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Author Topic: Aftermarket cast iron heads  (Read 3755 times)
junkyardjeff
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« on: February 25, 2018, 06:14:11 pm »

 Building a 92 351 for a truck that I will be using a 2 bbl carb,was thinking about finding a set of earlier heads but by the time I get them gone through I might have the same money that new cast iron heads would cost. I have been thinking about trying to find a set of GT40 heads but not sure if they would have large enough valves for a 351 to breath good enough. What is available that would work with a 351.
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347HO
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« Reply #1 on: February 25, 2018, 06:24:29 pm »

Budget number?
Expectation?
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... it was REALLY revving at like 4K...
If I saw that thing in my rear view Im pulling over to let you by, I be scared of that thing Huh? i dont know wich car is uglier ur or mine?
Javier
Ugly?  Easy now -- that's my baby and it's got lots of unique character!  When I drop that built 445" stroker in it you won't have any time to "pull over to let me pass" because I'll have already blown past you when you figure out what the hell was that loud noise behind you . . .  
z-adamson
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« Reply #2 on: February 26, 2018, 04:43:55 pm »

Building a 92 351 for a truck that I will be using a 2 bbl carb,was thinking about finding a set of earlier heads but by the time I get them gone through I might have the same money that new cast iron heads would cost. I have been thinking about trying to find a set of GT40 heads but not sure if they would have large enough valves for a 351 to breath good enough. What is available that would work with a 351.

GT40 heads are for a 302 and thus accept a 7/16in head bolt. This poses a problem because the 351 block has 1/2in head bolts. Last I checked the stock GT40 head would not accept a 1/2in head bolt without machine work. If on the other hand you are open to the 302x head, which is basically an aluminum GT40 head, it does accept the 1/2in head bolt and should work nicely.

If you are using a 2 barrel carb, I have to assume you have no interest in high RPM capability so GT40 heads should flow enough for the application.

FYI, I use a 347 with 302x heads in a lowish RPM application and they flow fine for my needs. A 351w with the same heads used under 5000rpm should be OK.
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juiced coupe
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« Reply #3 on: February 26, 2018, 05:09:29 pm »

GT40 heads are for a 302 and thus accept a 7/16in head bolt. This poses a problem because the 351 block has 1/2in head bolts. Last I checked the stock GT40 head would not accept a 1/2in head bolt without machine work.

While not as common as the Explorer heads, they were also factory installed on some 351s. First generation Lightnings and some marine 351 HOs had them.

At any rate, drilling them out isn't a big deal. A quality bit and a decent drill should make quick work of it.
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Doing more with less, or something like that.
http://sbftech.com/index.php/topic,20009.0.html

Quote from: Monte Smith
Bottom line, if it was the hot ticket, the fast guys would do it.............they don't

You might need some Titanium rods and a flow bench!  LMAO on floor

I honestly don't get it.

I'm sweating, my heart is racing, my clutch foot is twichin', and my right arm punched the computer screen doing an involentary 2-3 shift while reading all that. 
junkyardjeff
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« Reply #4 on: February 26, 2018, 06:30:34 pm »

I do not know how much new cast iron heads go for but I have 500 in the original heads on my 1970 302 and I did not have hardened seats put in,I am going to pull the heads off the 351 soon and see what size the valves are and compare them to the fresh set of 66 289 heads I have. I want a motor for torque and not high reving.
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z-adamson
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« Reply #5 on: February 26, 2018, 07:20:09 pm »

At any rate, drilling them out isn't a big deal. A quality bit and a decent drill should make quick work of it.

Pretty sure most would agree that this is not a job for a drill and a bit.

This is better done on a mill and with several bits rather than a drill and a bit.

One must go straight and remove a small amount of material at a time for good results. Not many folks can go dead straight with a drill and get a clean pass by removing that much material with a single pass, single bit.

A wise man once said..."Half of a degree off does not cut it".
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junkyardjeff
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« Reply #6 on: February 26, 2018, 09:34:18 pm »

I would pay a machine shop to drill them out,I do not trust me to do it.
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junkyardjeff
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« Reply #7 on: February 26, 2018, 09:35:45 pm »

The pull and pay has a Explorer with a 302 so how do I tell if it has the GT40 or P heads.
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juiced coupe
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« Reply #8 on: February 26, 2018, 10:00:07 pm »

The pull and pay has a Explorer with a 302 so how do I tell if it has the GT40 or P heads.

http://sbftech.com/index.php/topic,1268.0.html

I believe that the transition was mid 97.
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Doing more with less, or something like that.
http://sbftech.com/index.php/topic,20009.0.html

Quote from: Monte Smith
Bottom line, if it was the hot ticket, the fast guys would do it.............they don't

You might need some Titanium rods and a flow bench!  LMAO on floor

I honestly don't get it.

