Sound Advice
With the sound restrictions getting tighter at Laguna Seca and for
that matter all tracks, we are continually looking for better ways to quiet
our cars. The sound meter requirements over the last 10 years have
been tweaked more and more. Each time the meter was tweaked tighter
we seemed to know what to do and how to quiet our cars just that much more.
We started around 103 dba, then went to 100 dba, then 95 dba. When
the meter hit this last mark of 95 dba we started to separate the men from
the boys. The race cars with high strung motors were the most difficult
to tame. Technology came around with the Flowmaster muffler, which
seemed like a miracle. This muffler didn't cut down on power, it
enhanced torque, and it made the limit. Now we are at a new low limit
which is being strictly enforced, and this is as low as 90 dba. By
the way these readings at Laguna Seca are taken at 50 feet. Most
other race tracks take their readings at 100 feet. Quite a difference!
We don't claim to know the exact solution for quieting the car on the
racetrack, but are in a panic to perfect our readings. The advice
we offer below is merely some findings that we offer to you. We would
love to take advice from anybody and share it with others. Many cars
in our group pass with flying colors, we will try and list their formula.
We are also in search of other techniques all the time which we will try
for the future.
Exhaust Systems That Don't Work.
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Open exhaust, obviously doesn't work!
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Glasspack mufflers do not work!
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3 inch pipe Flowmasters don't work!
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Flowmasters with center inlet or center outlet don't work!
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3 inch pipe or larger Brand-X mufflers don't work!
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Shorter than 28 inch LoBaks don't work!
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Race style LoBaks don't work!
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Borla mufflers without catalytic converters or without a secondary muffler
such as a Supertrapp don't work.
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Monza style exhaust or European high performance mufflers on Ferrari's,
Porsche's, etc., don't work.
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Stinger type of exhaust on Porsche's & Mazdas, commonly known as expansion
chambers, don't work.
What Systems and Things Seem to Help.
Crossover pipes are a must. They lower decibels by some 2 - 6 dba.Crossover
pipes can be smaller pipe than your exhaust system. For example,
2 inch crossover would be fine for a 2 1/2 inch system. Consult
your muffler manufacturer for optimum placement of this crossover
tube in your system. This seems to be a great tool for gaining torque.
Another type of crossover tube in the form of a Siamese joining of smooth
flowing bends is called D-Gas and is recommended by Ron Bramlett
of Mustangs Plus in Stockton. Great results are reported on
the track, and a smoother pulse from this subtle crossover is achieved.
Contact Ron @ Mustangs Plus 209-944-9977, he claims to have a new
muffler he is working on as well.
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Diameter of Exhaust System
2 1/2 inch pipe is the absolute largest pipe that can be utilized to make
strict sound limits. Naturally 2 1/4 inch or 2 inch would even
be quieter. This even applies for necking down of side pipes.
The longer the pipe the quieter the system. Exhaust all the way out
the back of the car is going to be quieter than side exhaust.
Some believe routing both pipes, if dual exhaust is used, to the drivers
side of the car, helps divert sound away from the sound meter. This
can only be a crutch until sound is read on both sides of the track.
Large three chamber Flowmasters (approximately 16 inches or longer) with
offset in, offset out 2 1/2 inch pipe seem to get you just below
the limit. On certain days this system may be right at the limit,
especially if the atmosphere has any moisture present. Crossover
tube is essential. Try part # FLO-42553. This is the
quietest Flowmaster that they have currently. It will not sacrifice
power up to 400 HP. This will satisfy most of our needs.
By the way, Flowmaster has found their mufflers are quietest at wide
open throttle. They seem to smooth out the exhaust flow and that's
when they really do their job well. The latest versions of Flowmasters
are aluminized to hold off corrosion. By the way we are on
about the fourth generation of Flowmasters currently. You may
have the old ones.
Flowmaster offers complete Cat-Back systems, which may interest owners
of late model Mustangs & Corvettes, etc. Contact them for
your application. They also have developed new bolt on aluminum
heat shields which incorporate stainless steel straps. These might
be just the ticket for vehicles with converters, which generate more
heat. Great safety item!
