RE: 1.6 rockers v.s.TB mods,was:Magnum Performance Throttle Body?

From: Holloway,Frank T (Frank.T.Holloway@kp.org)
Date: Sun Aug 30 1998 - 14:55:26 EDT


In regards to the rockers in your Magnum engine, the ratio is already 1.6 so
changing to the aftermarket 1.6 ratio won't change lift and duration. The
1.7 ratio
rockers give you approx. 10 degrees additional duration and approx. .020 -
..025 inch additional lift with the factory cam. An additional benefit from
the roller rockers
is the reduction in friction and side loads on the valves. I don't know of
anyone personally that has actually measured the reduction in friction (you
would do this
by measuring the energy it takes to spin the valve train both before and
after the install). The side loads, only time will tell, I haven't heard of
any people with
excessive valve guide wear. Whether you do the TB or cam or rocker arms
first, I don't think really matters. The only technical issue would be can
you get enough
fuel to match the increased air that you will be flowing. The other issue
would be your wallet (the cost per horsepower gained). One other issue to
remember
would be the powerband alterations (increased duration generally raises the
torque and horsepower peaks of the engine). On the subject of the throttle
body, there
were a couple of posts with questions that I want to answer in one post. The
first TB that Bruce has uses stock plates (1.980 inch). The ridge in the
throttle body
above the plates is actually a radius to shroud the half of the throttle
plate that swings upward during throttle opening. This was intentionally put
in and I am
sure at a greater expense to Dodge to reduce the surge of power just above
idle. It would have been cheaper to just create a straight bore where the
throttle plates
reside. Un-shrouding of the blade halves that swing upwards occurs at
approx. 15 degrees throttle opening. On the first TB, we opened up the
throttle bores so that
un-shrouding occurs at approx. 7 degrees. Then we moved the boring bar
approx. .025 inch towards the rear of the TB to remove the radius on the
side of the
throttle bores where the plate swing downwards. The 8 degree taper in the
air horns was then machined and opened up to remove the casting marks and
reduce
the web between to two throttle bores. The 8 degree taper now starts .100
inch above the throttle plates. The throttle shaft was milled .080 inch and
re-tapped
for #10/32 button head machine screws. The milling was performed on the side
of throttle shaft where the head of the machine screw resides. I didn't
remove
half of the shaft on this first one because of the support for the throttle
shaft between the two throttle bores. The throttle body with the larger
plates gets a new
stainless steel throttle shaft. The shaft is actually easy to make, stronger
so more material can be removed from the shaft around the plates. necessary
because
the new plates are thinner, and doesn't need any special coating because it
will not rust. The plates that I ordered are 52MM plates from Edelbrock
(approx. $2.00,
from their BBK series TB's). They will need to be turned down and drilled to
fit. You can't get too crazy with plate size for two reasons, the support
for the throttle
shaft between the two throttle bores, and the outboard throttle shaft
bearing retention. In regards to removing the air horn, I don't know yet.
The throttle body is
quite short and the air horns actually straighten the air as it move down
through the throttle body. My feel is that this might cause more problems
than it does
good, the only way to know is to actually remove and flow again. We are
going to try this mod and I will let everyone know. The problem with
removing the
air horn is that once it is done, there is no going back. If flow decreases,
the TB is essentially garbage. We will flow the TB with the air horns
removed with some
type of bonnet or air box installed. The flow numbers on the first TB are
essentially the same up to approx. 10 degrees throttle opening, at WOT flow
has increased
13% (from 573 CFM to 640 CFM). You need to remember that the actual CFM
numbers could be inaccurate (the flow bench is pretty tired). What is more
important
is the % increase. Two additional things worth mentioning, the flow numbers
were generated with a air horn installed on the TB, and before
modifications, the
stock plates would not open all of the way (straight up and down, off by 3
degrees), had to machine the stop on the throttle shaft. I hope this answers
all of the
questions, but if it doesn't, let me know.......

        Frank

> -----Original Message-----
> From: O26ON4@aol.com [SMTP:O26ON4@aol.com]
> Sent: Sunday, August 30, 1998 8:26 AM
> To: dakota-truck@buffnet.net
> Subject: DML: 1.6 rockers v.s.TB mods,was:Magnum Performance Throttle
> Body?
>
> In a message dated 98-08-29 20:01:29 EDT, you write:
>
> << Hay Steve.
> Hold off on the throttle body for a couple of days. I have been playing
> with
> a couple of these (flow work, different shafts, different plate sizes,
> etc,
> etc, etc, etc).
> If this works according to plan, it could save you a lot of money.
> Frank >>
> Thanks for the advice.
>
> On another note, does anyone know if a modified TB or a set of 1.6 ratio
> roller rocker arms offers the best bang for the buck? After all, the
> object to
> creating more hp is to get air in and air out, the more air the more hp.
> Shouldn't increasing the lift be a better mod prior to the TB? I don't
> know,
> hopefully some of you guys with more experience can answer this. My
> philosophy
> is to modify in the correct sequence, i.e., always alleviate the
> bottleneck
> (which keeps moving) one step at a time. Obviously we all strive to do
> this,
> however, philosophies vary on how to accomplish this, especially when one
> is
> trying to achieve maximum improvement on a budget- better known as bang
> for
> the buck. Your comments are welcome.
> Regards,
> Steve Waller in Houston



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