Dropping the exhaust decibels on street motor

[Simmo]

As I get older I prefer my street toys to be quieter at idle and cruise, but I dont like to throw away power.

My latest project is a 68 Implala running a 533 with a mild cam that should peak at 5500rpm or less and make about 600BHP

I had a design idea Ive not seen before and was keen to get an opinion if it would quieten the exhaust much.

Car will run twin 3" pipes from collector to mufflers placed in front of rear axle. Pipe dia drops to 2,3/4 over the diff and exit behind rear wheel. 3" H pipe crossover immediately behind the collectors or as far forward as possible and a second crossover over the diff in 2, 3/4".

Now for the difference, on one side behind the first crossover I add an an electronic exhaust cutout like Summit SUM-670003. There is no exhaust diversion, just the blockage that forces one side across the crossover to combine with the other. All the pulses combined will run for about a one metre of straight pipe then through one muffler before travelling over the diff where they hit the crossover and exit through tail pipes on both sides.

An RPM switch say set at 3000RPM opens the cutout to give a free flowing exhaust when at WOT.

Interested in opinions whether this will quieten the exhaust much.

[lefty o]

its sure as heck going to get louder at 3000rpm.

[Tom68]

As I get older I prefer my street toys to be quieter at idle and cruise, but I dont like to throw away power.

My latest project is a 68 Implala running a 533 with a mild cam that should peak at 5500rpm or less and make about 600BHP

I had a design idea Ive not seen before and was keen to get an opinion if it would quieten the exhaust much.

Car will run twin 3" pipes from collector to mufflers placed in front of rear axle. Pipe dia drops to 2,3/4 over the diff and exit behind rear wheel. 3" H pipe crossover immediately behind the collectors or as far forward as possible and a second crossover over the diff in 2, 3/4".

Now for the difference, on one side behind the first crossover I add an an electronic exhaust cutout like Summit SUM-670003. There is no exhaust diversion, just the blockage that forces one side across the crossover to combine with the other. All the pulses combined will run for about a one metre of straight pipe then through one muffler before travelling over the diff where they hit the crossover and exit through tail pipes on both sides.

An RPM switch say set at 3000RPM opens the cutout to give a free flowing exhaust when at WOT.

Interested in opinions whether this will quieten the exhaust much.

You're not taking advantage of the volume (cubic feet volume) in you system with that, I'd look at restricting it at the outlet at low RPM.

Also lots of low speed ignition advance should help, fires out before the valve opens.

[In-Tech]

Vacuum advance distributor(if carb'd) with lot's of advance at low load, that thing might want as much as 60 degrees. Check out this stock 2017 CTSV LSA spark table. This is for fast burn heads and not even our lazy ass BBC open chambers

