Do car exhaust mods actually do anything?

I see people saying like 5-10 hp increase for a $4,000 exhaust system, is that really worth it?

you wont be able to utilize it without a tune. it does usually sound better but that is subjective

Depends on everything upstream of the exhaust.
Maybe you'll get 5hp up top between 6.5 and 7 but lose 10 between 2 and 6.5

It's more about the sound vs the performance gain. For performance you'd have to get headers to replace your exhaust manifold for real gains. But a cat back exhaust is a simple mod one can do with a wrench.

When you put the way you did, of course not
Who would?

>Being poor

Not cause of the pipe, but when you remove the catalytic converter you're kinda unplugging the exhaust resulting in better flow and more power. Pipe diameter is specifically engineered from the factory for optimal power, only worth going bigger if you turbo or supercharge.

Huh? How did anything I say have to do with being a poorfag?

He's insinuating that people with more money than brains would spend the supposed 4k just to upgrade the sound.

That's exactly why I deleted the muffler, but I started thinking about what the sound and performance gain would be if I had paid thousands for some aftermarket exhaust system.

It seems like it is totally not worth it without actual tuning

You can do it with only a wrench?

The piping makes a big difference. Especially if stock exhaust is not an H or X pipe. And most do cat back when thinking about exhaust mods.

>Not worth it without tuning
An engine is an air pump. Without the right flow, backpressure and tuning for said values, it's no bueno.
Case by case basis for a restrictive cat.
As above.

What car do you have? A proper exhaust sounds tons better than cutting mufflers off. Depends on your horsepower goals but if doing any serious mods a proper exhaust is needed. Resonation and drone start becoming factors. If you like the hillbilly no muffler sound but also want proper exhaust at a touch of a button. Check out exhaust cut outs.

An exhaust makes a difference without a tune. The ECU on a factory tune can still make some adjustments.

Depends on the car and what it's able to adjust for as to whether or not it runs any better.

I have never heard of a cat back changing things so drastically that it throws a check engine light.

It's an e60 530i, it sounds way, way better since I deleted the muffler

what do when my N/A econo shitbox comes with 4-2-1 equal lenght headers already and they are totally happy and oversized?

An econobox isnt going to come with good headers.

If the drone isnt too much for you then it'll be fine. Might consider a turndown tip to make sure it doesn't burn the undercarriage.

>implying you can't replace a manifold with a wrench

what do you use? a hammer?

A full exhuast system is replacing headers, deleting catalytic converters if you want to and pipes and the muffler and yeah a good quality exhuast system will go for around 4k or more but if you want to do a simple cat back exhuast i don't see how that will increase power.

Also aftermarket systems are lighter than oem lose weight

What literally matters most is the surface finish inside the header. Shitbox headers are usualy just cast metal.

It scares children so yeah it's worth it.

It's a lot more labor intensive

Sounds like a personal problem.

so uh, you gonna replace them freeze plugs?

Core plugs, and yes. Every single one of them.
>Gee I wonder why my bellhouse drain was blocked
>Gee I wonder why I'm losing coolant really slowly

Worst core plug I've ever seen.

If you remove all restriction from your exhaust, you can easily get around 50hp. After a proper tune, I got an extra 35 from my setup, and it's still emissions compliant. High flow exhausts are great for reducing engine bay temperatures too.

>Getting 50hp from a 1.6L engine with exhaust mods

the drone is only occasional and doesn't really bother me. Even if it were worse it would still be worth it because the sound revving up from 0 to 60 is crazy good now.

I've thought about it but it probably would get me in trouble in my state

Ya'll need a lesson in exhaust theory.

As someone has already pointed out; an engine is an air pump, a system designed to allow for air flow. A system is only as good as it's weakest point.

So if you have a free flowing intake, and a restrictive exhaust, the system as a whole suffers.

Next you have flow vs velocity (larger diameter vs smaller diameter). Flow will allow the easy movement of air, but you won't have any back pressure to get it moving. So you have a gain of power up top, but a loss of power down low (great for track days). Velocity has a more restrictive path which allows for back pressure, which in turn gives more low end grunt, at the cost of high end flow (manufacturers want this so you feel the "giddy up and go" when you first start accelerating).

Then there's the Venturi Effect, where you mate a larger pipe to a smaller one with a defined transition point. This sort of allows the "ramming" of air (not to be confused with short-ram intakes). It's more like a way to get a lot of air, densely focused on a single point, but have a "buffer" or "pillow" of air behind it to give velocity down low, but flow up top (sort of a compromise in between).

Next up is Turbo vs NA. A turbo wishes to spool, which in-turn, allows for exponential growth of boost. So you let it flow as best you can. It has positive pressure compared to atmospheric.

NA (normally) only deals with atmospheric pressure (14.7). The only way to increase that, to allow for more air going through your air pump is to either make your pump "bigger", breathe "more", or breathe "better" (cubic inch displacement, rpm, volumetric efficiency)

This is because your engine is measured in Cubic Feet per Minute.

