Siamesed Runner TPI Questions...

[Doug Dayson]

Thanks all for the responses...

So Dave, I was thinking the same except for this argument to the contrary re
the Holley Two-Barrel TBI.

To me a 406 with a mild 6000 redline (800 rpm over my current dual-plane power
peak, figure that the single-plane will bump the power peak a few hundred rpm)
will require a 634 cfm TB (assuming 90% VE). Now, a 670 cfm two-barrel TBI
rated @ 3.0-in.Hg equals only 473 cfm @ 1.5-in.Hg.

This pressure drop rating 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, do you have any experience with that
as it would certainly be big enough. I believe the latest versions come with
their modern Commander ECM and software, and progressive secondary throttle
linkage, as well as better injectors. Comments?

Thanks for all the help!

Doug



David & Cheryl Haggard wrote:

>    Assuming similar volumetric efficiencies, head configurations, exhaust,
> camshaft about 8 degrees "longer" in the 400, and lots of other variables--
> An induction system supporting 6000 rpm on a 350 **should** support about
> 5200 on a 400.
>    All else being equal, and all applicable disclaimers included. So if you
> have a 350 with its power peak at 6000, its induction should peak your 400
> at 5200 or so.
>    There are so many variables at work here, I'd hate to say for sure. Like
> I said, "all else being equal." All I can say is, try it. You may be
> thrilled with the result. You may be grossly disappointed.
>
>    If it were me, I'd opt for an Edelbrock or Weiand single-plane manifold
> and Holley's 670 cfm TBI.
>
> Dave Haggard
>
> > -----Original Message-----
> > From: owner-gmecm at diy-efi.org
> > [mailto:owner-gmecm at diy-efi.org]On Behalf
> > Of Doug Dayson
> > Sent: Thursday, May 31, 2001 4:08 PM
> > To: gmecm at diy-efi.org
> > Subject: Re: Siamesed Runner TPI Questions...
> >
> >
> > Hmmm, I was under the impression that the difference in rpm
> > potential between
> > two identical intakes compared on a 350ci and a 400ci would
> > be approximately
> > 500 rpm, as in the 350ci should see approximately 500 rpm
> > more air etc. Is this
> > close?
> >
> > As Bruce knows I'm happy with my power curve and rev range
> > the way it sits with
> > the dual plane and the carb. I'm primarily looking for better
> > economy and high
> > altitude performance, but if I can gain something in the
> > switch to EFI I'll
> > take it (either a mid-range bump with TPI or better top-end with a
> > single-plane/TBI or MPI or Mini Ram).
> >
> > Looking at the curves from the dyno runs below it seems as if
> > the TPI intakes
> > made power to 6K rpm or a little better (on a 350ci crate
> > motor). Would I be
> > correct in guessing that they would pull to 5500 rpm on a 400ci?
> >
> > If so with my current power peak at about 5150 rpm it might
> > not be so bad? I
> > generally shift at 5500 rpm or so and my shift recovery rpm
> > is 3100 rpm in
> > first to second (3.06 to 1.62), and 3450 for second to third
> > (1.62 to 1.00). To
> > me if I can improve torque from 3000 rpm to 5500 rpm I go faster, yes?
> >
> > The Super Ram increases the plenum volume a lot over a TPI,
> > is this what
> > supplys the extra air for higher rpm work?
> >
> > Thanks...
> >
> > Doug
> >
> > Bruce wrote:
> >
> > > Naaaa,
> > > IMWO, it varies on a case by case evaluation.
> > > For a new guy TBI will always be easier to build from the ground up.
> > > For a very large displacement engine, MAP is the answer,
> > and cam/rpm will
> > > guide my response.
> > >
> > > 5+7 are mute in my opinion, most of the problems for them are cross
> > > fire/ignition.