Code: Select all

	Main Spark Advance Vs. Load Vs. RPM - High Octane
 
  Load Index                                                                                                RPM Index
                0     1     2     3     4     5     6     7     8     9     10    11    12    13    14    15    16    17    18    19    20    21    22    23    24    25    26    27    28    29    30    31    32  
        0      28.0  28.0  28.0  28.0  28.0  32.0  33.0  34.0  38.0  42.0  48.5  55.0  55.0  55.0  55.0  55.0  55.0  55.0  55.0  55.0  54.0  52.0  50.0  50.0  50.0  50.0  50.0  55.0  55.0  50.0  50.0  50.0  50.0 
        1      28.0  28.0  28.0  28.0  28.0  32.0  33.0  34.0  38.0  42.0  48.5  55.0  55.0  55.0  55.0  55.0  55.0  55.0  55.0  55.0  54.0  52.0  50.0  50.0  50.0  50.0  50.0  55.0  55.0  50.0  50.0  50.0  50.0 
        2      28.0  28.0  28.0  28.0  28.0  31.0  32.0  34.0  37.0  40.0  44.5  49.0  48.5  48.0  49.0  49.0  50.0  48.0  47.5  48.0  44.0  46.5  45.0  47.5  48.0  45.5  44.5  44.0  44.0  44.0  44.0  44.0  44.0 
        3      28.0  28.0  28.0  28.0  28.0  31.0  32.0  34.0  37.0  40.0  46.0  42.0  42.5  43.5  45.0  44.0  44.0  42.0  42.0  41.0  42.0  40.0  42.0  44.5  44.0  41.5  40.0  40.0  40.0  40.0  40.0  40.0  40.0 
        4      28.0  28.0  28.0  28.0  28.0  31.0  34.5  37.5  39.5  42.0  45.0  40.5  40.5  40.0  41.0  41.0  42.5  40.5  40.0  39.5  39.0  38.0  39.0  40.0  40.5  38.0  38.0  42.0  42.0  38.0  38.0  38.0  38.0 
        5      25.0  25.0  25.0  27.5  28.0  31.0  32.0  34.0  37.0  38.0  41.0  38.0  38.0  38.0  38.5  39.0  39.5  39.0  38.0  38.0  36.5  36.0  36.0  37.0  36.5  35.0  35.5  40.0  40.0  37.0  37.0  37.0  37.0 
        6      20.0  20.0  20.0  25.5  25.5  27.5  29.5  32.0  34.5  35.5  37.5  35.5  36.0  36.0  36.5  37.5  37.5  37.0  36.0  36.0  35.0  34.0  34.5  35.5  34.0  33.5  34.5  37.0  37.0  36.0  36.0  36.0  36.0 
        7      15.0  15.0  15.0  21.0  23.0  25.5  27.5  31.0  32.5  33.0  35.0  34.0  34.5  35.0  35.5  36.0  36.0  35.5  34.5  34.0  34.0  32.5  33.0  33.5  32.0  32.0  33.5  34.0  34.0  35.0  35.0  35.0  35.0 
        8      11.0  11.0  11.0  17.0  20.0  23.0  26.0  27.5  29.5  32.0  32.5  33.0  33.5  34.5  34.5  34.5  34.5  34.0  33.5  33.0  33.0  31.5  31.5  32.0  30.0  29.5  31.5  31.5  31.5  33.5  33.5  33.5  33.5 
        9       9.0   9.0   9.0  12.5  17.5  20.0  24.0  24.0  26.5  28.0  31.5  31.5  32.5  33.5  33.5  33.5  33.5  33.0  31.5  32.0  32.0  31.0  30.0  30.0  28.5  28.0  29.0  29.5  29.5  31.5  31.5  31.5  31.5 
       10       7.0   7.0   7.0  10.5  15.0  17.5  21.0  22.0  24.0  26.0  29.5  30.0  31.5  32.5  32.5  32.5  32.5  32.0  30.5  31.0  31.5  29.5  28.5  29.0  26.5  25.5  27.0  28.5  28.5  30.0  30.0  30.0  30.0 
       11       4.5   4.0   4.5   5.0  11.0  15.0  18.0  19.0  21.5  24.0  27.0  29.0  30.5  31.0  31.0  31.0  31.0  30.5  29.5  30.5  29.5  28.0  26.5  28.0  25.5  25.0  26.0  27.0  27.0  28.0  28.0  28.0  28.0 
       12       3.0   3.0   3.0   3.0   9.0  13.0  17.0  17.5  19.0  21.5  25.5  28.0  29.0  30.0  30.0  30.0  30.0  29.5  28.5  29.5  28.5  27.0  25.5  26.5  24.5  24.0  25.0  25.5  25.5  26.5  26.5  26.5  26.5 
       13       3.0   3.0   3.0   3.0   7.0  10.5  15.5  16.5  17.5  20.0  22.5  26.5  27.5  29.0  29.0  29.0  29.0  28.0  27.5  28.5  27.0  26.5  25.0  25.5  23.0  23.5  24.5  24.0  24.0  25.0  25.0  25.0  25.0 
       14       2.0   2.0   1.5   2.0   6.5   9.5  14.0  16.0  17.0  19.5  22.0  25.0  25.5  28.0  28.5  28.0  28.5  27.0  26.5  27.0  26.5  26.0  24.0  24.5  22.5  22.5  24.0  23.0  23.0  23.5  23.5  23.5  23.5 
