This is one reply in an interesting discussion on the Megasquirt EFI list for
anyone considering an exhaust system upgrade........
----- Original Message -----
From: Jim
To: tuning@msefi.com
Sent: Wednesday, August 29, 2007 4:56 PM
Subject: Exhaust backpressure vs. MAP
Hey Scott , you are inadvertently spreading old wives tails .
Reducing "exhaust back pressure" is not the whole story ,
exhaust tuning starts to come into play with a properly designed
exhaust system .
You can have 2 different systems ,
and each will have it's own personality and require a different tune ,
even when both have virtually no measurable back pressure ,
and either one will probably make more torque after re-tuning than a
system that does have back pressure .
And BTW , one of them may only marginally boost low-end torque ,
and the other may boost it so much that the engine will knock without
ignition advance changes .
Both ignition and mixture requirements will change to one degree or another .
A "low back pressure exhaust" does not necessarily reduce low-end torque ,
it might , with a completely stock factory tune ,
but after re-idealizing the VE Table and Advance Table you will
probably have a nice boost across the board .
"Exhaust back pressure" is never "necessary" and
never increases torque all by it's self ,
unless you are limited to a fixed factory tune that was specifically designed
for a particular combination with a certain amount of back pressure .
Installing a properly tuned exhaust system is , and always has been ,
the most cost effective power increase that you can get ,
and is always the recommended first step for increasing engine power
since any other method of increasing power will
put more flow through the already restrictive stock exhaust system .
Many late model cars have had a serious amount of factory R&D done on
their exhaust system ,
so the exhaust manifolds are sometimes better than
any set of headers you can buy ,
but the rest of the system usually still leaves lots of room for improvement
.
...................Jim
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'95 GM 4.3 Vortec V-6
Single Plane Intake w/ported GM TBI Injection
Ported Heads , stock roller cam retarded 8 degrees
MS-II , V-3 board , v2.871t7 Beta Code
EDIS ignition , Innovate WB-02
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This post is at:
http://www.msefi.com/viewtopic.php?p=178363#178363
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