5.3 downpipe size
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Teching In
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5.3 downpipe size I have 5.3 with a single turbo currently running a 2.75" downpipe all the way to the side of the front of the tires with a magnaflow 3 in out muffler. Is this size too small of a exhaust on the 76mm turbo i have? The exhaust outlet on the turbo is 3". I didnt pay too much attention to the id and od of the pipe when installing. I feel the truck kind off bogs down at 4k rpms when it gets to my max boost i have it right now at only 5psi. Can i keep the 2.5 downpipe and add a 4" after the down pipe? Or should i just remake my entire exhaust and go full 4 inch all the way?
Last edited by Jon91; Aug 21, 2021 at 08:58 PM.
2.75” is small for any v8. You will see quicker spool and more power with a better flowing downpipe / exhaust combo. 4” if you can fit it would be great and I personally would not do smaller than a 3.5”. But I’m also always planning for the future.
I have 5.3 with a single turbo currently running a 2.75" downpipe all the way to the side of the front of the tires with a magnaflow 3 in out muffler. Is this size too small of a exhaust on the 76mm turbo i have? The exhaust outlet on the turbo is 3". I didnt pay too much attention to the id and od of the pipe when installing. I feel the truck kind off bogs down at 4k rpms when it gets to my max boost i have it right now at only 5psi. Can i keep the 2.5 downpipe and add a 4" after the down pipe? Or should i just remake my entire exhaust and go full 4 inch all the way?
I have a 3" downpipe, connected to an aftermarket catback, also 3", and I really like having the full exhaust, for cruising, but it simply will not make power like it does with the cutout open, just beyond the starter.
Mine does the same thing, seems to "hold back" and labors to rev, with exhaust closed.
With the admittedly undersized 3" DP open, it pulls hard to 6800 rpm, if I want it to.
Will gain MPH and quicker ET up to about 18psi, but at 20+, hits a plateau...no doubt due to backpressure.
For comparison, on a race day (bracket race where I had entered 2 classes).
My regular class, with exhaust open, and tried an 11.50 Index class with it closed...just to see how much car would slow down.
I made 1st time run with 4# boost, cutout OPEN, and went 11.05@133.7,
13 minutes later, with same boost, cutout CLOSED, went 11.72@121.8
So, after my storybook above, lol, it may be an issue of you having a muffler, more than the undersized DP, although the 2.75" DP is too small, for sure...as is my 3" DP, for my combo.
My long term plans are to swap the turbine housing from .96 to 1.25, and run a 4" downpipe, open, full time...
(I literally have EVERYTHING, even the 4" outlet turbine housing, to do this, just too lazy, LOL)
My 4000#+ turd's been 9.76@141.7 with 15-16# using the transbrake, and
9.88@147 with 22.5#'s, footbraking it, so I'm pretty confident it'll go 9.50's at 150, if it can breathe.
I'd bypass the muffler if possible, and run it to see if the cork is still there.
Thread Starter
Teching In
Joined: Aug 2019
Posts: 19
Likes: 3
Mine is also the vs racing 78/75 .96ar turbo. Im going with the full 4 inch. I even got the 3 to 4 vband adapter and just run it straight with no muffler to the front side of the rear tires and see if that solves it 🤞
In my 4th gen Trans Am, I have a decent running 6.0 with a Gen2 VSR 78/75 turbo (.96 a/r). It has a 3" outlet.
I have a 3" downpipe, connected to an aftermarket catback, also 3", and I really like having the full exhaust, for cruising, but it simply will not make power like it does with the cutout open, just beyond the starter.
Mine does the same thing, seems to "hold back" and labors to rev, with exhaust closed.
With the admittedly undersized 3" DP open, it pulls hard to 6800 rpm, if I want it to.
Will gain MPH and quicker ET up to about 18psi, but at 20+, hits a plateau...no doubt due to backpressure.
For comparison, on a race day (bracket race where I had entered 2 classes).
My regular class, with exhaust open, and tried an 11.50 Index class with it closed...just to see how much car would slow down.
I made 1st time run with 4# boost, cutout OPEN, and went 11.05@133.7,
13 minutes later, with same boost, cutout CLOSED, went 11.72@121.8
So, after my storybook above, lol, it may be an issue of you having a muffler, more than the undersized DP, although the 2.75" DP is too small, for sure...as is my 3" DP, for my combo.
My long term plans are to swap the turbine housing from .96 to 1.25, and run a 4" downpipe, open, full time...
(I literally have EVERYTHING, even the 4" outlet turbine housing, to do this, just too lazy, LOL)
My 4000#+ turd's been 9.76@141.7 with 15-16# using the transbrake, and
9.88@147 with 22.5#'s, footbraking it, so I'm pretty confident it'll go 9.50's at 150, if it can breathe.
I'd bypass the muffler if possible, and run it to see if the cork is still there.