       15       1.5   1.5   1.5   2.0   5.5   9.0  11.5  14.5  16.5  19.0  22.0  23.5  24.5  26.5  27.0  26.5  26.5  26.0  25.5  25.5  25.5  25.0  24.0  23.5  22.0  22.0  23.0  22.0  22.0  21.5  21.5  21.5  21.5 
       16       1.5   1.5   1.5   1.5   4.5   7.5  10.5  14.0  16.5  18.0  21.0  22.5  23.5  25.0  25.0  25.5  25.5  24.5  24.5  25.0  25.0  24.0  24.0  23.0  21.0  21.0  22.5  21.5  21.5  20.5  20.5  20.5  20.5 
       17       1.5   1.5   1.5   1.5   4.0   6.5   9.5  13.5  15.0  17.0  19.5  21.5  23.0  23.5  24.0  24.5  24.0  23.0  23.0  24.0  24.5  23.0  22.0  22.0  20.5  20.5  22.0  20.5  20.5  20.5  20.5  20.5  20.5 
       18       1.5   1.5   1.5   1.5   3.0   5.5   8.5  12.0  14.0  16.0  18.5  20.0  22.0  22.5  23.0  23.0  23.0  23.0  22.5  23.0  22.5  21.5  21.0  21.0  20.0  20.5  22.0  20.0  20.0  20.0  20.0  20.0  20.0 
       19       1.5   1.5   1.5   1.5   2.5   4.5   7.5  10.5  14.0  16.0  17.5  19.0  20.5  22.0  22.0  22.0  22.0  22.0  22.0  22.0  21.5  21.0  20.0  20.0  20.0  20.0  22.0  23.0  21.0  20.5  20.5  20.5  20.5 
       20       1.5   1.5   1.5   1.5   2.0   4.0   7.0  10.5  13.5  15.5  17.0  18.5  20.0  21.0  21.0  21.0  21.0  21.0  21.0  21.0  20.5  20.0  20.0  20.0  20.0  20.0  21.0  21.0  20.0  20.0  20.0  20.0  20.0 
       21       1.5   1.5   1.5   1.5   2.0   4.5   7.0  10.5  13.5  15.5  16.5  18.0  19.5  20.0  20.0  20.0  20.0  20.0  20.0  20.0  20.0  19.0  18.0  18.0  18.0  18.0  19.0  19.0  18.0  18.0  18.0  18.0  18.0 
       22       1.5   1.5   1.5   1.5   2.0   4.5   7.0  10.5  13.5  15.0  16.5  18.0  19.5  20.0  20.0  20.0  20.0  20.0  20.0  20.0  20.0  19.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0 
       23       1.5   1.5   1.5   1.5   2.0   4.0   7.0  10.5  13.5  15.0  16.5  18.0  19.5  20.0  20.0  20.0  20.0  20.0  20.0  20.0  20.0  19.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0 
       24       1.5   1.5   1.5   1.5   1.5   4.0   7.5  10.5  13.5  15.0  16.5  18.0  19.5  20.0  20.0  20.0  20.0  20.0  20.0  20.0  20.0  19.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0 
       25       1.5   1.5   1.5   1.5   1.5   4.0   7.5  10.5  13.5  15.0  16.5  18.0  19.5  20.0  20.0  20.0  20.0  20.0  20.0  20.0  20.0  19.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0 
       26       1.5   1.5   1.5   1.5   1.5   4.0   7.5  10.5  13.5  15.0  16.5  18.0  19.5  20.0  20.0  20.0  20.0  20.0  20.0  20.0  20.0  19.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0 
       27       1.5   1.5   1.5   1.5   1.5   4.0   7.5  10.5  13.5  15.0  16.5  18.0  19.5  20.0  20.0  20.0  20.0  20.0  20.0  20.0  20.0  19.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0 
       28       1.5   1.5   1.5   1.5   1.5   4.0   7.5  10.5  13.5  15.0  16.5  18.0  19.5  20.0  20.0  20.0  20.0  20.0  20.0  20.0  20.0  19.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0 
       29       1.5   1.5   1.5   1.5   1.5   4.0   7.5  10.5  13.5  15.0  16.5  18.0  19.5  20.0  20.0  20.0  20.0  20.0  20.0  20.0  20.0  19.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0 
       30       1.5   1.5   1.5   1.5   1.5   4.0   7.5  10.5  13.5  15.0  16.5  18.0  19.5  20.0  20.0  20.0  20.0  20.0  20.0  20.0  20.0  19.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0 
       31       1.5   1.5   1.5   1.5   1.5   4.0   7.5  10.5  13.5  15.0  16.5  18.0  19.5  20.0  20.0  20.0  20.0  20.0  20.0  20.0  20.0  19.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0 
       32       1.5   1.5   1.5   1.5   1.5   4.0   7.5  10.5  13.5  15.0  16.5  18.0  19.5  20.0  20.0  20.0  20.0  20.0  20.0  20.0  20.0  19.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0  18.0 
 

