4.3L mercruiser and ALpa 1 output.... What should I be geting?

[Goat1314]

Hi All



I was wondering if I could get the Islander owners out there to let me know what speed they get at 3500 RPM



I have a 1989 Starcraft Islander 24ft with a 4.3L Mercruiser (approx 190hp) with a alpha 1 drive,



I Get 27 mph at 3500 RPM and 31MPh at 4100RPM



The reason I'm asking is I checked the compression and I'm over 150psi in each piston after I rebuilt the engine in the spring and I'm wondering if I'm getting all the performance I should be from it?



This is my first I/O and I have no clue what I should be getting out of it



Any input would be appreciated

 

[thumpar]

Re: 4.3L mercruiser and ALpa 1 output.... What should I be geting?

That is a pretty big boat to be pushing with a 4.3l. What is your WOT RPM?

 

[bonzoscott]

Re: 4.3L mercruiser and ALpa 1 output.... What should I be geting?

Sorry, not a Starcraft Islander owner, but that's an aluminum boat... right? Depends on the weight. As Thumpar stated, 24 foot sounds pretty big for a 4.3. At this point, I think you're doing pretty good unless the boat is only 2500 lbs.

 

[achris]

Re: 4.3L mercruiser and ALpa 1 output.... What should I be geting?

It's quite difficult to give you an exact answer. I will give you examples of how things vary.

Example 1. 20' GRP cabin cruiser. 1994 4.3LX. 23" prop. WOT 4600rpm, 39 knots.
Example 2. Same engine as #1 (literally, the same engine!), in 23' GRP cabin cruiser. 19" prop. WOT 4800rpm, 36 knots.
Example 3. 20' Ali cabin cruiser. 1991 4.3LX. 18" prop. WOT 4700rpm, 34 knots

Examples 1 and 3 are the interesting contrast... Basically the same engine and same size boat (but the GRP is a lot heavier), but the hull shapes in Ali are not nearly as efficient of GRP... It would not have mattered if we dropped a 454 in the tin boat, 34 knots was all the hull was ever going to do...

Chris.....

 

[Goat1314]

Re: 4.3L mercruiser and ALpa 1 output.... What should I be geting?

It's a aluminum boat Deep V with a 19"prop WOT (that's Max RPM right?)_is about 4500 RPM, 2500 to 2650 pounds sounds about right it doesn't weigh much

 

[achris]

Re: 4.3L mercruiser and ALpa 1 output.... What should I be geting?

Max recommended at WOT for that engine ... 4400-4800... If you're getting 4500... Great... (Personally, I like to go a bit higher. A 17" prop will take you to about 4900, and if you're not always at WOT, then give it a try... I think you'll find the boat far more 'responsive' and have a lighter feel to it...)

Chris......

 

[ricohman]

Re: 4.3L mercruiser and ALpa 1 output.... What should I be geting?

I have a 2011 Islander 221 with the 4.3. At 3500rpm I am about 33mph.

 

[Goat1314]

Re: 4.3L mercruiser and ALpa 1 output.... What should I be geting?

I have a 2011 Islander 221 with the 4.3. At 3500rpm I am about 33mph.

Makes sense ... yours is probably a 4.3 LX or it has direct injection and electronic controlled ignition. Thats all really fancy stuff my 89 can only dream about lol

 

[Bondo]

Re: 4.3L mercruiser and ALpa 1 output.... What should I be geting?

Makes sense ... yours is probably a 4.3 LX or it has direct injection and electronic controlled ignition. Thats all really fancy stuff my 89 can only dream about lol

Ayuh,... I'm runnin' a '74 221 Islander with a 1990-something early, 4.3LX, 'n knock down 43 mph at 47/ 4800 rpms,...