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The amount of information here, and some of it is dated, is kind of all over the place.
Maybe a few here that have direct experience can offer up suggestions for a 4" over the axle system.
Mufflex has a few to choose from: https://mufflex-performance.com/18-1...gle-cat-system
Most everything I'm finding are just resellers. And 4" doesn't appear easy to come by.
Anything I'd get would be adapted to my already fabbed y-pipe. I'd like to keep it as a single exhaust for the sake of simplicity. That would be right down to a single tail pipe as well. That doesn't mean that a full dual is out of the question. It would probably make muffler selection easier and with that would be quieter. But also heavier.
I suspect that the panhard bar(s) would need modifications as well. Db's are somewhat of a concern but not a deal breaker if something fits. Don't need stainless either.
Go with the single 4". Easier fit, larger muffler, no drone. I'm running a custom fabricated 3" true dual and I hate it. The fab work is excellent and it will support any power level, but it's loud. I have cats, bullet resonator and spin tech mufflers. The worst part is the heat transfer into the floor and the drone at steady state cruising. With a dual setup you take up any free real estate which limits muffler size. I wanted the perfect setup and paid dearly for it. I underestimated the drone. It's beautiful, but painful to drive. I could have had a fully optioned fabricated 9" rear end for the price I paid for this exhaust.
Has anyone considered oval pipe, at least in some sections?
Yes, I did originally but it was too impractical without any real benefit. A single 4" is only 1.5" squared less flow volume. Qwktrip makes 570 N/A rwhp through a single 3.5" mufflex system. It's only a matter of time before I make the change.
Go with the single 4". Easier fit, larger muffler, no drone. I'm running a custom fabricated 3" true dual and I hate it. The fab work is excellent and it will support any power level, but it's loud. I have cats, bullet resonator and spin tech mufflers. The worst part is the heat transfer into the floor and the drone at steady state cruising. With a dual setup you take up any free real estate which limits muffler size. I wanted the perfect setup and paid dearly for it. I underestimated the drone. It's beautiful, but painful to drive. I could have had a fully optioned fabricated 9" rear end for the price I paid for this exhaust.
I appreciate that bit of honest feedback Shifty. I can't say I'm a fan of the current crop of dual exhaust although it's great that there's some interest for our models. It's more the muffler placement that bugs with them tucked up at the rear. Truth be told, I'm not really a fan of the traverse muffler either having grown up in the muscle car era and having the real estate for a couple of turbo style mufflers forward of the rear axle. But it is what it is. The single is certainly less complex.
I'm no stranger to the cost of having something custom fabbed up. I don't recall exactly being twenty years ago, but the header modifications (Hedman long tubes), stainless 2 x 2-1/2" to 3'' y-pipe and crossmember slice and dice wasn't cheap. I will say though that even after all these years and countless removal and reinstallations, that it still fits like the day it was built despite it taking a couple of hefty hits. If and when I ever upgrade, I'll remove the entire system, headers to tailpipe, and save it as a complete assembly. I'm sure I could get some ROI selling it too.
You mention volume. As in loud. That's something that I think would be more of a problem with one muffler. It has to have sufficient capacity so as not to limit output. Like 900 CFM worth of capacity in my case. In the single muffler world that equates to LOUD. Or at least the research shows.
As for your drone, wouldn't a change in muffler architecture alter that?
As for Mr. Q and his results. I'll bet he's down 10% or more with that arrangement. Take 570 RWHP, factor in the drivetrain loss and at a minimum that's 650+ at the crank. 1200+ plus worth of system airflow before it starts to cork things up. I'm not sure that one 3.5" pipe and whatever muffler is in there is capable. That said though, we all know that his 570 at the tire is more than a handful on the street. Where would another 80 HP get him? (If it was me, I'd have a track specific deal and, as the saying goes, let it eat.)
