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Brand new 1991 Larson 19b 43L

time_warp

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"Last August I was lucky enoug

"Last August I was lucky enough to purchase my Grandmother's 1991 Larson All American 190BR 4.3L Mercruiser / Alpha I and trailer for $1000. The boat was a constant source of turmoil in my family, and consequently had really never been used. When I went to see it at Cal Marine in Door County, I was extremely pleased to see a time warp sitting in front of me. The engine hours read 64, and the condition could only be descibed as "brand new". I had them replace the impellors, and summerize it, and I enjoyed it for about 12 trips before returning it to Cal for the winter. My only complaint is speed. It runs flawlessly, but tops out at about 45mph, according to the speedo. I would like to break the 50mph barrier. How realistic is this? I would love any and all opinions within a reasonable budget. Is a supercharger available for this engine? Are trim tabs beneficial for this application? Any practical or performance "hop-up" suggestions would be greatly appreciated. The manuals say I have a #48 78120 A40 19P prop. Thanks in advance!"
 
"Hunt...

Next time you come


"Hunt...

Next time you come across a deal like that, you need to give me a call.

As for the speed, 45 isn't actually that bad. There are alot of things that effect top speed. The shape of the hull, the weight of the boat, size of the prop (dia. and pitch), ripple on the water.

Smaller props raise RPM of the motor and give better hole shot. Larger props give higher top end mph but may not let the engine get to top RPM. Guy G has a prop selection guide that he may post for you on this post.
A slight ripple on the lake will get some air under the hull and reduce the amount of boat that is actaully in contact with the water. This will reduce the drag and give higher top speed.
Likewise, while at top speed, trim the motor up by about 25 - 30%. This lifts the front end of the boat and lets even more air under the hull. You will actually feel the boat excellerate while doing this.
Superchargers are certainly good for performance, but they cost alot and kill fuel mileage. Superchargers work on the principle of stuffing air/fuel into the cyl. By overloading the cyls you get a huge amount of available power, but all that extra volume in there raises cyl head temps way up. Most times, the addition of a supercharger requires a lowering of compression ratio to keep those temps down.

Wrench"
 
"45 mph is great for a 4.3L!

"45 mph is great for a 4.3L!

The prop selection guide isn,t mine; I think it's Rod Stewart's?

<center><table border=1><tr><td>http://www.marineengine.com/discus/icons/mime_msexcel.gif""" align=left alt=""application/vnd.ms-excel"">prop finder
[url=""][b]Copy of Boat_Speed_Finder-79780.xls[/b][/url] (22.5 k)</td></tr></table></center>"
 
Guy;
Thanks for the correctio


Guy;
Thanks for the correction; I did create and post that spreadsheet originally. I intended it to be used by anyone who might benefit.

Hunt;
If you have any difficulties using it send me your specifics and I will be happy to assist. One bit of info needed is the boat weight. This should be in your original paperwork or sales brochure.

My 21 ft Mirage had a 180 hp 4.3 originally and it would top out at 47 MPH. It had a 1.81 drive ratio and a 21" pitch 5 blade High Five prop. So you are close.

Rod
 
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