FC3S Header Talk

[Whizbang]

Who makes the best header for the 13B in our second generation cars? I hear a lot of this and that about what design is better over another, but rarely any proof.

[TehMonkay]

SDJ was the best but rotary innovation went under however another person bought the rights to reproduce it, they're on rx-7 club.

[farberio]

And they don't make them.

There are a couple of sources for headers, the question you should ask is do I want to pay the money for them? You are talking $500-700

[TehMonkay]

Last i checked they made a couple of one offs for the right price.

[need RX7]

Anyone know anything about what design elements (pipe diameter, length, bends, etc) make for best torque/horsepower, and optimizing powerband and stuff like that? Like for someone who was going to fabricate their own?

[farberio]

Originally Posted by TehMonkay

Last i checked they made a couple of one offs for the right price.

I called a couple of times and they said they were too busy to make any.

[farberio]

Originally Posted by need RX7

Anyone know anything about what design elements (pipe diameter, length, bends, etc) make for best torque/horsepower, and optimizing powerband and stuff like that? Like for someone who was going to fabricate their own?

A lot of it has to do with your own car, port types and the like. R&D is everything.

There is some good info here, just ignore the flywheel junk.
http://www.rx7club.com/showthread.php?t=801325

[Flooder]

Racing beat. Nuff said.

[Fidelity101]

Well I answer your question with another question. How long is a piece of rope? It depends...

Originally Posted by fidelity101

okay you want to get use of scavenging in your exhaust system, primarly the header by a low pressure area created in the exhaust system that can be used to "draw" the exhaust out the chamber. I know how to explain how reversion works on a piston engine but I'd have to look into it further for a rotary. BUT if you reduce reversion you increase volumetric effeciency and power so you basicaly build your header for RPM range.

now you want low power? then you need to utilize equal length tubing with a maximum variation of +/- .5" the bends (as long as they aren't crush bent or 90 degree bends) won't affect the flow, the length and tubing size will. By going from a 2.5" (outer diameter) primary pipe to a 2.0" (outer diameter) primary pipe you increase the exhaust velocity speed providing more low end power since you want the smaller tubing to maintain a high enough velocity when there is less exhaust volume at lower RPMS.

have you considered thermal coatings or wraps? With thermal coatings you can use those to retain heat in the exhaust system since as the gases cool they loose velocity, velocity increases scavenging at high speeds and reduces reversion (reverse flow at low RPM) and not to mention reduce underhood temp so you can get cooler air into your intake for MORE POWA! Thermal wraps do a better job but I wouldn't recommend them for a street vehicle since they tend to retain moisture and will rot your pipes alot faster.

smaller pipes better low-mid range power, so basically from going to a larger pipe to a smaller pipe you move your power curve more over to the left hand side of the graph (X axis is RPM, Y axis is exh velocity or power) steeper slope.

you generally want to keep around 240-260 feet per second when an engine is operating at peak torque.

to calculate the pipe size you need there is a formula

1. desired RPM at which max tq is to be produced
2. multiply CID of one cylinder (or rotor)
3. divide by 88200
the result is cross sectional area of the pipe required

4. now divide that by 3.1412
5. take the square root
6. multiply by 2
the result is the necessary inside pipe diameter.

by changing the pipe size you shift the torque curve around by going from a larger pipe to a smaller pipe your causing the engine to take away torque from one RPM and add it to another.

increasw the length, adds tq below to engines tq peak, and vice versa.

the lower RPM range the header is required to work the longer the pipes need to be.

you can also use a collector to produce more tq below the peak but will decrease tq after the torque peak, typically you want your collector to be 3/4" bigger than your primary pipe diameter.

hope this helps!

You can build a flow bench for pretty cheap and there are instructions online.

[farberio]

Originally Posted by Flooder

Racing beat. Nuff said.

Racing beat is ok...for a stock car...

I would not call it a great header or the end all be all header. However, it is cheap and readily available which makes it a popular choice.

[Flooder]

Most people who buy the header are putting it on stock cars/daily drivers. If anyone builds a serious track car, where every horse power matters, it's usually a turbo setup.

[farberio]

Which by no means makes it a good header, only a good choice for most people.

[Max777]

Originally Posted by Flooder

Most people who buy the header are putting it on stock cars/daily drivers. If anyone builds a serious track car, where every horse power matters, it's usually a turbo setup.

Unless they run in the ITS class, for which, at least as far as I recall, the turbo setup is illegal?

correct me if I'm wrong please.

EDIT: At least I remember reading about some class for Second Gen RX-7's that stated the engine has to be N/A and ecu only has limited tuning done to it....

[farberio]

I am not familiar with all of the rules, but I do know that AWR's header is designed specifically for ITS class.

[TehMonkay]

ecu must stay in the same case, which is why the rtek is used

Ports and intake manifold must stay the same.

It's all in the exhaust and tuning.