CFM Continued...

[CLsnyder]

----- Original Message -----
From: Frederic Breitwieser <frederic at xephic.dynip.com>
To: <diy_efi at efi332.eng.ohio-state.edu>
Sent: Thursday, May 06, 1999 6:18 PM
Subject: Re: CFM Continued...


> a stock 350 ci engine.  I'm looking for an EFI intake system for my twin
> turbo 434 ci engine.

Aaaaah.

> The guy putting the turbos together said that the stock TPI is a good
choice
> because it will give me something really important for a fun to drive
street
> car, great throttle response and low end torque.

>This is true, because the runners are smoothly curved, and long.  Typically
>longer runners give you more low-end torque, however at higher RPMs your
engine
>will wease to death.  Several manufacturers have come up with variable
length
>runners... the one that sits in my mind is the new Ford Taurus... long
runners
>for low end grunt, and shorter parallel runners for higher RPMs.


When it comes to forced induction RAM tuning has a lot less advantage than
in NA engines. The turbo does the ramming for you, so short and sweet
reduces flow restrictions - particularly if run off a fairly large plenum.

Instead of a 2500/3000rpm spool up range you could size for smaller turbos
and
have them spool up faster, thus taking even more advantage of the longer
runners... but then your high end will suffer from runner length as before,
but
even more from grossly undersized turbos.  but, it will take off the line
quite
nicely.

I'm doing this with my Dodge truck actually... 383 cid stroked to 431, two
small
turbos, then a max RPM of 4000 RPM.  Great for towing, not top speed.  Its a
6000lb truck anyway :)

You might get more performance by using a much larger throttle body, and
doing
some runner port work.

> with 15 lbs of boost it seems to me that the stock TPI is still small for
a
> 434 performance engine, or will the boost really make up the difference
for
> the small tubes?

I believe the velocity would be too great for your engine... but I am not an
expert in this area.  For my dodge engine, I've already drilled out the
manifold, welded in injector bungs, and going to use the TPI GM setup to
manage
the dodge motor, and instead of the GM TPI manifold, I'm just using the
dodge
intake with all the GM "stuff" attached.  You might consider that approach
for
your engine... chose a carb manifold that suits your needs and application,
then
mill into it some injector bungs.  Its a fair amount of work, but in the end
I
believe its worth it.

--

Frederic Breitwieser

Xephic Technology
"Leadership in IT"
Bridgeport, CT 06606

Web: http://www.xephic.dynip.com
Voice: (203) 372-2707
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