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Just got dual Super 40 Flowmasters.....

Derrick

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Sep 22, 2004
Messages
108
Location
Texas
Corvette
1975 Coupe
I have a question for you guys. I have a 75 vette with a true dual exhaust system, headers, and gutted cats. There is also an H pipe in the system about 2 feet in front of the mufflers.

Last week a got the local muffler shop to install a set of Super 40 Flowmaster mufflers, because I've heard that they are some of the loudest mufflers you can get. When I went to pick the car up it actually wasn't that loud at all???

My question is, Is there anything that could be causing my car to be so quiet? I have gutted cats, headers, and new mufflers, so I doubt that anything is clogging the exhaust.

As far as my engine goes...its an L-48, with a Holley Street Avenger 670cfm carb, holley dominator intake, and that's about it.

Could it be possible that I need a more potent ignition system (MSD) that'll increase the spark and help to burn all of the gas I'm feeding it. I've heard that the HEI system in the 75s weren't that great...

Any help would be greatly appreciated!
 

81 Corvette

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Joined
May 12, 2003
Messages
525
Location
Toledo
Corvette
1981 Pearl White
i've got the basic flowmaster 40's and they are plenty loud on a 50 mile drive.

my gf supposedly can hear my car pulling into our apt complex and we are the third building from teh street, and on the backside of the building.

i've got headers and a highflow cat before the mufflers
 

Derrick

Well-known member
Joined
Sep 22, 2004
Messages
108
Location
Texas
Corvette
1975 Coupe
I know that mufflers normally get louder after they are "broken in"...How long did it take before you noticed a difference in sound / tone?
 

yellow77

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Joined
Jun 17, 2004
Messages
184
Location
Tulsa, OK
Corvette
1977, Bright Yellow
Derrick, I have flowmaster 40's on 2 1/2 inch duals with the stock rams horn manifolds, and its loud. It was loud immediately they were installed, I drove a 600 miles round trip and had my son with me, we had to raise our voices to hear each other talk. Do you have a 2 1/2 inch system, are there any crimps in the piping, etc that might restrict the flow?

Cheers

Richard
 

Yoda

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Administrator
Joined
Oct 12, 2000
Messages
4,884
Location
Amarillo, TX
Corvette
1981 UL5
:w Richard,

I have the Flow Master 40's on Rare and I personally don't think they are all that loud, but everyone else says it sounds great. I do notice a resonance rumble if I load her down in third. I let one of my buddy's drive her and told him to get into it a couple blocks from home... With the Quad opening and the sound of the exhuast... Let's just say it sounds different from being in the driver seat :D

Oh.. as I idle around town, it does set off some car alarms :D which makes for some fun ;LOL

Bud
 

Derrick

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Joined
Sep 22, 2004
Messages
108
Location
Texas
Corvette
1975 Coupe
The previous owner of my car had the car lowered...it actually scraps the ground if I have a passenger and hit a dip in the road. The exhaust pipes are a bit dented, but not that badly.

The weird thing is that the car is loud at 2000rpm, but once you step on the gas it just sounds regular. The car has the same quiet sound cruising down the highway at around 70 to 80 mph. I have 3.70 gears and a 3 speed auto, so cruising at 70 or 80 the rpms are way up there.
 

brusso

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Joined
Oct 20, 2003
Messages
369
Location
wareham, MA
Corvette
1975 red coupe
yellow77 said:
Derrick, I have flowmaster 40's on 2 1/2 inch duals with the stock rams horn manifolds, and its loud. It was loud immediately they were installed, I drove a 600 miles round trip and had my son with me, we had to raise our voices to hear each other talk. Do you have a 2 1/2 inch system, are there any crimps in the piping, etc that might restrict the flow?

Cheers

Richard
I've got this same set up and yes it's loud. I think that an H pipe (like on yours) quiets it down a bit.
 

Derrick

Well-known member
Joined
Sep 22, 2004
Messages
108
Location
Texas
Corvette
1975 Coupe
Are you guys running an auto or manual trans? I have a 3 speed auto, with 3.70 gears, so cruising down the highway I'm at about 5k rpms. The loudest tone from my exhaust comes between 1800 to 2500 rpms.