[Walter R. Malik]

Splitting the exhaust into more outlets and using more mufflers in "parallel" will quiet the exiting sound level without exhibiting a cruising "drone".

[F-BIRD'88]

If you want dual exhaust to appear to be quieter to a listener both in car and out run the dual exhaust tail pipes close together on one side or the other at the back of the car. Like a europeon sports car.
The now mono exhaust sound is much less intense to the listener VS stereo dual exhaust.

[mag2555]

This is ment for a chuckle.

Do what NASA does when they lunch a rocket.

To to reduce the massive sound pressure that has been shown to cause damage early in the lift off phase ( to the rocket engine) they pour tons of water into the flame basin.

The production of steam reduces the DB level, not to mention keeps the lunch pad and structure from melting down.

[bthomas]

Hemholtz resonators aka j-tubes. Worked awesome on a friends car. Exhaust cutouts were added to the ends on the j-tubes to allows for that bark when needed too.

[Simmo]

Some good information here, thanks.
Running both pipes together on one side would sound different. I will definitely look at this.
The J pipe looks interesting.
And InTechs comment on advance at cruise. Is the theory that the motor would be under very light load at cruise I can run so much advance? Im planning on using a throttle body on an L72 intake for the original look. Divider is already cut down. Probably run a HEI for ease. Probably stuck with 2" primary pipes on the headers but will try and get them as long as I can.

[tjs44]

I was never able to get 3in as quite as I wanted,went back to 2.5 and made a huge diff.FWIW,Tom

[stealth]

Add the longest set of bullet mufflers you can fit prior to the main mufflers..

[skinny z]

And InTechs comment on advance at cruise. Is the theory that the motor would be under very light load at cruise I can run so much advance?

Generally, yes. Lighter engine loads will have higher manifold vacuum and the incoming air/fuel will tend to be less dense. That being the case, more ignition timing is needed to get peak combustion pressure in the right place due to the slower burn rate.
Same can be said if the cruise AFRs are tuned to the lean side.
As an example, my carbureted small block with a 236@.050" (288 advertised) cam, is tuned for a lean cruise of 16:1.
Steady state light throttle on the highway at 2400 RPM (75 MPH) is seeing timing in the mid to upper forties. (3.73 w/.07 OD and lockup converter).
Highway mileage is pretty good at 20+ mpg.

[BLSTIC]

Is there room behind the axle for another pair of full body straight through rear mufflers? I'd be more inclined to do that than force half the exhaust to go through four 90 degree mitre joins for the majority of the cars life.

[1980RS]

I have a 2.5 system on my street car with a set of Hooker Aero chamber mufflers. Sounds good, nice and quiet and no drone in the car like my old Slowmaster Stupid 40's.

[Steve K]

I put a set if Bullets in front of my ultra flows and it toned it down a bit. Not a window rattler any more