[DeTomaso] someone school me on the Holman Moody manifold

[Daniel C Jones]

> This is taken from Dailey's Pantera Place (pg 35).

That was something I wrote many years ago before I launched the
351C dyno testing project.  In testing, we've found the Blue
Thunder is not that good out-of-the-box.  It has 4 good runners
and 4 bad runners.  However, after some time on the flow bench,
Dave McLain came up with a fix that brings the bad runners up
to match the good ones.  The fix involves cutting down the
divider and blending the plenum entry.  IIRC, the Dave charged
Mike $150 for the port work.  Depending upon the engine, that
it can be worth a lot of HP.  On Mike's 408, the ported intake
was worth 35 HP at 5800 RPM.  On an iron headed 408C engine, it
was worth around 50 HP.  Mike's intake had been milled flat so
it would fit under a stock Pantera engine screen while the other
one had a canted carb pad and a 1" spacer.  On the 351C dyno
engine, we're waiting to test the Blue Thunder.  We had a
clearance issue with the big cap distributor so it didn't get
tested in the first round.  Plans are to test it over the
Christmas holiday.

> "I'm told the Blue Thunder is a copy of the Holman-Moody 351C
> dual plane high rise. "

Others have claimed it's a Shelby design that Holman-Moody copied.
I'm not sure of the chronology but they are similar intakes.
I have seen two different Shelby 351C intakes.  The lower one was
basically a Ford aluminum dual plane with Shelby logo while the
taller one was the same as the Holman-Moody and Blue Thunder intakes.

> Dan and I did a back-to-back dyno test comparison of about ten
> different intakes on my 408 stroker Cleveland, and found that the
> Blue Thunder was basically the equal of the tall, single-plane
> tarantula-style Holley Strip Dominator--but my Blue Thunder allows
> the carburetor to fit under the engine screen (because the top of
> the intake has been milled off to lower it and level it).

There was very little difference between the ported Blue Thunder
and the Holley Strip Dominator or Edelbrock Scorpion single plane
intakes.

> We tested a 2V Air Gap on my 4V head motor and it did surprisingly well.
> It fell on its face at 5000 rpm though.

The Edelbrock Performer Air Gap was better below 4500 RPM, compared
to the ported Blue Thunder and the single planes.  Above that, it
gave up 15 to 25 HP.

> It would be great to see how it works with proper 2V heads.
> Dan felt that it was a really, really well-designed manifold,
> arguably the best 2V head intake you can buy.  The only downside
> is that it's tall and won't allow the use of the engine cover.

The Edelbrock Performer Air Gap 2V did well on the 351C dyno engine
with iron 4V heads.  We've not tested that engine with 2V heads yet
but will at a later date.  We did test the Performer Air Gap on
Orville Burg's 393C with ported Aussie 2V heads and it was beat by
the single plane intakes (Holley Street Dominator, Parker Funnelweb
and Weiand Xcelerator 2V).  I expected the tall Funnelweb to do well
but I thought the Performer Air Gap would beat the Street Dominator
and Xcelerator.  However, both of those 2V intakes performed very
well on the 393C.  It will be interesting to see if the trends change
on the 351C engine with open chamber 2V heads.  BTW, TFS has a new
single plane intake for 2V heads (along with the fuel injection
intake) but I've not tested it yet.

> If street driving is your thing and you want a power band of 2500-6500
> rpm, the Edelbrock RPM Airgap is hard to beat.

Smaller cubic inch engines (relative to port size) repsond better to
dual plane plenum effects.  On the 393C we tested, the dual plane
plenum just presented an unneeded restriction to flow.  Even down at
2500 RPM, the single plane Funnelweb was as good as the dual plane
Performer.

> I have to ask, if you are not racing, what % of the time you are
> at 3000-4000 rpm versus 6000-7000 rpm?

For me, when I'm at full throttle, I want the best average power between
shift points, since that is what yields the best acceleration.  At lower
RPM, I'm more worried about part throttle response.

Dan Jones