[DeTomaso] Questions on 4v heads

[JDeRyke at aol.com]

In a message dated 10/25/10 7:19:04 AM, dave at damardirect.com writes:

> Hi Jack,
> What is your opinion on exhaust port plates? W/o intake port stuffers?
> 
Never actually used either; I got lucky in 1990 and found a lightly used 
pair of SVO aluminum heads that already had closed chambers, adjustable 
valvetrain and raised ports.   Generalizations are worth what you pay for them ($0 
here), but my understanding on 351-Cs is, 
1)- intake port stuffers can make maybe 20-30 bhp extra (~10%) on a real 
350+bhp engine, at some rpm levels, depending on the intake & carb they're 
paired with. 
2)- Exhaust plates do less than intakes but can pick up maybe 10-20 more 
bhp (~3-5%) on a real 350+ horse engine, again over certain rpm levels. Lots 
of caveats- including starting with closed-chamber iron heads, semi-equal 
length headers and more open exhausts than stock Ansas. There are 2 designs I'm 
aware of: cast-stainless or cast-bronze to take the heat, and are bolt-ons 
between the heads and header flanges, not welded, pinned or glued. 
Port plates are Band-Aids for head design problems. Both intake or exhaust 
plates need replacement or at least tuning of other engine parts for most 
drivers to even notice them except that they may change the exhaust note. A 
couple of vendors sell these; I'd call around and ask them what effect they've 
seen on something like your engine- and have a parts list handy 'cause they 
will ask whats in there. FWIW- J DeRyke