Difference between GT40 and GT40P Heads - Ford Mustang Forum
 
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post #1 of 12 (permalink) Old 04-04-2010 Thread Starter
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Difference between GT40 and GT40P Heads

I would like to know if anybody know what the real difference in the GT40 and GT40P heads are, and which ones would better suit my car. Also, I've heard that its good to advance the timing on our cars as well what would be a good starting point. My buddy said i should be able to go 14degrees and still run 93 Octane.
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post #2 of 12 (permalink) Old 04-04-2010
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Your friend is right about the 14* base timing and 93 octane.
The GT40s are GT40Ps are very close. Apparently the Ps outflow non-Ps by a very small margin, but they require special headers. This pic should help.

That said, if I were you I would try shooting higher. GT40 heads were more popular in the days when there weren't as many aftermarket heads. Now a days you can get a pair of brand new and complete Trick Flow Twisted Wedge heads for $1100. Once you get a pair of GT40 heads (~$300) have them freshened up (~$250) and have them ported to flow respectively well (~$350), add it up: $900, and you will still have 50 extra pounds of weight.
I can speak for this, I currently have GT40s on my setup. If I were to do it again I would start with TFS TWs or AFR 165s.
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post #3 of 12 (permalink) Old 04-04-2010
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The P heads have slightly smaller valves (1.84/1.54 I think) but they are arranged for a more efficient burn. This is why different headers are required. The P head's spark plugs go straight in as opposed to the traditional angle. Advancing your timing to 14 or so on premium always worked for me. The P heads are good for about 30 horses bolt on with no other mods. The GT40 heads have slightly bigger valves (1.94/? i think) with a traditional spark plug placement. If I recall correctly the GT40s can be hogged out to perform better than GT40Ps but it takes someone who knows what they are doing. The cams that work best with both these heads keep the lift under .500. Something along the lines of a Ford B or E bumpstick.

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post #4 of 12 (permalink) Old 04-04-2010
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Quote:
Originally Posted by Snake Pliskin View Post
Something along the lines of a Ford B or E bumpstick.
Neither. With GT40 heads the best cam is the stock cam with a set of 1.7 roller rockers.
As for valve sizes, see that picture I posted.

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post #5 of 12 (permalink) Old 04-04-2010
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As far as having to have special headers...that just depends on how much work you want to do in the future. A pair of typical shorty headers will work, but it is a good idea to 1) put new plugs in before you put your headers on. (you can't replace them with the headers on) & 2) buy some plug wires with 90* boots so they will clear the headers.

I spent $150 bucks on my GT40P heads. I pulled the valves, cleaned everything, gasket-match ported the exhaust, and put them on. Probably spent 275-300 with the gaskets, wires, plugs and all.

I will say that it did seem like I lost a lot of power in the process. I think it is mostly related to other issues though. It still runs pretty good.

As far as the cam...a stock cam + 1.7RR will put it in the ballpark of a E and B cam.

I am putting an F cam in mine eventually...I work with guys that have had good experiences with the F cam and GT40Ps with stock valve-trains. ...like...an occasional 7k rpm with no valve float kind of good experiences.


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post #6 of 12 (permalink) Old 04-04-2010
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you can also run the p heads with long tube headers because there is a little more room between exhaust ports that the shorty's

95 mustang gt 5 speed, explorer intake upper and lower, bbk 70mm throttle body, bbk lowering springs, bbk CAI, bbk ud pullies, dynomax Bullets, bbk off road h-pipe,bbk longtube ceramic headers, gt40p's, still working on a cam... not sure yet
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post #7 of 12 (permalink) Old 04-05-2010
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Quote:
Originally Posted by mustangmiller View Post
you can also run the p heads with long tube headers because there is a little more room between exhaust ports that the shorty's
Yes, and that's a good upgrade.

