Edgefevah
New Member
- Joined
- Dec 21, 2012
- Messages
- 219
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- Location
- Calgary Alberta
- Vehicle Year
- 1993
- Make / Model
- Ford
- Engine Size
- 4.0L
- Transmission
- Manual
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Have you tried it yet?
There is often some confusion on how tuned exhaust systems work.
A tuned exhaust will produce negative pressure at the exhaust valves, so when exhaust valve first opens exhaust is pulled out, this lessens the load on the engine to push it out, highest negative pressure will occur at a specific RPM which can be tuned by pipe size and length, near this RPM will be the "power range" for that tuning, low-range, mid-range, or high-range.
Factory exhausts are tuned, for most part, for mid-range.
Add-on headers are usually tuned for low-range, but "Racing Headers" are tuned for high-range.
None of these add power, unless factory exhaust wasn't tuned, they just change when the highest negative pressure occurs in the RPM range and this is when the engine will have extra scavenged power, so you are not adding power just adjusting when the power occurs.
The low pressure is created by creating velocity in the smaller pipes at the exhaust valves, when the smaller pipe's flow gets to the larger "collector" pipe it creates a suction effect on the other smaller pipes connected to that collector.
So as each cylinder dumps it's exhaust it creates negative pressure at the other cylinders exhaust valves on that bank.
"H" and "X" pipes on dual exhaust systems are added for the same reason, to try and maintain lower pressure by scavenging the velocity in the system.
Back pressure myth comes from this negative pressure tuned exhaust.
For example, say there was a factory tuned exhaust on an engine using 1.25" exhaust pipe at the exhaust valves, and the owner decided to make a "free flowing" exhaust system and put on 2" pipes at the exhaust valves.
Result would be a loss of power.
Owners conclusion would be that this engine needs back pressure at the exhaust valves for best power............................but that isn't correct.
By increasing the pipe size and lowering the velocity, the owner, in effect, increased the pressure at the valves by eliminating the negative pressure, so lost the tuned exhaust benefit.
No engine, except 2-strokes, run better with back pressure, it is truly a myth
Hey gotta revive this old thread. I’ve recently inherited a truck that turned out to have the cat cut off. I do the have the remaining piping and muffler, just not the cat. The part you’ve created looks exactly like something I would need to replace the missing cat. Can you provide some more details on making of this marvel of yours? ThankView attachment 17935 so I got rid of my cats on my truck so I could put a high flow cat on it. Made this so that it was the oval part at the end of the y-pipe to 2.5" round exhaust piece. Might actually make some for anyone wanting to replace their cats with a higher flowing one.