GT40P heads in a '67 289 'Stang???

Cmyheini67 · Dec 10, 2004

Anybody swap a set of C6AE heads for a sweet pair of GT40P's? How much did this mod cost? My '67 notchback set up:

#(289 + .30), port matched stock heads
#Erson Street/Strip Cam -- 294 deg duration/.504" valve lift
#Reworked C4 w/ shift kit...2800 stall converter....8" w/ 3.70s
#Edlebrock Performer RPM high-rise intake manifold
#Edlebrock 600cfm Performer carb
#Hooker headers w/ 1 5/8" primaries...3" collectors

SadbutTrue · Dec 10, 2004

you will probably need new headers (also unlikely to be as good as yours), and GT40Ps are pretty weak heads... probably the weakest aftermarket head out there. If your current heads are ported well, the power difference won't be much. I'd say stick with your current ones unless you go with a better set of heads.

ratio411 · Dec 10, 2004

I can confirm the header problem.
We mocked a set of P heads up on a car not to long ago... the headers were a terrible fit.
Not only do the plugs have less angle, they are moved laterally along the head.
The plugs are under the primary pipes on most cylinders, instead of under and over.
It doesn't look bad until you bolt the headers up, otherwise we wouldn't have gotten as far as we did.
Dave

65fastback2+2 · Dec 10, 2004

SadbutTrue said:
you will probably need new headers (also unlikely to be as good as yours), and GT40Ps are pretty weak heads... probably the weakest aftermarket head out there. If your current heads are ported well, the power difference won't be much. I'd say stick with your current ones unless you go with a better set of heads.

I find it odd that the best flowing GT40 heads are the GT40P's

dmoody · Dec 10, 2004

I'm going to be putting GT40P heads on my 68. I did have to buy special headers from CJ Pony Parts. I think the manufacturer of these headers only produced a limited run of them because I know they aren't offered anymore.

Anyway the GT40P heads are supposed to be the best production heads Ford has ever offered for the 302. Now if you're expecting the heads to flow as well as the Edelbrock, AFR, twisted wedge, etc then you're dreaming. But they far outflow anything else you'll get from Ford unless you get a professional to port them. The reason why the spark plug is in such a strange location is to get a better flame travel from the spark and thus a more efficient burn. This helps power and gas mileage.

d

SandSprite · Dec 10, 2004

To answer the question-- it's hard to say. You will lose compression since the heads you have are 54cc and the gt40p are about 60cc, but they out flow the 66 heads.
http://www.jason.fletcher.net/tech/flowdata/castiron.htm
http://www.stangpro.com/html/articles/gt40p_files/gt40p1.htm

GT40P's are one of the best Ford heads put on a production car. The header issue makes them less desirable though. I am looking to get a 1999 explorer 5.0, but I haven't decided on which headers to go with. MAC makes some that are supposed to fit, and both central coast mustang and ford power train make P headers.

http://www.macperformance.com/store/category.cfm?SID=3&Category_ID=346
http://shop.centralcoastmustang.net/osb/showitem.cfm?Category=2
http://www.fordpowertrain.com/Headers.htm

D.Hearne · Dec 11, 2004

SandSprite said:
To answer the question-- it's hard to say.

GT40P's are one of the best Ford heads put on a production car.

They came on car motors? What cars?

65fastback2+2 · Dec 11, 2004

D.Hearne said:
They came on car motors? What cars?

the GT40 duh

D.Hearne · Dec 12, 2004

65fastback2+2 said:
the GT40 duh

Oops! you let Fords best kept secret out. Now everyone's gonna know the GT40's been back in production since 1996.

mustangracer · Dec 13, 2004

According to fletch's 5.0 page the P heads flow 12-17% better than any other ford stock head. And yes they were stock on the later 5.0 explorers. So if your swapping in an explorer engine, I wouldn't be in a hurry to ditch them, if you are concerned about cost. They also flow better enough on the exhaust that you shouldn't run a split pattern cam with them, which unfortunately I didn't know before I installed mine.

I used them on my 289 with pretty good results. I suppose after the total between heads & headers I could maybe have gotten TFS or something, but then I would have also needed pushrods/guideplates/rocker arms also, which were included in the heads I bought.

They are a good middle ground for someone looking to run a reliable street engine though. And the lean burn design probably helped me get a 22 mpg average driving cross country even with a 650 4bbl and hotter cam.

SadbutTrue · Dec 13, 2004

best ford production head isn't as big a deal as most of you guys make it out to be. None of the GT40 heads are known to be huge performers. The fact that he will lose compression and have to settle for special headers (which are likely a compromise design and won't flow as well as his current one) will offset much of the gains he makes.

Save up for a decent set of Performer RPM heads or something of that sort. For six or seven hundred you can have a head that is better in pretty much every way.

Fireracer34 · Mar 25, 2020

SadbutTrue said:
you will probably need new headers (also unlikely to be as good as yours), and GT40Ps are pretty weak heads... probably the weakest aftermarket head out there. If your current heads are ported well, the power difference won't be much. I'd say stick with your current ones unless you go with a better set of heads.

I hope this helps somebody, these headers work on GT40"P" heads and with a AOD transmission.
Sanderson Headers FF3GTS-SEC
After so many fails and time, I wanted to share. See the pictures.
Doug

geoklass · Apr 2, 2020

RCI offers Long Tube Headers that will work with the GT-40P head, and clear the spark plugs...

GT40P heads in a '67 289 'Stang???

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