Proppy, Prop Prop Prop! SO CONFUSING!

[jimmbo]

Jimbo

mmm. Not so sure either of us are spot on here.
Here is my thinking. But having not looked it up, please excuse me if I’m wrong.

The 90hp I had was from around 1990. It was the 3 cylinder model and I’m sure the same base engine as the 75hp. Pretty sure it’s the same gear ratio too. It certainly wasn’t having the same specs as you say above in terms of rpm range at least.

Where I may be wrong is that the posters engine is from 1984. Maybe that’s a different case altogether? The 90 of thre same age was probably a straight 6. Maybe that’s where you are thinking and perhaps rightly so. But I was comparing my 1990 ish era 3 cylinder.

I just assumed the 90, was an inline 6, after I posted I recalled there was a 3 cylinder looper made, starting in about 87. Me bad.

The gearcases on the 3 and 4 cylinder loopers were different from the cases on the inline sixes and 66.6 inch fours. The 3 cylinder loopers did use the 2.3:1 ratio, the 4s had a 2.07:1 ratio. I have never tried swapping the old cases with the looper cases.

 

[QBhoy]

I just assumed the 90, was an inline 6, after I posted I recalled there was a 3 cylinder looper made, starting in about 87. Me bad

No worries. It was a fair assumption you made with the age of the engine the original post stated. All the best !

 

[Faztbullet]

The OP motor is a 1984 Inline 4 same as the early 850HP motor.

 

[Texasmark]

75 quits at 5250 where 90 goes on out to 5500
Both are 3 loopers
Both are 84.6 cu in.....3.5x2.93" Over square
Both run 2.3 gearboxes
Since nobody publishes torque curves who knows what they look like...usually torque peaks and drops at WOT....question is how far how fast.

 

[jimmbo]

An 84 75hp would be a 4 cylinder.

 

[comstox]

An 84 75hp would be a 4 cylinder.

Yes it is! (4 cyl.) And........ I AM HEADED TO THE LAKE in 10 minutes and I'll have proper RPM data on the new 17p prop and notes for you guys to chew on!!! I feel like the Pointer Sisters! "I'm so excited...., and I just can't hide it... I'm about to test my prop, and I think I like! I like it!" Okay... I added the part about the prop in there but you get the picture.

 

[comstox]

Okay boys & girls! My new 12-1/4" 17p at MAX WOT RPM of 5500, got my boat at just shy of 40Mph. The out of the hole acceleration is OUTSTANDING. I was just by myself this morning but from what I know about my boat, I can get up on plane and up to 20Mph in about 3 - 4 seconds!
I do like the old 12-3/4" 19p prop for higher Mph @ WOT (45Mph,) But all-in-all, the 17p takes me where I wanna go!
I MAY get the 19p prop for more top end speed.
Thanks for all of your help and advice!
Glen

 

[Faztbullet]

See post #2....

 

[comstox]

See post #2....

21 pitch is pretty steep for a 75Hp unless its on a super light hull..The 17P sounds a whole lot closer to being right.

Yep.... you pretty much NAILED it Faztbullet!

 

[QBhoy]

I might give myself a hi 5 for prediction haha.

 

[comstox]

I might give myself a hi 5 for prediction haha.

I perceive thou art a prophet. A Proppedy, Prop Prop Prophet! - You deserve the Hi-5 AND the praise of us... less prophety boat people! Thanks Qbhoy!