I'm sweating, my heart is racing, my clutch foot is twichin', and my right arm punched the computer screen doing an involentary 2-3 shift while reading all that. 
junkyardjeff
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« Reply #9 on: February 26, 2018, 10:30:46 pm »

I think its a 97 and looks like my 92 351 has E7s so maybe I will not change them and have the broken bolts removed.
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jtmustang
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« Reply #10 on: March 23, 2018, 03:48:40 am »

The pull and pay has a Explorer with a 302 so how do I tell if it has the GT40 or P heads.

I’m late to the party...but any 302 in the explorers/mountaineers will have either std gt40 heads or “p” heads
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scienceguy
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« Reply #11 on: March 23, 2018, 07:42:58 am »

GT40 heads are for a 302 and thus accept a 7/16in head bolt. This poses a problem because the 351 block has 1/2in head bolts.

I drilled out my old 289 heads out for 1/2" 351W head bolts back when I had trouble keeping head gaskets on it with nitrous.  (pre MLS or Loc-Wire days)  I set it up on a drill press in order to drill straight.  First, I used a 1/2" bit, but the hole was a little small.  I then used a 33/64" bit, but a much more common 7/32" probably would have worked just as well...  and given a little more room for error for drilling the holes. 

I'm assuming the GT40 heads can be drilled the same way.  Just be aware that there are GT40 heads, as well as GT40P heads.  I believe the 'P' heads came on Explorers, and had a differently angled spark plug that often interferes with conventional headers. 

Good Luck!
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1966 Mustang, Toploader 4-speed
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vristang
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« Reply #12 on: March 23, 2018, 05:13:46 pm »

At any rate, drilling them out isn't a big deal. A quality bit and a decent drill should make quick work of it.
Pretty sure most would agree that this is not a job for a drill and a bit.
If I were to do this (and I am playing with the idea of gt40 heads on a j/y 351w), I would probably hand drill, using a drill guide to start.
Or, better yet, would be to use a reamer with an appropriate pilot size.  Haven't priced reamers recently though...
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CDW6212R
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« Reply #13 on: March 23, 2018, 05:23:09 pm »

The pull and pay has a Explorer with a 302 so how do I tell if it has the GT40 or P heads.

http://sbftech.com/index.php/topic,1268.0.html

I believe that the transition was mid 97.

That's a useful link. The GT40's will have three bars on the end, the GT40P's have four bars.

To tell with a stock Explorer, the 96 and early 97's have GT40 heads. The late 97 to 2001 are all GT40P heads. They all have an elbow from the TB to the intake. That elbow is different for GT40 heads, it is perfectly flat on top. The elbow with GT40P heads has a rounded shape on top. You can place a drink on the elbow that has a flat top. I only have a picture of the most common GT40P elbow(and intake).


* Explorer intake 01.jpg (27.29 KB, 576x432 - viewed 60 times.)
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Don

1991 Mark VII LSC Special Edition, soon to be OBDII and 4R70W, then GTC body kit and 347.
1998 Mountaineer, plans for A4WD and KB 2200 blower later, XP8 parts, paint and a 332.
1973 Ranchero and 72 Sport front end ...will be a 351 Clevor, EFI and 4R70W.
scienceguy
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« Reply #14 on: March 23, 2018, 08:59:49 pm »

At any rate, drilling them out isn't a big deal. A quality bit and a decent drill should make quick work of it.
Pretty sure most would agree that this is not a job for a drill and a bit.
If I were to do this (and I am playing with the idea of gt40 heads on a j/y 351w), I would probably hand drill, using a drill guide to start.
Or, better yet, would be to use a reamer with an appropriate pilot size.  Haven't priced reamers recently though...

I leveled the heads up on a drill press, and used a conventional bit to drill all 20 holes.  (2 heads) 
Worked just fine.  That was around 25-30 years ago, and I had to go to my neighbor's house back then, as I didn't have a drill press yet.  lol  The holes for the short bolts are nothing.  I sweated the longer holes more, but since they were already drilled out fairly large from the factory, a good bit stays pretty centered. 

Just make sure they are level front/back as well as side/side before starting the hole.

Good Luck!
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1966 Mustang, Toploader 4-speed
Pump Gas, Flat Tappet 306
9.88 @ 135.67
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