I have a 3" downpipe, connected to an aftermarket catback, also 3", and I really like having the full exhaust, for cruising, but it simply will not make power like it does with the cutout open, just beyond the starter.
Mine does the same thing, seems to "hold back" and labors to rev, with exhaust closed.
With the admittedly undersized 3" DP open, it pulls hard to 6800 rpm, if I want it to.
Will gain MPH and quicker ET up to about 18psi, but at 20+, hits a plateau...no doubt due to backpressure.
For comparison, on a race day (bracket race where I had entered 2 classes).
My regular class, with exhaust open, and tried an 11.50 Index class with it closed...just to see how much car would slow down.
I made 1st time run with 4# boost, cutout OPEN, and went 11.05@133.7,
13 minutes later, with same boost, cutout CLOSED, went 11.72@121.8
So, after my storybook above, lol, it may be an issue of you having a muffler, more than the undersized DP, although the 2.75" DP is too small, for sure...as is my 3" DP, for my combo.
My long term plans are to swap the turbine housing from .96 to 1.25, and run a 4" downpipe, open, full time...
(I literally have EVERYTHING, even the 4" outlet turbine housing, to do this, just too lazy, LOL)
My 4000#+ turd's been 9.76@141.7 with 15-16# using the transbrake, and
9.88@147 with 22.5#'s, footbraking it, so I'm pretty confident it'll go 9.50's at 150, if it can breathe.
I'd bypass the muffler if possible, and run it to see if the cork is still there.
All of my reading and incessant questioning of friends who go fast basically say the same thing... no such thing as too large a diameter for exhaust... and long exhaust runs hurt power/performance.
For my S485 1.32 85/96 I did 4" to the fender, but my turbo outlet is 5". Maybe once I really start to lean on this combo I'll get tempted to redo the exhaust in 5" but I'm nowhere near that point.
But to the OP, I'd do 3" with a cutout near the turbo.
For my S485 1.32 85/96 I did 4" to the fender, but my turbo outlet is 5". Maybe once I really start to lean on this combo I'll get tempted to redo the exhaust in 5" but I'm nowhere near that point.
But to the OP, I'd do 3" with a cutout near the turbo.
Last edited by Pro Stock John; Aug 24, 2021 at 01:15 PM.
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Thread Starter
Teching In
Joined: Aug 2019
Posts: 19
Likes: 3
I have vbands almost every feet of my exhaust and removed my muffler and the pipe after the downpipe, so basically i had only the downpipe and wow its just spools like almost 500rpms faster and whistles really loud now but it's really loud. I'll leave the 4" downpipe just by itself but its a daily driver so I'll try to do a 4" cutout and put a 4" straight pipe to the side of the rear of the truck.
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I have vbands almost every feet of my exhaust and removed my muffler and the pipe after the downpipe, so basically i had only the downpipe and wow its just spools like almost 500rpms faster and whistles really loud now but it's really loud. I'll leave the 4" downpipe just by itself but its a daily driver so I'll try to do a 4" cutout and put a 4" straight pipe to the side of the rear of the truck.
I have a buddy running Loudvalves for his exhaust. His Nova is super quiet when not bosting, he has a 2.5" exhaust with muffler and it sounds like a mildly cammed quiet car. Once he boosts it sounds hellish.
https://loudvalves.com/
TBH my 4" fender exhaust is a bit loud for me, so at some point I'd like to figure out something that incorporates a loudvalve setup.
His Nova is Sweet Pea on FB.
https://loudvalves.com/
TBH my 4" fender exhaust is a bit loud for me, so at some point I'd like to figure out something that incorporates a loudvalve setup.
His Nova is Sweet Pea on FB.
I run a cutout on my Nova as well. 5” to 4” with a 2.5” system just up stream of the cutout. I can tell you this, I made two rips this morning and the cutout didn’t open (my fault, fudged a setting) and it wouldn’t make over 15 psi with dome pressure that usually nets me 22-23 psi. Still ran fairly well considering. Bigger is better when it comes to exhaust and I’ve seen results that for very psi of backpressure POST turbine, is worth about 2-3 psi PRE turbine. Zero is obviously the target. I waited 3 weeks for my cutout to come from China way back when, but it was about $50 shipped FYI.
Super quiet. Smaller system exists in the factory location behind the right rear wheel. All I hear going done the road are the injectors, fuel rail echoes, valves clapping, all other LS engine noises. I’ve come to fooling myself into pretending I’ve got a set of Jesel rockers on it.
I have 5.3 with a single turbo currently running a 2.75" downpipe all the way to the side of the front of the tires with a magnaflow 3 in out muffler. Is this size too small of a exhaust on the 76mm turbo i have? The exhaust outlet on the turbo is 3". I didnt pay too much attention to the id and od of the pipe when installing. I feel the truck kind off bogs down at 4k rpms when it gets to my max boost i have it right now at only 5psi. Can i keep the 2.5 downpipe and add a 4" after the down pipe? Or should i just remake my entire exhaust and go full 4 inch all the way?