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Hi guys, I thought I read where someone used a vacuum cutout instead of a boost cutout for faster response. Has anyone tried this?
I'm assuming since I have a small cam, overdrive and 3.25 gears the car should still be in vacuum cruising on the highway.
Eventual plan would be to install it into my 4" side exit then have my current downpipe/full exhaust welded in before the cutout. I would think it would flow better and help spool. Seems like a win win but 2nd opinions welcome.
I just bought some vacuum cutouts for my new twin turbo build. I tested one out real quick and it closed easily as soon as the motor started. It’s a 5.3 with sloppy stage 2 cam.
I plan to run them to vacuum with an air bleed so they open at stopped idle then close back up as soon as I start moving and then will open again under boost.
I may put a solenoid valve in line depending how it works out.
im kinda copying my z06 setup when it had a leaky vacuum line. It ended up being exactly what I wanted and the ecu or extra control boxes couldn’t do.
Vacuum cut out will be loud for a sec or 2 after startup, not a problem unless you're trying to be stealthy. I made my own , it's like a tractor rain cap only horizontal
- counterwieghted to stay closed until exhaust pressure/ velocity pushes it open
- it's a huge 3.5" turbo style muffler ( motorhome I think ) when open exhaust goes through only the first section and not back through the Z . Basically a straight through muffler when open but still muffled.
-initial testing yrs ago was 6lbs backpressure WOT closed and 0 open , I've since turned it up quite a bit but doubt it's a restriction even now
- dirt cheap and only a hinge , no other moving parts to fail - not even a spring
- this muffler could only fit a truck application, it's huge . Not much louder than a stock truck , quieter than any aftermarket exhaust
................................. vacuum cutouts.....................
.................................................. ................................I tested one out real quick and it closed easily as soon as the motor started. .
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IF true " Stealth " was the goal, ie totally stock, quiet single truck exhaust until , say about 3 to 5 PSI of manifold pressure, would a BOOST activated CHINESE 3 inch Loud Valve be reliable ?
Is 5 PSI enough pressure to open up such a valve ?
Will the chinese valves close securely under spring pressure to maintain quiet cruise ?
IF true " Stealth " was the goal, ie totally stock, quiet single truck exhaust until , say about 3 to 5 PSI of manifold pressure, would a BOOST activated CHINESE 3 inch Loud Valve be reliable ?
Is 5 PSI enough pressure to open up such a valve ?
Will the chinese valves close securely under spring pressure to maintain quiet cruise ?
im building dual 3” down pipes to the front bumper with 2” dual exhaust to the back of the motor and joining to a 3” single. When valves are closed I’m hoping it’s very quiet.
as far as stealth, who are we all really trying to fool? I’m doing it for comfort while cruising down the road. Sure it is loud for a second on start but lots of GM cars are the exact same setup.
The only time I have messed with a vacuum operated cutout was on a friend's car. With a large cam it made the cutouts a horrific rattletrap at idle. A day at the dentist was less annoying.
You can buy a baby 12v vacuum pump super cheap. They seem reliable as well. I had mine for years. I used it to activate the (normally open VAC cutout) before starting (don't want to wake the kiddo). That setup worked extremely well. To take full advantage of a cutout I pair them with super restrictive exhaust and an OEM style muffler. I ran my 3" down pipes into a single crush bent 2.25 system over the axle to an OEM 4 cyl muffler. In my application, the exhaust was so restrictive I wasn't able to make enough boost to open a boost activated cutout. But I did have OEM like sound levels when I wanted. Or dual open 3" dumps off each turbo. Best of both worlds IMO.
I don't understand why some run nice flowing expensive heavy exhaust system that are pretty loud anyway... Then install dumps. Seems counter productive, expensive, and heavy.
4cyl mustang look and sound... Has that sweet 1.5" tail pipe! lol
Last edited by Forcefed86; Jan 6, 2024 at 11:01 AM.
Electric- Nice that it's loud and rowdy whenever you want. You can sit in traffic and cruise and lope away if desired. Boost also comes on harder from a fixed gear roll on as the exhaust is already uncorked. It can rattle after awhile though and you have to deal with wiring it up.
Boost- Easy install, just hook up a vacuum line to it no wiring. You don't have to think about anything. Loud pedal=open cutout. But that's when it opens, no loud noises at idle and cruise.
I have a boost activated one (spring close, boost open) which I plumbed into exhaust manifold pressure to open it. While parked and clutch pressed, I can blip the throttle and it opens.
True story. I've heard they fail pretty often though.
I had one on my last car for four years.
They last a while if you don't put them really close to the turbo, mine was under the driver floorboard under my feet and it lasted until I sold the car and made a huge difference in performance.
Depends who you buy yours from. BadlanzHPE makes an in house electric cutout that they actually stand behind and they aren't expensive. Had a couple issues with them over the years and they fixed it every time. Even made me a custom cutout with thicker blades for free on one of my setups.
Depends who you buy yours from. BadlanzHPE makes an in house electric cutout that they actually stand behind and they aren't expensive. Had a couple issues with them over the years and they fixed it every time. Even made me a custom cutout with thicker blades for free on one of my setups.
Mine was made by QTP iirc, it didn't rattle or give me any issues, so I'd use them again for sure.
A friend of mine used one and had it really close to the turbos, like less than a foot away, and it failed after a year.
You can buy a baby 12v vacuum pump super cheap. They seem reliable as well. I had mine for years. I used it to activate the (normally open VAC cutout) before starting (don't want to wake the kiddo). That setup worked extremely well. To take full advantage of a cutout I pair them with super restrictive exhaust and an OEM style muffler. I ran my 3" down pipes into a single crush bent 2.25 system over the axle to an OEM 4 cyl muffler. In my application, the exhaust was so restrictive I wasn't able to make enough boost to open a boost activated cutout. But I did have OEM like sound levels when I wanted. Or dual open 3" dumps off each turbo. Best of both worlds IMO.
I don't understand why some run nice flowing expensive heavy exhaust system that are pretty loud anyway... Then install dumps. Seems counter productive, expensive, and heavy.
4cyl mustang look and sound... Has that sweet 1.5" tail pipe! lol
I like your style. I appreciate a (mostly) quiet car too. I call it happy girlfriend/drive through mode. I will look into a little vacuum pump as well. I like the idea of being able to keep it forced shut when needed.
Used one of these dirt cheap janky things... Worked really well. Just be sure you get the correct one for vac or pressure. Some have 2 ports. I'm not sure if a pressure pump will have enough umpth, but vac worked great. Can also plumb it into the cars vac supply with a vac solenoid.
I have a boost activated one (spring close, boost open) which I plumbed into exhaust manifold pressure to open it. While parked and clutch pressed, I can blip the throttle and it opens.
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Can you clarify ( confirm ) You have the Boost activated cutout connected to EXHAUST manifold pressure, and not Intake manifold pressure ?
I like the failed position closed (quiet)so I went boost activated loud valves. I would have had to do the quiet vacuum pump thing had I used the other one. I had a QTP Oval on the down pipe before when I was single turbo. No issues that way either.
My setup is pretty slick now with the Huron Hidden Twins going to 3” down pipes y’d into Boost Loud Valves tied to a Hooker True duals with stock exhaust tips.
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Boost cutout vs vacuum cutout 
I will look into a little vacuum pump as well. I like the idea of being able to keep it forced shut when needed. 