Speaking of which, as an alternative to a bigger pipe for me, I do have plans to cut into my fancy y-pipe and place cutouts in an appropriate place. The I can tune the secondary length and have open headers on track days. I'd still have a crippling exhaust for street duty but then again, I can't say I'm much of a street racer anymore.
Has anyone considered oval pipe, at least in some sections?
I was deep into that bit of research when I put in the long tubes. It was at the time, and probably still is very expensive. As it turned out, my fabricator, long time friend and shop owner managed great ground clearance even with the OEM crossmember although that had to modified somewhat. It's a beer can's diameter at the lowest point so 99.9% of the time, it clears whatever it needs too. I will say though, that on day one after the installation, two grown men, their golf clubs and luggage for a weeks holiday lowered the ride height considerably. Two minutes into the trip, I crossed a culvert hump in the road and left the first beauty mark in the stainless. Ouch.
Could be that oval tubes might have made the difference.
I always figured that 2 x 2.5" would more than satisfy my output. Something that could be an everyday thing and not track specific.
Looking at the single, and the muffler volume notwithstanding, a 3.5" might get it done too.
Just have to look deeper into what muffler spec is available. I've seen Mufflex, Spintech, Flowmaster, Borla and Magnaflow all in this size range. Race duty rated as well (and that probably = LOUD).
I'm running a single 3" now and into a Flowmaster low series muffler. I'll bet the CFM is 300 at best. IIRC, it's an American Thunder series from 1998. Who knows what muffler that really is.
I put in a cutout right at the bend after the axle and before the muffler. Taking off the 3" cap on track days yielded a gain of 1.5 MPH in the 1/8th. One glory run with no tuning. Just point and shoot.
That says a lot to how crippling the current arrangement was, and still is. And that was with about 100 HP less that I have now.
Qwktrip makes 570 N/A rwhp through a single 3.5" mufflex system. It's only a matter of time before I make the change.
I have Stainless Works (sold through Hawks).
I have no idea what power I make, the tires spun any time above 420 lb-ft and the dyno just kept reporting that torque as long as I was spinning. 570 RWHP is because we stopped the run around 7,000 RPM with tires spinning.
420 lb-ft @ ~7000 rpm ---> 570 RWHP
My actual torque and power curve are unknown. Usually an LS7 will make torque into the 500's.
I have no idea what power I make, the tires spun any time above 420 lb-ft and the dyno just kept reporting that torque as long as I was spinning. 570 RWHP is because we stopped the run around 7,000 RPM with tires spinning.
420 lb-ft @ ~7000 rpm ---> 570 RWHP
My actual torque and power curve are unknown. I sure as heck make a lot more than 420 lb-ft.
I've no doubt about that power output. I'm familiar with your engine spec. Get you car on a hub dyno! That's my objective.
As for the exhaust, you say a Stainless Works 3.5"? I'll have to check into that. Do you know which muffler is in play here? Single out I'm assuming?
I was deep into that bit of research when I put in the long tubes. It was at the time, and probably still is very expensive. As it turned out, my fabricator, long time friend and shop owner managed great ground clearance even with the OEM crossmember although that had to modified somewhat. It's a beer can's diameter at the lowest point so 99.9% of the time, it clears whatever it needs too. I will say though, that on day one after the installation, two grown men, their golf clubs and luggage for a weeks holiday lowered the ride height considerably. Two minutes into the trip, I crossed a culvert hump in the road and left the first beauty mark in the stainless. Ouch.
Could be that oval tubes might have made the difference.
It would be a lot of work and welding, but if I had the time (who does?), I might slice round pipe and add sections to make it oval.
And as far as drone goes, don't forget about frequency. 8 cylinders vs 4 firing into one muffler will double the exhaust frequency, possibly eliminating the drone.
I always figured that 2 x 2.5" would more than satisfy my output. Something that could be an everyday thing and not track specific.
Looking at the single, and the muffler volume notwithstanding, a 3.5" might get it done too.
