allow the 103dB levels only
during a small portion of the mid-day, from 10am to 12pm and 1pm to
3pm. Earlier or later, it's still 92dB.

All other users of the track get to run under the "everyday" rules,
which require a very firmly enforced 92dB(A) at all times. The Jim
Russell Racing school located at the track runs under the 92dB rule
every day of the week, for example. It's always amusing to watch folks
pull into the paddock with tow vehicles that are louder than their
race cars...

This year, two of the big-money events have pulled out of Laguna (the
FIM GP and IMSA), so the schedule there is a bit up in the air. But
the weekends with relaxed sound requirements will certainly go to
organizations that will bring mammoth wads of money for the track and
the businesses in Monterey County, and not to the smaller clubs. So,
while there are a handful of dates that allow more noise, they are
effectively off limits to most club uses.

-skod

- --
Scott Griffith, Sun Microsystems Lumpyware
expatriate SCCA New England Region Flagging/Communications worker
(and driver, of anything that turns both right and left,
and can pass tech...) Return Path : (email redacted)