To Straight Pipe, or Not To Straight Pipe?

by "Camshaft Chris: Skyline/McLaren/Porsche Fanboy" (camshaft-chris)
Published 08/15/2017 at 13:59

Tags: Straight Pipes For Dummies ; Exhausted ; Straight pipe ; Ford ; Crown Vic ; Crown Victoria ; exhaust
STARS: 1

A buddy of mine suggested I straight pipe the Crown Vic instead of wasting money on better mufflers and high-flow cats and such. After a little research, I read a few things saying that straight pipes can actually cause you to loose power because it releases all of the back-pressure. Is there any actual truth to the power loss? And I know, the Crown Vic is no rocket ship, but that’s exactly why I can’t afford to lose any power over how little it already has...

End game here is that I want a nice rumble from the exhaust when I’m on throttle, but not anything that’s gonna wake the kiddos when I start up the car to head into the office in the morning. I found one video on YouTube that I liked the sound of and the guy described it as a straight pipe with no mufflers and all four catalytic converts “plugged”. Any idea what that means? Are they just old cats that are all gunked up? Or is this some sort of slang that I missed out on?

Link to aforementioned YouTube video: https://www.youtube.com/watch?v=kyk6LrPZBkA&t=11s  

Replies (41)

"Takuro Spirit" (takurospirit)
08/15/2017 at 14:01, STARS: 2

Do it. There’s SO MUCH pipe under the Crown Vic that even straight pipes aren’t that loud.

Here’s what mine sounded like with glasspacks:

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And from inside:

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"crowmolly" (crowmolly)
08/15/2017 at 14:05, STARS: 3

If the cats or mufflers are plugged up you will feel a difference just due to the restored breathing. The backpressure thing is a myth.

An open exhaust (I’m including straight pipes here) will be very loud, especially on cold days. If the local PD is the type to take issue you may get unwanted attention.

TBH if it’s mostly stock I’d put some Magnaflow mufflers on and call it a day. You *might* lose a few hp vs. straight pipes.

"crowmolly" (crowmolly)
08/15/2017 at 14:05, STARS: 1

If the cats or mufflers are plugged up you will feel a difference just due to the restored breathing. The backpressure thing is a myth.

An open exhaust (I’m including straight pipes here) will be very loud, especially on cold days. If the local PD is the type to take issue you may get unwanted attention.

TBH if it’s mostly stock I’d put some Magnaflow mufflers on and call it a day. You *might* lose a few hp vs. straight pipes.

"Alfalfa" (alfalfa-romeo)
08/15/2017 at 14:06, STARS: 1

That is correct in the straight pipes, some back pressure is actually ideal. It’s one of those commonly held misconceptions among car people that less back pressure always equals more power.

"TheD0k_2many toys 2little time" (thed0ck)
08/15/2017 at 14:08, STARS: 1

backpressure is a myth. the more open the exhaust is the better. there is a reason racecars are not muffled (except at tracks with decibel limits)

My powerstroke is straighpiped coming out the passenger side. But it has a turbo to quiet it down. My Miata has no cat or resonator but i have a Vibrant performance straight thru muffler and i think it sounds good

"Smallbear wants a modern Syclone, local Maple Leafs spammer" (smallbear94)
08/15/2017 at 14:14, STARS: 5

Back pressure isn’t a myth, but the general understanding of it is. Less back pressure always equals more ability to make power. However, bigger pipes do not always equal less back pressure. Make the pipe too big, and the flow slows down far enough to create MORE back pressure.

"lone_liberal" (token-liberal)
08/15/2017 at 14:16, STARS: 0

How old are you? If you’re under 25 then, sure, go with the pipes. If you’re over put some mufflers on because that cool-ass noise will eventually grate on you and you’ll get tired of the car sounding like you’re gunning it every time you take off from a stop light.

"CobraJoe" (cobrajoe)
08/15/2017 at 14:21, STARS: 10

You don’t want back pressure, you want properly sized tubing.

Too large of tubing, and you’ll lose low end power because there’s not enough exhaust flowing to fully empty the cylinder of exhaust gases. Too small of tubing and you won’t flow enough volume to fully empty the cylinder of exhaust gases.

It’s a balancing act, but usually if you have a near-stock engine, keep the stock pipe size. Just get rid of the restrictions like poorly bent tubing and restrictive mufflers.

