Siezed GT40

TRBenj wrote: TimSpangler wrote: I believe that biggest difference in the GT-40 (at least I know from an automotive perspective) was the airflow. The GT-40 eliminated a lot of the airflow restrictions and generally allowed the engine to "breathe" better. I believe the GT40 and the other PCM HO 351w's (carb/TBI) shared the same longblock (block/heads/cam/pistons). The only difference was the intake (and of course the fuel system). They all performed similarly well, and had similar hp ratings (285-310hp).

I think that it was the short block that was the same. The heads I know where different between the std and the the GT-40. (at least from an auto perspective), but yeah they all were close in performance.

TRBenj wrote: Note that I said "HO" PCM's above. They made both a 240-255hp "standard" version, as well as HO (aka Pro Boss) versions (starting in 1992). First carb, then TBI ('94-95) and then multiport (1995-2002). All HO PCM's used GT40 heads, the GT40 MPEFI included.

Any idea where they get the 15hp difference in the 240-255hp Standard versions? I've seen both ratings listed, but it sounds like basically the same motor.

Bri892001 wrote: TRBenj wrote: Note that I said "HO" PCM's above. They made both a 240-255hp "standard" version, as well as HO (aka Pro Boss) versions (starting in 1992). First carb, then TBI ('94-95) and then multiport (1995-2002). All HO PCM's used GT40 heads, the GT40 MPEFI included. Any idea where they get the 15hp difference in the 240-255hp Standard versions? I've seen both ratings listed, but it sounds like basically the same motor.

I know that the GT-40 heads had larger valves.

TRBenj wrote: Tim, I think Brian's question was what the differences were between the 240 and 255hp "standard" 351w's.

Gotcha. That's what I get for tring to work and surf the net at the same time.

So has anyone used the GT-40P castings? With the different plug angle they look as though they may be a better head for a marine application. I know they were rumored to be a better head than the GT-40.

TRBenj wrote: TimSpangler wrote: So has anyone used the GT-40P castings? Oh yes, very common upgrade around here- Im surprised you havent heard of them. Ive been running them for 6 years on my '90. Youre correct that the plug angles are a bit better for our upswept manifolds. The smaller chambers and slightly better flow make them a very good, economical head choice when upgrading a Ford.

I've heard of them, used to run them on my Mustang back in the day. Very economical replacement for the E7. Wasn't sure if it was the same here. on the auto side, the plug angle was a bit of PITA. I suppose most of the upgrade from the auto side can be used here as well.

Makes sense.

Silver15 wrote: One notable difference between the GT40 and older engines, is that it turns the opposite direction.

^^That is not quite correct.

The vast majority of PCM engines used in CC's have been LH (standard) rotation since 1989. This includes all of the HO versions that were introduced in '92 (carb), '94 (TBI) and '95 (MPEFI GT40), as well as the standard (non-HO) versions.

slmskrs wrote: I want to re-confirm that rotational direction is based on looking at the engine from the rear. A LH rotation engine turns the crankshaft pulley clockwise when viewed from the front (which is where I am usually looking at it from). :)

This is correct.

Oh, okay. I wasn't sure which ones were which. I know the older ones such as the one in or older Nautique spin the opposite direction. This posed a confusing discussion when we were buying a starter.... The technician said that it was evident that it was spinning one direction while we suggested that HAD to be impossible. Can I get some people's opinions on the best oil for the Gt40? Synthetic?
Jake

Okay, Thanks, TRB. I'll search up a thread on that. Unfortunately, it seems that we've run into a more immediate problem, though. After the boat ran great for several days with the new alternator etc, we finally cleaned up the interior and put it all back together to use it for the summer. As soon as we put the boat in, I noticed it was running a little rough. Trying to plain out I could feel it hesitating. Drove for 15 minutes or so back to the house and it never fixed itself. I could feel when it would surge into full power and then pull back again almost as if a cylinder was getting bad spark or something. Our good friend, Art, came over to take a look at it. (Very experienced Correct Craft mechanic of many years)Based upon what cylinder was not firing (confirmed with heat gun) and the engine's horrid mantainance history, he diagnosed it as a burned out valve. Great. I guess this means we'll be pulling the heads. Again, this hasn't been 100% confirmed. Could still be a fuel or spark issue. So, now we're back at square one. A little frustrating, but can't complain. Hopefully sourcing rebuild parts for these heads won't be too much of a hassle.
Jake

Silver15 wrote: ..I noticed it was running a little rough. Trying to plain out I could feel it hesitating... I could feel when it would surge into full power and then pull back again almost as if a cylinder was getting bad spark or something...Based upon what cylinder was not firing (confirmed with heat gun) and the engine's horrid mantainance history, he diagnosed it as a burned out valve...

But it sometimes gives full power? Wouldn't a burned valve miss consistently. I would imagine that as a perfectly timed miss coming with every engine rotation.

I know my, older more simple, engine is supposed to get 89. I'd imagine the GT-40 would have the same or greater requirement. 87 is not high enough, whether or not that's what's causing the problem is another question.

Mine will not run on regular. I run premium, but could probably run mid grade.

FYI,

Donald

Silver15 wrote: Strangely enough, the problem turned out to be a spark plug,

How'd you determine it was a plug?

Also, my GT40 manual says use 89, which is what I've always used with no problems.

Hey, all, I'm back with a problem. Boat has been running excellent and faithfully pulling me skiing with no issues until today when the tranny started slipping on hard turns and takeoffs halfway through my run. Come to find out, the fluid was low as I had figured. It's definitely leaking from somewhere because the bildge is a nasty oily mess now. Could it be one of the main seals, cooler, or hoses to cooler? Filled it back up and ran it watching closely for leaks. Can't see any. Anyone had a similar problem? I'm stumped. Thanks in advanced!
Jake.