[DeTomaso] Difference in Headers

Daniel C Jones daniel.c.jones2 at gmail.com
Sat Jul 10 10:56:29 EDT 2010

> I presently have what I believe (?) may be a set of Hall's
> headers on my car that were on it when purchased in 2000.
> These headers measure 2" OD. & were on a set of open
> chamber 4V iron heads.

2" primary diameter is of no benefit on your cylinder heads
and camshaft.  Also, the collector on the Hall header is of
a poor design.

> Today I made a great buy on a new & never installed set
> of PI Big Throat headers with primarys that measure
> 1-3/4" OD.

Those should better match your heads and cam.  An unported
iron 2V flows around 160 CFM at your maximum cam lift.
That port requires only 1 5/8" primary internal diameter.
the ported Aussie 2V's we recently dynoed on Orviller Burg's
393C made 205 CFM on the exhaust side.  Those ported heads
require no more than 1.8" primary ID.  We tested them with
1 3/4" headers and they performed very well.  I've been out
of town on business travel but Dave McLain finished up testing
on Orville's 393C with Aussie closed chamber 2V heads.  I'll
try to summarize it when I get the chance.

> Could any change in performance, sound, mileage,etc. be
> expected with these smaller tube headers.

Exhaust velocity will be higher with a smaller primary diameter
so the note should be a little sharper.  Power should pick up
across the board but the big restriction with Pantera exhausts
is generally the mufflers.  On a 400 HP engine, the stock and
Euro GTS mufflers can cost 50 HP.

Dan Jones

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