"feather-throttle-not-hair" (feather-throttle-not-hair)
08/15/2017 at 14:23, STARS: 4

Backpressure is always bad, but too open of an exhaust on an NA car isn’t good either. Something something exhaust pulses, suction, a huge exhaust isn’t great on an NA car (all that goes out the window with turbos, as big as possible is best there.)

Also, i’d at least have a cat on there. Catless cars are stinky and terrible for the environment. Its not like you’ll be polluting twice as much as the average car, its way way way more than that.

"sony1492" (sony1492)
08/15/2017 at 14:26, STARS: 0

Power improves when the motor can consume more air so loosing power to lack of back pressure dosent make since(because that pressure is not allowing the gasses to pull each other out). Each event the gasses move toward to tailpipe where pressure is less and if timed right the gasses from each explosion can be used to pull the next events gasses, which is what tuned headers do.

Stock cats don’t add resistance, the reason they are larger than the rest of the exhaust is so that there is the same room for air to flow in between the substrate(the material inside)

Straight pipe will be too loud all the time, I’d go with magnaflow or something.

"Alfalfa" (alfalfa-romeo)
08/15/2017 at 14:27, STARS: 0

You’re right, I suppose equating flow velocity to back pressure isn’t the best way of putting it. But like you said, certainly more complex than just big pipes making more power.

"ateamfan42" (ateamfan42)
08/15/2017 at 14:28, STARS: 2

After a little research, I read a few things saying that straight pipes can actually cause you to loose power because it releases all of the back-pressure.

Back pressure being “good” for power is a old old old motoring myth. It stems from people “upgrading” to too large exhaust and noticing a drop off in low-end torque.

What is important for good performance is exhaust velocity , which scavenges exhaust gases from the cylinder.. A correctly sized pipe will keep the flow fast. Too big, and the flow slows down, robbing power on the low-end. Too small, and the restriction gets big, robbing power on the high end.

"Smallbear wants a modern Syclone, local Maple Leafs spammer" (smallbear94)
08/15/2017 at 14:29, STARS: 5

That idea is a classic example of mixing up correlation and causation. You do want as little back pressure as possible. Always. The closer you get to zero back pressure, the more you make/can make.

The essence of that theory is people would find they got more power with a smaller exhaust than with a larger one, so naturally you need back pressure, right? Wrong... what’s going on is the larger pipe is creating more back pressure than the smaller one. Remember, an engine is basically an air pump. The problem is that when you are using a pipe size that’s bigger than you need, the engine isn’t actually able to pump hard enough to keep the entire exhaust flowing, essentially turning the air in the excess exhaust volume into an obstruction.

This also explains why the most common complaint about “I don’t have enough back pressure” is “I’ve got less low end torque”. The power could feel totally fine when you’re winding the engine out, because you’re pushing a lot more air at the top end... but as a direct result of having an exhaust sized for a free-flowing top end you’ve got lots of dead air plugging the pipes at low revs.

Basically it’s all a compromise, pick what you want and go for it. If you want revs, size it bigger, if you want low end grunt, size it smaller... but in either case screw what your gut says. Do your homework and check the CFM before doing anything.

"jasmits" (jasmits)
08/15/2017 at 14:30, STARS: 0

Honestly no matter what you do to the exhaust it probably won’t affect your power enough to notice in either direction

"crowmolly" (crowmolly)
08/15/2017 at 14:32, STARS: 1

I’m not denying that backpressure doesn’t exist. That’s why I said “the backpressure thing is a myth”. I meant the whole “you need backpressure” myth. Maybe I was unclear.

My understanding is that flow velocity is key. You want good velocity and minimal (close to zero) backpressure.

"RacingShark" (racingshark)
08/15/2017 at 14:34, STARS: 2

check out Engine Masters on youtube. they do a lot of A/B testing for engine mods. The problem with straight pipe is that is loud all the time. If you have the $, you can install a bypass valve.

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"Berang" (berang)
08/15/2017 at 14:34, STARS: 0

Straight pipes will just make your car sound annoying, and it will be most annoying for you if you ever drive the thing anywhere.