Street LowBaks 32 inch or longer seem to get the job done, keeping with
2 1/2 inch pipe & a crossover tube. Stay away from the
race version of the LowBak. Some have reported 24 inch LowBaks
working with fairly healthy motors and keeping well below the sound limit.
These seem to be the answer for sidepipes for Cobra's, yet must incorporate
an additional Supertrapp attached to the end. Nevertheless
this is far less restrictive than just Supertrapps.
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Supertrapps & Supertrapp Mufflers
Supertrapps definitely work! They are more restrictive than most
of the race style mufflers, but they allow you to stay on track with
no black flag. You can tune them on the spot for the most power
possible. Supertrapps seem to be the real answer as a secondary muffler
system. They are the assurance you need to tune your car quiet
when all else fails. Supertrapp mufflers with the plates on
the tail end are less restrictive than just the plates by themselves.
These may warrant looking into for side pipes and Cobra's.
These act more like a muffler than can be imagined. A stock Mustang
GT with catalytic converters will register down in the low 80's for
decibels. If your car was designed to work and run with catalytic
converters, it will be just fine. Catalytic converters definitely
help and work! Don't take them off! If you take them
off you place yourself in the same position as the vintage cars.
That is, constantly trying to find a solution. If your
car is tuned for catalytic converters, stick with them! They
don't give up that much power. There are some companies that offer
Hi-Flo catalytic converters that claim 50 -100 % gains in flow, which
mean less back pressure. This would be the avenue to pursue
while still keeping sound levels down. One such company is
Random Technology in Stone Mountain, GA., with their Super High Flow converters
404-978- 0264. Another source is M & M Distributing, Mesa, AZ.,
who carries Mor-Flow Converters 800-408-2287. Dynomax is a
most recent developer of hi-flow converters. They are cheap and affordable.
A final source for aftermarket high flow converters is Summit Racing
Equipment at 330-630-0200.
Most stock street mufflers seem to work, these are somewhat more restrictive
than the so-called performance mufflers. Remember, 2 1/2 inch
pipe. Don't forget the crossover tube! Naturally 2
or 2 1/4 inch pipe would be even quieter!
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Walker/ DynoMax Turbo Mufflers
Turbo mufflers, as mentioned, seem to work. Aiming the exhaust to
the ground in front of the rear axle causes a resonance
& may cause you to be over the limit. Once again don't forget
the crossover tube and out the back is the best method of quieting
the car within the limit using turbo style mufflers. One of
the better known brands is Dynomax, although this information could be
applied generally to all brands. The Dynomax seems to be very efficient
for dollars spent, robs very little horsepower.On very high strung
motors or race motors, 2 1/2" Dynomax may be just over the
limit. It may take 2 1/4" pipe to actually do the job. In the
Dynomax line, stick with Super Turbo models, nothing less. The Ultra
Flo model will not work.
Dynomax offers complete Cat-Back systems, which may interest owners
of late model Mustangs & Corvettes, etc. Contact them for
your applications.
Beware of using Borla mufflers without catalytic converters! See
above. We have not seen anyone claim to conquer Laguna with
Borla's by themselves. Using Borla mufflers, with 2 1/4" pipe may
be the way to make them work. We know they work with
catalytic converters and or Supertrapps on the ends. Let someone
else try them first as a primary muffler. On the plus side these
are stainless steel, carry a great lifetime warranty, and naturally
these mufflers claim great power gains.
Borla offers complete Cat-Back systems, which may interest owners of
late model Mustangs, Corvettes, & SHO's. etc.
Contact them for your applications. We are confident that these systems
with catalytic converters would pass the sound limits.
Edelbrock has come out with a new line of mufflers. They are referred
to as the RPM Series Mufflers. We don't have information on
them yet, but know they have been vintage racing with two or three
sets of them in the development stage. They claim good torque benefits,
little horsepower loss, and many of the advantages of Flowmaster
mufflers. These mufflers are stainless steel, and offer lifetime
warranty like the Borla mufflers. They claim to be quieter than
Flowmasters, yet we can't attest to the power relationship. We will
report when more information is available.
Edelbrock offers complete Cat-Back systems, which may interest owners
of late model Mustangs & Corvettes, etc. Contact them for
your application.
