The Great Hot Rod Turbo Muffler

Show Down
Originally published in the July 1984 issue of Hot Rod
magazine

HOT ROD StaffWriterJan 01, 2023

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By Marlan Davis
The main thing that separates hot street cars from race cars is
mufflers. Heck, you've got blowers, injectors, roller cams, ported
heads, and anything else you can name on street cars these days.
''Joe Street" can tell you anything you want to know about those
parts, too—lift, duration, blower overdrive, port flow … just ask him.
But ask him about his mufflers, and the conversation stops. He
doesn't know. More important, he doesn't stop to realize that
everything else he does to cram more fuel and air into the engine is
futile if this larger mass has no way out.
Wanna test mufflers? Then try this Gale Banks Engineering 454
Chevy 9.4:1 "street engine'' that cranks out 539 hp. It produced
enough mass airflow and noise to really put the mufflers to the test.
HOT ROD figured that it's time for hot rodders to know more about a
muffler than whether it is round or oval. A muffler is an important
piece of equipment on any street car, even if it is totally stock. It
should be considered as one of the first areas of modification, and
you should know what you are buying. As you will find out from our
test, there are plenty of choices depending on what your wants are.
Thereisa difference in mufflers.

Our test included 22 different sets of ''turbo" mufflers. The turbo

muffler is a generic take-off on the famed Corvair turbocharger
muffler. It gained prominence more than 10 years ago, when
another HOT ROD muffler test showed that this "conventional"
muffler could outperform the straight-through glasspack designs
while at the same time being quieter, more mellow, and very
compact.

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Since then the aftermarket has produced numerous copies and

evolved into designing totally new "turbo" (readreverse
flow)mufflers. Besides the Corvair turbo there were a couple of other
original equipment manufacturer's mufflers building a reputation.
They were the Chrysler hemi and the Chrysler Imperial. The hemi
design bested the glasspacks in that HOT ROD test also. Both of
these mufflers are much larger than the turbos and more expensive,
but many a street rodder found ways to hang 'em.
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All mufflers were connected to the 2½-inch headpipe system that

featured a balance crossover tube. Short tailpipes were installed to
obtain realistic power and noise data.

Going into the test the objectives were simple: learn as much as we
could about mufflers. In particular, which muffler makes the most
power, which muffler is the quietest, and which design is the best.
We were curious about how much power loss the mufflers accounted
for and how much the rest of the exhaust system devoured.
Everyone around the office had their own theory about the
relationship of backpressure to power loss through the muffler.
These theories and others would be put to the test.

The Number 1 item you need to test high-performance mufflers is a

high-performance engine. Something with a high airflow mass that
could tax a muffler's capacity. Only then would we have a measure
for comparison. A 539-horsepower 454 Chevy rat motor would
represent the high end of the street spectrum and push enough hot
air at 6000 rpm to do the job.
SEE ALL 9 PHOTOS

American Exhaust's Sonic Turbo 45121 was the top dog on the
horsepower chart, but the amazing thing was that the next 12
placing mufflers were within 2½ percent of the winner.
SEE ALL 9 PHOTOS

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We cut a few of the test mufflers up to see what made them tick.
Basically, there are two internal designs. The one on the right (A)
has a resonating chamber (this design is used on the original
Corvair turbos); the design on the left (B) is typical of most
aftermarket turbos and is a multi-tube "S" flow design. Many factors
seem to affect performance, like neckdown (arrow 1) and the size
and type of perforations (arrow 2).(Illustration: Rick Geary)

The question came up during the test preparations, "Why use an

engine, why not just flow them on a flow bench?" In fact, another
magazine just did a muffler test that way. Itsoundslike a logical test
procedure, but it doesn't account for 1100 degrees of heat, exhaust
gas pulsing, acoustics, or resonance. And how do you take a decibel
level reading of a muffler on a flow bench? Like we said, this is going
to be "A REAL TURBO MUFFLER TEST."