"TheRealBicycleBuck" (therealbicyclebuck)
08/15/2017 at 14:36, STARS: 1

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"TheD0k_2many toys 2little time" (thed0ck)
08/15/2017 at 14:38, STARS: 0

counter point i have cars with no cats and they smell amazing. also e85 cars with no cats smell good too

"crowmolly" (crowmolly)
08/15/2017 at 14:38, STARS: 1

Back pressure being “good” for power is a old old old motoring myth. It stems from people “upgrading” to too large exhaust and noticing a drop off in low-end torque.

Might be even older than that. Back in the day people would cut off restrictive exhaust systems and not re-jet, so they’d have a lean condition.

"Smallbear wants a modern Syclone, local Maple Leafs spammer" (smallbear94)
08/15/2017 at 14:38, STARS: 1

Yeah, we’re saying the same thing. I just felt like embiggening on your comment.

In any case I could have phrased mine better too, so meh...

"CobraJoe" (cobrajoe)
08/15/2017 at 14:40, STARS: 1

I definitely made the mistake of buying headers that were too large for a near stock engine when I was younger. A stock ‘86 Mustang GT does not need 1 5/8in primary tubes. At least the losses down low weren’t horribly noticable, and I believed I made more power up higher.

"crowmolly" (crowmolly)
08/15/2017 at 14:42, STARS: 1

CRAM IT MAN I WANT MY TRUE DOOOLZ

"sony1492" (sony1492)
08/15/2017 at 14:43, STARS: 1

You can’t smell oxides of nitrogen

"TheTurbochargedSquirrel" (thatsquirrel)
08/15/2017 at 14:45, STARS: 0

Straight pipes will do a very good job of waking the kiddos.

"feather-throttle-not-hair" (feather-throttle-not-hair)
08/15/2017 at 14:51, STARS: 0

MAYBE YOU CANT!

(but for serious, every catless car i’ve ridden in/driven has been stinky. But this is just my experience)

"feather-throttle-not-hair" (feather-throttle-not-hair)
08/15/2017 at 14:52, STARS: 1

*shrugs*

I have friends that run no cats. Hell, my race car doesn’t have cats. I’m not mad at them or anything, but to me, the tradeoff on the street isn’t worth it. 2-3 hp isn’t worth the environmental destruction and in my experience, they smell worse.

"sony1492" (sony1492)
08/15/2017 at 14:57, STARS: 2

O2 is probably reading wrong because it’s seeing lean(normally the cat would consume some of the oxygen in the catalytic conversion) so the car starts richening the mixture and BAM now it smells like unburned fuel and who knows what.

Fairly sure everything the cat cleans up is odorless.

"Flynorcal: pilot, offshore sailor, car racer and panty thief" (flynorcal)
08/15/2017 at 15:30, STARS: 0

No set of mufflers will cost you more than the time and effort it will take you to put on a straight pipe. If you’re trying to save a few bucks, this isn’t the place.

You’ll have to swap your legal stuff in for emissions, your engine management will have no idea what’s going on so you’ll likely spend enough in wasted gas alone to pay for a set of mufflers. On top of that, whatever HP you might get will likely be lost with your gas mileage.

There’s also the very unlikely but very expensive chance you get caught without your cats and I’ve no idea what kind of fine/impound/seizure results from that but you’d be exactly one police stop away from finding out. I’ve never heard of anyone getting caught but I’m sure it must happen. Folks who run straight pipes tend to be the same sorts of folks who get pulled over as not all attention is good attention, and cops tend to know what Crown Vics sound and (more importantly) *smell* like.

It’s a fun thought and if it were a track car go for it, but on the street the risk/reward/hassle seems like a bad trade off.

"Camshaft Chris: Skyline/McLaren/Porsche Fanboy" (camshaft-chris)
08/15/2017 at 15:38, STARS: 1

Meh, I don’t see it as having a high cost of time / effort. I have easy access to a lift and a welder, so no big deal there.

As for the all the emissions / legality stuff, two words can circumvent that: South Carolina. We have no emissions testing here. I’m not planning on pulling the cats either. This would just be cutting the muffler out essentially.

"Camshaft Chris: Skyline/McLaren/Porsche Fanboy" (camshaft-chris)
08/15/2017 at 15:39, STARS: 0

Definitely going to leave the cat on there. I’m only talking about cutting out the muffler and putting in a straight pipe there. The cats on this car about built in to the exhaust manifold and I really don’t want to mess with all that, lol.