The formula for this is:
CFM = CID x RPM x VE รท 3456

The more air, the more fuel can be added to reach roughly around stoicametric (I think I'm spelling that right) of 14.7 parts air to 1 part fuel. Obviously it's harder to add air than it is to add fuel.

>back pressure

Oh look, somewhere I can contribute.

First of all:

>I see people saying like 5-10 hp increase for a $4,000 exhaust system, is that really worth it?


Actually, not just no, fuck no. $4k for 5-10hp? Even if that horsepower figure is true, that's a complete garbage return on investment. Most cars can be tuned for $500-1000 and with zero other mods pick up a solid 10-30 horsepower on an N/A car, even more on a turbocharged car.

The only time an exhaust system that expensive becomes worth it is if it's worth it to you otherwise -- a lot of the real nice systems are full stainless, high quality show piece stuff -- but largely moot for a street car. If it's sound and looks you want, without spending a ton of money, have a muffler shop swap out your mufflers with something more free-flowing and have them swap your exhaust tips out with what you want.

Next question, power. The thing to remember about the majority of cars is that when they leave the factory, the exhaust and intake are not a restriction. 90%+ of the time, those two systems are designed specifically to match the engine, maybe have a little bit of headroom so that they aren't a restriction. But if you have an otherwise stock car and swap out the exhaust, you're not going to notice any appreciable difference in horsepower. The only exception to this is exhaust headers, but again, this is situational.

Both exhaust (and intake) modifications are supporting mods. You get little/no power from them alone, but they allow you to get a little more from other mods like tuning, engine work, cams, etc.

Now you have your cylinddr head , which, I don't care what anyone says IS THE POWER PRODUCTION POINT OF YOUT ENGINE! So many people want power, but don't ever consider their head! Other than compression ratio and actual displacement, every other part of your bottom end is designed to handle power, not make it.

Springs and retainers are pretty much the limited of your valvetrains rpm, but you can rev the fuck out of an engine and go past your powerband.

Camshafts pretty much dictate the powerband of your engine. Do you want lower-end grunt? Mid-range power (most manufacturers like this), or high rpm capabilities? It's all based on your camshaft. Ofcourse, you also have different types of variable valve systems: VVT-i vs VTEC vs i-VTEC (just timing, just lift, timing and lift).

Valves can be reduced in weight, or changed in size with cylinder head porting to increase flow of... your...

...okay, I think you get it. Not gonna write a fucking thesis for you. Just do more research than some 16 year old kid saying "straight pipe is better!" Because a cat, a resonator, and a muffler have benefits as that a straight pipe will eliminate and reduce large portions of your powerband while giving minor gains to one specific portion.

Cat adds desirable back pressure.
Size increase allows for flow.
Resonators allow for sound frequency cancellation (think of it like your radios tuning dial to cancel certain sounds and amplification of others).
Mufflers allow for sound reduction (think of it like your radios volume dial).

M8 you should go and watch /Drive's "no more exhaust myths" video. The guy really goes into detail how choosing the right sizes can lead to exhaust scavenging, improving VE.

The reason (aside from 2smoke and that stuff) the backpressure is good myth still clings around is because when people straight pipe their car, they lose bottom end torque. Hence they think the backpressure was good for dem torks. What actually happened when the straight piped their car, was that they fucked up the OEM's exhaust scavenging. Look at motorcycle exhaust full systems. The proper bundle of snakes ones, or the ez pz V4 systems, can really open up ways to get more hp when tuned. Without proper scavenging, there's (relatively) more exhaust gas staying in the cilinder and based on the type of system, less clean air is being pulled in through help of the exhaust gas vacuum. That is one of the things used to bump NA VE up to 130%.

Tl;dr: EG temp, EG velocity, EG scavenging. One or more of the three is being fucked up leading to tork loss. Engines do not need backpressure. 2smoke need not apply

Don't forget about weight saving too

you have no fucking idea what you're talking about m8. please never post again.

You're right in everything except the back pressure part. The scavenging you're referring to is caused by pressure waves rebounding which is to do with primary length alone. It has nothing to do with back pressure.

*Primary length and matching cylinders so they don't interfere with each others pressure waves at the collector (systems such as Tri-Y, Bundle of snakes, 4-2-1 etc)

on a shitbox with a tiny 1.6 no but on a big v8 replacing this with a set of nice headers and a decent exhaust it could

Holy shit, that is aweful. Good luck.

lol this is such a generic bullshit statement.

What if your car has amazing headers from factory but 3 cats and the most god awful exhaust routing in history.

What if your car can be retuned to boost up to 400hp but the stock exhaust system is 2.5"

Nearly all mods are a case by case basis but universally breathing mods are generally the cheapest return on investment and labour time and often can net large weight savings relative to effort spent too.

No exhaust system costs $4000, most """tuner""" cars can have full T304 systems for about $350-500 for the decent stuff and even OVERNIGHT JDM PARTS are like $1200 max.