Replaced 4.3 (190hp) w/ 4.3 (220 hp)-Tachs too high

[Pleinold]

I replaced a volvo gm 4.3 L 190 hp (2 barrel) with a 4.3 220 h.p (4 barrel) and can't get the prop size right. Started with a 14.25 x 21. Tached at 5400. Too high. Went to 23 pitch. Still taching at 5000-5100. Still to high. Can't find a 14.25 x 25. What should I do? Is it possible that tach is wrong and incompatible with new engine. Also, where is the sending unit wire for the temp gauge connected to this engine? Is it right in front or at the rear of the engine. I'm not getting a temp. register on the gauge. Thanks much!

 

[Pleinold]

Re: Replaced 4.3 (190hp) w/ 4.3 (220 hp)-Tachs too high

I forgot to mention the stern drive is an SX.

 

[steelespike]

Re: Replaced 4.3 (190hp) w/ 4.3 (220 hp)-Tachs too high

If you give us the boat,stern drive, rpm and gps speed someone here should be able to figure out if tach is whacky.Or perhaps you could borrow a shop tach.When searching for a prop keeping the exact diameter is not necessary.Diameter varies with prop design.If the prop is for your application the diameter only needs to physically fit your drive.
Your rpm drop is right on the rule of thumb of 200 per inch of pitch.
Based on that you should have tried the 25 first it appears it would put you at about 4,600 to 4,700 rpm.

 

[CharlieB]

Re: Replaced 4.3 (190hp) w/ 4.3 (220 hp)-Tachs too high

Is there room on the drive for a slightly larger prop?

14 1/2 or 14 3/4

Each additional 1/4 inch of dia will also take off RPM

14 3/4 X 23 may do it.

Also, when you are running these tests, is the boat loaded, fuel tank full, normal # of people and gear?

Lightly loaded and low fuel tank will give higher WOT RPM, a couple 3 or 4 hundred more rpm is NOT a cause for alarm. I would MUCH rather see that than low RPM.

 

[Pleinold]

Re: Replaced 4.3 (190hp) w/ 4.3 (220 hp)-Tachs too high

Thanks for the thoughts. Yeah, the boat was almost empty with gas and had only two adults on it. I've put thirty gallons in today and will see what we get. Don't have the GPS capability but the engine was a new replacement through Barr that only can with a 4 barrel. The Sx drive is like 178:1 (or something like that). In regard to the 141/4 versus 14/34, what am I measuring--lenght of shaft over which prop slides? I'm pretty sure if that's the case I can get another 1/2 inch out of it. I'm not familiar enough with different props to know what will work and what will not. I've always stuck with the standard 21 that same with it but now that's not an option. Thanks to everyone for chiming in. I learned my leason about self winterization earlier this year and thus the new engine. Don't want to screw anything else up.