I'd invest in a set of TFS TWs or AFR 165s. Out of the box they'll outflow most ported GT40 irons and they have much more ultimate potential. Plus you drop 50 lbs off the front of the car.
I agree, go with a good set of aftermarket heads. I personally recommend Trickflow. A good head right out of the box. It is the only head that you can put on with 2.02 valves and not flycut the pistons. Man, you would think I was a salesman for Trickflow.
If you port the GT-40 heads they will be maxed out and flow just OK. But if you buy a set of TFS head they flow the same as ported GT-40 heads if not better out of the box, and later down the road you can have the TFS heads ported and they will flow great. Basically what i am trying to say is buy TFS so you can go faster later down the road with out buying another set of heads. Great, now i think i am confused.
I had been leaning towards getting a new set of alum.-heads. Now thats what i'm going to do. A few years ago there wasn't as many choices as there are now, are the TFS the best head out for the money or should I go with an AFR,Canfield, or Yates. I'll be useing them on a N/A setup that might see a small spray sometimes. And eventually on a Turbo or Supercherged setup.
If you are looking for a head to use with a power adder with out porting them, then go with the AFR 165. They are CNC ported from the box and the Exaust side of the head flows better than a TFS. But the TFS heads are $300 cheaper and you can use that money else were.
Hey guys, I am brand spankin new here, so I don't want to rock the boat. But, I have raced 5.0's for many years (starting in 1988). I would like to give my humble opinion. Do NOT lean towards new aluminum heads. Heres why:
I have a set of old steel GT-40's (ported by Ron Anderson Performance) that have flow numbers that are better than out of the box TFS. By better I the flow matches my car. They have good flow numbers as far as amopunt goes and more importantly, they have high velocity flow. Ron Anderson himself told me that most new aluminum heads are over kill for a 9:1, 302, only reving to 6200. He told me in cases like that a good set of old GT-40's will make your car faster than aluminum heads with huge valves. His words not mine and he has been doing this for over 30 years by now.
get your GT-40's done by a pro and with all that money you save get more go fast goodies and you'll be way ahead of the game. I've personally seen a 1988-1989 5.0 (not sure which year it was) make 368 horsepower on a dyno with ported stock 5.0 heads, ported stock intake, good cam, good exhaust and throttle body. Putting a good set of ported GT-40's would move that very close to 400 hp.
Just because you can get higher flow numbers from a head doesn't mean your car will go faster. Its similar to "overcamming" a car. Just my 2 cents.
Time is knowledge and I agree with smak_daddy. I have seen all out racing heads on stock blocks with stock cam. They don't go faster they go slower. ALL the parts need to match the set up.
One other factor that no one has even discussed is heat and durability. I talked with a buddy that has some aluminum Edelbrock heads....he loves em. I asked him what he would go with if he were to do it again. He said a good iron head. On the street, in CA or other hot climate, if an aluminum head gets hot....it will warp and be ruined much easier than an iron head. GT 40 heads, Darts or World or other iron head was his choice for a car that is driven on the street. Certain years of mustangs also have had some cooling problems (94-95's) add underdrive pulleys and then some hot city driving and if you aren't watching....your new expensive aluminum heads will be toast. Something to think about.
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95 GT Convertible
BBK shorties, X-pipe, Magnaflow CB
CAI, 70mm TB, GT40 intake, 1.7 RR, UD pulleys
SFC/braces/JR, AUC Arms
1966 C Coupe - New restoration project
2004 Chev Silverado 4X4
Theres no question that the combination is the key. I use Edelbrock heads and can beat several of my friends that run the "better" TFS and AFR heads. On the other hand I have a couple friends that beat me that are using the GT40s and GT40-Ps.
A quality port job on the GT40s can make a very fast car. I know a few guys that make just over 290rwhp with the GT40/GT40-P heads and they both run low 12's.
Gt Dan thanks for making the point about the heat. I didn't give that too much thought until now. With the temp being soo high here there's a better chance of warping them and I don't want that.
I was wondering how much it should cost to have the stock heads ported? I have a friend who has a shop and could do the work for me. I was thinking of having him do it. I haven't recieved a quote yet but another one of our friends said that they a bit too high on the work he was going to have done.
Depends on how much work you want to have done. Good port work could cost an easy 450.00. On top of that you might want/need springs, guides, seals and odds are a good valve job.
Get some quotes but dont be surprised if the total gets close to 600 or so dollars.
Don't even worry about warping aluminum heads. Yeah, if you let your motor overheat several times you might have a problem. Otherwise, it'll never happen. Get a good temp gauge and shutoff if you hit 230+.
95 Cobra Heads 