Just have to look deeper into what muffler spec is available. I've seen Mufflex, Spintech, Flowmaster, Borla and Magnaflow all in this size range. Race duty rated as well (and that probably = LOUD).
I'm running a single 3" now and into a Flowmaster low series muffler. I'll bet the CFM is 300 at best. IIRC, it's an American Thunder series from 1998. Who knows what muffler that really is.
I put in a cutout right at the bend after the axle and before the muffler. Taking off the 3" cap on track days yielded a gain of 1.5 MPH in the 1/8th. One glory run with no tuning. Just point and shoot.
That says a lot to how crippling the current arrangement was, and still is. And that was with about 100 HP less that I have now.
How the heck can a 4" pipe pass through that opening? I have the 3" SLP and it barely fits.
I've had this 3" Flowmaster cat back for decades and it was direct and easy swap. That what's in the picture above along with the 3" cutout I described.
For the 4" or duals over the axle, the panhard bar relocation kit is required so as to open up that area.
That's another pro in the pro/con process. One less part to buy (panhard bar) and from own bit of research, 3.5" would be enough pipe for this engine (although because of the length and bends involved the actual flow capability is difficult to calculate). The muffler would be the key though. And that's a volume vs flow thing.
As mentioned above, a single muffler will kill most of the resonence in a system. The panhard relocation bars aren't that expensive. I'm running the founders one out of caution. WS6store still sells the Holley 2.5" dual setup for our cars. Can't comment on drone but the smaller pipes will certainly help. Likewise, a new rea gear may help as well as it will put the engine in a slightly different rpm range. 1900rpm in 6th gear will rattle your bones.
I like the idea of a single rather than what comes along with duals. There's a weight factor but how much I can't say. Packaging, is discussed is another issue but as Holley has demonstrated, it'll all fit. Regarding the Holley, the local speed shop here in Alberta (https://jbspowercentre.com/) will bring that system in if I order it. Or so there website says anyway.
Over at Hawks, they offer the 3.5 inch with a Magnaflow muffler. Interestingly, they've rated it a 325-400 HP. Not sure what to make of that.
One thing I can say, and this is expressed by many who hear my car, is that little dinky 10 series (?) Flowmaster has a great sound. At least at idle. I put that down to the higher compression and cam profile providing a nice "crispness" overall. It is however a power robber at full song. On the highway while cruising or in the city, never a drone or an unpleasantness. Highway revs are ~ 2500 locked up in OD.
Over at Mufflex, anything listed at 3.5" is capped at 400 HP. Even their 4" offerings state 400 HP. Some of that though appears to be muffler dependent.
Something to consider for context is since an engine is an air pump, if your exhaust size at least equals your intake diameter you should be fine. The intake is at ambient pressure and the exhaust is pressurized so there is savaging. Adding boost only helps. No one would run stock exhaust manifolds, but with boost physics takes over.
Those sizing charts are probably just for reference. The greater the compression the greater the delta between intake and exhaust. Those charts likely don't take that into account.
What I'm seeing there is a 10% swing in output based on the muffler alone. I'll take 40 HP's any day of the week.
Which is something I've mentioned here more than once.
I do wish though that Engine Masters was somewhat more scientific. At least comparatively speaking. Where are the merge collectors on the dual exhaust? (I suppose being able to watch the video might answer some of that).
To give a sort of comparison, these are the results from the capped/uncapped back to back tests I did during an 1/8 mile afternoon of racing. (Single cutout picture posted above)
Not quite as pronounced as the video's results but certainly the performance gain was there. The muffler was still in play but part of the exhaust exited before it got there.
The engine in that car would produce about the same results as EM in dyno trim.
Something to consider for context is since an engine is an air pump, if your exhaust size at least equals your intake diameter you should be fine. The intake is at ambient pressure and the exhaust is pressurized so there is savaging. Adding boost only helps. No one would run stock exhaust manifolds, but with boost physics takes over.
Those sizing charts are probably just for reference. The greater the compression the greater the delta between intake and exhaust. Those charts likely don't take that into account.
