exhaust cutouts? gains, pros / cons?

scotty49

scotty49

Not-quite-so-new-guy
Jan 22, 2019
12
28
3
#1
I have a 523 hp / 527 TQ 406 SBC in my Lemans and have full dual 2.5" with H pipe exhaust that's very quiet.
I was considering electric dumps. looking for tips, tricks, and opinions on what gains I might expect at the track, etc...

Thanks!
 
TURNA

TURNA

Geezer
Jul 24, 2009
6,344
8,040
113
Socialist NY
#2
I have them........never used them........

I have to open them manually.
 
B

bracketchev1221

Master Mechanic
Jan 18, 2018
313
283
43
#3
Depends on how restrictive your exhaust is. 2.5 may be a little small for a healthy small block. I would try to have them the same diameter of the collector.
 
Turbo Zach

Turbo Zach

Royal Smart Person
Sep 8, 2015
1,283
1,940
113
50130
#5
I think they are more for fun than anything. I have a neat cuttout for my car when I get to the exhaust. It is boost activated. Opens halfway at 7psi and all the way at 10psi. I like my car mostly quiet when going down the highway, but when I get on it I want it to be loud. Should kind of be like a qjet opening the back barrels. Well I hope it will anyways. I have a turbo six so it is a little different sound and deal though.
 
M

Max Headroom

Not-quite-so-new-guy
Sep 8, 2011
48
5
8
#6
The biggest downside to any exhaust system is that, all exhaust systems, even straight pipes with no muffles, will send a revers pulse back up the pipes to the engine. These reversion pulses are actually pressure waves (not actual gas) that can easily travel against the direction of the flow of the exhaust gas. The large majority of these pulses are created when the exhaust system changes size, up or down or direction. There is a pulse created where the header meets the pipe (Unless they are the same size and properly joined.), another anytime the pipe changes direction (Bends, elbows, etc.), another where the exhaust enters the muffler and again where the exhaust leaves the muffler and finally where the exhaust leaves the tailpipe. Resonators create them and even a long enough
straight run of pipe will make them.

All this being said, dumps can make a difference in power. However, the difference they make depends on several factors. The biggest difference is on engines with cam profiles that promote weak cylinder exhaust gas scavenging. The reverse pulses make the scavenging much less effective, causing a dirty intake charge, which in turn results in reduced power when the piston fires.

As a general statement, I would think that an engine making 1.28 hp/inch with only a 3.75 in stroke would benefit from dumps. They should however, come directly off the header collector in order to eliminate the restriction of the exhaust pipe. They should also be as close to straight off the collector as possible. They will be illegal loud when open.
 
jlcustomz

jlcustomz

G-Body Guru
Nov 22, 2011
555
208
43
#7
I made a cutout after my x- pipe going into a 3.5" ovaled single exit piped into a drivers side exit in front of the rear wheel. Cable operated for instant on & off. I feel that a length of pipe gives better sound quality rather than dumping under floor, some late models adjust through exhaust.
Though a good setup can increase power, I call it mostly for fun & for adjustability. Loud is especially fun with a stick shift revved up in low gear on both accel & deceleration. Loud as hell is cool, but not all the time. Being able to open exhaust under an underpass or tunnel & rev it up, then going back to legal sounding is the best of both worlds.
My setup has been broke for a while & debating what my next exhaust will be, but just like a good equalizer on a stereo, it's good to have some adjustable control.
 
xitabl442

xitabl442

G-Body Guru
#8
I had read somewhere that you should draw a line with a crayon, where the crayon stops melting is where the cutout should go. I would research that though. I have electric cutouts strictly for the noise. I put them before the X pipe as I think the X absorbs the cackle.
 
motorheadmike

motorheadmike

Comic Book Super Hero
Nov 18, 2009
3,193
5,761
113
Ottawa, Ontario Canada
#9
Wagon has dual electric cutouts, and the TBSS has a single electric cutout. Both are QTP. I figure I will put a 4" boost actuated one on the Monte.

Moar noize the better.
 

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