Confusing results on prop switches.

[Incog]

I have a 1973 SS194 Slickcraft.

The engine is an unknown V8 mercruiser (may not be the original engine). Previous, now deceased, owner stated that it was a chevy 350. Hopefully not a car engine! I have checked every place described in these forums for a s/n, rated hp, or any information on the motor. All speeds are GPS.

The original prop was a 23p aluminum and WOT 50-54mph @ 5200rpm. For the first 3 years, I throttled back and ran at 4600rpms

Unfortunately, I hit a small rock while pulling the boat out for the winter.

A friend gave me a 17p aluminum prop which does WOT 42mph @ 5200rpm.

While it is difficult to remember the hole shot of the 23p, I think that it was very close to the 17p. I didn't use the boat last summer & just got it in the water yesterday.

Reading on the forums, a merc 350 should be running 3800-4200 rpm's at WOT. Following the theoretical formula for pitch vs rpm, I would have to go up to a 29p prop to get my rpms down to 4000. Of course my boat knows nothing about theories, as a drop of 6p did nothing to change the rpms (unless I am hitting a rev limiter). A crazy marine mechanic stated that I could run at 5200 rpms on my motor. :facepalm:

Per iboats, the original boat came with a 140hp, 165hp, or a 225hp engine. Again not sure if it is the original.

Finally the questions.

1. Would it be safe to assume that I have the 225hp engine due to the speed characteristics describe above?

2. Would there be a non-noticable rev limiter on the engine that would cause a 17p to run the same rpms as a 23p.

3. Seriously, should I consider buying a 29p for a boat that I bought 5 years ago for 2500.00?

or

4. Should I just fix the 23p and continue running at 3/4 throttle.

Normally, I only run fast for about 15 minutes to get to the fishing grounds, then troll @ 2.2 mph for hours.

I will post pictures of the entire setup this weekend.

Thanks in advance for any help.

 

[Bondo]

Re: Confusing results on prop switches.

I have a 1973 SS194 Slickcraft.

The engine is an unknown V8 merccruiser (may not be the original engine). Previous, now deceased, owner stated that it was a chevy 350. Hopefully not a car engine! I have checked every place described in these forums for a s/n, rated hp, or any information on the motor.

The original prop was a 23p aluminum and WOT 50-54mph @ 5200rpm. For the first 3 years, I throttled back and ran at 4600rpms

Unfortunately, I hit a small rock while pulling the boat out for the winter.

A friend gave me a 17p aluminum prop which does WOT 42mph @ 5200rpm.

While it is difficult to remember the hole shot of the 23p, I think that it was very close to the 17p. I didn't use the boat last summer & just got it in the water yesterday.

Reading on the forums, a merc 350 should be running 3800-4200 rpm's at WOT. Following the theoretical formula for pitch vs rpm, I would have to go up to a 29p prop to get my rpms down to 4000. Of course my boat knows nothing about theories, as a drop of 6p did nothing to change the rpms (unless I am hitting a rev limiter). A crazy marine mechanic stated that I could run at 5200 rpms on my motor. :facepalm:

Per iboats, the original boat came with a 140hp, 165hp, or a 225hp engine. Again not sure if it is the original.

Finally the questions.

1. Would it be safe to assume that I have the 225hp engine due to the speed characteristics describe above?

2. Would there be a non-noticable rev limiter on the engine that would cause a 17p to run the same rpms as a 23p.

3. Seriously, should I consider buying a 29p for a boat that I bought 5 years ago for 2500.00?

or

4. Should I just fix the 23p and continue running at 3/4 throttle.

Normally, I only run fast for about 15 minutes to get to the fishing grounds, then troll @ 2.2 mph for hours.

I will post pictures of the entire setup this weekend.

Thanks in advance for any help.

Ayuh,... #1,... I'd assume you have a 260hp...

#2,... Nope, not unless it's a 'puter controlled motor...

#3,... I'd change the outdrive's Gear Ratio, I doubt yer's is Right...

#4,... That's up to you, But, I'd figure out what's Wrong with it, Myself...

 

[Incog]

Re: Confusing results on prop switches.

Thank you for the reply.

For years I have been content just knowing that the boat started and left the dock. Finally my a-retentive side has surfaced and I want to know more information. Talk about frustrating! I spent another hour this morning going over the engine / outdrive for numbers. Eureka! I found 41 GM 3970010 stamped on the bell housing. Unfortunately after another hour of internet research, that just tells me it is a gm 350.

Right under the word merCruiser in the picture below is a serial number that is almost impossible to read. I think it is A672092. The A might be a 4, and most of the other numbers are rough guesses. Ugh! I really have to remove that lettering on the back of the boat!

However, this is a post for another section of the forums.

Thanks again!