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post #8 of 12 (permalink) Old 04-05-2010
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The GT40p's also do not have the air ports in the back of the heads for the cross over tubes. Ford and BBK shorty headers will work on both GT40 and GT40P. The BBK aren't designed to work with the p heads and have some clearance issues, which will end up costing some additional money and time when changing plugs. If you plan on upgrading to aluminum heads in the future. You will still be able to use both of these headers, as well as MAC and BBK longtubes (other longtubes will probally work but I'm not sure which ones) with other heads besides the GT40P's and save you some money when you upgrade heads, because you won't have too buy another set of headers. Total cost for the heads will be whatever you pay for the heads plus $150 for a trickflow spring upgrade kit plus $20 for a Sears spring compessor tool. If you can pull the heads yourself, they are a good low buck upgrade. If you can't pull them yourself, then the cost of the heads plus shipping will be too much and not worth it. Late 95 to 97 1/2 Explorers have GT40 heads after 97 1/2 have GT40P. GT40's have 3 vertical lines on each end of the heads, GT40P have 4 vertical lines. If you can pull them yourself, pick up the intake manifold too. On the front of the lower intake manifold, look for a part # that ends in BA. These intakes also have a small round hole in the middle of the intake runners. These are the more desirable Explorer intakes because they have the egr provisions and can be tapped for the act and coolant lines. Either head would suit your car. The GT40P have a smaller and revised combustion chamber and will increase compression ratio to approximately 9.5, they also flow slightly more in stock form than the GT40'S. GT40's also cost more than the GT40P's.
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post #9 of 12 (permalink) Old 04-06-2010
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The heads are almost identical, the exhaust valve on the gt40's are like .5 bigger then the P's and the runners are a hair larger.... the combustion chamber is different from the reg gt40's and the P's.. The major difference is the plug placement which optimizes combustion, the P's also seem to have a better velocity due to the runner shape which is another reason they are better then the reg Gt40's but they are only better if we are talking about porting them.

I bought the gt40p's because in the long run they are better for my setup.

head specs

http://i580.photobucket.com/albums/s...inderHeads.jpg

2nd
a stock 5.0 cam isnt close to an E cam even with 1.7 rockers... The stock cam is .444 + the 1.7's and thats .474 lift .and the E cam is .498. Use an E cam with 1.7 to get .528 and then we are talking.

People say they get into the 12's and 11's with the stock cam and 1.7's, but you have to look at what car and setup they r using.. A car with an auto trans and a SN95 body style will not get that quick in the 1/4 with a stock cam, without a power adder..

But a stock cam will net high 12's on a n/a motor.
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LOL GT40P are not better for anyones setup. If you have reg gt40 there is no reason to swap Itll be a waste of time and $. The P's are slightly better but unless you got them for $150 and were able to just bolt them on they are a waste. Good for 20hp over E7's.
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Quote:
Originally Posted by spdjnky_42 View Post
LOL GT40P are not better for anyones setup. If you have reg gt40 there is no reason to swap Itll be a waste of time and $. The P's are slightly better but unless you got them for $150 and were able to just bolt them on they are a waste. Good for 20hp over E7's.

i have two sets of p heads 1997 and 2000 and 1 set of regular gt40's off a 95 cobra. Sitting in my storage room.. All the tags read identical except the exhaust valve size from the P's to the reg gt40's.. the Gt40's are 1.58 and the P's are both 1.54 on the exhaust, the cc's are different on all 3.. the Gt40's from the cobra are 60.4cc, the 1997 P heads are 62.9 and my P heads from a 2000 ford truck are 58.3cc.. i think it was done with the water/plexiglass method...

the cc of the heads can have a major effect on the power. 5cc is a good bit of compression.Especially with the higher velocity flow of the P's, thats the small edge they have over gt40's.. But ported Gt40's outflow the P's but ported P heads outflow Gt40's from what i have read..

IMO-they are all better then the standard E7 heads, even better then ported E7's..(i even have a set of those)

I you can get a setof P's for a good price as stated from above. with low miles, snag em. they are great for a budget build..
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post #12 of 12 (permalink) Old 04-07-2010 Thread Starter
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Well it seems as if i already have GT40 heads on my car. I just installed a complete MSD Ignition on it and i figured might as well replace the plugs while I'm at it. Well i got the plugs for a 1994 Mustang GT and the threads were too big. So i was like what the hell, so i looked up how to find out what heads you have, and for sure there was the GT casting hiding right behind the Alternator. So do i need to get plugs for a 1994 Cobra??
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