CrossFire/'7747

[David & Cheryl Haggard]

   I mic'ed the original runners at 1.38" X 1". My heads' intake ports
measure 2.00" X 1.25". That meant 3/4" there was a 3/4" step from the
manifold outlet to the head inlet. Great for anti-reversion, but not much
for flow demand over 560 cfm.
   With the major surgery I performed, the intake runners now measure 1.65"
X 1.20", over their full length. This leaves 0.350", over 1/3 inch, of the
original exit step, which will still help anti-reversion quite a bit. But
the manifold should now support up to about 800 cfm of flow demand. An
excellent match for my heads, which have been flow-tested at 192 cfm per
port, or 768 cfm.
   This puts the major restriction to flow where it belongs on a carb or TBI
setup-- at the throttle butterflies.
   Note-- I did all this with the assumption that if it doesn't work well,
I'll buy an Edelbrock C-26 Dual-Quad manifold to hold my dual 2-bbl TBI's.

Dave

> -----Original Message-----
> From: owner-gmecm at diy-efi.org
> [mailto:owner-gmecm at diy-efi.org]On Behalf
> Of Marc Piccioni
> Sent: Monday, July 23, 2001 7:31 PM
> To: gmecm at diy-efi.org
> Subject: Re: CrossFire/'7747
>
>
> What is your runner size now?
> -----Original Message-----
> From: David & Cheryl Haggard <david at newcovenant.com>
> To: gmecm at diy-efi.org <gmecm at diy-efi.org>
> Date: July 22, 2001 06:16 PM
> Subject: RE: CrossFire/'7747
>
>
> >> FWIW,
> >> just remember, the air's velocity goes up with the smaller
> >> bores, and making
> >> the bends to the ports just might try to drop the fuel out of
> >> suspension
> >> more so, then larger single bores, would.
> >> Bruce
> >
> >   Just the kind of feedback I'm looking for.
> >   But actually, there is very, very little more bend in my
> runners now
> than
> >there were originally. The runners are mainly just taller.
> >   As I see it, the Crossfire may force compromises no
> matter what you do.
> >Originally, the runners are very straight, and make for high
> air velocity.
> >But they're so small you can't get high-rpm power out of
> them. They're
> built
> >for gobs of low-end torque.
> >   Opening up the runners as I have will support rpm well
> past my targeted
> >6500 rpm red line in my 305. But how my low end will suffer
> I won't know
> >until everything is bolted on and tuned up.
> >   Temporary unemployment has put a serious hold on my
> build, which was
> >supposed to be done last month. As it is, I just ordered my
> timing set this
> >weekend. A Cloyes "TRUE" roller set for "small block Chevy originally
> >equipped with roller camshaft." 80 bucks from Jeg's. Ouch!
> Cam and rockers
> >are on hold for a bit longer. When the budget will clear
> them, I'll build
> it
> >and we'll see for sure.
> >   <sigh>
> >   I looked into the Offenhauser Crossram manifold, but
> decided it's way
> too
> >much manifold for a streetable 305.
> >
> >Dave Haggard
> >   1988 Formula Firebird
> >   305 2 X 2-bbl CFI (under construction)
> >   http://www.newcovenant.com/firebird/
> >
> >-------------------------------------------------------------
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