The test procedure was relatively easy to define. You don't test 500-
plus horsepower engines on a chassis dyno because the rear wheel
slippage is too great at anything more than 200 horsepower at the
rear wheels. An engine dynamometer has the ability to point out
minute power differences if it has the correct instrumentation and a
seasoned dyno operator. We found both at Gale Banks Engineering
in Azusa, California. Gale also provided us with the blueprinted 454
that was able to withstandmore than 40 full-power 6000 rpm runs
with no engine deterioration.

2.Sound Level on Engine Dyno

Noise measured using Radio Shack decibel meter positioned level
with left-hand exhaust pipe, 15 feet from pipe tip at 45° angle.
Muffler temp stabilized to 800° F. with light engine load (15 hp at
2500 rpm).

Mufflers are represented on 1-10 scale, with 10 being the

loudest.
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A typical street exhaust system was mocked up with 2½-inch o.d.

headpipes with a crossover pipe to balance the system. Tailpipes
were also connected to the test mufflers for accurate decibel and
horsepower readings. Probes for backpressure and temperature
were placed before the mufflers, and an additional temp probe was
placed at the muffler exit. Hopefully, we would see a correlation
between backpressure and powerandheat and power.

The exhaust headers were the only oddball pieces by necessity. A

set of Hedman 4-2-1 boat headers with 21/4-inch primary tubes
were used as they were the only style that would clear all obstacles
on the dyno. The 4-2-1 collectors have proven to have excellent
torque producing capabilities, but in this case they measured 4
inches in diameter. So the neckdown to 2½-inch head pipes was
quite severe, which may account for the seemingly large power loss
of 30 hp for the headpipes alone without mufflers. The engine with
open collectors blasted out a 539 hp baseline. The horsepower
number dropped to 508 hp with headpipes.

Next, the superhuman task of testing 40 sets of mufflers (the 22

sets were randomly retested to verify repeatability) was
accomplished. The results were shocking! The top 13 finishing
mufflers all tested within 13.2 horsepower, or within 2½ percent, of
each other. American Exhaust's Sonic Turbo 45121 came out the
winner, producing just 12 hp less than open headpipes. That's
incredible to think a set of mufflers only costs a 538 hp engine 12
horsepower-your waterpump absorbs more power. And when you
consider this figure in real-world terms, namely rear wheel
horsepower, you're probably talking 10 hp or less, and with 500 hp,
that's undetectable on the clocks or your seat of the pants.

At the other end of the scale there were mufflers that made
substantially less power, like the Chrysler street hemi. It was down
33.1 hp, and thatisa number that you can feel in the seat of your
pants. However, the street hemi was the third quietest, and like we
stated earlier, your wants in a muffler system should be the deciding
factor. Power or noise,, the choice is yours. A few mufflers like the
Exzostec, the Borla, and the Ermie Immerso "Thunderbird" struck an
excellent compromise between power and quietness.
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Chevy used two different mufflers on turbocharged Corvairs. We

affectionately named the one on the left (part No. 3869877) the
"trash can,'' and the "oval'' (part No. 3858442) is the granddaddy of
all modern turbo mufflers, yet still managed to place fifth.
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Chrysler's Imperial (top) and street hemi mufflers did not live up to
their past reputations. However, the Imperial muffler was among
the quietest, and its exhaust note was real mellow.

3.Muffler Specifications
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The clear winner on the noise chart was the Chrysler Imperial. Its
mild note was closely followed by the Pacesetter Monza. Both the
Chrysler Imperial and hemi mufflers are larger than the turbo variety
(see dimension chart), so mounting problems should be considered,
especially on later-model cars. The noisiest muffler was the original
GM Corvair turbo, as it possibly should be. First of all, it was
designed to muffle an exhaust note already partially silenced by a
turbocharger, so a great deal of sound reduction wasn't needed.
Also the 'Vair muffler was used to produce a desirable tone for the 6-
cylinder's exhaust note.

