Throttle(s) before or after plenum chamber?

Egil Kvaleberg egilk at sn.no
Mon Feb 3 12:21:42 GMT 1997


I am wondering about making modifications to the inlet system of my Triumph 
2.5 Lucas mechanical injection.

It is a pretty conventional injection style arrangement, with a long
cylinder-shaped common plenum chamber with six equal tracts consisting of
a trumpet, a piece of rubber tube, a throttle body plus the inlet port of
course.

       |  |   |  |   |  |   |  |   |  |   |  |
       |  |   |  |   |  |   |  |   |  |   |  |
       |--|   |--|   |--|   |--|   |--|   |--|   <--- throttles
       |  |   |  |   |  |   |  |   |  |   |  |
     +-|  |---|  |---|  |---|  |---|  |---|  |-+
     | /  \   /  \   /  \   /  \   /  \   /  \ +------
     |                                           <--- from air filter
     |                                         +------
     +-----------------------------------------+

These six throttles are a major pain to set up correctly, and with a bit
of wear in the spindles entering the equation, entirely impossible to get
synchronized in a reliable manner.

What would happen if I replaced this with one large throttle before the
plenum chamber? I am imagining that it wouldn't matter as far as max.
power output (under WOT) is concerned, but would there be other disadvantages
with such a layout? Theoretically slightly slower throttle response, perhaps,
but would it be noticeable?

(I would imagine that changes to the fuel curve would be required, but I'm
going to have to alter that anyway due to other changes)

Also, I am having this feeling that the inlet runners are far too short
for such a low RPM engine. They are currently approx. 9.5 inches - to move
the 2nd harmonic point down to a usable point for this engine would
require runners over twice the current length. Any experience or
referrences in this area? 

Egil                            
-- 
Email: egilk at sn.no  Voice: +47 22523641, 92022780 Fax: +47 22525899
Snail: Egil Kvaleberg, Husebybakken 14A, 0379 Oslo, Norway
URL:   http://home.sn.no/home/egilk/




More information about the Diy_efi mailing list