Low resistance headers - why don't manufacturers put them on as standard?

[fuzzybabybunny]

I've always wondered... why don't low resistance intake and exhaust headers come standard with stock cars? Wouldn't they give cars better mileage and power? They wouldn't be any more expensive to make and design, would they? I know nothing about cars.

 

[Andrew1990]

I believe it is due to higher emissions.

 

[Arkaign]

In no particular order (if I understand this to be describing high-flow intake and exhaust systems) :

* - noise
* - emissions
* - lack of effect (many/most stock setups do nothing but make more noise with more open intake/exhaust)
* - baffle(s) for protection against water or loose debris (these are features in virtually every stock intake system but typically reduced or deleted in performance aftermarket conversions

In short, for the most part a particular setup can be tuned to give a little more power when combined with a professional tune and good aftermarket parts, but fuel economy doesn't get affected much (probably the opposite due to heavy-foot syndrome with a nicer-sounding more responsive car, lol).

 

[angry hampster]

It also depends on the motor. The late model Jeep 4.0L does not benefit from a header, the stock steel tube unit is very good.

The VR6 in my GTI is the same way. A ridiculously expensive header and a whole weekend of work might net me 1-2HP.

 

[fuzzybabybunny]

Ah... I see. So would you say that for the most part low resistance intakes are a waste of money if you're going for performance gain?

And how would a low resistance intake increase emissions? More air in -> greater amount of fuel burned -> more emissions?

 

[Bignate603]

It also depends on the motor. The late model Jeep 4.0L does not benefit from a header, the stock steel tube unit is very good.

There is a benefit to the aftermarket headers on the 4.0 but not anything to do with extra power. The stock headers on the XJ tends to get cracks over time, a high quality aftermarket replacement is less prone to cracking. I wouldn't be surprised if the TJ has a similar issue.

 

[Zenmervolt]

Ah... I see. So would you say that for the most part low resistance intakes are a waste of money if you're going for performance gain?

And how would a low resistance intake increase emissions? More air in -> greater amount of fuel burned -> more emissions?

Both intakes and headers, unless the stock setups are horrendous due to packaging concerns, are really only beneficial under wide-open-throttle. (Turbocharged cars are an exception here as a good aftermarket exhaust can allow the turbo to spool faster, but that's a special case.)

Intake design is dictated largely by acoustic concerns once a basic amount of airflow is met. You'll notice that most stock intakes include extra chambers that go nowhere. These are resonators that are used to reduce the intake noise that is generated at certain combinations of RPM and throttle opening. Most of the perceived increase in power from aftermarket intakes comes not from actual power gains but from the noisier nature of the aftermarket intake. People interpret more noise as "faster" on an almost instinctual level.

ZV

 

[SSSnail]

A lot of new cars nowadays are already at their peak efficiency with regards to the intake and exhaust for the engine they come with. It's not uncommon for people to install aftermarket equipments and lose powers.

The aftermarket parts would only improve performance if the engine itself has been enhanced, through either combustion or volumetric efficiency.

 

[exdeath]

1) Cost.

2) Headers sometimes cause issues with O2 sensors (warm up time or something) which alters emissions and fuel economy. Sometimes little things like that makes the difference between 22 MPG or 23 MPG and avoiding gas guzzler fees, etc.

3) OEM parts are designed to be adequate for a specific power/RPM target and give good average power over the whole curve. Changes to intake and exhaust alter the volumetric efficiency of the engine over different RPM ranges, and move around power in the RPM range often at the expense of other regions. Also on well tuned engines to begin with, such modifications do little by themselves unless they become a restriction to much larger modifications that actually increase the flow demand of the engine (eg: boost).

4) Assembly. Installing long tube headers is a human labor intensive process, requiring careful routing above, through, and below other parts. You can't pre-assemble an engine with long tube headers and drop it in the car with a robot. Parts spec'ed out for a production car have to consider the entire picture; delivery logistics, manufacture time constraints (cast manifolds can be mass produced in large volumes), assembly packaging, etc.

5) Headers = bad ground clearance usually and unsuitable for 99% of people who buy the car and never modify it.

6) One size fits all; some cars require things like different clutch housings and remote oil filter adapters to fit headers on them. More unnecessary expense and extra parts logistics when trying to meet a price point and delivery time frame.

Some cars do come from the factory with tubular headers. The E46 M3 for example. However that is also a highly tuned engine from the factory that leaves very little on the table to find any power with aftermarket parts. That engine is pretty tapped out and sees next to nothing in gains without adding a turbo or supercharger.

