Small is BETTER for Cat Back Exhaust ? ! ?

[VictorCrown]

Hi Guys,

I have been saving up and finally ordered what I think just may be the definitive breathing treatment for a naturally aspirated Marauder engine. Here it is front to back:

- K&N Cold Air Intake KN57-2563 from Performance Peddler

- Stainless Works Long tube Headers from D'Agostino Racing

- Magnaflow Mirror Finish 3" in/out 94319 CATS with Air from Planet Magnaflow

- custom welded 3" stainless H-Pipe balance tube yet to be built

- Rear Cat delete and under axle Cat Back mandrel bent stainless tubing

- Flowmasters which cannot be ordered until I determine back axle tube diameter


So here's my question:

How small should the exhaust tubes be after the H-Pipe to make sure that the car doesn't lose low end torque?

From what I've heard there needs to be at least a bit of back pressure from a free flowing exhaust to make sure you don't have to wait until high rpms to get a power surge

I will be fabricating it, so it can be any diameter. Is 2.5 best or would 2.24 or even 2" give better lower end torque?

[offroadkarter]

if you run 2" you will be 1/4" under stock, 2.25" is stock, 2.5" really is the better way to go, but i think most people who get cat backs and arent putting out enough power to spin the world get a full 2.5" system. Its plenty really.


Oh yeah, flowmasters arent for flow, keep that in mind

[VictorCrown]

if you run 2" you will be 1/4" under stock, 2.25" is stock, 2.5" really is the better way to go, but i think most people who get cat backs and arent putting out enough power to spin the world get a full 2.5" system. Its plenty really.
Oh yeah, flowmasters arent for flow, keep that in mind
Hi Offroadkarter,

Thanks for your helpful reply!

With the long tube headers, pulleys, cold air intake, php spacer, hi-flow cats, and SCT tune the engine should be above 350hp, probably not enough power in your book but still requiring flow reduction downstream to keep low end torque.

The stainless works headers end in 3" diameter so I went with 3" Cats. I figured I may as well even out the exhaust (and boost the deep note burble) by keeping the diameter at 3" for the H-Pipe although it could also be smaller in the same diameter as the rest of the exhaust behind the Cats.

What I was wondering is whether 2.5" is small enough to retain or increase low end torque. I really prefer instant torque at low rpms rather than high hp in the revs. It is not only more satisfying in terms of acceleration and grunt but it also gives more grip on the road with engine braking in dips and curves.

My stock exhaust is 2.25" given that it is a new Marauder engine transplanted into a Crown Vic. I'd rather run all new exhaust as I plan to re-use the double exhaust from the Crown Vic to replace the single exhaust on my Town Car. As I plan to also delete the rear Cats this shouldn't be that much more complicated.

Thanks for your remark regarding the Flowmasters. I didn't know that they were notoriously bad for preventing free flowing exhaust. As my car is a 'sleeper' disguised as an old retiree cruiser, I'd rather not provoke the local authorities with a loud exhaust note. It can be deep, just not raucous or provocative. I was recommended the Flowmaster 40 or 44 series in 18" length, they are said to be fairly quiet and they didn't sound like tin cans as some others do on YouTube.

I'd much appreciate if you had a recommendation, as I've sort of eliminated the Aero Turbines as they'd blow my stealth cover. :lol:

[Peace2Peep]

Flowmasters are pretty loud in my book. I would probably look at a larger magnaflow muffler and include the resonator reducer weights(or whatever they are called). I thought the Aeros were supposed to be quiet...oh man! I don't know! I like em deep sounding and loud!

[offroadkarter]

If you want quiet but good sounding mufflers you can look into magnaflow's

If you want your car to sound like God eating orphans, SLP Loudmouth II's! :D

The stock exhaust is actually bigger than the crown vic duals, IIRC both of our H pipes are 2" diamater, but our piping is 2.25" while their stock is full 2"

I think 2.5" will be fine, really if you goto even a 2" you wont be improving low end torque that much,and you will be defeating the purpose of your LT's and 3" up to the H pipe...

4v's arent known for their off the line torque, I'd suggest throwing in a set of 4.10 gears also. Stall converter would be great as well, 3000 or 3500 if you really want to move off the line

And yes with your new exhaust, keep the stock exhaust harmonic dampers (the big black cylinder thingies) so you dont have any bad vibrations.

[ImpalaSlayer]

fyi stock exhaust is NOT 2.25" rather its 2"

[babbage]

Hi Guys,

I have been saving up and finally ordered what I think just may be the definitive breathing treatment for a naturally aspirated Marauder engine. Here it is front to back:

- K&N Cold Air Intake KN57-2563 from Performance Peddler

- Stainless Works Long tube Headers from D'Agostino Racing

- Magnaflow Mirror Finish 3" in/out 94319 CATS with Air from Planet Magnaflow

- custom welded 3" stainless H-Pipe balance tube yet to be built

- Rear Cat delete and under axle Cat Back mandrel bent stainless tubing

- Flowmasters which cannot be ordered until I determine back axle tube diameter


So here's my question:

How small should the exhaust tubes be after the H-Pipe to make sure that the car doesn't lose low end torque?

From what I've heard there needs to be at least a bit of back pressure from a free flowing exhaust to make sure you don't have to wait until high rpms to get a power surge


You don't need any backpressure - you do need exhaust velocity and running 3" duals will kill velocity and you'll lose power. Flowmasters are crap look at CFM flow rates. Magnalfow or Borla would be much better. I don't care for the sound of Flowmasters but you may like it.

Good luck, post some pics of the project when you are done. The consensus here is that you do need a dyno tune to realize the full benefit of the headers.