> > > On a wet manifold, ya there can be problems, but generally
> > at the higher rpm
> > > levels.
> > >
> > > I'd watch getting too short of runner.
> > > Heck, I advocated the connected runner idea for a long time now,
> > > What I would do if I were you is start measuring things out
> > for the plenum
> > > volume and see where you are
> > > Bruce
> > >
> > > > This thread over here too?
> > > >
> > > > Its not for everyone... but it is possible to extend the
> > range of the TPI
> > > > more to popular liking...
> > > >
> > > > Think of how the siamesed runners shift the curve. Now
> > say "what if" the
> > > > runners were siamesed all the way down?  more shift.
> > Now... hmmm.. what if
> > > > the siamesing was extended all the way INTO the base?  no
> > need for large
> > > > runners or a ported upper intake now... cause you're
> > drawing from 2 runers
> > > > simultaneously!  reversion is a concers, especially with
> > #5 stealing fuel
> > > > from #7 in the cycle of things but cam overlap management
> > can help here.
> > > >
> > > > Here is Mike's URL with dynos of some different TPI
> > intakes.. including
> > > the
> > > > siamesed-base.
> > > > http://www.eecis.udel.edu/~davis/z28/winter01/dyno/
> > > >
> > > > again.. not for everyone... just another idea for the
> > mix.. complete with
> > > > dyno data.
> > > >
> > > > Oh.. the siamesed-base dyno will be re-done soon. A
> > problem was found with
> > > > the motor setup and is now repaired.. the dyno
> > comparisons illustrate the
> > > > mod well enough (a zero dollar mod I might note) .. but
> > the next set
> > > should
> > > > show more of an appropriate comparison. stay tuned! ;-)
> > > >
> > > > -Dave Z
> > > >
> > > > 89 Iroc - '730 - 383 large tube MAP TPI, ZZ3 cam ,dry NOS 50 shot.
> > > > 12.79 @106 / 12.08 @ 112.   www.delanet.com/~tgp
> > > > 92 25th annev convertible  305 / T56.  268 mph in a
> > perfect vacuum.
> > > > ----- Original Message -----
> > > > From: Bruce <nacelp at bright.net>
> > > > To: <gmecm at diy-efi.org>
> > > > Sent: Tuesday, May 29, 2001 5:15 PM
> > > > Subject: Re: Siamesed Runner TPI Questions...
> > > >
> > > >
> > > > >
> > > > >
> > > > > > Researching EFI updates for 71 Vette with 406/400.
> > 218 @ .050 110 LSA
> > > > flat
> > > > > hyd
> > > > > > cam with TFS Twisted Wedge heads and headers etc, currently a
> > > > well-dialed
> > > > > Q-Jet
> > > > > > and Performer dual-plane (hood clearence). Power peak
> > is at 5200 rpm
> > > and
> > > > > the
> > > > > > torque peak is about 4000 rpm.
> > > > > > So, since TPI stuff is cheap I was wondering how
> > siamesed runners
> > > would
> > > > > effect
> > > > > > the power curve?
> > > > >
> > > > > Just the oem stuff.
> > > > >
> > > > > > A stock or big tube TPI (with big manifold base) will
> > kill power over
> > > > 4500
> > > > > rpm
> > > > > > with a 406ci, but I'd think that the siamesed runners
> > would behave
> > > more
> > > > > like
> > > > > > the shorter runners of the Lingenfelter/Accel Super
> > Ram as they're
> > > > > partially
> > > > > > open etc. What do Ya'll think?
> > > > >
> > > > > Still no plenum volume.
> > > > > If you happy with what you have how about, a TBI?.
> > > > > Maybe a  Weiand 7527, or 7546 manifold, then up grade
> > one of them to TPI
> > > > if
> > > > > you want to progress further.
> > > > >
> > > > > > Would a Big Manifold Base/TB Siamesed Runner TPI
> > set-up be able to
> > > > support
> > > > > a
> > > > > > 406ci through 5600 rpm?
> > > > >
> > > > > Would be a real push to even try
> > > > > Bruce
> > > > > > TIA...
> > > > > > Doug
> > > > >
> > > >
> > > >
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