TBI Manifold Preference...???

[Doug Dayson]

Hi Punisher, thanks for the help!

Question though...to me a 406 with a mild 6000 redline (800 rpm over my power
peak) will require a 634 cfm TB (assuming 90% VE). Now, a 670 cfm two-barrel
rated @ 3.0-in.Hg equals 473 cfm @ 1.5-in.Hg.

This pressure drop thing appears to be a top-end limiting factor to me. GM
however does run these 670 cfm TBI's on their BB's don't they? It seems to me
that the 670 cfm TBI would only support a 454ci to 4000 rpm or so, is this GM's
redline on their 454's these days?

Am I thinking ballpark here or am I really missing something?

Holley also has a 900cfm four-barrel TBI, any experience with that?

Thanks for all the help!

Doug

The Punisher wrote:

> Doug:
> I have a setup very similar to what you describe. Its in an S-10 pickup so
> weight will be similar to youre vette.
> the engine is a 406 small block with 11:1 comp. I used world products dart2
> sportsman2 heads. I think the sportsman's flow a bit more air, but the TFS
> wedge's got a much better chamber(and possibly more detonation resistant).
> I applied thermal barrier coating on the piston tops,combustion chambers,
> valve's, and exhaust ports. I air-brushed it on after SAND-blasting(NOT
> glassbead), then cured it in the oven.
> I use crane 1.6 rockers and have a hydraulic cam just slightly bigger than
> yours.
> I have a torker2 manifold with a custom made 1.5" spacer and a 670CFM holley
> 2 barrel injector. I made my own spacer to center the TBI over the center of
> the plenum and ported it to a very smooth transition. The TBI is wider than
> the 4150 type opening and I did not want to disrupt flow with a sharp angled
> adaptor like the holley one.
> I still dont have a proper computer on it, I have been using an old analog
> Pro-Jection unit for control. It would be much better with a 747. BUT it
> does run better with the crappy pro-jection box than it does with a 600
> holley vaccum secondary or an edelbrock(weber)600. Not quite as good as the
> 800 double pumper I had though.
> The guy at holley said that a TBI would be fine on a single plane because
> you are not trying to get a stronger signal to a venturi like on a carb.
> I cant realy think of a low rise manifold that would be much better than a
> torker2 for a 406.seems like there is a low rise single plane WEIAND but I'm
> not sure. Certianly a victor jr. would run alot better, but there goes youre
> hood clearence.
> If you run a medium/high rise single plane made for a dominator carb, you
> can use a short adaptor plate with no airflow problem. I have seen a few of
> these manifolds(torker4500 ?).
> Also you might consider a medium/high rise manifold made with a spreadbore
> flange. then you could use a short spacer. But I dont know how much having
> the TBI at the back of the plenum instaed of centered will hurt mixture
> distribution. Thats why I used an old torker2.
>
> Good luck
> The Punisher
>
> >From: Doug Dayson <djdayson at home.com>
> >Reply-To: diy_efi at diy-efi.org
> >To: diy_efi at diy-efi.org
> >Subject: TBI Manifold Preference...???
> >Date: Tue, 22 May 2001 12:21:37 -0700
> >
> >Hi All...
> >
> >I'm looking into possibly converting my 71 Vette 406/400 to TBI (from a
> >well-dialed Q-Jet).
> >
> >Engine specs...
> >
> >406ci, TFS Twisted Wedge heads, 1 5/8" X 3" Headers, 218 @ .050 110 LSA hyd
> >flat tappet cam with .485 lift with 1.6 Rockers, medium-rise dual plane
> >and 750
> >Q-Jet. Current powr peak is at 5200 rpm, torque peak at 4000 rpm (a
> >reasonably
> >mild and streetable 406).
> >
> >Old Vettes suffer from low hood lines so high-rise manifolds won't fit.
> >This
> >leaves my options at low-rise single plane (Torker II) and medium-rise dual
> >plane (Performer etc).
> >
> >Now I know that the Performer manifold is killing the power over 5000
> >rpm so
> >I'm considering the Torker II for use with a TBI.
> >
> >To my undersatanding, since the TBI doesn't require manifold vaccuum to
> >properly meter and atomize fuel will the single- plane/TBI combo deliver
> >similar low rpm performance as the current dual-plane/Q-Jet?
> >
> >If yes, then I should be able to see increased performance from around the
> >torque peak up past the power peak with the single-plane/TBI, as well as
> >comparable low-end to the current dual-plane/carb, yes?
> >
> >What do Ya'll think?
> >
> >TIA...
> >
> >Doug
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