This really seems to be a popular addition to my information. This
company makes an X-pipe bolt on fabricated crossover for the late model
Mustangs, including the 4.6 liter variety. Their mufflers are good
and adequate especially when used with the cats. Quality and fit
really seem to shine with Bassani.
There are many companies forming mandrel bent pipes lately. This
enables one to go with a small diameter tubing, utilizing quieter readings
while still keeping up good flow characteristics. A normal 2 1/2" pipe
system with normal muffler shop bends will reduce down to around 2.5 square
inches of exhaust flow. The mandrel bent tube will maintain 3.14
square inches throughout. This is commensurate to other pipe diameters.
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Latest Attempts and Technology
The latest race muffler set-ups are proving that single exhaust systems
are the most advanced. They offer virtually no penalty of power,
yet quiet things down. Consult your muffler manufacturer. Along the
lines of two devices, we saw a Flowmaster system with either Lobaks or
glasspacks welded in- line to help cure the problem. This worked!
The system was 3 inch, sort of an exception. The motor was
a 377 c.i. Windsor stroker!
Harley Davidson motorcycle pipe baffles. We have seen these inserted
in the end of the exhaust system to help quiet the system a bit more.
Naturally you will need a straight shot of pipe at the end to incorporate
this.
A 2nd Crossover pipe. Think we emphasized the crossover pipe enough?
Some are now claiming another decibel or so when you add another
crossover pipe after the mufflers.
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Reducers and Trick Pieces
If you are fabricating an exhaust system and want the smoothest transition
of exhaust gas possible. Here are a few part numbers from Flowmaster
on Venturi Reducer Cones. They reduce pipe diameter from one
size pipe to another with the least amount of restriction.
#R3025 3" reduces to ..... 2 1/2" 8" long
#R3530 3 1/2" reduces to 3" 8" long
#R2424 2 3/4" reduces to 2 1/4 " 8" long
If you are fabricating a single exhaust system and want to blend in
two pipes with the smoothest transition possible here are a few part
numbers from Flowmaster. These are referred to as Force II
Scavenger Series Y Collectors.
#Y-200250 2" inlet y's into
2 1/2" outlet 16 1/2" long
#Y-214300 2 1/4" inlet y's into 3"
outlet 17 1/2" long
#Y-238300 2 3/8" inlet y's into 3"
outlet 16 1/2" long
#Y-250300 2 1/2" inlet y's into 3"
outlet 16 1/2" long
#Y-250350 2 1/2" inlet y's into 3 1/2" outlet 17 1/2" long
#Y-300350 3" inlet y's into
3 1/2" outlet 17 1/2" long
Noise is noise! It doesn't have to be exhaust sound to be noise and
trip the meter. Here are a few of the things that might play havoc
with the sound meter, while you are aiming at the exhaust system.
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Quick change rear-end, like a Franklin
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Flex fans for the radiator
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Gear drive timing sets
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Weber carburetors with velocity stacks
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Mechanical fuel injection with velocity stacks
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Turbo charger swooosh!
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Cam timing. Who can tell us what is the best type of cam to
run for sound? Lots of duration or little duration?
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Compression ratio, the more you have, the more the bang.
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Exhaust leaks, holes in pipes or bad connections, etc.
We are looking for more information all the time. Please pass on
what seems to work for your car if you have licked the sound problem.
Here are some areas that really need attention or help. We have made
progress in many of these areas, yet the more the merrier when it comes
to ideas, thoughts, & results.
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Side pipes, Cobra's, 'Vettes, etc.
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GT-40 bundle of snakes exhaust
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Nascar, old or modern, includes Trans-Am old or modern
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Vintage race small blocks
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Late models with off-road pipe option
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Rotary Mazda motors, Porsche Turbo's and modified 911's
Most recently we saw the neatest bundle of snakes exhaust. The owner
left the stock bundle of snakes exhaust headers on the vehicle. What
followed was a slip fit arrangement atop the engine which mated to two
turbo style mufflers which made the grade of 92 decibels or lower.
He used a stainless steel (which has nothing to do with sound levels) which
enhanced the look of the system. He simply slips the exhaust off
and attaches the straight dump pipes which attach to the main header system
and you're all set for the power throbbing sound at tolerant race tracks.
For a table of comparison and sample readings taken of club cars at
Laguna Seca, click here .
