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Discussion Starter #1
As shown in my signature, I'm running a maggie with intake, 1-7/8" long tubes, and front 2.8" pulley on the jack shaft. The exhaust is 3" up to the x-pipe, after which I believe it's 2.5" and runs to the stock mufflers. With the amount of air flowing through my engine, I feel that the stock mufflers are holding me back. However, I'm hesitant to change them out as I don't want things to get too loud. I have three young children, including a two month old, and the stock mufflers are already fairly loud with the long tubes.

So, in a search for a unicorn, can anyone say if there is an axleback offering that fits the following:


  1. Similar in sound level to stock mufflers, although a bit louder would be ok
  2. Significantly less restrictive than the stock mufflers
  3. Minimal drone/raspiness (DOD is disabled, though)
  4. Available in axleback (don't need full cat back)
Any thoughts? I'm obviously looking to have my cake and eat it too by having a free flowing exhaust that isn't overly loud, but I'm curious if there are any options out there.
 

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demonstrated few years back on this forum or the other, contrary to internet facebook engineers, the stockers were good to 450rwhp before any power delta observed - they are not that bad and the restriction is not a cliff.

I've built a few exhausts for my 8. (I have LSA). I'm currently running kooks mids (no cats) true 2.5" cat back pipe with a magnaflow muffled x, vibrant resonators and dynomax VT's. Not obnoxious by any means and cruising almost stock quiet. I'm very pleased with the VT's - nice deep voice, no drone. BTW, the valve rattle I know someone will bring up is history. I might hear the flappers on cold start, only cold start and it's not sharp diesel truck metallic -just different.

Since your posts show you are willing to understand science, here is a link to exhaust worth digesting.
 

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Thanks. As an engineer by trade, I'm all about the science side of things :nerd:

I did a bit of reading in the article, and, if estimating 600 hp at the crank if the exhaust were to be fully unrestricted, I would need minimum dual 2.7" diameter piping to not create any backpressure:

2.2 cfm per open-pipe hp: 600 * 2.2 = 1320 cfm

115 cfm per square inch of piping for zero loss from backpressure: 1320 / 115 = 11.48 sq.in. total

Per exhaust bank: (11.48 sq.in. / 2 banks) = 5.74 sq.in per bank

5.74 sq.in. = 3.14159 * radius^2; radius = 1.35 in.

Therefore, ideal diameter = 2.7"

With a portion of mine at 2.5", the piping is slightly restrictive, and limits the system 'no backpressure' CFM per bank to: 115 cfm/sq.in. * 3.14159*(2.5" dia./2)^2 = 565 cfm.

[Obviously, this doesn't take into account my high flow cats, but I'm pretty sure that I've blown out the cores on them anyway...]

As such, mufflers flowing over 565 cfm would be effectively invisible in terms of creating significant back pressure. At least that gives me a baseline for what I should be looking into. It would be nice to know what the stock mufflers flow to know whether or not there's much restriction to them. I doubt that anyone has bench tested them, though.

As for the dynomax VTs, they sound great in theory, but the reviews that I've read noted a number of valve failures resulting in rattles.
 

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Glad to see you have the details. Science so much better than internet jabber. Hard to really nail the exhaust as you have not only the volume aspect but the add in the velocity / proximity to the heads and total system length. But as engineers, we will get close enough to kiss the girl.

As for the VT's the flapper is not new, it's OEM on a few vehicles (I think nissan is one of them). They do have a lifetime warranty - but will cost you you time. The internet blows thing out of proportions it's dominated by 85%'rs (5% think, 10% think they think, 85% would rather die than think).

I have two sets VT's no issues at all. Would have no issue buying again.

BTW, on the intake side, the general rule is 1.5cfm/HP. Using 1.5cfm, one can evaluate the trade off of going >4in tube vs MAF resolution.
 
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