xcomunic8d

welcome to X’s LS Boat Swap. A somewhat interactive boat build. Our target power is 450-500hp. But I’ll settle for 400ish if it saves me 3k or so.

So I have a boat that needs an engine… it’s a ‘72 Seacraft Seafari 25’ beauty. I’ve been doing a total rebuild and I won’t bore you with the details but it’s a complete restoration. From the factory it came with twin I/O’s. Maybe 351 based Mercruisers totaling 500hp. Someone pulled out the twins and converted it to a 2 stroke 200hp O/B. Given the weight, cost, and wait time for a O/B as well as the originality and hydrodynamics, my buddies convinced me to go back to factory.

I pulled a 5.3 LMG? Out of a friend’s 2008 Silverado for free. Was happy to find 243 heads in it. I also have a Mercruiser Bravo 3 dual prop outdrive rated for 600hp. this mates up via the flywheel (LS style to be added) and merc connector that bolts to flywheel.

Began by Tearing engine down to the block. I was surprised to find flat-top pistons in the engine? Thought these had dish from factory.
Deleted the AFM by tapping the pedestals and putting sealant and set screws in as well as ordering a new valley cover plate
took to machine shop for cleaning, mic’ing, honing, and surfacing of block and heads and had new cam bearings installed

my pistons are as much as .009 under the 3.780 bore. I’ll be replacing those. flat top H1132CPA is my plan. Domed would be nice for compression but I’m concerned about clearances and will cost vs power be worth it? I suppose $200 is not a lot of money in the overall build cost.

my plan:
upgrade the bearings with kings xp main and connecting rod bearings
New pistons
new oil pump
new timing chain
Upgrade trunnion- whatever the best I can get from summit is at that time straub or similar.
new main cap bolts (already got summit brand) and head bolts (ARP)
ill start with the factory TBSS intake manifold with a cable 102mm TB with an adapter if I’m unhappy I’ll upgrade to Fast LSXRT
porting the 243 heads, lapping valves, and upgrading springs for cam

ill be using the Holley terminator x
exhaust manifolds are special and will be sourced probably marineenginedepot.
I’ll get the rest of exhaust tips, flappers, hose, mufflers through summit as is just about everything else above.

I hope summit doesn’t mind me direct depositing my paycheck there for the next few months.

so now to my camshaft dilemma. There is a thing called reversion on boats with exhaust. With both valves open at BDC you can actually suck water into combustion chamber if your cam is too large and/or if you don’t have fully sleeved headers. I will not have sleeved LS headers as they are 4-6k for stainless. I’ve called many places and I’m told up to .227 will be ok with standard elbows and risers.

I’m thinking about using TSP stage 4 High Lift Truck Cam 223/226.
after calling TSP Nd speaking to tech support Lonnie? He’s worked on LS swapped boats and recommended stage 2 high lift truck cam. 212/218. That’s what I ordered through Michigan motor sports.
https://www.michiganmotorsports.com/...nd-gasket-set/

Torque is more important to get the boat up on plane and will spend most of its life 2k-4K high speed trolling around 13-15mph. Occasionally I’ll jump on it to fly to and from the grounds at max rpm per conditions.

summit 8720r1 was on the list.
https://www.summitracing.com/parts/sum-8720r1

hardin Marine
https://www.hardin-marine.com/p-1096...-cam-only.aspx

questions:
anyone else done this?
have I missed anything?
any other cams to consider?

G Atsma

All Gen IV 5.3's have flat tops since they use 243/799 heads with larger chambers. Compression is a bit higher than the Gen III

xcomunic8d

Thanks for that g. I’ve just heard lots of people talk about adding flat top pistons and I found them. I guess they must not be aware of difference from gen3 to gen4

G Atsma

As an aside, pistons from a Gen III 4.8 are flat top and go right into any Gen III 5.3 for a good compression boost.

gnx7

iTrader: (28)

I ran a 5.3 with Z06 cam, ported TB, and MarinePower exhaust manifolds. The exhaust manifolds cost 3x of the motor ($500). Should be fun!

I would suggest a heavy multicoat on anything steel before install... and a clear coat on anything aluminum. Corrosion is real... Yearly I quickly scuffed/painted the coil packs and the TB could be wiped down. Overall it ran great for about 4-5 years and then corrosion got into the injector harness and/or the injectors failed. I paid the big $ for a marine alternator which failed after about a year. Then swapped in a truck starter which lasted 4 years.

Wish that the TerminatorX was out back then... as we weren't going to put a Holley HP on it. We spend well over $1K tuning it as our tuner buddy had to come out 3x to get it right with us on the boat... the exhaust crossover definitely added power... and needed a retune.

xcomunic8d

Thank you!
for sure corrosion is a huge challenge on anything here rain, saltwater, humidity. It’s going to be painted for sure.

I’m planning on doing through transom 4” exhaust. I’ll put inline mufflers in but I expect it will sound amazing. Those manifolds are now about $1500. I agree on the starter alternator you pay a lot for the fancy housings and coatings but supposedly not as likely to spark causing you to blow up the boat. The reasoning makes very little sense to me.

did you have a raw water pump? I’m going to run closed cooling with heat exchangers and I need to install a raw water pump where the a/c compressor was or install a crank mounted one which seems really difficult due to needing a machine shop to fab a flange for the dampener bolt. I have a plan to buy the merc water pump and mounting bracket and make it work somehow.

grubinski

Following … I have an old 16 foot Century Resorter that will be getting restored in the next few years. I **may** repower it with an LS 5.3 … or I may just rebuild the Greymarine/AMC 327 that’s in it now and convert it to EFI.

G Atsma

Whoa! AMC 327... Time machine from the early-mid sixties! And a marine version no less.
If you do EFI on it, let us know if you document it in a forum a give a heads up on which one...

xcomunic8d

So block came back from machine shop awhile back.

