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I'm concerned that my exhaust could be too restrictive. Right now I have:
ARH 1.75" headers
ARH Y-pipe with cat's
SLP dual-dual intermediate pipe, over the axle, muffler & tips
manual cutout between axle and muffler inlet
Goals:
* I don't want to buy 1 7/8" headers because it's a lot of money for not seeing significant gains until the upper RPM range
* I want to keep using catalytic converters because I don't like the rasp of catless designs
* I like the 'quiet' muffler designs such as the dual/dual
* The car is lowered (about 6" between ground and front LCA chassis bolt, 3" clearance between ground and lowest part of y-pipe) so I don't have much to work with on clearance
* I haven't found enough information on whether there is a con to using a lowering upper panhard brace on a car which will see autox and open track activity. If I lowered the upper brace I would have more options.
* I don't want a significant weight increase
* I don't want a significant increase in NVH
* I'm open to switching back to an electric cutout, but I've not read of any vendor designs where both the motor & the seal work properly for years.
My opinion would be to ditch the cats and y-pipe in lue of a catless x or h pipe. You talk about not wanting rasp, and that's totally understandable. Typically with a dual setup, you don't experience the rasp, especially since you plan on running quiet mufflers. In regards to those, Magnaflow is quiet. They make several different mufflers that would be quiet at idle and during normal driving, but sound aggressive under throttle.
The merge designs on the arh system are a work of art lol. So unless the op has a botched one it should be more than fine. Op honestly with your list of restrictions and wants I dont see much room for improvement. The cutout will help but only when you have it open lol.
If you were open to a set of true duals and larger headers (more noise, nvh, clearance loss..) then we could talk and there is some power to be picked up there. Remember no one modification to that list will pick up a lot of power.
Bigger headers 5-10
Catless 5
Cutout/Duals 5-10
Add all that up though and there could be an easy 20hp there depending on setup of course. Honestly though the exhaust most likely wouldnt be raspy with the good merge on the arh y. But thats up to you, my suggestion is if you want more power and you want to stick to that list look into other bolt ons for power.
I guess I should note that I agree if you plan on staying with the y-pipe setup, then there really isn't anything more you'd want to do in regards to cost per HP/TQ outcome. Aside from cutouts, your setup is pretty dead nuts on.
What about something like Hawks Sinister 4" system? I've been considering that to get rid of my dumps to improve clearance and lessen sound. i obviously would be adding a muffler to the system.
IMO, the 3" single pipe isn't really sized to support anything beyond full bolt-on's, even with the LS1 5.7 engine. So yes, stepping up to a 3.5" or 4" Y-pipe merger exit and all the way out through the muffler is worth some hp/tq gain. The only down side to a 3.5-4" cat-back system is that only a few companies make them. I do know Stainless Works offers a 3.5" system which is the only Stainless Steel system available that I know of, then there's Mufflex which is the major player in this market segment, but they don't offer a stainless steel option which is a shame. There's also the Hawks Sinister system, but you need to add your own muffler.
IMO, a Mufflex cat-back with either a Hooker Maximum Flow, Borla XR-1, Dynomax Ultra Flo, or Magnaflow will do the trick.
IMO, the 3" single pipe isn't really sized to support anything beyond full bolt-on's, even with the LS1 5.7 engine. So yes, stepping up to a 3.5" or 4" Y-pipe merger exit and all the way out through the muffler is worth some hp/tq gain. The only down side to a 3.5-4" cat-back system is that only a few companies make them. I do know Stainless Works offers a 3.5" system which is the only Stainless Steel system available that I know of, then there's Mufflex which is the major player in this market segment, but they don't offer a stainless steel option which is a shame. There's also the Hawks Sinister system, but you need to add your own muffler.
IMO, a Mufflex cat-back with either a Hooker Maximum Flow, Borla XR-1, Dynomax Ultra Flo, or Magnaflow will do the trick.
A little bird told me that Mufflex will build a stainless system for you if you ask nicely. A poster on this forum claims to have one.
The choice of single or dual exit would only be cosmetic for me... I would prefer the symmetry of duals but I guess it wouldn't be a deal breaker... depends on the gains elsewhere. I'm more interested in gains under the whole torque curve than just some power above 5500RPM.
Staying with a y-pipe: What is the OD of the ARH y-pipe merge? For some reason I thought it was 3.5" but I think my intermediate pipe is 3"? I don't recall using any sort of reducer between the pipes. What material is the SLP dual/dual i-pipe, muffler & exit pipes made out of? So to use a 4" intermediate pipe I'd presumably need a 3.5" ID inlet to 4" ID outlet slip fit connector, the 4" intermediate pipe including over-the-axle then I'd either need to reduce it again to use the Dual/Dual muffler or find another muffler which meets my goals and has a 4" inlet.
I'm not against true duals but there's the clearance and additional weight concern.
There will be weight reduction if you have the true duals dumped at the rear axle. That's how mine's setup and I love it. Sounds great and looks like a true old muscle car when looking at it from behind.
Sell the 1 3/4" and buy 1 7/8". I was only out $200 when I swapped over my Kooks headers. Buy the Kooks TD kit and never have to worry about your exhaust again! My old setup was aluminized kooks y-pipe (heavier than stainless) and GMMG...my Kooks TD's were only like 5lbs more that that. Clearance is not an issue and I'm lowered 1.25", they actually tuck up higher than my old setup until close to the axle.
Before and after dyno from my 1 3/4" to 1 7/8" swap. Same dyno, same brand header. Notice I lost nothing down low. 20rwhp 15rwtq increase from just the header swap.
True duals dumped at the axle would violate the 'no significant increase in NVH' I found that the upper panhard brace needs to be straight to react to cornering loads on the frame end of the panhard. If that frame tower is allowed to flex it will eventually crack off.
The Kooks duals are nice, it says it requires the BMR custom upper panhard bar ($220) and and their drive shaft loop ($120). Why would an exhaust system require a DSL?
ARH 1 7/8 headers: $unknown, can't find price without y-pipe
Kooks true-dual kit: $2000
BMR DSL: $120
BMR PHR: $220
Sale of existing ARH 1 3/4 w/ y-pipe: -$unknown
Since I can't convince myself to buy TFS255 heads for 20-30rwhp gain, I feel the Kooks true duals are the same issue. Not enough gain for the cost.
I'd also think the Kooks true dual would likely be louder than you want since the mufflers are very small. FYI, most PHB relocation kits are only designed for a stock height car, and only offer additional exhaust clearance as it's only benefit.
So with a lowered car most kits are incomplete, and you would still need to relocate the PHB mount on the rear-end assembly to correct it's working angle. So figure on needing more $$$ to the overall cost to do it right.
Call maryland speed, you can get the TD's for a few hundred cheaper than that. You don't need a DSL but you have to remove the tunnel brace for the duals to fit, it's just a safety thing. MWC sells a DSL that is lighter and better than BMR's for $90. Founders sells a PH relocation for $90 but I don't know how good it is. That you definately need.
I will say the Kooks setup is not quiet and I have it with cats. But it is quieter than my GMMG was since there is 0 rasp.
09-10-2014, 10:52 AM
Can I improve my exhaust? 
I found that the upper panhard brace needs to be straight to react to cornering loads on the frame end of the panhard. If that frame tower is allowed to flex it will eventually crack off.