I know this subject has been beat to death, but here's my two cents.
Avoid mechanical secondaries at all costs.
My Tiger is stock, but my other car is a 1966 Mustang with a 289 bored .030
over with a 280 degree advertised cam favoring duration on the exhaust side,
ported heads with oversized valves(they came from Chevy of all places), high
rise manifold (Edelbrock Performer RPM), and headers.
This is where the grief/debate comes in. I am running a 750cfm Holley with
vacuum secondaries from summit racing equipment. One of the reasons for this
is because the 715cfm that Shelby used on the GT350 mustangs was not
available. Another reason, my research prior to the build indicated that
Ford's like cams that favor the exhaust side, and they prefer to be
overcarbed. I've read the Holley book, and I know what they say in theory
(something around 500cfm), but I also know what works on the street(so does
Mr. Shelby). I've run an Autolite 4150 (stock), a Holley 600cfm, and the
750cfm (with different jets), and I have no flat spots and instant response.
I'm running a 3:00:1 gear in the back with oversized ZR rated tires and a
factory 4-speed. She'll spin the wheels in any gear with excellent low end
response to boot.
Another thing, you can change springs as well to adjust when the secondaries
kick in. I found no need on my carb.
Thanks,
Travis
B9472584
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