Which type do you all think and recommend? I have heard that 4-2-1 gives better number in the midrange. 4-1 gives better number up top.

Thanks,
ARLY

 

My recollection is that a 4 to 1 provides more back pressure (i.e., torque), so should provide more low to mid range punch. And 4 to 2 to 1 is more free flowing so provides more rpms for a higher top end. :smile:

 

Concur, Jaz. At least that's the way it worked when I was building 14,000 rpm race bikes. 4-2-1 builds high RPM hp, while 4-1 builds midrange torque.

 

So why are most race headers use 4-1 headers? That is because racers want power up high correct. I've been checking on race headers and I see that is what most opt for when racing. Any thoughts anyone?

Thanks,
ARLY

 

Since I don't autocross and have no desire to drive around town in the top third of the rpm band. I choose my modifications to enhance mid-range rpm. Should I ever buy a header, I will be a 4-1.

I can see why autocrossers would want a 4-2-1, though. And if I were building an autocross car, I would opt for the 4-2-1.

 

I'm not an engineer and I knew very little about exhausts.... but I was thinking the other night about this. Rather, I was thinking about a 4 - 2 exhaust. The exhaust tunnel running the length of the car could handle two pipes, so why not have a true dual exhaust system?

 

Someone needs to do a shootout on the same car using a consistent dyno:

Stock Header > 4:1 > 4:2:1 > Stock Header

Positive results for any headers have been sketchy to say the least.

There is a huge amount of theory that goes into header design, but little of it is bourne out in practice.

 

ain't that the truth... velocity, density, temp, boundry layers... so many variables... good exhaust systems are also engineered to evacuate spent gasses while "pulling" the incoming fuel/air charge into the cylinder at just the right velocity to completely fill the cylinder without overshooting into the exhaust. 'Course cam timing plays a part in that as well, and is a great reason to "degree" one's cam... but that's another topic.

 

Really, the best way I can think of making a header is to build an exhaust flange that bolts to the head that has stubs coming off it. Clamped onto the stubs are pipes of several different lengths with several different collector designs. An engine dyno with a normal, healthily modded MCS engine would provide the builder with feedback on what works and what doesn't. Of course, once a nice design is found and built, it will be quickly copied by Megan Racing and sold on eBay for pennies.

 

There's some really cool discussion in these two tech articles:

http://www.burnsstainless.com/TechAr...ry/theory.html

http://www.burnsstainless.com/TechAr...struction.html

Running two tubes down our tunnel might be possible, but they would need to be about 1.25" max diameter each. I'm at 2.5" all the way back, and even with some minor elevating, I hit the top of the tunnel...

 

To maintain the same effective hydraulic diameter, the twin tubes would need to be even bigger than that since the area of each pipe would be smaller than half the size of the single pipe.

 

That's right !! 4-2-1 gave better TQ at midrange...but 4-1 did make you more exciting at higher RPM...how ever it depand what driving habbit you pursue..