Main exhaust bottleneck? In my opinion the whole thing.
First I made a po'boy air intake Z tube, I felt a little more HP, probably
mostly do o the colder air. Next I replaced the cat back exhaust system to
a single 3" and found that to increase throttle response AND torque
substantially. Then I replaced the intake and Throttle Body with a real Z
tube and F&B TB. Throttle response went way up, HP went up on anything
above 2K RPM, but low (really low) end torque diminished a bit. I wouldn't
recommend that last one if your looking to tow a lot. I have a set of JBA
headers in my bed room that I'm not sure if I'll ever get to put on, but I
suspect they'll have the same effect as the TB change.
I think there's 3 cats on 4.7Ls (except 2000 non-cali daks). one on the end
of each header then one further downstream after they've merged.
Jay W
505/287 Dakota
>Date: Wed, 29 May 2002 10:02:01 -0500
>From: "crm" <tb.crm@verizon.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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