The same will be true with the new 5.0 400 HP Mustang V8. It's one thing to take a junk 190 HP 5.0 liter engine and add parts to it to get 400 HP. But when it already comes with most of those parts to make 400 HP from the factory, you're not going to be able to do a simple intake/exhaust and see any gains, as most of the bolt ons and tuning where already done for you.

 

[MotF Bane]

Both intakes and headers, unless the stock setups are horrendous due to packaging concerns, are really only beneficial under wide-open-throttle. (Turbocharged cars are an exception here as a good aftermarket exhaust can allow the turbo to spool faster, but that's a special case.)

Intake design is dictated largely by acoustic concerns once a basic amount of airflow is met. You'll notice that most stock intakes include extra chambers that go nowhere. These are resonators that are used to reduce the intake noise that is generated at certain combinations of RPM and throttle opening. Most of the perceived increase in power from aftermarket intakes comes not from actual power gains but from the noisier nature of the aftermarket intake. People interpret more noise as "faster" on an almost instinctual level.

ZV

So that's why idiots put fart cans on their shitboxes.

 

[HannibalX]

Because they fvcking leak!

 

[bmaverick]

Nearly all pre-OBD-2 cars do better with performance exhaust. The dumb OBD-2 computer gets messed up if the exhaust is changed. Or you buy the performance exhaust and get the PCM a performance chip... That's about it.

My camaro is ODB-1 so I got the performance exhaust and K&N performance intake. Hp is noticeably increased and the throttle response is so wicked now.

My next power boost is going from 16psi to 17 psi injectors while side gaping the plugs. That may be it for me because the engine would redline smashing the pedal down to the floor and holding it then.

 

[OS]

I think the reasons are well covered already, i want to note again though the manufacturer aslo tunes the motor across the entire rpm range and throttle loads.

 

[Zenmervolt]

Nearly all pre-OBD-2 cars do better with performance exhaust. The dumb OBD-2 computer gets messed up if the exhaust is changed. Or you buy the performance exhaust and get the PCM a performance chip... That's about it.

This has nothing whatsoever to do with OBD-1 vs OBD-2 or anything like that.

Any EFI computer is "expecting" certain flow characteristics for an engine. If you change those flow characteristics, you need to re-map the tables in the EFI computer to account for those changes or else the engine will not run as well as it could.

My own weekend car, for example, is a 1986 944 Turbo. This is well before OBD-1, let alone OBD-2, yet in order to allow it to run properly with my mild modifications, I had to replace the eeprom with one that used tables built to handle the modifications I've made. My EFI Harley (which is also non-OBD-2 as motorcycles are not subject to OBD regulations) likewise required re-mapping the ECU for the engine to run properly after replacing the exhaust and the intake. It would have run very lean had I not replaced the mapping tables with ones designed for the new parts.

OBD-2 or not, if a car is EFI and you do anything that makes a significant difference in the amount of air you can flow through it, you need to re-program the ECU. If you don't, you're running a very large risk of having your mixture off by a dangerous amount.

My camaro is ODB-1 so I got the performance exhaust and K&N performance intake. Hp is noticeably increased and the throttle response is so wicked now.

If there is any significant difference on a dyno (which experience tells me to doubt from just a K&N and an exhaust unless you went all-out with long-tube headers), then chances are you really are in need of a proper tune. I'll almost guarantee that your mixture is off.

My next power boost is going from 16psi to 17 psi injectors while side gaping the plugs. That may be it for me because the engine would redline smashing the pedal down to the floor and holding it then.

Uh... Fuel injectors are rated by flow rate (i.e. lb/hr), not by delivery pressure. Raising the line pressure can increase the flow rate of a set of injectors as long as you're within the acceptable range for the injectors, but if you walked into an auto parts store and asked for "17 PSI injectors" they'd either look at you funny or outright laugh.

Furthermore, 17 PSI is incredibly low for an EFI system. Typical EFI fuel pressure is 35 to 45 PSI at the fuel rail. If your car is only getting 16 PSI at the fuel rail, it's a miracle that it can even idle.

As far as side-gapped spark plugs, that's an old wive's tale. An electric spark will always take the fastest path to ground. You won't get a larger or a more powerful spark by side-gapping your plugs and you won't see any power increase. It's just as much BS as the "+4" plugs or "Splitfire" plugs. A good, old fashioned, copper plug with the proper gap will do just as well.

ZV

 

[LTC8K6]

I'm going to guess that he has an older TBI Camaro...for which those PSI numbers would be correct. However, it is still the flow rate in lbs/hr that is important.