While the air pump analogy has it's merit I don't think it's entirely accurate. At least not in the sense of air in and air out being equal. Think of the two air streams. Cool air coming in moved by the difference in atmospheric pressure against whatever suction is created with piston moving down (as well as whatever scavenging is produced by the open exhaust valve at overlap) mixed with the further cooling effects of the fuel (carbed NA) vs the blisteringly hot and very high velocity air leaving the engine exiting under the residual combustion pressure and the piston moving up the bore.
Makes you understand why you can feed an engine to 500 HP with 4 x 1-3/4" butterflies, yet it takes 8 x 1-7/8" exhaust tubes to get it out. Not to mention the dynamics of rapidly cooling exhaust gases and how that has to be accommodated in exhaust design. Witness stepped headers.
PipeMax can give some great insights into how the induction side in terms of CFM differs from the exhaust side. Of course there are many dynamics to consider but in my thinking, it's not exactly air in = air out when you factor in temperature, density and velocity.
But like the induction side, you don't want any restrictions to airflow in the exhaust (although the intake port itself is somewhat complex in terms of shape and cross section). That can be seen in the Engine Masters results posted above. The straight through muffler wins.
You're going to be too old to drive the car before you make a decision....
A couple of things there Mr Q.
I don't need to make a decision really as once the snow is gone, that heap of mine is good to go. This is the first time since 2016 I didn't put away in pieces at the end of the season! I'm kind of stoked about that.
The exhaust is just an off-season musing. Something I'd like to do although my plan for a long time is to keep the wheezy exhaust that's on there now and put the collector extensions via cutouts I've prattled on about. Race day stuff. And I really do hope to get a lot a track time this year.
As for old...I'm way ahead of that game. My hope is that I have what it takes to keep wrenching once I'm retired! On many levels.
My car is twin turbo, so the power numbers aren't apples to apples, but I have two three inch down pipes into a single four inch and Magnaflow muffler. I added a cutout to control the sound. It’s not loud at all (again, because if the turbos).
I had to use oval sections for my downpipes, as they ended up being the lowest part. No ground clearance issues for the 4” section.
As mentioned above, a single muffler will kill most of the resonence in a system. The panhard relocation bars aren't that expensive. I'm running the founders one out of caution. WS6store still sells the Holley 2.5" dual setup for our cars. Can't comment on drone but the smaller pipes will certainly help. Likewise, a new rea gear may help as well as it will put the engine in a slightly different rpm range. 1900rpm in 6th gear will rattle your bones.
wonder if you can analyze what the exhaust frequency is at this condition and build a Helmholtz resonator in the pipe to eliminate it.
wonder if you can analyze what the exhaust frequency is at this condition and build a Helmholtz resonator in the pipe to eliminate it.
I actually looked into this since there are some muffler manufacturers that offer this. Many newer cars have them on their intake piping as well as exhaust. Unfortunately, it comes down to cost and physical space under the car, so I punted.
I run a Helmholtz resonator on my Vortec 454 Suburban, with the formulas out there, it allows you to tune to an RPM vs just the frequency. It works, quite well. Years ago I put one on a 5.0L Coyote powered F150 as well. Space is definitely a problem, but you could probably J-pipe under the muffler maybe? You don't have to match the diameter of the pipe, could probably use a 2" OD chunk and get away with it.
I used a Hawk’s Sinister 4” system with a Hooker Max Flow and had a custom 3” Y-pipe built with a Flowmaster dual 3” to 4” merge. It isn’t crazy loud at idle but will scream at WOT and has a similarly smooth sound to a Dynomax Ultraflo, Magnaflow, or any other large straight-through muffler with batting.
Dynatech split flow. Ive never heard it outside at wot, but im told its quite loud. I love it. Idle sound burbles like a through hull boat exhaust. In the cabin wide open sounds like a cross between a vette and a asphalt late model. High pitched but not raspy if that makes sense
