Baja Islander 240 w/ Mercruiser 7.4L
 

Hello All,

First off I want to thank everyone for their input on this forum. There is a lot of information and I have taken advantage of it greatly. However I have a question regarding the power plant in my 1991 Baja Islander.

I have been looking for specs on this setup but have fell short. I did run across a pdf file online yesterday that is a service manual for Mercruiser. However I am not finding anything that jumps out as for my application.

When trying to compare the Serial number information in the manual to mine nothing matches. Which makes me assume that it doesn’t.

So here is my serial number and my model number. If anyone has information available to me on this that would be great.

Serial: OD446675
Model: 4-74B11ODS

Any and all information would be awesome. If anyone has a service manual similar to the one I posted for my application that would be great.

Thanks In Advance.

(I am not allowed to post URL’s until I have 10 posts. If anyone wants to message me and I will message you the link.)

According to Mercury's parts catalog that is not a valid serial number but according to mercruiserparts.com it is a 454 mag, bravo, 1988-1992 (gen v big block, 365 hp). Does that sound right? If it is you can buy service and parts manuals from them: https://www.mercruiserparts.com/bam/...ly/31808/961/0

On a side note, those of us with the Baja Islanders have found the Revolution 4 prop to be pretty ideal over the stock 3 blade.

I attempted to get to the ID plate down by the started but was unable to at the moment. I’ll try again in a few days (recently had shoulder surgery). I know this may not be of help but the boat has 530 original hours on it. The owner was very meticulous on caring for it and gave me a lot of records for it for service and what not. So I am going to assume it is the original engine.

I did go ahead and snap these photos of the top. I am trying to dial in on this critter so I can be more educated when making decisions.

I see where you said it was a Gen V. Is this the same as the L-29?

On another forum called Boater Ed there was a post with all the Mercruiser service manuals listed. I am torn between a couple different manuals based on the description.

What are everyones thoughts as to which manual I should be searching for?

*Cant Upload Pics. Guess It Considers Them URL’s*

Is there a particular pitch that works best. Our purpose is typical skiing and tubing. Will do some fishing but more interested in optimizing the power side of it.

I read somewhere that talked about being able to gain some power and lowering the RPM’s also (another reason I am trying to get a full spec sheet on this engine). Was is the ideal top end RPM range?

If you’re stock 3blade is 23” which is common then you drop 2” for a four blade so a 21” would be equivalent. I use my Islander for tubing and wake boarding and that Rev4 prop was a game changer.

Here are some pics of info from the boat.

Does this help narrow anything down as to my powerhouse here?

https://cimg5.ibsrv.net/gimg/www.off...dd6ee8cc5.jpeg
https://cimg6.ibsrv.net/gimg/www.off...3065a51e0.jpeg
https://cimg8.ibsrv.net/gimg/www.off...af35f725f.jpeg

When you say “equivalent” are you referring to engine RPM’s at that point or equivalent to the 3 blade (with the exception of surface area)?

i apologize for all the questions. Thanks for all the help.

https://cimg6.ibsrv.net/gimg/www.off...50071c228.jpeg

This is the info from my prop.

Ok. So I dug up this pdf for Mercruiser 7.4 but I am wondering if it is a match for my power plant?

still kinda up in the air on this. I am looking for something similar. Any tips?

https://d3gqux9sl0z33u.cloudfront.ne..._8.2_litre.pdf

You have a standard 7.4L 300HP engine. You do not have a 454 Magnum.
Your prop is a 19P. Your boat weighs well over 4000 lbs. depending on how
much extra crap you are carrying around. Since your engine is 29 years old
I'm quite sure it is not putting out 300 HP at the prop like it did when new.
Your prop must be in great condition or you will lose RPM's and speed.
If your prop is in great shape then use it for towing tubes or skiers.
Your target RPM's are 4200-4600. Shoot for 4600 RPM when full throttle.
A 21P Mirage Plus would be my choice for a good all around prop.
I had a similar boat with the exact engine as you and I ran low 50's MPH
with a Mirage 21P.
I will assume that the boat, engine, nor prop has been modified during the past 3 decades.
If not then you will need to do prop testing for your boat's best performance.