I've been posting a few comments on exhaust, but most of it is theory
(proven in other applications). In general, there is a positive correlation
between exhaust pipe diameter and peak horsepower and torque. In other
words, small diameter pipe will place the hp and torque peaks low in the rpm
range, whereas large-diameter pipe will place the hp and torque peaks high
in the rpm range (plus give you higher peaks overall).
Same can be said for pipe length. Short pipes will give you lotsa hp, but
it will be higher in the powerband. Long pipes will give you less hp, but
it will be lower in the powerband where you use it in everyday driving.
This information applies to intake systems as well, with the same
relationships occurring. The real art is in perfecting pipe diameter and
length to take advantage of scavenging (or Ram-air effect in case of
intakes) to give you "free turbocharging".
Much of this info is available in the PowerPro Series book "How To Build &
Modify Intake & Exhaust Systems". It's an informative book for anyone
interested in learning all about intake and exhaust systems.
-----Original Message-----
From: brian duffey <brian.duffey@intelsat.int>
To: dakota-truck@buffnet.net <dakota-truck@buffnet.net>
Date: Monday, February 22, 1999 1:33 PM
Subject: DML: Exhaust Magic...
>O.K. All, I'll try to keep this brief… but unfortunately, this is not a
>Yes/No question. There has been much talk lately about exhaust systems,
>backpressure, HP gains & torque losses. I have been looking for a new
>exhaust and have (had?) decided on the Gibson Single Cat-back (truck is a
>'95/5.2L - Auto, 4x4,Ext Cab). I've seen a lot of comments that with a 2.5"
>pipe (or larger), the loss of backpressure would result in decreased
low-end
>torque. Can anyone give some real world examples and/or suggestions?
>
>I'll be adding the Mopar HiPo comp. at about the same time. Already have
the
>K&N open element FIPK and F&B Stage 1 TBI. Hopefully not too long after
>those mods, I'll have the Leach Headers installed.
>
>What is the diameter of the Leach Y-pipe going into the Cat? If I go with
>the HiPo Comp, Gibson Cat-Back, Leach Header route will my result be just
>top end gains, or can I expect to gain some low end? I really need to
>increase my low end. Up about 1800-2000 RPM onwards my DAK starts to move &
>runs great at highway speeds. What I need to gain is low end for 4x4 and
>also quicker starts off the line. As an alternative route, would getting
>just the Gibson muffler and having the pipes custom made at 2.25" be a
>better approach for my goals? (I'd still get the Gibson Slash tip - 3" -
for
>the finishing touch!)
>
>I understand the theory behind getting the airflow thru the engine exhaust,
>but it seems like finding the right back-pressure/flow rate is kind of
black
>magic. Any comments from those experienced in the Dark Arts?
>
>Thanks all & sorry for the long post!
>
>Duff
>'95 SLT 4x4 CC 318 4spd/OD - 3.55 LSD
>MSD 6AL - MSD Blaster Coil
>MSD 8.5 wires - K&N FIPK - F&B Stage I TBI
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