So what the difference between short, medium, and long headers and which is the best?

Also one another question is about the cat back (I know it's not on the header lol) but what are the gains/losses of not having one and having one?

 

well... i'll shorten the other 345344545 threads about this for you.

generally, the longer the tube, or the larger the diameter of the pipe, the higher in the powerband you will see gains.

for example, a shorty might give you the largest jump at 4000 while a long tube may be be best for above 7000.

same with the size of the pipe, the larger the diameter, the happier it will be at high RPM.

with a cat back, it's really 90% sound. with a header/dp, you'll get a little more out of it, but don't expect a total kick in the ass.

 

Your right about the larger pipe diameter, but I believe that longtube headers actually make more low end power due to resonance.


I got this off an exhaust fabricators site:

"There are many ideas about header pipe sizing. Usually the primary pipe sizing is related to exhaust valve and port size. Header pipe length is dependent on wave tuning (or lack of it). Typically, longer pipes tune for lower r.p.m. power and the shorter pipes favor high r.p.m. power. The collector package is dependent on the number of cylinders, the engine configuration (V-8, inline 6, etc.), firing order and the basic design objectives (interference or independence). The collector outlet size is determined by primary pipe size and exhaust cam timing."

 

thats a great thing to point out.

 

I can assure you it's all fine and dandy in THEORY, but when you get to building a header all the theory goes out the window.
The best part is that you can have all the design tools in the world at your disposal and just putting a piece of crap formed collector on the header will negate all the effort.

Everything you have ever read about production headers is 80% B.S. and only 10% solid truth. The other 10% is dumb luck.

With that in mind the best header is the one that was independently dyno proven to make the most power for the given modifications you have on your car.

Don't listen to all the people and companies that want to sound like they know WTF they are talking about with length, ID, material, exit diameter, etc. unless they have an independently dyno backing up all the hype.

Case in point: The same people who wanted to sue a header company last year dynoed that header and it made 15 HP across the board on the LSJ. In this case design had a lot to do with it, but price and failure to deliver product in a timely manner did the product in.

Screw what the people say look at the dyno charts - beyond that it's hype.

 

so what hearder do you recommend then?

 

Yea, I'm curious as well.

So next dum question too, is running high or low rpms the best?

 

That really depends on you. Where do you want the power? Low end for a better pull at lower rpms on the take off or high end for a stronger pull at higher rpm range and higher speeds. For example, if you plan on auto cross then low to mid range power would be best for coming out of turns, curvy areas, and when you won't be going into long straightaways. High end power would be best for going straight, granted you have enough space to get to high speeds, so your peak power won't drop off early and you'll be able to continue picking up speed easier than a car with low end power, which would struggle at high speeds and possibly top off earlier. So it all just depends on what you want to do with it.

 

come to think of it ive never seen any dyno comparisons on headers before... it would certainly make it easier to decide...

 

you're not likely to either. the only semi-fair way to do it would be to take a car and try like 5 different headers on the same car, same day. and, well, that's just a big pain in the *****.

 

yeh... oh well, they did one for the vibrant here

https://www.cobaltss.net/forums/modern-performance-81/dyno-test-vibrant-headers-cobalt-ss-78019/

but thats the only one ive seen.

 

Would you recommend a 3'' or 2.75''? Whats the benefts and loses for the 3'' compared to a smaller hole?

 

i wouldn't get a 3", you would lose too much back pressure because the 2.4 isn't boosted. Something around 2.5 would be best.

 

for you all who worry about backpressure so much
http://www.uucmotorwerks.com/html_pr...torquemyth.htm
its not a problem if you get your car properly tuned after re doing your exhaust system.

 

What happens if I decide to drop in a supercharger or turbo? The purpose of this thread is to see if I should wait to do a header and dp untill after I do a mod like that. I don't want to buy one thing then need a new one after I put in either a SC or turbo.

 

imo, if you plan on upgrading to forced induction, you should do that first. worry about other things later.

 

Alright that was the answer I was looking for, thanks!

 

ok, I have a supercharged model. it is totally stock right now, but i am doing alot of upgrades to it. i know once i upgrade it i will need the 3" but if i put the 3" on it stock will i be ok?

 

header/dp is the most restrictive part of your car... with your sc you should be able to use those 3" pipes. but id look into replacing that air box too.

 

Just to reiterate this. You can all post ever link to every word written on the internet by every magic tuning master from Smokey Yunick to Mike Kojima, but until they produce a dyno proving that the header you want for your car did in fact produce the stated results it's all B.S. Mike Kojima ironically did in fact design a header that produced 20 HP over stock on a SE-R and backed it up with dyno results.

My stated performance results were from a header that had only a 2.5" opening at best.
It's not the size of the exit that makes or breaks the header it's the velocity of the exhaust gas - something that no formed collector can maintain. 3.0" opening is not necessarily better, especially if it slows down the exhaust creating a low speed or back pressure zone.

 

already done!

 

sweet