Three CATS. One main CAT on the exhaust line and one after each
short-manifold (for CA CARB emission vehicles).
I would cautious those who add headers without replacing the CATS with the
HI-FLOW version. The standard CATS will not last and will burn out the
internals.
However, the first change is the air intake, thermostat (180), and plug
changes to one colder. Once this is accomplished, then either add the JET
CHIP Stage II or have someone modify your ECU unit. Next is the TB unit and
exhaust (3 inch). I usually go with the one inch per hundred HP range on
single exhaust system. If you can find someone to replace your CAT, go with
the hi performance 3 inch version. Then apply the JBL headers. Remember the
key word is BACK PRESSURE. To much exhaust and not enough back pressure
will rob your vehicle of power.
You will be pushing the truck from the normal 18XHP at the wheel to 20X
without adding the exhaust system.
When it comes to flow dynamics (exhaust size), talk to Bruce Bridges.
--------------------------------------
Steven St.Laurent
C4i System Engineer
C4i Engineering Branch, PSD, MCTSSA
MARCORSYSCOM, U.S. Marine Corps
Office (760) 725-2506 (DSN Prefix: 365)
"Never be content with somebody else definition
of you. Instead, define yourself by your own beliefs,
your own truths, your own understanding of who
you are. Never be content until you are happy with
the unique person GOD has created you to be."
-----Original Message-----
From: crm [mailto:tb.crm@verizon.net]
Sent: Wednesday, May 29, 2002 8:02 AM
To: dakota-truck@dakota-truck.net
Subject: DML: Exhaust bottleneck?
Hello all,
Can someone pinpoint the main exhaust bottleneck for a 2001 Dak QC with a
4.7? After doing a lot of reading (here and elsewhere), I seem to be running
into 2 or 3 differing points. One the one hand, many seem to suggest a new
muffler will really free up the exhaust. One the other, I have heard that a
new muffler wont do much because the main bottleneck is at the cat. And then
on the 3rd "hand", I have read that if you dont replace the stock 2.5" pipes
with a 3" catback, neither hi-flow muffler nor hi-flow cat will help. And I
guess to round it all out (4th hand), I've heard that the 3" pipes will rob
you of low end torque, which is what you need for towing and the like
correct?
If it makes a difference, I dont use the truck for towing. Mainly for
driving to work and around town and the occassional day trip. No racing,
other than the normal youthful exuberance on the freeway or at the light.
Basically, I am not looking to build a mean street rod or anything, just a
truck that can sh*t and git if I tell it to.
I dont want to spend money for the same thing 2 times, so I want to make
sure I do it right the first time. I just ordered a Z-tube last night and if
I can figure out what's best I hope to get some exhaust work done this
weekend. I'd like to use stock pipe if possible and avoid getting a whole
new catback system until later on.
Also, is it correct that the 4.7 Dak's have 2 cats? Like a pre-cat and then
a main cat?
Thanks in advance!!
-adam
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