You can tell the difference between the GT40 and GT40P by the markings on the end of the head.
The GT40 has 3 bars and also has the casting GT on the corner and the GT40P has 4 bars on the end of the head and has GTP casted on it.
From what I've read the GT40P perform a little better even though the exhaust valve I believe is a little smaller.
The GT40P heads will raise the compression slightly and require a certain header, some people use shorter spark plugs and wires with an angle on the boot and just go throught the trouble of taking off the header when needing to get to the plugs.
The GT40 will just bolt on. IMO they are a little pricey for stock iron heads, unless you can find for a good deal. If you look on like ebay they are generally around $400 bucks and sometimes higher with shipping and that's used. Throw in another $2-3 hundred you can get a set of used ford racing x303, trick flow, or Edelbrock heads. Just make sure you don't get the bigger 2.02/1.06 valves otherwise you'll have to worry about the pistons. Trick flow is the exception you can get away with running the bigger valves, just don't get too big of cam.
It all depends on how much you really want to save. Here's a couple of links on the flow numbers and horsepower tests.
Unltimate Guide to 5.0 Cylnder Heads, Part 1
Unltimate Guide to 5.0 Cylnder Heads, Pt 2
The GT40 has 3 bars and also has the casting GT on the corner and the GT40P has 4 bars on the end of the head and has GTP casted on it.
From what I've read the GT40P perform a little better even though the exhaust valve I believe is a little smaller.
The GT40P heads will raise the compression slightly and require a certain header, some people use shorter spark plugs and wires with an angle on the boot and just go throught the trouble of taking off the header when needing to get to the plugs.
The GT40 will just bolt on. IMO they are a little pricey for stock iron heads, unless you can find for a good deal. If you look on like ebay they are generally around $400 bucks and sometimes higher with shipping and that's used. Throw in another $2-3 hundred you can get a set of used ford racing x303, trick flow, or Edelbrock heads. Just make sure you don't get the bigger 2.02/1.06 valves otherwise you'll have to worry about the pistons. Trick flow is the exception you can get away with running the bigger valves, just don't get too big of cam.
It all depends on how much you really want to save. Here's a couple of links on the flow numbers and horsepower tests.
Unltimate Guide to 5.0 Cylnder Heads, Part 1
Unltimate Guide to 5.0 Cylnder Heads, Pt 2
a fuel pump upgrade wont affect your fuel mileage. mustangs have a return style fuel system. so all the un-necceary fuel to pressurize the rail is returned back to the tank. your fuel mileage problem lies elsewhere, not the fuel pump.
If you only get 140 miles per tank with stock gears, you have either a lead foot or some serious tune issues. I get 270 MIles per tank mixed city/highway driving in a stock Mustang with a 5 speed. My previous 5 speed Mustang with3.55 gears, Explorer intake and 70 MM MAF would do 230 miles per tank mixed city/highway driving.
Here's where to strt to isolate any tune problems you have.
Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.
Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.
See Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical
If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.
The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.
89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.
The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.
There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.
What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems.
Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.
Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.
Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.
Or for a nicer scanner see EQUUS DIGITAL FORD CODE READER (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.
Here's where to strt to isolate any tune problems you have.
Dump the codes and see what the computer says is wrong…Codes may be present in the computer even if the Check Engine light isn’t on.
Here's the link to dump the computer codes with only a jumper wire or paper clip and the check engine light, or test light or voltmeter. I’ve used it for years, and it works great. You watch the flashing test lamp or Check Engine Light and count the flashes.
See Troublcodes.net Trouble Codes OBD & OBD2 Trouble Codes and Technical info & Tool Store. By BAT Auto Technical
If your car is an 86-88 stang, you'll have to use the test lamp or voltmeter method. There is no functional check engine light on the 86-88's except possibly the Cali Mass Air cars.
The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.
89 through 95 cars have a working Check Engine light. Watch it instead of using a test lamp.
The STI has a gray connector shell and a white/red wire. It comes from the same bundle of wires as the self test connector.
There is a single dark brown connector with a black/orange wire. It is the 12 volt power to the under the hood light. Do not jumper it to the computer test connector. If you do, you will damage the computer.
What to expect:
You should get a code 11 (two single flashes in succession). This says that the computer's internal workings are OK, and that the wiring to put the computer into diagnostic mode is good. No code 11 and you have some wiring problems.
Codes have different answers if the engine is running from the answers that it has when the engine isn't running. It helps a lot to know if you had the engine running when you ran the test.
Trouble codes are either 2 digit or 3 digit, there are no cars that use both 2 digit codes and 3 digit codes.
Alternate methods:
For those who are intimidated by all the wires & connections, see Actron® for what a typical hand scanner looks like. Normal retail price is about $30 or so at AutoZone or Wal-Mart.
Or for a nicer scanner see EQUUS DIGITAL FORD CODE READER (3145) – It has a 3 digit LCD display so that you don’t have to count flashes or beeps.. Cost is $30.
no kidding . . . I would probably do a little tune up first.
A friend of mine had a 92gt with ported gt40p heads, a ported cobra intake, an e-cam, 3.73s with a t5 and that thing would get 23-24mpg on the highway.
To answer your questions, doing the exhaust has its pros/cons. I would rather have a 2.5" exhaust with a x-pipe than your 3" straight out with some flowmasters.
It won't lose/gain any power but it will cost some to have a nicer and quieter exhaust.
The only way that kind of budget setup works anymore is if you can do the work yourself. I can find gt40 or gt40p heads all day for $300 but I don't spend much because I would port the heads myself and only let the machine shop surface or mill them. Same with the labor for the intake and the cam.
If you do it all yourself you might have $700-800 in swapping everything out BUT if you have to pay a shop to do it, it would be at least twice that.