Pro-Boss, GT-40 or stand. 351?

What you are asking for is the differnce between the 351 windsor engine and the 351 cleveland engine. The windsor is theone that most older ski nautiques and thecleveland would be the one that puts out more horsepower. The windsor used regular 5/8" spark plugs where as the cleveland used 14mm spark plugs which are a little bit smaller. The windsor also had a 5 bolt straight valve cover and the cleveland had a 8 bolt 2 plane valve cover.

Farkum, I think you are a little offbase. To the best of my knowledge the 351 Cleveland was never put into a Ski Nautique, only Windsors were used. Windsor heads of different designs used both 14mm and 18mm spark plugs.

The regulary 351W, pro boss, and GT-40 are all 351 Windsor engines, however I don't know enough of the details to tell the difference. I believe the GT-40's were all fuel injected and had intake manifolds similar to what was on the '87-'93 5.0L Ford Mustang

Thanks guys, I concur, GT-40 is fuel injected, but are all EFI motors GT-40s? GT-40 started in 95, 94 had carb, Pro Tec with and w/o injection. How do you tell 90-93 carb motor if its a Pro Boss or regular 351? I guess i dont know how motor is improved to be a Pro Boss 300 horse. Heads? Cam? Looking for exterior ways of identification, other than a decal kit. Any help is appreciated.

in the front of the engine and the lower part of the head the high output motors have 3 lines or slash marks. The standard 351's have 2 of these lines/slash on the lower portion of the head. i looked at both my motors and the pro boss has 3, the 95 sn with fuel (EFI)injection has only 2.