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    Posted: February-08-2019 at 11:57am

83 2001 hull

Im considering installing GT40P heads. My rebuild 351w has about 105 h0urs on it.   Guessing its 240-250 range after 30 over with stock heads.   Im running the original prop that has been re worked a couple of times and i had it turned down to a 13x12 due to RPM issue that turned out not to be prop related now its turning 4700 after timing and carburetor corrections.   

Guessing i can change props with the anticipated 15-20% gain in hp
any thoughts?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: February-08-2019 at 12:44pm
The old junk prop warrants a change, nothing about the modifications themselves would. The choice would be based on budget, conditions and boat usage... Acme 540 would be the standard for all around use at normal altitudes.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rosconole Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 1:46pm
You want GT40 3 bar heads not GT40p heads. unless you like burning plug wires and fighting trying to get manifolds to fit. Look on craigslist or ebay. Save yourself some pain. they were used in the following applications OEM : iron GT40 heads were used on the 93-95 Cobras, the 93-95 Lightnings, Marine 351's from 89 to 97, Marine 5.0's from 92-97. Plus a few Australian applications
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Orlando76 Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 2:03pm
What’re you basing the gt40p complaints on? I’m running the 4bar p’s with no plug or wire issues and if I recall the plug angle is easier then the 3 bars. But I run that amazon vr1 oil too so I won’t get much time out of my motor to give it a fair comparison.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gary S Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 2:08pm
Not to mention the cracking issues and the higher price. P's on a marine engine are no problem,been done here many times with all flavors of exhaust manifolds.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote 8122pbrainard Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 2:08pm
Originally posted by Orlando76 Orlando76 wrote:

But I run that amazon vr1 oil too so I won’t get much time out of my motor to give it a fair comparison.

Todd,
You had better switch to that Amsoil stuff ASAP before the engine goes!



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Post Options Post Options   Thanks (0) Thanks(0)   Quote rosconole Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 2:27pm
Here you go all you wanna be engine builders.

WHAT IS THE DIFFERENCE BETWEEN GT40 HEADS VS GT40P HEADS?
The GT40 & GT40P heads had a few differences that are note-worthy, the most importantly being the bump in compression. The GT40P heads had a small combustion chamber ranging from 58-61cc while the GT40 heads had a 63-66cc combustion chamber. The GT40 heads have thermactor holes built in to connect to the EGR/smog equipment whereas the GT40P heads us an external EGR connective system. The GT40P heads also had a different spark plug placement making header choice important. GT40P specific headers are needed unless you use spark plug wires with 90 degree boots to clear the heads.


WHAT ARE THE GT40 HEAD POWER GAINS?
Although you will see different gains more mods, we can give you a ball park power gain that you will see from doing the swap. Most stock engines can expect an increase of 20-40 horsepower over stock heads (at the crank), so around 15-30 rear wheel horsepower.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Orlando76 Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 2:39pm
Still don’t get it. You’re getting your info from the mustang boys. Marine manifolds sweep upward making plug issue a non issue.

Steve- I’m off of Sadler rd. I believe I have a 13x13 fed you could try out. Without a doubt the acme 540 out runs anything though. And you could check out my disaster professionally built 351 with disaster heads if you wanted to take advantage of the Gt40p’s.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Orlando76 Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 2:44pm

My GT40P heads
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rosconole Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 2:47pm
The don't make as much power either that's why they are so cheap. more material for porting as well. I have a virgin set, buying 2 more sets next month, They continue to go up in price for a reason.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rosconole Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 2:56pm
Hopefully you atleast put a edlebrock performer intake on to match up to the head better. its good midrange power for the application 10-20 hp. would you give you close to PCM HO output. of 285...
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 3:51pm
Originally posted by rosconole rosconole wrote:

You want GT40 3 bar heads not GT40p heads. unless you like burning plug wires and fighting trying to get manifolds to fit. Look on craigslist or ebay. Save yourself some pain. they were used in the following applications OEM : iron GT40 heads were used on the 93-95 Cobras, the 93-95 Lightnings, Marine 351's from 89 to 97, Marine 5.0's from 92-97. Plus a few Australian applications


Roscoe

You need to get a little real life experience with Gt40's and Gt40p's in a boat and quit quoting auto related information.

In the boat applications, like everybody else said, the plug angle makes it easier to change plugs and gives no issues at all with burning wires etc. And the manifolds fit just as easily as on the Gt40 heads.

And power wise not much difference at all between the 2 but plenty of people will argue that you get a little teensy bit more from the 40p's.





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Post Options Post Options   Thanks (0) Thanks(0)   Quote rosconole Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 4:19pm
Its general information not auto related, Auto related would be a different rpm range and transmission. Why didn't they put Gt40Ps in as OEM in a boat if they are such a great cylinder head then?
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Orlando76 Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 4:23pm
Partly because the GT40 was around some good time before the GT40p.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 4:28pm
Well let's see, we're talking boat engines.

Like I said get some real life experience with both in a boat and see how much sense your plug and manifold comments make
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Gary S Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 4:41pm
I had more clearance issues with the cylinder head studs than the plugs

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Post Options Post Options   Thanks (0) Thanks(0)   Quote TRBenj Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 4:46pm
Ross, out to lunch again buddy!

P’s flow just as good if not better out of the box and offer about a point of compression with a stock 351w with their smaller chambers.

The p-heads debuted on the 302 about the same time the 351w was deep sixed on the Auto side. The p’s were never paired with the 351w from ford (Auto/marine/industrial) but that doesn’t mean they arent a great combo. Installed a set on my 351w around ‘06 and they’re still going strong. Have a pair on my 331 stroker now.

Regular gt40 heads command more $ because the car guys like them better (header fitment issues with the p’s) but seem to be more prone to water jacket cracking based on the prevalence of that complaint on proboss boats.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rosconole Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 4:55pm
Don't involve my ham sandwich in this! im busy cutting grass and kicking ass while you guys are putting out salt!

I just don't like the spark plug location period. Their were other issues just in general with them when they had them in explorers. Thats why so many of the explorer intakes are out in circulation. I would rather use a dozen other cylinder heads for a little more $.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote KENO Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 5:01pm
Maybe a little of your amsoil will help wash that ham sammich down.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rosconole Quote  Post ReplyReply Direct Link To This Post Posted: February-09-2019 at 8:40pm
Got about 10 gallons for all my pre war diesel and ATF needs!! In case I need to make a Kilo 2 way average run loaded down with Gt40 heads i am hoarding!
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Post Options Post Options   Thanks (0) Thanks(0)   Quote rosconole Quote  Post ReplyReply Direct Link To This Post Posted: February-10-2019 at 10:49am
I've got a lead on free tubes and ropes for all you guys !
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