Prop

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?

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

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.

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.

My GT40P heads

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...

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?

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

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.

Maybe a little of your amsoil will help wash that ham sammich down.

I've got a lead on free tubes and ropes for all you guys !