v6 - v8 mercruiser.

wondering what else i need to consider when doing this. the boat is a '96 18.5' lund tyee, which currently has a 4.3. the boat seems just slightly under powered, and yes, i do plan to play with props first, but i am thinking of eventually dropping in a 350 instead of the 4.3. other than exhaust issues and making a new doghouse, and of course using marine fuel and elec. parts, what else should i worry about? are the side mounts the same? how much difference in power can i get out of a 350?( built specifically for this boat)

Re: v6 - v6 mercruiser.

Re: v6 - v6 mercruiser.

Lund = Aluminum right? A 4.3 should move that boat around nicely. I have an 18' FG boat, about 2800 including normal pax load, and I have a decent holeshot and +/- 48mph top end running a 21" Hustler. Different props = different results, but that Hustler is my baseline.

There were two different 4.3s in '96, the "L" a 2bbl with 155php and the "LX" a 4bbl with 175php. Unless you boat is unusually heavy, or you carry alot og gear/people either version should do OK.

Are you sure you are making full power?
Are you trimming the drive properly?
You said you will get the prop specs, so we'll wait for those. Is it in perfect condition, and what are your WOT numbers?

Re: v6 - v6 mercruiser.

Re: v6 - v6 mercruiser.

Ayuh,... I'm with Shabah on this 1,... A 19' barge with a strong runnin' 4.3l should flat out Fly...

96 is a transition year,... Verify whether or not it's got the Vortec heads on it...
With the Vortec heads,+ a 4bbl. carb is the Perfect package for that boat...

Re: v6 - v8 mercruiser.

currently, I'm running both a 19" cleaver style SS prop(which is currently being straightened), a 21' alum, and a 21" SS(unsure of make). the boat works well, although i thought it would do better. with all three props, I'm getting 46 mph(gps)@ 4600. my holeshot is not too good, but i'm having a prob with what seems like the ignition cutting out. Will start a new thread about that when the ice melts(April-May)
The boat has a 4bbl, but non-vortec heads. The engine was rebuilt from a 91 jimmy, and I changed freeze plugs to brass, head gaskets were fel-pro, which are okay.
I haven't been able to properly test the 19" because it was just slightly bent, and caused a vibration at speed.
I'm not sure of the weight of the boat, but it is heavy. the floor has been changed, before I got it, and the transom is good, except for 4-5 square inches where it meets the floor one one side. everyelse feels solid. didn't think this small area would really affect anything, but will fix it eventually.
the boat is also hard on fuel. at least it seems that way. i don't have any numbers, but a friend also has a lund 18(newer,lighter) with a 140 suzuki, and i burn three times the fuel that he does, with similar loads. there does not appear to be a hook in the hull, and i can trim it a good way up before it porpoises.
any ideas to help would be appreciated.

Re: v6 - v8 mercruiser.

I have an 88 4.3 with 4brrl carb and points ign. in my 21.5 1972 Fiberglass Slickcraft Hardtop and it's perfect power 35-40 mph depending on conditions my boat weighs about 3000 lbs. Somethind else going on there is what i'm thinking too. Before you repower it, as said weigh it. Here's a thought> have you checked the gear ratio in the drive you have on there? Maybe someone repowered the boat and the ratio is wrong. 46mph is pretty fast. As far as the whole shot deal if it was an automotive engine it most likely had a lesser lobed cam than a marine version. IMO.

Re: v6 - v8 mercruiser.

Hi,

Like Mr Bond-o, I'm with 180shabah. Look at my signature... I had a 1994 4.3LX previously, and it was great. I was running a 21" prop and it was still running out to just over 4900 rpm and getting me traveling at about 40knots. That engine is currently in a friends boat, a 23' Carribean Crusader, heavy, deep Vee fibreglass hull and he's getting about 36knots....

I do have another friend with a tin can, also with a 4.3LX and he can't get over about 34 knots...It's just the hull shape... They can't make tin cans like plastic boats....

Chris........

Re: v6 - v8 mercruiser.

46 at 4600 is pretty good. Holeshot and fuel consumption are sepratw issues though. Comparisons to the OB powered boat are meaningless. His x-dimension can be optimised, his boat is lighter, his engine is lighter (4.3alpha = 900lbs) and is ON the transom, not infront of it. Hull design (beam, deadrise, etc) is likely different also.

Do you have any data we can work with?
gph at different speeds
time to plane
time to 30mph
actual weight of the boat