Early 90s SN Horse Power Ratings

[Cascade]

How does someone to go about finding the correct HP ratings for older SN. I am looking at sereral early 90s SN and I am getting told various HP ratings from the owners. Looks like the same 351w in several of them but one owner says 240 HP and another says 290 HP. Any distinct markings or obvious numbers that would help so that the average Joe can tell what they are going to be purchasing?

[TRBenj]

RE: Early 90s SN Horse Power Ratings

The difference between boats with 240-255HP and 285-310HP 351w's is the heads. The HO motors (ProBoss, some ProSki TBI and GT40) have GT40 heads that add ~45 HP.

The identifying mark on the heads can be seen in this picture. This is a picture of GT40P heads, which are different from GT40 heads. Notice the 4 bars on the side of the head on the GT40P's- the GT40's will have 3 bars in the same location.

[MNSuperAir]

RE: Early 90s SN Horse Power Ratings

Look at the exhaust also. My '91 sport had a 240hp 351 with a single exhaust out the back of the boat while the pro boss had 2.

[TRBenj]

RE: Early 90s SN Horse Power Ratings

As far as I know, every Ski Nautique from 1989 with the 351w has had single outlet exhaust. I believe all the 350 chevys are the same as well. The only true dual exhaust I have seen on a Nautique since '88 was on the few boats with the Python motors.

[pachanga]

RE: Early 90s SN Horse Power Ratings

how hard would it be to convert to a dual exhaust? Is the tiller in the way? can you just eliminate the junction box and run straight out the back? Just wondering if anyone knows. thanks

[TRBenj]

RE: Early 90s SN Horse Power Ratings

The rudder hardware is mounted on the opposite side of the single exhaust. I believe there is room to run another pipe, but it wont be symmetrical with the one that is already there.

[pachanga]

RE: Early 90s SN Horse Power Ratings

Bummer! thanks

[DavidF]

RE: Early 90s SN Horse Power Ratings

TRBenj is correct. However, the rudder hardware can be moved out of the way. Basically you need to make a bracket to hold the rudder torque tube clamping block to the mounting bolts for the strut. Should then be adequate space for a 3" exhaust pipe.

[jos]

HP rating

Hi,

The PCM engine number will tell you the story. In the CC/PCM manual found on the PN site you can break down this number into the data of your boat.

I have a 1990SN 245HP not such heads.

[TRBenj]

Re: RE: Early 90s SN Horse Power Ratings

TRBenj is correct. However, the rudder hardware can be moved out of the way. Basically you need to make a bracket to hold the rudder torque tube clamping block to the mounting bolts for the strut. Should then be adequate space for a 3" exhaust pipe.

Im gonna revive this thread. I am curious what you mean by the "rudder torque tube clamping block," DavidF. Are you referring to the bracket supporting the steering cable? My thought was that the 8" rudder arm would pose more of a space constraint. As it swings perpendicular to the centerline of the boat, it is within 3" of the port stringer. I saw this pic yesterday and I am curious how the exhaust and rudder hardware are mounted on the V-drive big block BF Nautiques.

I know all the boats prior to '89 routed the dual exhaust outbound of the main stringers. How do the newer boats with the big block Pythons route their exhaust?

[DavidF]

RE: Re: RE: Early 90s SN Horse Power Ratings

That is a good question. I was just hypothesizing on my response. I cannot remember if the tiller arm is high enough for the exhaust to pass under, it would be close and might requre a slightly flattened exhaust tube/pipe to make work.

Yes, I am talking about the clamp block that holds the steering cable to the side of the stringer. The clamp block holds a torque tube (so to speak) that the cable slides in and out of. This "tube" is what is repositioned in the clamp block to center the steering wheel for straight ahead running.

[TRBenj]

Re: RE: Re: RE: Early 90s SN Horse Power Ratings

I understand now. On my boat, the "torque tube" is mounted just off the centerline of the boat, so there is plenty of room between the cable and stringer. My tiller arm is mounted at the perfect height to prevent running an exhaust hose next to it- though if it were raised or lowered, it may be possible to sneak one by. Still, I think the tiller swings back too far to allow a symmetrical mounting of a dual exhaust. It would be very cool to have a setup that looked like this: