I can see a "pin" with two round plates 90 degrees from each other and have the pin rotate so one is closed and the other open. It wouldn't be hard to do and I'm surprised there's not something like that out there.
Cutouts for Strip only, beneficial?
- Thread starter Kent mosby
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Oldiron440
Well-Known Member
One thing to consider when determining if it’s worth it or not is the size of the exhaust after the cut out. Having 255 cid going through 2.5” at 6500 there would be a benefit you would think but as I said before headers with a collector extensions make more power that open headers and you actually need to tune the length of the extension so it’s not as simple as having an exit for the exhaust before going through the rest of the system.
I would approach this with building a system that will cos the least amount of power loss, probably a 3.5” system with race bullets.
I would approach this with building a system that will cos the least amount of power loss, probably a 3.5” system with race bullets.
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I was just typing "tuned" collector extension lol
33IMP
Well-Known Member
With a properly sized and efficient exhaust system, I'd bet cutouts get you LOUD, and that's it. But frankly, I've always raced corked up, so I'd pass on extra noise for no reason.
Map63Vette
Well-Known Member
This. As is often said, an engine is an air pump. It's a complete system and there are a lot of things that work together to tune it to specific conditions. Needing "back pressure" is one of those myths that always annoys me as it's focusing on the wrong thing. Back pressure is not what you need, though it's often the easier thing to measure. What you are really after is flow velocity to help pull the gas out of the pipes. Back pressure is often just the side effect you see from that because a narrower pipe will flow faster, but at slightly more restriction. The other thing to be aware of is where that restriction is in the system. You could just crimp the end of your tail pipe if you think you need back pressure and it would only hurt you, but stepping down the whole system from 3" to 2.5" could net the same change in pressure, but better overall flow in some cases.
Though to the point of the original post, I doubt open headers will make much difference at all if you have a good exhaust system on the car to begin with. I have some electric cutouts on my car for pure novelty factor more than anything. They are fully variable so I can open them as much or as little as I want, so I just call them the volume switch for the exhaust. I love the way they sound fully open while idling, but I do think they are a bit trashy sounding to drive around town with open. If I crack them just a bit it's not too bad, but they stay closed more often than not anymore. I've debated hooking them up to the Raspberry Pi and Megasquirt setup to automatically control them with rpm, but they don't move near fast enough and it would likely wear the motors out as I'm pretty sure they aren't meant to be used that much.
MopaR&D
Nerd Member
Cutouts will pick up power especially if the exhaust system is a bit undersized or restrictive to begin with for the size and HP of the engine. What's really important is to have the cutouts sufficiently downstream of the collectors to keep the secondary tuned length. Iirc around 30-44" depending on the effective RPM range of your engine. However if the pipes coming off the header collectors aren't the same diameter as the collectors (for example, immediately goes from 3" down to 2.5" like most systems) there's no secondary tuning happening anyway.
33IMP
Well-Known Member
Engine masters did a cutout episode deliberately trying to make the cutouts look good. They failed in my opinion
They used a hugely powerful big inch bbc, that should have had a 3 1/2 or 4 inch system with straight thru mufflers.
Instead they used a 2 1/2 system with turbo mufflers (on an 800 hp engine!?!)
Of course the cutout looked good.
But even EM admitted if the cutouts were installed too far back, the engine sounded like ****.
My personal opinion? MOST street driven cars with mild cams sound like **** uncorked.
They used a hugely powerful big inch bbc, that should have had a 3 1/2 or 4 inch system with straight thru mufflers.
Instead they used a 2 1/2 system with turbo mufflers (on an 800 hp engine!?!)
Of course the cutout looked good.
But even EM admitted if the cutouts were installed too far back, the engine sounded like ****.
My personal opinion? MOST street driven cars with mild cams sound like **** uncorked.
Yep, I watched that before posting and did not believe what they were saying and all you guys confirmed my suspicions
If your exhaust system is designed with the cutouts in mind, you'll see benefits. If not and they are just "add ons" it's less likely.
famous bob
mopar misfit
summits website says/used to say , a 500'' engine needs 3 1/2'' exhaust , I have 3 1/2'' dual dumped on mine , 3.5 bulllit mufflers , with 3.5 spiral tubed drove up inside and tack welded , before dumping , 3.5 h pipe added later , never had any drone or problems , but it is a hair loud ...
Ironmike
Well-Known Member
agree 100%. Hell, mine is by no description "mild", and i still think it sounds like crap with open cutouts. Now drop the mid pipes and put on a 13 inch, 31/2 extension...........music to my ears. Shakes the whole damn neighborhood. they just LOVE me.
Carnut68
Well-Known Member
I see about .050 difference between open and closed on my sbc G body. 1/2 MPH. All steel upper 10. street car. Full exhaust w/Xpipe 2.5in. It does help you hear your own car while wearing a helmet against a louder car.
Oldiron440
Well-Known Member
I have a 292” Ford W and I use 3” bullets with turndowns, basically header mufflers with turndowns and they don’t slow the car a bit.
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