Header Extension - Define....

[Greg72]

I was reading the latest HOTROD magazine this weekend, and they had a header shootout in there.

They kept talking about using an 18" Header Extension as a way to fatten-up the bottom end torque of the motors. It looks like nothing more than an 18" section of tube that is the same diameter as the collector..... which makes me wonder: What makes that any different than simply having the exhaust (of the same diameter) bolted directly to the headers???

Is there something more exotic going on inside a header extension??

 

[dyeager535]

What you are doing with the "extension", which is really just lengthening the collector, is tuning the exhaust to compensate for the shrinking volume of the exhaust as it cools.

Most don't understand that at least for a "standard" engine, the exhaust system does not need to be the same diameter all the way back, and to get the most out of it, does indeed need to be "stepped down" properly to maintain good flow. Poor flow anywhere equals a loss of efficiency.

The gains are probably fairly small, so applicable to racing more than day to day use, BUT, if you look at the cost of tubing and what not, if you were able to go from 3" to 2.25" (for a made-up example) you'd also realize cost savings, as well as reduced noise.

Pretty certain Vizard explains it here:
http://www.popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/index.html

To me it would be interesting to see how quiet you could make the vehicle interior necking the exhaust down, while keeping power production the same or better. Of course, I don't think many, if any of us, have the resources to accomplish the sort of testing it would take. Ignoring the fact that every engine is going to want something different.

For wheelers that would also mean more ground and drivetrain clearance.

 

[Greg72]

Thanks for the link!

That article has some great info.....unfortunately Fig 9. (the ultimate exhaust setup for power) is a thumbnail .jpg that is too small to read!!!

I like the concept of 2.2CFM per HP as a measure of exhaust flow requirements. I don't know how many muffler manufacturers spec CFM in their literature, but I'll check it out. I also was interested to see how a large inlet diameter muffler can be coupled (with a reducer) to a smaller exhaust system to prevent loss of flow once the pulses hit the muffler.....

Any idea where I can find "resonator boxes"????

More research.....more reading....

 

[dyeager535]

Any idea where I can find "resonator boxes"????

I wonder if those are not what you are now seeing on some OEM applications, maybe they aren't called that though. They look like the newer catalytic converters to me, cylindrical, larger diameter than the pipe that feeds them.