What did we learn other than which muffler produced the smallest
power loss and which muffler was the quietest? We learned that no
one internal design seemed to have a distinct power or noise
advantage over another. Each muffler company has achieved nearly
equal goals with very different designs. The charts point out that
there is no direct correlation between power loss and noise because
some of the better performers were also very quiet. And we found
no correlation between backpressure and horsepower. Several
experts in the muffler field claim that backpressure cannot be
accurately measured at any single point in the system (the way we
measured backpressure). Likewise, no direct correlation between
power and heat loss across a muffler can be made. It seems to be
strictly a function of muffler construction and materials, not
efficiency.

In the final analysis we learned a lot from this test. We also raised as
many new questions as we answered about the inner dynamics of
high-performance mufflers. It seems exhaust system transition from
head collector to muffler can be as critical as your choice of muffler.
Bigger is not necessarily better, as the top power producer was not
a 2½-inch in-and-out muffler but instead a 21/4-inch I/O … surely a
mystery to us.

We sampled every turbo muffler we could find. If one of your

favorites is not represented, it is likely because the manufacturer
declined to participate in the test up front or withdrew later when
their mufflers did not perform up to the standards. The buying
decision is, yours; about the only thing we didn t cover here is price,
and that's a major consideration when you are looking at results this
close.

The best bit of information gathered from this whole exercise is that
the aftermarket muffler companies have come a long way since our
last muffler test 10 years ago, and that's hot rodding at its best—
always improving the breed.

1.Peak Horsepower on Engine Dyno

Readings taken at engine's 6000 rpm with muffler temperature
stablized at 1100 degrees F. HP figures corrected to standard
atmosphere and pressure conditions.

Exhaust system dimensions (inches) -Headers: Primary tubes

2½ ID X 38 long; 4-2 neckdown, 4. main collector 4D X 12 long,
reduces to 3½exhaust pipes, Inlet dual long with 2½ D crossover
pipe) exhaust, dual 2½D x 25 long,

539 hp

Baseline test #1

(open headers)

508 hp

Baseline test #2

(headers, exhaust pipes with crossover tube)

496-482 hp

American Exhaust Sonic Turbo

45121

Exzostec 5300-250

Maremont 19825

478-473 hp

Ermie Immerso 3680

GM 3858442 "oval" turbo

Borla stainless steel

American Exhaust 45122

Hedman Walker 21348

Supreme 151005 GM 3869877 "trash-can turbo

Thrush Turbo 500 No. 570

American Exhaust Prototype

467-454 bp

Walker 21927

Walker 17833

American Exhaust CA Turbo 40122

Chrysler Imperial 3583992

Pacesetter Monza/Quick-Trip 651734

Chrysler 2781300 street hemi Carlson

Manufacturers
AMERICAN EXHAUST(Blackjack/Cyclone) 18933 S. Reyes
Compton, CA 90221 (213) 603*0465

SUPREME MUFFLERDIV./Arvin Automotive 1222 Hutchins Ave.

Columbus, IN 47201 (812) 379-3284

BORLA INDUSTRIESINC. 2639 Saddle Ave. Oxnard, CA 93030

(805) 983-7300

CARLSON MUFFLERSALES INC. P.O. BOX 419 Riverdale, GA 30274

(404) 478-8851

CHRYSLER CORP. (See your Chrysler dealer)

EXZOSTEC PRODUCTS614 E. Walnut Carson, CA 90746 (213) 323-

6400

GENERAL MOTORS CORP. (See your General Motors dealer)

HEDMAN HEDDERS9599 W Jefferson Blvd. Culver City, CA 90230
(213) 839-7581

ERMIE IMMERSO ENTERPRISES INC. (Thunderbird Products)

18700 Susans Rd. Rancho Dominguez, CA 90221 (213) 537-1800

EXHAUST SYSTEMSDIV./Maremont Corp 250 E. Kehoe Blvd Carol

Stream, IL 60187 (312) 462-8500

PACE-SETTERINC. (Monza/Quick-Trip) 3455 S. La Cienega Blvd. Los

Angeles, CA 90016 (213) 233-0207

THRUSH INC., A Gidon Cd 172 Bethridge Rd. Rexdale, ON M9W 1N3

Canada (416) 746-4422

WALKER MFG./Div. of Tenneco Automotive 1201 Michigan Blvd

Racine, Wl 53402 (414) 632-8871