YACT: headers

Goosemaster

Lifer
Apr 10, 2001
48,775
3
81
Let me get this straight.

Hearders are tubes put in place to prevent backpressure in the exhaust manifold when it comes out of the cylinder, right?

WTF is with People and their sensationalism of these thigns then? Do they really make a differnce? THey are just TUBEs, right? Shouldn't the initial connector on the eshaust manifold be the only important factor. Obviously you have to then run those tubs to the Catalytic Convertor and the muffler, so they can't decrease i nsize as to create back pressure....$$$


Basically, what kind of performance increases or increases in overall engine efficiency do you see?

BTW< I have beater right now, so I am only asking to learn, not to apply....then again, a Honda accord with tubes all over the place...hmmm...lots of possibilities...:cool:


<----nnoB to cars...AKA knows nothing AKA ignant Bastid


 

BornStar

Diamond Member
Oct 30, 2001
4,052
1
0
The headers replace the manifold. They reduce backpressure by giving each cylinder essentially it's own path down the exhaust. Eventually they connect in a diameter where the cross sectional area is equal to the sum of the areas of the other tubes.
 

Eli

Super Moderator | Elite Member
Oct 9, 1999
50,419
8
81
An engine is a pump.

ANYTHING you can do to increase the flow of air in, and exhaust out, will increase efficiency and therefor power and performance.
 

Kadarin

Lifer
Nov 23, 2001
44,296
16
81
Headers do not prevent backpressure, but properly designed ones will reduce backpressure by providing for a smoother, cleaner flow path for exhaust gas to get out of the cylinder and out into the exhaust pipe. Generally speaking, the narrower and longer each individual tube, the higher the velocity of the outgoing gas, and the more torque the engine will make at a lower speed. At higher rpms, total volume comes into play, and the header reaches an upper limit as to how much gas it can move. Top-end power can suffer if the header itself becomes the limiting factor (not likely on a riced-out Honda). On the other hand, an engine with an excellent intake, cylinder heads that breathe well at high rpm, and a cam that is designed to make power at higher rpm will benefit from a header (or pair of headers) that have a larger tube diameter and shorter "primaries", the individual tubes that come off each individual exhaust port. The larger pipe diameter means slower gas velocity which translates to lower bottom-end torque, but increased top-end horsepower on the right setup.

A *very* common misconception is that "some backpressure is needed for good low-end torque". This is not true: Backpressure is exhaust gas pressure that acts as a force against the piston rising to TDC on the exhaust stroke. Reducing backpressure adds power and torque. However, (and this is a BIG however), reducing backpressure at the expense of exhaust gas velocity WILL reduce low-end torque. The reason for this is that high exhaust gas velocity out of the exhaust port has a big effect on reducing gas pressure inside the cylinder during the exhaust stroke, resulting in improved torque at lower speed. To put this concept into very simple terms, you will most definitely NOT gain any low-end torque by sticking a potato in your exhaust pipe in an effort to increase backpressure.
 

Eli

Super Moderator | Elite Member
Oct 9, 1999
50,419
8
81
Originally posted by: Astaroth33
Headers do not prevent backpressure, but properly designed ones will reduce backpressure by providing for a smoother, cleaner flow path for exhaust gas to get out of the cylinder and out into the exhaust pipe. Generally speaking, the narrower and longer each individual tube, the higher the velocity of the outgoing gas, and the more torque the engine will make at a lower speed. At higher rpms, total volume comes into play, and the header reaches an upper limit as to how much gas it can move. Top-end power can suffer if the header itself becomes the limiting factor (not likely on a riced-out Honda). On the other hand, an engine with an excellent intake, cylinder heads that breathe well at high rpm, and a cam that is designed to make power at higher rpm will benefit from a header (or pair of headers) that have a larger tube diameter and shorter "primaries", the individual tubes that come off each individual exhaust port. The larger pipe diameter means slower gas velocity which translates to lower bottom-end torque, but increased top-end horsepower on the right setup.

A *very* common misconception is that "some backpressure is needed for good low-end torque". This is not true: Backpressure is exhaust gas pressure that acts as a force against the piston rising to TDC on the exhaust stroke. Reducing backpressure adds power and torque. However, (and this is a BIG however), reducing backpressure at the expense of exhaust gas velocity WILL reduce low-end torque. The reason for this is that high exhaust gas velocity out of the exhaust port has a big effect on reducing gas pressure inside the cylinder during the exhaust stroke, resulting in improved torque at lower speed. To put this concept into very simple terms, you will most definitely NOT gain any low-end torque by sticking a potato in your exhaust pipe in an effort to increase backpressure.


Bwhahaha... :D

Nice post.
 

Compton

Platinum Member
Feb 18, 2000
2,522
1
0
I just ordered some headers, I'll let you know if they make a difference.
 

CraigRT

Lifer
Jun 16, 2000
31,440
5
0
Originally posted by: Compton
I just ordered some headers, I'll let you know if they make a difference.

as well am putting a longtube header on my car before summer
 

DougK62

Diamond Member
Mar 28, 2001
8,035
6
81
You can get huge gains from headers depending on the application and how restrictive the stock manifolds are. The GM 3400 V6 (a relatively small engine) dynoes a 15+whp gain with some well made headers. That's insane. I've seen V8's get upwards of 50whp.

 

JulesMaximus

No Lifer
Jul 3, 2003
74,537
916
126
Headers do make a difference and cheap headers are not worth your money IMHO. I bought a 2 year old Mustang GT in 1996 and the previous owner had installed a pair of MAC headers which were individually flanged (meaning each tube had its own flange that bolted to the heads individually). They kept leaking and I must have had the gaskets replaced 3 times before I finally ordered a pair of Ford Motorsport shorty headers. These really made a difference in performance-I noticed an increase in power off the line and the engine sounded more throaty. I think the MAC headers were actually hurting performance because of the way they were designed, they were probably no better than the stock manifolds (but hey, they looked pretty! Nice shiny chrome).
rolleye.gif


Many cars come from the factory with a heavy steel exhaust manifold/manifolds. They reduce the amount of space required for the engine because they generally tuck in real close to the side of the engine and they cost less than a good set of headers. They also use cast steel and are very thick and heavy to help control heat buildup in the engine compartment. There are better ways to do this though even with tube headers through the use of high tech coatings.