[offroadkarter]

fyi stock exhaust is NOT 2.25" rather its 2"


the H pipe is 2", the piping after is 2.25"


Or so i've been told by the 100% factual forum

[VictorCrown]

Flowmasters are pretty loud in my book. I would probably look at a larger magnaflow muffler and include the resonator reducer weights(or whatever they are called). I thought the Aeros were supposed to be quiet...oh man! I don't know! I like em deep sounding and loud!

Hi Peace2Peep,

Another poster here showed some numbers comparing multiple muffler brands and models for torque, hp and decibels at idle, 2000rpm and wide open throttle which was impressive if indeed accurate as some hinted that the study was sponsored to make the Borla's look good. They do indeed seem pretty nice, at least their ProXS model as I imagine their XR racing units would be quite a bit louder. There are YouTube video clips with the Aeros which do sound quite a bit louder than I want to be when passing a yearning trooper with an itch in his ticket book.

My ideal mufflers would not constrict exhaust, but would make it low key at idle or when cruising gently past the law, but would really roar when you feel like opening it up on an empty country road. Some of those mufflers in that test show just that, low decibels at idle and low rpm but higher decibels than the Borla's (120db versus 110db) when flooring the gas. I'll be checking them out and probably not going with the Flowmasters which some here think aren't quite the stuff.

Cheers,

Vic

[VictorCrown]

If you want quiet but good sounding mufflers you can look into magnaflow's

I'll definitely be checking out sound bites on the web to hear what they sound like, maybe guys with Mach I Mustangs use them?

If you want your car to sound like God eating orphans, SLP Loudmouth II's! :D

I a world without law enforcement I'd go for that throaty dragster sound...

The stock exhaust is actually bigger than the crown vic duals, IIRC both of our H pipes are 2" diameter, but our piping is 2.25" while their stock is full 2"

The entire exhaust will be new, so I need to know whether to make the H-Pipe in 3" (like the Cats) or 2.5" diameter.

I think 2.5" will be fine, really if you goto even a 2" you wont be improving low end torque that much,and you will be defeating the purpose of your LT's and 3" up to the H pipe...

Thanks for recommending the sweet spot in exhaust pipe size for this setup, at 2.5" after the Cats OR after the H-Pipe. I thought that having a larger diameter H-Pipe would produce a deeper resonating sound, that low pitch thump I much prefer over the screechy scream of an X-Pipe. I also presumed that it might work better without first reducing the size, but on second thought using a 3" to 2.5" reducer before the H-Pipe would speed up the flow before evening it out in the H-Pipe, possibly causing the H-Pipe to perform its task better?

4v's arent known for their off the line torque, I'd suggest throwing in a set of 4.10 gears also. Stall converter would be great as well, 3000 or 3500 if you really want to move off the line

My original non PI 2 valve engine got off the line really fast thanks to its reduced transmission gearing and tall rear axle towing gears plus the 15" wheels designed for towing which are like adding extra gearing to your rear axle. Smaller wheels is a case of smaller is better unless you can explain to me one performance feature of larger wheels to justify sacrificing the lighter suspended weight and quicker acceleration of small ones.

And yes with your new exhaust, keep the stock exhaust harmonic dampers (the big black cylinder thingies) so you dont have any bad vibrations.

Thanks for this advice, I wasn't paying attention to them and will definitely make sure I keep them for reuse.

[VictorCrown]

You don't need any backpressure - you do need exhaust velocity and running 3" duals will kill velocity and you'll lose power. Flowmasters are crap look at CFM flow rates. Magnalfow or Borla would be much better. I don't care for the sound of Flowmasters but you may like it.

Good luck, post some pics of the project when you are done. The consensus here is that you do need a dyno tune to realize the full benefit of the headers.
Hi Babbage,

You've already given me loads of good advice for the engine swap and I am finalizing a bit late the parts for the implant. I read another post here saying that smaller diameter does NOT equate with better torque. However, too large a diameter will kill power production. The test data without mufflers shows just that, lower power and torque than even with the worst mufflers = truly edifying data.

I'm leaning towards the Borla ProXS if I can find them cheap and IN STOCK as most places say 22 days before shipping if not worse. Also, I need to be sure what diameter pipe I'll be running all the way back before ordering them, but from the advice so far I'm guessing 2.5" is just about ideal.

The Dyno tune is going to be mandatory as my car is vintage and uses a non programmable OBD-I chip which can't be tuned, a new one needs to be burned to replace it anyways. They're giving me a featureless non optimized limp to the dyno tuning station starter chip before putting it on the bench and tweaking the beast for the highest potential torque. I can't wait and am sort of hoping that the mufflers won't delay the entire project given that the two shops are 15 miles apart on well policed roads, so mufflers are a must.

Cheers,

Vic

[VictorCrown]

I think Red answered my question in another thread, he posted this sound clip giving the result of Borla ProXS mufflers with Stainless Works long tube headers:

http://www.mercurymarauder.net/showcase/misc.php?do=downloadfile&i=11638

However, this sure seems to me like begging for attention, his other mods are similar to my engine mods, so this sure seems like a loud muffler unless it was recorded with a microphone next to the tips...

[ctrlraven]

Aero Turbine AT2525 mufflers for 2.5" pipe, I was a Flowmaster man 100% but will never go back to them. Aero Turbine throatiness > Flowmaster Drone.

2.5" pipe from headers back is plenty fine.

[VictorCrown]

oh my gosh - D'Agostino Racing just called and said it would be at least a month before I would get the Stainless Works long tube headers! He's looking into Kooks instead as well as sources for shorties. I bet it will take a performance loss without them. :(

What would be second best to Stainless Works units?

TIA

Vic

[ctrlraven]

It's either Kooks or SW headers.

[ImpalaSlayer]

the H pipe is 2", the piping after is 2.25"


Or so i've been told by the 100% factual forum


ive just got done doing the exhaust, its 2 inchs says my mic.