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Comparing cutouts. Would there be a gain if I go with a 2" cutout on a 3" single exhaust system? I see cutouts are 3" y-pipes with one of the ends routed to bypass the muffler. My idea is a cutout that has a 2" to bypass the muffler. Would that bring any gains in flow? Below is a drawing for reference.
WHY would you want the cutout to be smaller than the exhaust system in mind?? Unless you do not want the full gain to be had with a cutout..... (smh....)
Im looking to use an external wastegate and have the cutout open by boost. So my main concern is would a 2" cut out gain me anything vs having the original 3" exhaust. Looking for a set up similar to the pic. Wondering how good this would be vs my current 3" exhaust that has no cutout.
Basically you will have a controlled leak. Do not expect much gain from a 2" leak in the pipe. Sure, something is better than nothing, but not worth the expense of a wastegate just for a 2" hole in the pipe.
The link below shows about one that was done using a 60mm wastegate as the opening device. I think its a good idea. Maybe two 38mm wastegates can be used to make it a 3" opening.
How much do you plan on gaining for the cost of the wastegates?? I doubt it is worth it. Is this for a race car or street car? If race, you don't need the muffler, so the cutout is not necessary. If street, the cutout will make it too loud, so that shoots that down too. This is all much ado about little gain. A properly sized and engineered muffled exhaust system will do you much more good then this very expensive cutout system.
Not sure if I will put cats. 2.5" coming from stock truck manifolds. Turbo is located where battery used to be. Its a 7275 Precision. Using a Precision 46mm wastegate currently vents to atmosphere. Exhaust after turbo is 3" all the way to rear control arms then merges to 2.75" stock exhaust with muffler.
OK. Wanna do this right? Run a full 4" system after the turbo all the way back over the axle with a 4" muffler and tailpipe. It CAN be done, nothing half-*** about it. It will run, and run well all the time and not waiting to leak out of a small cutout.
Even better! Expand it in stages. You mentioned wanting the equivalent of 4" worth of flow capacity, so I thought, DO 4" and be done with it! You will have something that will work in ALL situations, rather than only when you open a cutout. Get her done, and post results here. It should be good!
I'm kicking around the idea of a cutout in my 99 and if I do it will be right where the pipe bends to go up over the axle. there's enough room and I won't have to worry about it hitting the ground (I'm lowered). I'm doing a 2.5" cutout on a 3" pipe. Not worrying that much about a performance increase, just looking for an occasional loud car.
Just run a regular 3" cutout like everyone else runs (if you are running 3" exhaust, which is lighter and cheaper and easier) and then run a 3" boost actuated valve on the cutout. Like so:
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Exhaust Cutout Sizing 