"Camshaft Chris: Skyline/McLaren/Porsche Fanboy" (camshaft-chris)
08/15/2017 at 15:41, STARS: 0

Thanks for this! I think that answers my main question then. I’m sticking with the stock tubing size. Just cutting out the muffler. So that should be just fine right?

"Camshaft Chris: Skyline/McLaren/Porsche Fanboy" (camshaft-chris)
08/15/2017 at 15:43, STARS: 0

The actual length of the exhaust on the Vic is enough that I think it won’t be as loud as if I were doing it with a Mustang or something. A friend of mine did the same thing with his E39 540i and you can’t hear a thing when it’s idling. It’s only when he gets on the throttle that you can tell the difference.

"Camshaft Chris: Skyline/McLaren/Porsche Fanboy" (camshaft-chris)
08/15/2017 at 15:47, STARS: 0

I don’t think I need to put glasspacks on there, lol. Though I do have an old Cherry Bomb laying around... I think I’ll just stick with cutting the muffler out and see how that goes.

Also, what wheels are those?

"Camshaft Chris: Skyline/McLaren/Porsche Fanboy" (camshaft-chris)
08/15/2017 at 15:49, STARS: 0

With the Crown Vic though, I think the length of the exhaust will negate a lot of the sound. A friend of mine did the same thing with his E39 540i and you can’t tell it has no mufflers until he gets on the throttle.

"Sovereign, Purveyor of Coupes" (sovereign-automotive)
08/15/2017 at 16:02, STARS: 0

Back pressure is a myth, however, I encourage you to look into the scavenging effect. Too much flow *can* be a bad thing.

"CobraJoe" (cobrajoe)
08/15/2017 at 16:21, STARS: 0

I guess it should be said that your mileage may vary... Different cars have different power ranges and different reactions to upsizing the exhaust pipes.

I can say that I had a ‘96 CVPI a while ago (with the factory dual exhaust). I had the cats cut off and glasspacks welded in, and it made a “blatt blatt blatt” noise on hard acceleration. Not long after that, I hacked the tailpipes off in front of the axle and it sounded a lot better and felt stronger.

Maybe it’d be worth going for one size larger, simply just to force the muffler shop to get some new bends over the rear axle. On my CV, it was practically a corkscrew bend to get over the axle and the dual 2in pipes did not move much air. Though, it must also be noted that the P71 has better rear end gears than most civilian models and I had it tuned to shift at slightly higher RPM, so low RPM grunt wasn’t quite as vital.

Stock size pipes with better mufflers and less constricting bends should be enough, but one size up probably won’t hurt anything on a full length exhaust. Either way, you might be happier with the results if you find some other opinions on a forum dedicated to the car.

"RacingShark" (racingshark)
08/15/2017 at 16:28, STARS: 0

make sure you get the x-pipe though. Without the x-pipe, it sounds like 2 4cylinders screaming at each other. I had a dual exhaust, no crossover x-pipe and small cherrybomb mufflers on my 635csi. It was loud and sounded terrible.

"Takuro Spirit" (takurospirit)
08/15/2017 at 16:44, STARS: 0

Juts stock steelies with trim rings

"feather-throttle-not-hair" (feather-throttle-not-hair)
08/15/2017 at 17:21, STARS: 0

Makes sense. I’d say then, just go as loud as you’re willing to put up with, straight pipe isn’t great for performance, but all of this stuff is going to have a pretty small effect on acceleration regardless.

Panthers are fun, my best friend had a couple of them at one point, the second one with an LSD, which made all the difference, at least when it comes to 2nd gear donuts with 4 people in the car (in the rain.)

"Flynorcal: pilot, offshore sailor, car racer and panty thief" (flynorcal)
08/15/2017 at 17:31, STARS: 0

I had muffler bypass pipes for my 911. Same end result. 50lbs lighter and a lot louder. Too loud actually. I think since your engine and the end of your exhaust aren’t on the same end of the car it might not be so bad.

Yeah if you’re just talking about cutting out sound deadening 

When I think straight pipes, it’s for pure performance. Hence no cats as that’s where the performance is lost, not the muffler so much.