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lasherman

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"I have a 1978 family runabout

"I have a 1978 family runabout (Blue Water Industries)with an OMC 120 motor and a Cobra ll out-drive (13 spline). My engine plate has model#990242S1 stamped on it and serial# 636450. The engine block has GM27700 on it.

The boat is a closed bow about 16-17feet fiberglass. I am also looking for 2 new props, one for playing and one for speed (fishing) (WOT rpm around 5200 unk. speed)Any pitch thoughts?"
 
"Wow, somebody went through a

"Wow, somebody went through a lot of effort to repower that boat. The Cobra didn't come out until 1986 and I don't know what a Cobra II is. There is a big difference between a 2.3 and a 2.5. The GM in the block SN designates it at GM. That makes it a 2.5 or 3.0 and I don't recall them ever uning the 2.5 with the Cobra. The 2.3 was a Ford engine. 5200 RPMs is way too high for your engine. 4400-4600 is more like it. With a four banger you don't have a lot of options regarding props. I don't know if two different pitch props will still fall within the operating range of the engine. If so, they will be a 15" and a 17", provided you have the right gearcase on it (1.98:1). Regarding speed, don't expect a big difference in speed from one prop to the other, you just don't have enough torque to really make a difference in a 17' boat.

That's my two cents and I probably overcharged you."
 
"Actually the 2.5 was first us

"Actually the 2.5 was first used in 1986 with the Cobra and then the 2.3 from 1987 onward. The 2.3 should be in the 4200-4600, it was the 2.3 that was 5200-5600.

Got any pics of this setup???

What size and pitch are you running now?"
 
"No idea what current pitch is

"No idea what current pitch is, old prop thats been there for ever. Also its an 0MC 400 outdrive.


376711.jpg
376712.jpg
376713.jpg
"
 
Thats a 400 stringer drive. 12

Thats a 400 stringer drive. 120/ 2.5 motor. 4200-4600 wot.

a fully mechanical late model stringer 83-86' vintage.

WOT should be used only for a few minutes a 17-19 pitch should do.
 
that drive is 1978-1981 hydrom

that drive is 1978-1981 hydromechanical shift 400 series
no rectangular zinc.... so it's not full mechanical.

CobraII? heehe... where'd that come from?
 
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