I'm thinking about getting the shop to relocate the mufflers directly behind my gutted cats and eliminate the h-pipe. Hopefully running a couple feet of 3 inch pipe after the mufflers will enhance the sound.
 

brusso

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Joined
Oct 20, 2003
Messages
369
Location
wareham, MA
Corvette
1975 red coupe
Mine is a Three speed auto with stock rear end. I think the gears are like 2.55's or something less than 3.00. At 70-75 mph I'm reving about 3,000 rpm.
 

Derrick

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Joined
Sep 22, 2004
Messages
108
Location
Texas
Corvette
1975 Coupe
Alright...that makes sense then. If I were at 3,000 rpm cruising 70mph then I would probably have to yell at my passenger for them to hear me.

I just thought that the greater the rpm, the louder the sound.
 

81 Corvette

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Joined
May 12, 2003
Messages
525
Location
Toledo
Corvette
1981 Pearl White
i've got 3.54 and turn 2600 rpm at 60, but i ussally cruise at 3500 rpm or about 80. seems the loudest is below 2000rpm.

this is with a fairly stock motor, headers, hi flow cat, and 40's
 
L

longhorn294

Guest
I put a set of 40 flowmasters on my '71 about a month ago on Friday and Monday had them taken off. Not loud enough? Sounded like some junked-out pickup with rusted-out mufflers. Not a good loud sound at all, just noisy.
 

Glensgages

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Jan 10, 2003
Messages
757
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State-of-Confusion
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Black '82 Coupe
atmmac said:
Straight PIPES!!! :D
[Professor Turgeson]
"Good answer... good answer.
I like the way you think:
I'm keeping my eye on you!!!"
[/Professor Turgeson]
 

80vette_ca

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Joined
Jan 2, 2003
Messages
93
Location
Regina, Sask, Canada
Corvette
1980 L82
Nothing like open headers, wow that is just loud :D
 
M

mike weyman

Guest
i was told by an old performance engine builder and better than novice 1/4 mile racer, that you should spray some spray paint on the exhaust pipes near the headers . with paint wet start the engine,at the point where the exhaust stops burning the paint off the exhaust pipe you insert the "H" or "X" pipe this is supposed to be the best place for a crossover.the pipe allows each spark to fire into two exhaust pipes instead of one, as only one plug fires at a time . this would account for the lower than expected sound level.
As far as the muffler location goes , the farther back, the louder the sound level.move it up towards the front and it will be quieter.
 

Glensgages

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Joined
Jan 10, 2003
Messages
757
Location
State-of-Confusion
Corvette
Black '82 Coupe
mike weyman said:
i was told by an old performance engine builder and better than novice 1/4 mile racer, that you should spray some spray paint on the exhaust pipes near the headers . with paint wet start the engine,at the point where the exhaust stops burning the paint off the exhaust pipe you insert the "H" or "X" pipe this is supposed to be the best place for a crossover...
Mike, this is also used to determine where to cut-off 'extensions' that drag-racers bolt onto the headers to optimize collector length:
not sure it is done with wet paint, though, and have never used/heard this method being used to determine placement of cross-over pipes.
Good point, none-the-less
 

GTR1999

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Sep 4, 2003
Messages
1,146
Location
New Haven CT
Corvette
1969,1972,1975
brusso said:
Mine is a Three speed auto with stock rear end. I think the gears are like 2.55's or something less than 3.00. At 70-75 mph I'm reving about 3,000 rpm.
Stock auto gears were 3:08's on most cars, some had 2:73 later in the run.
 
M

mike weyman

Guest
glen, i guess it is a relative formula, i've only heard of it for x or h pipe locating, oh well, maybe it does both.mike
 

captras

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Joined
May 11, 2004
Messages
58
Location
Sugar Land, TX
Corvette
1975 Red Convertible
How about chambered exhausts...anybody use them or know how they compare performance and sound wise in comparison with Flowmasters...etc.!
 

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