You will have to divide them into (at least) three categories in order to be
able to get a fair assessment.
First, all iron heads. The GT40P heads might be one of the best just because
of the valve size - didn't these come with 1.94/1.54 valves? The issue with
Tiger fitment on these is that they do not have the "traditional" spark plug
location and angle and so they may interfere with headers. The E7TE heads
(standard on trucks and Mustangs from '87 on) were the best "traditional" OEM
head as far as I know... and a good base platform for porting if you're so
inclined. I have a couple of sets of the E7TE heads and a set of 1.94/1.54
valves sitting on a shelf just in case I get motivated to build a set of
cheater heads for my 5.0.
There are a couple of vendors of iron aftermarket heads, for race engines in
classes where aluminum heads are not allowed. These heads will typically give
better performance than the OEM heads out of the box, and they'll either have
or allow the use of significantly larger valves without having to compromise
the port shape or inside radius. But they cost a lot more than pulling GT40P
heads from the junkyard, if you don't factor the cost/time equation on
rebuilding and/or porting the heads.
The inline-valve aluminum heads are a significant upgrade to the iron heads
just because you can run the compression about a point higher than on the iron
heads. Plus, they're 25 to 35 pounds lighter per side so you save substantial
tonnage where it really counts. There are lots of vendors and you can get a
lot of different valve sizes and port/chamber volume combinations, although
they're generally oriented towards the 5.0 to 347 end of things. If you're
building a 289 then you will have to do some work to get the compression ratio
you want.
Going up from there you get the canted-valve aluminum heads such as the Trick
Flow Twisted Wedge series. These heads allow larger valve sizes and better
port orientation than the inline valve heads so they can have better
performance in the ultimate limit.
With the aluminum heads you have to be careful of the overall height as well
as the exhaust port height. Some vendors increase the thickness of the block
flange to increase rigidity, as well as increasing the height of the valve
cover rail. Raised-exhaust-port heads give better exhaust flow, but standard
Tiger headers will not fit.
I haven't listed specific brands and models... I'm sure that some of the other
Listers can put in their favorites. Even though I've acquired some parts for a
performance iron head build, there is so much extra potential in the aluminum
heads that I'd most likely go in that direction. At one point I had a set of
Trick Flow heads but they went to Tim Ronak and onto his killer 350 Lunati
stroker - now I'd probably look at one of the AFR heads just because I've
heard good things about them and they're relatively inexpensive.
Cheers,
Theo
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