 

[bruceb]

On newer computer controlled engines, emissions can still be met with better intakes and exhaust headers. All depends on where the O2 and Intake Air Temp sensors, along with where the Mass Air Flow sensor are located. They may need relocating for a car designed to have better intakes and exhaust. Main reason is many car owners, prefer a nice quiet car and do not want to hear the motor, like a lot of car enthusiests like to do.

 

[JulesMaximus]

Mainly because of noise, cost, and emissions. Contrary to popular belief most people don't want cars that make a lot of noise.

 

[alkemyst]

I believe it is due to higher emissions.

lol.

It's more to do with both added noise and complexity/problems.

 

[JulesMaximus]

lol.

It's more to do with both added noise and complexity/problems.

Well, many aftermarket headers are marked "off road use only" or "Not legal for sale or use on pollution-controlled motor vehicles." Mainly because the manufacturers don't want to go through the expense and hassle of getting them certified by the state...at least that's the way it is here in California. This is certainly true for some of the Ford Motorsport headers.

http://www.summitracing.com/parts/FMS-M-9430-P51/Application/?prefilter=1

 

[SSSnail]

All emission modifying equipments are illegal to use in California, unless they are CARB (CA Air Resource Board) approved.

 

[alkemyst]

Well, many aftermarket headers are marked "off road use only" or "Not legal for sale or use on pollution-controlled motor vehicles." Mainly because the manufacturers don't want to go through the expense and hassle of getting them certified by the state...at least that's the way it is here in California. This is certainly true for some of the Ford Motorsport headers.

http://www.summitracing.com/parts/FMS-M-9430-P51/Application/?prefilter=1

If it's the automaker putting them on at factory build, it's not aftermarket.

 

[Demon-Xanth]

It's primarily due to the fact that headers complicate the installation process and tend to get rather hot. Next up is cost, then noise.

 

[Kadarin]

All emission modifying equipments are illegal to use in California, unless they are CARB (CA Air Resource Board) approved.

Yep.

However, there are many 50-state legal headers for different vehicles out there where the manufacturer went through the CARB certification process to get an Executive Order (EO) number. On the '05 GTO I used to own, I had installed a set of JBA "shorty" style headers which had such an EO#.

Headers per se don't affect emissions all that much so long as they have provision for the existing emissions equipment (which typically means it has a fitting welded on for the oxygen sensor to screw into).

Most OEM car manufacturers don't use a very efficient tubular header due to cost (it's much easier and cheaper to cast the piece). Noise is also a secondary concern.

 

[Zenmervolt]

I'm going to guess that he has an older TBI Camaro...for which those PSI numbers would be correct. However, it is still the flow rate in lbs/hr that is important.

Absolutely right. That's what I get for not looking it up more extensively. Being a Ford guy, I tend to associate throttle-body injection with trucks and I didn't run all the way through. I did think that GM's TBI ran at closer to 13-14 PSI than 16-17 though, but you're probably more knowledgeable than I am about GM systems.

ZV

 

[Arkaign]

Absolutely right. That's what I get for not looking it up more extensively. Being a Ford guy, I tend to associate throttle-body injection with trucks and I didn't run all the way through. I did think that GM's TBI ran at closer to 13-14 PSI than 16-17 though, but you're probably more knowledgeable than I am about GM systems.

ZV

As an aside, this guy seems to have really gone through everything imaginable on those motors, and has a section that gives some great detail on ideals for performance :

http://www.tbichips.com/305mods.htm

"So what size injector or fuel pressure combo to use? Well here is a basic guideline.

305 up to 200hp the 305 injectors are fine. If you go more than that which pretty much a cam upgrade and exhaust will do then upgrade to the 350 truck injectors.

Stock 210hp 350 V8 up to 240hp the stock 55lb 350 truck injectors at the factory 9-12psi is fine.

from 240hp to 260hp the fuel pressure should be bumped up to 13-14psi on stock 350 truck injectors which will change their flow rating to 60lb/hr

From 270hp to 320hp you need to change the fuel pump as the stock pump can't maintain pressure over 270hp and you need to run 18psi on the 350 truck injectors for a flow rate of 68lb/hr

From 320-360hp this is where you should be looking at the 454 injectors and run them at the 13psi for their 82lb/hr flow rate. You can run them at the stock 9-12psi and still be fine for this power range.

From 360-400hp you need to bump the fuel pressure up on the 454 injectors to the 18 psi to increase their flow rate to 96lb/hr.

For over 400hp you really should be looking at alternative injection system but for up to 450hp you would need to run 24psi of fuel pressure to increase the lb/hr rating on 454 injectors to 112lb/hr and that is as much pressure as I recommend applying to a set of TBI injectors."