Don't hold me to this but I believe they came on some 90+mustangs gt or cobra I am not sure. They definitely came on the first gen lightning, and a few crate motors. From what I have read they are a very good up grade from other stock heads. Gt40P heads came on explorers I think they are pretty close performance wise to the gt40 just have a little better combustion chamber. The only drawback to the p's are they require a different header than what the 302 and 351 would usually use then again some have used them and fit regular headers I think it's probably more on a case by case basis as to weather or not the header with fit your application. Hope this helps some
I could not find any data from Canfield, World Products, of the GT-40Y heads... for heads in this size range...must be a secret or something. But their heads are all almost 180cc+ heads which barely fit in this ~160cc range.
GT-40 irons have 1.84/1.54 valves
GT-40P irons have 1.84/1.48 valves
GT-40X are aluminum heads with 1.94/1.54 valves
GT-40 irons came on 93-95 Mustang Cobras and up to 1997 5.0 Explorer (I think 1997). The P came out after the true irons left the market around 1997. The X head is a FMS part. The iron heads only came on 5.0 motors (and the 93-95 Lightnings)...to use on 351W you will need to drill out the bolt holes to 1/2".
All of the GT-40 variety wake up to port work (well any head). Clean up the valve throats, open up the exhaust port, open up the intake port, clean up the short radius from the intake to the valve, deburr the combustion chamber, and a 3 angle valve job is great. I would not port match the intake and exhaust to their respective Fel-Pro gaskets, you could slow down velocity and lose power. Stock valve sizing is best to stay with per head inorder to keep up velocity.
Any of these heads will easily give you 20-30hp over the stock E7 and 30-40hp depending on amount of port work involved.
to a good tech article comparing the GT-40's to GT-40P's. Personally, for what I do with my Bronco I felt the "P" was the best choice. I recently purchased a set in excellent condition from a guy on ebay who seemed to have a limitless supply. I won't have the money to tear the engine down 'til next spring because my E4OD is junk and needs to be replaced. So I can't tell you whether it woke up my 351 or not...
Thank you all for the info and the link. I've printed it off and will digest for a few days. I may have a few more questions, but the quantity and quality of info is excellant, possibly more than I expected.
As I recall the Explorer and 351W Lightning heads have a larger combustion chamber than the Cobra heads. I believe they were around 64-65cc and the Cobra's 60cc...this is going off memory so it may not be super accurate!
Looks like ~15% better flow on intake and ~17% on exhaust in stock GT-40 form. With slight port work (Clean up the valve throats, open up the exhaust port, open up the intake port, clean up the short radius from the intake to the valve, deburr the combustion chamber, and a 3 angle valve job) ~25% on intake and ~38% on exhuast end.
Non "P" heads take any stock header/manifold. P's can take stock headers it is just a PITA to change spark plugs.
If you use the 5.0 GT-40 heads on a 351W, you will need the head bolt holes drilled out to 1/2" from 7/16".
The GT40 head was used on the 1993-1995 mustang Cobra 302. The 1st gen lightnings used a larger chambered GT40 head on its 351 for lower compression (there is a bolt on spacer kit available to use these with 302 head bolts). The explorer heads are GT40 "P" heads which feature slightly improved runner design and different plug angle, which make a standard header difficult to fit. Hence the "P" specific header.
The first 5.0 Explorer heads (96 to maybe 97.5) were GT-40's. After then were GT-40P's. Don't know about 40's but my 40P's don't have thermacter bumps in exhaust port and don't have thermacter opennings in ends of head either. FMS mustang shorty headers outlet matches pretty close to stock Y-pipe on passenger side on truck but drivers side exits at the back of the block by the bellhousing bolt holes (and high pressure fuel lines on EFI). Good luck with your project.
My understanding was that any Explorer/Mountaineer w/302 from 97 on had the "P" head. Also check ebay...
In recent history 302/351W heads are the same (with the exception of a slight difference in combustion chamber volume and head bolt diameter). Any 351W manifold will fit.
As far as headers, spark plug angle is the only issue. If you can find a header that clears the plug your ok. Some people ding the primary with a ballpeen hammer, others remove their header to change a plug etc. Ford makes a stainless shorty header that clears the plug a GT40P head, but it is for the Mustang. I'm not sure about the exit angles in a truck... It is available through Summit and other places.
central coast mustang has a shorty header designed to use gt-40p heads in 86-95 trucks$219 doesn't state if they are coated in any way. So if you don't wanna try different headers or bang on your new ones or take them off to change plugs this is an option.
my little bit- the gt-40p's were on 97.5 explorers & mountaineers till the 302 was replaced, and car craft had a good article on the gt-40s (budget iron heads put to the test- feb of 02) and just put a set on a budget ($2500) 351w- that one is on the racks as we speak
in the iron head articlethey said that the theoretical max power is 391 horse!
it also does not have any of the thermacator air passages (thank you ford!)
I also hope that they work well- I'm planning on putting a set on the 302 im building for my 61 falcon!