GT40 Heads

[SquamInboards]

So here is a tech question for you engine guys. I've been doing some research on throwing GT40 heads on an '87 block and I'm a bit confused. It seems like they only made GT40 heads for the 302 which I realize can fit a 351 except what I dont get is:
1. Won't the head studs or bolts be the wrong size for a 351
2. Will an '87 PCM 351 block work with the GT40 or does it need to be an H.O. with the appropriate pistons, cams, and rockers? Does it matter if it is a roller cam?
3. I thought for sure my GT40 heads are cast# F9ZE AA but did I read wrong and mistake the 4 for a 9 (F4ZE AA)?
4. F3ZE and F4ZE heads appear to be similar, will both work?

This is where I got some of my info for reference.

[SquamInboards]

RE: GT40 Heads

More info
"The 1993-95 Cobra GT-40 head is little more than a marine head with larger valves and ports. This
fact all by itself makes the GT-40 a good, economical head for 5.0L/5.8L performance. Economical
because it is a common head. Just look for 1.84/1.54" valves, “GT” markings, and F3ZE/F4ZE
casting numbers. Ford part numbers are F3ZZ-A and F4ZZ-A. These heads are also available from
Ford Racing as M-6049-L302. Properly outfitted, these heads use the F3ZZ-6564-A roller rocker
arm with a 1.7:1 ratio."

[TRBenj]

RE: GT40 Heads

1. GT40 heads came from the factory on both 302's (Mustang Cobra, Explorer) and 351w's (1st Gen Lightning). If your heads came off a 302, then they have 7/16 bolt holes and need to be drilled out to fit a 351w (which uses 1/2" bolts). Any machine shop can do that for you.

2. No, you can bolt them up with no other mods- though to take full advantage of the increased flow, I highly recommend a cam and intake upgrade while you have it apart. ProBoss engines did have different pistions than the base 240hp version, but Im not convinced that the cam was any different. You can reuse all of your stock 351w valvetrain parts (lifters, rockers, pushrods). Whether the heads came from a roller cam motor or not makes no difference. Be sure to check lifter preload at every valve.

3. Youre probably reading it correctly. The first digit in the casting number indicates the decade (F = 1990), and the second digit indicates the year. Im not sure when the GT40 heads stopped being produced, but it wouldnt surprise me if they were made through 1999. The last production car they came installed on would have been the early '97 Explorer/Mountaineer (before they switched to GT40p), I believe.

If you dont already have a set of GT40's on hand, I recommend you look for GT40p's instead. In addition to being (usually) cheaper, theyll outflow the regular GT40's in the RPM's we're concerned with AND give you a boost in compression ratio with their smaller chambers.

[SquamInboards]

RE: GT40 Heads

Awesome, thanks for all the info Benj. I've read a number of debates over the two GT40 heads, many of them quite heated. Most arguments come down to each heads flow which seems to have data supporting both sides which makes it tough. Do you think that the power band is better on the GT40s for our target RPMs where as the GT40 heads really see HP gain above 5k or so? We'll see how it goes, BTW are you from Somerville? I'm a Cambridge kid myself.

[TRBenj]

RE: GT40 Heads

Im not originally from around here, but Ive been in Medford for ~4 years.

[SquamInboards]

RE: GT40 Heads

That's right, Medford. Cool, well thanks for the info.

[TRBenj]

RE: GT40 Heads

NP. For less extreme builds (under 6k RPM, .500/500 of valve lift), the P heads are the way to go, no doubt. The GT40's have a slight advantage beyond that. I have the P's, and combined with an upgraded cam and intake they make great power across the midrange- right where you want it.

[asd]

RE: GT40 Heads

TRB, do you know what kind of power can be expected by putting just the GT40P heads on a stock 240hp motor?

And does anything in the fuel delivery system need to be changed..like the carb settings? or can you simply bolt on and go?

I'd actually like to improve power at idle as well...(my engine bogs at engagement when cold but runs fine once warmed up) any idea what affect the heads might do to that part of the equation?

Thanks

[TRBenj]

RE: GT40 Heads

asd, I would expect the P heads to add a solid 45 hp when bolted on alone. My dad added regular GT40 heads to his '92 years ago, which is the main difference between the base and HO (285/300hp) 351w.

Like I said before, I highly recommend a cam ($180) and intake ($150) upgrade while you have it apart and replacing gaskets anyways. Depending on the parts chosen, a hp level of 320 is pretty realistic.

Carb jetting may need to be revisited to ensure youre not running lean- but nothing drastic. Just the heads alone probably wouldnt warrant opening it up.

I wouldnt recommend running it hard when cold- if it bogs, then its a carb issue or the engine isnt warmed up. Just give it a few minutes.