351W different varient specs?

as far as I know almost same engine, difference is ho was carbed (or also protec FI) and the gt40 has the multiport fuel injection

Basically and someone will come along to correct me if I am wrong PCM engines were available in stock carb (approx. 240 hp) versions in both righthand and left hand rotation with relatively mild cams..

By 1989 the vast majority were standard rotation and hooked up to a gear reduction transmission to turn the RH prop that has been a Correctcraft mainstay for many decades.

In 1991 they released an optional ProTec engine management system.. Which was electronic ignition with nanny functions.

In 1992 there came an optional 285 hp “Pro Boss” option. The primary difference is the GT-40 heads and a slightly hotter cam. In 1992 this was still a carb engine, also in 1992 on both standard and pro-boss engines the “Pro Tec” engine management system became standard equipment.

Around 94 through early 95 there was a ProTec TBI Pro Boss that utilized a Holley copy of the GM 4V throttle body. It also used GT40 heads and likely the same cam as the proboss. When this system fails (coil packs are a typical first failure) unlike the earlier pro tec ignition system boats you cannot simply convert to a regular distributor because the fuel and ignition are both handled by the same computer.

In 95 they started the EEC-IV based tuned port “GT40” engine. It also utilizes the same heads and cams as the earlier pro boss engines. As you noted it has a difficult to find upper and lower intake manifold – very early ones utilized a more rare tubular upper intake manifold, later ones a cast version.   There is a pcm version of a marinized TFI distributor (still available) and the whole thing runs open loop but is otherwise basically automotive/truck components.

In the reference section there is a detailed manual covering theory of operation.   It does utilize a knock sensor (listed as optional in the manual).

It really is a pretty cool system, compact and efficient. Just very expensive to put together from scratch.

The tuning is PCM proprietary and locked.. unless you know a guy who can do a thing… which would be useful if you wanted to heavily modify your engine, apparently switching from a GT40 head to a GT40P head doesn’t cause any noticeable difference.

So, if I understand things right, the 285 "HO" is a 240 with better flowing heads and a cam to shift the torque curve up a bit in the RPM Range.
The GT40 is a 285 with port EFI. Was it rated at 310 and at what RPM?

If the HO doesn't give up any low end, then I suspect most of the top end gain is due to the different head design allowing the engine to breath better and spin up higher.

I'm with you on the rev thing. If the HO makes more power than the Standard at the same RPM then it has to be developing more torque at this RPM. If it makes more power at a higher RPM then the torque doesn't have to increase, only the revs, thanks to better breathing.

This has probably been covered in other threads, but to save me some searching time, do these HO heads have an automotive equivalent?