thanks for the info, I can see the conflicting info, its the same as the old 2V vs 4V debate on the clevos...

Will go with gt40p's I think, as it is not a drag car, just a nice streeter, daily driver, might add a mild cam at the same time....., I should see some good results as the car already has el gt intake, injectors and computer plus ducted cold air intake to the k&n panel filter I feel the heads are holding it back from unleashing its full potential.....

I just went thru the same exercise in the last 6 months with a set of GT40P's out of a T3 stroker BOLTED onto my 5.0L ED.
These already have the larger valves from factory and some little port work.
To get them to work properly you probably need to spend about $1000 in porting work to get them to roughly where alloy head starts.
If you go the larger valves check for Piston to valve clearance. Scrap the springs etc and rebuild from scratch. By the time you spend all that money plus initial purchase price, you may as well have outlayed for a set of Alloy GT40X's or Edlebrock RPM etc etc.
Depending on which make of headers you have there may be some heating and bashing so you can get at the spark plugs. Pacemaker PH4000 fit. You will need 90 deg boots. And make a special tool for extracting #5 plug.
Whilst they may BOLT ON they also create a few issues of their own.
Having said all that I did manage 240rwhp.
However listen to what XR9UTE has to say and seriously consider the alloys.
I ended up with Edelbrock Performer RPM's #60259 at $1700. - These I think you could consider to be true BOLT ON horsepower out of the box.
Dyno will be next week.

Richie.

Where did you get these for that price?

Here in Perth - A1 Hi Performance. I think they are now $1800. A wholesaler on east coast had them at $1400 at one stage.
The 60259 do not have exhaust crossover for EGR and use 3/8 studs for RR.
They have AFR's for around $2400.

Richie.

Ohh that is such a loss , no port to heat up the intake manifold as well, decent 3 way catalytic converters take car of that part of emissions anyway. I aways block that port on Cleveland heads, I always use LPG and the cooler the intake the higher the performance.

Do "A1 Hi Performance" have a website or do you have a phone number for anyone interested?

Hmm this is getting confusing...don't mean to ask again but Im considering a head change down the track so if anyone can give me a definitive answer that would be great. Will a pair of GT40X's bolt straight on to my XHII V8 or will I have issues? I know I'll have to change the plugs to 90deg ones but thats nothing big at all.

-Will I be able to use the sames intake, headers
-Will everything else on the motor work fine?

A quick shop on JEGS tells me that if I bought GT40X's they would not be compatible with the 1986 5.0L which is the windsor in my car if I'm not mistaken. Says I need to use special head bolts, also need to have the pistons notched as they are flat tops or is my 1998 engine got nothched ones?

you have notched pistons and its always a good choice to get new bolts anyways however i couldnt tell whether theyre different.

If your car came with that motor from the factory, then those heads will fit. Just tell them its a '89 to '93 stang motor and they will then agree.

You must change the headbolts (stock cant be re-used), so when you buy new ones, get them to suit 351W heads on a 302W block....they will come with the washers you need to install those heads.

You really should check piston to valve clearance, because they are larger than stock.

"Out of the Box" the GT-40X are a bit rough (to say the least). If you aren't prepared to spend a little on porting, or do it yourself, you might be better off with the Edelbrocks.

Ive got a stack of photos of brand new unported GT-40X heads over here, http://www.fordforums.com.au/showthread.php?t=52113

Here is the website.

A1 Hi Performance