The evoTT is not that loud. Nor is the FI intimidator exhaust I had before that (2.5" piping). The problem, esp with 5AT, is loud low frequency drone up until about 3k rpms. It is killer with all these exhausts. The APS has no
X-pipe and relatively small mufflers (smaller than FI, about same size as evoTT). I don't think it will fare any better. I daily drive my G and after two years of various exhaust systems, I only want to hear the motor and BOV and that's it.

 

I'll throw some basic information in here that is propably undersood by most, but maybe not. Anyway, it does not hurt to spell it out in the context of this thread.

1. A predominant factor in the operation of the turbo's turbine is the pressure differential between the input side of the turbine and the output side.

2. The cross-sectional area of any tube is Pi*r^2.

3. As the cross-sectional area of the exhaust is decreased, there generally is a corresponding increase in the pressure of the output side of the turbine.

In other words, as you decrease the efficiency of the exhaust, you decrease the ability of the turbo to create boost.

 

but teh real question is, is a a cross sectional area difference of 325mm^2 (70mm to 60mm piping) create a significant increase in back pressure as to reduce power enough to be noticable.

Everyone knows smaller pipe, more restriction. But such generic responses dont help anyone.

 

Well, I just gave the formula. But, you are right, for those that are too lazy (or incapable) to use the formula it will not be helpful. However, for those who are not lazy, it will be.

For example, let's compare a 2.77" (Greddy Evo TT) to an APS 2.5" true dual exhaust. Based on Pi*r^2, the Evo TT has a cross sectional area of about 24.1 square in. The APS 2.5" exhaust has a cross sectional area of about 19.6 square in. Thus, ignoring other factors such as the mufflers, tube length, etc., the Greddy Evo TT will have about 23% less back pressure than the 2.5" exhaust. The turbine's performance will change accordingly based on the exhaust system used.

 

I think there have been several anecdotal reports on this site that report 2.5" piping sufficient for up to about 550 whp (DJ) and 14 psi as Zivman I think noted.

More generally, there is extensive published data that documents that on turbo'd engines, any amount of backpressure results in a decrease in whp. What's "significant" to you?

Here's one table on the 'net (I think for a turbo'd acura) published by Dave Stadulis of SMS Products relating HP to exhaust cross-sectional area (this is the guy that sourced me 4.25" 200 cell metallic cats):

OD (in.)....ID (in.)...Area....%Increase......HP.......HP/in^2
2.25........2.120.......3.53.....0%...............200....... 56.66
2.50........2.370.......4.41.....25%..............275....... 62.34
2.75........2.620.......5.39.....22%..............318....... 59.00
3.00........2.870.......6.47.....20%..............400....... 61.83

I couldn't find specific testing parameters and what was held constant, because I know if you don't correct for it, certain factors, like wastegate spring pressure change based on exhaust backpressure. Take as a point of reference only. It does look like Dave found that approximately 60 hp/in^2 was fairly constant for that setup.