The pistons were badly out of spec. Something like .009-.010

Just placed order for engine parts a little over $2k not including terminator x and exhaust manifolds.

Have the following on order from summit:
KGB-mb5013xp Main bearings
KGB-cr807xpn Connecting rod bearings
Slp-h1132cpa pistons, wrist pins, and snaps
Mah-41859cp piston rings
ARP-234-6301 connecting rod bolts
Clo-9-3658tx3 timing chain- THIS TIMING SPROCKET INCOMP W/ 4X Cam Sensor!
Clo-9-5417 timing damper
Mah-95-3561 gasket kit
ARP-134-1003 cam bolts
ARP-134-1501 timing cover bolts
ARP-234-2503 crank bolt
ARP-434-1202 exhaust header bolts stainless
Sdm-pce229-1006 flywheel
ARP-330-2802 flywheel bolts
Sum-htlskit2 ls7 lifters and trays
Sum-141560 trunnion upgrade

Already have arp head bolts and summit brand main cap bolt kit.

Planning on getting exhaust manifolds, raw water pump at marine engine depot.
Planning on getting terminator x 990-505 through Amazon or Holley directly.
Local Mercury dealer is sourcing a bravo transom assy and timeline. Looks like sept.
Outdrive is scheduled for rebuild/reseal 7/26 in shop.
I have a plan for heat exchangers on the closed cooling system more to come on that.

Will keep parts list updated and pics as is relevant.

xcomunic8d

So far it’s a pretty basic build. Pistons are in and rotate fine. Camshaft, pushrods, spring should be here Friday. I put the summit trunnions together today.

I ordered the crank mounted raw water pump adapter, bracket, and bushing today from marine engine depot. I’ll be getting the Johnson f6b-9 pump from Amazon.

anyone have suggestions on a fuel pump. I have 2-55 gallon tanks in this beast. Boat tanks have filler lines, vent lines, and pickup lines. They normally never have an intank pump. The plan is to have 2 water fuel separators and filters just after the tank then merge into my fuel pump (need help here. Thinking an evil energy 300lph? Something not terribly loud but I can insulate it I suppose). Then I’ll probably run a fuel filter/regulator with a return line. The tbss also has a return line so I’ll probably just y those 2 returns together back to the tanks. Looks like holley terminator x is kind of picky according to Holley paperwork.

suggestions appreciated.

xcomunic8d

So here’s some catch up. Came out of a junked 2008 Silverado my friend was getting rid of and moving off island.















parts have come in. I’m most excited about the camshaft. I ended up ordering the exhaust manifolds from Hardin marine. The guy at marine power explained the cost for O2 sensors I needed and managed to talk me out of a sale. Went with Hardin price was nearly the same. Should arrive Monday.

xcomunic8d

Lots and lots of parts came in. I haven’t taken pics of each of the unboxing. I figured you see them installed.







here’s my 12 yo son putting in his first batch of lifters.






so I’ll be finishing up the front cover, rear cover, oil pan tonight or tomorrow.
I’ll reassemble the heads soon and hopefully have the engine mostly back together by early next week.

the outdrive goes to the shop on 7/26 and I still need the gimbal housing and misc parts (like shift bracket, bell housing, heat exchanger).

grubinski

That's getting him started right.

xcomunic8d

So I caught a mistake when I was reviewing my project. And trying to order a Holley terminator x. The timing set I ordered is compatible for a 1x sensor not a 4x sensor.

i 2 day aired a different cam sprocket in. It was a BTR.

wrong sprocket:


right sprocket


I tried to break my collarbone yesterday so my son is installing the second head under dads close supervision. I was helping some older friends pack and move off island. I had just repaired the bumper on their avalanche. I was up to my elbows in grease and filth due to rain and conditions. I went out back fo wash off. I went one way and mud went the other. My shoulder landed squarely on a lava rock. Boy that hurt.



torquing rocker arms






the exhaust manifolds are here and look awesome. That’s a follow-up post shortly with more research I did and info that will help the next guy.

xcomunic8d

So it’s kind of bad news, good news, bad news.

bad news #1. Can’t find a Holley terminatorX 550-905 or 905t anywhere. If anyone can make a suggestion on where to find one or a different tunable system that has a harness, O2 sensors, and supports MPFI. Otherwise, I’ll be waiting until mid-late August (hopefully).

good news, as I was thinking through how the elbows and risers work along with closed cooling it occurred to me that water might be flowing over O2 sensors. That would be catastrophic. I didn’t want to change these out regularly. I see no worries fir that.



you can see the O2 bungs here.


water inlet passage:


exit:

i do have the parts to install a crank mounted raw water pump. It’s kind of cool when you think up an idea to have a machine shop build and then a little discouraging to find it’s already made. But I suppose that is reinforcement you are on the right track. I’ll post those pics and parts when the whole system is here.

Bad news #2- this is kind of painful

the bravo 3 outdrive I purchased needs a full rebuild. Gear set, cone clutch, shims, seals, bearings, everything- but case, props and shafts are done.
I’ve really considered going alpha route but I’m too far in to turn back now and Bravo is clearly better suited for my application.

I was told it’s pushimg $7k for that job before I buy the gimbal housing another 3k. I got the parts list and found a way to trim some costs down. I expect it will be 4.5k-6k. And then the gimbal housing at 3k. A new alpha is under 3k for whole thing and while that appeals to my wallet. I don’t think that is a wise long term choice. But oh this one hurts, ouch really bad…

we decided to go with 1.81 gear ratio. Originally it was a 2.0 gear ratio. We considered a 1.65 but we’re concerned somethings gonna give as that was not designed for these shafts as well as the load on the engine. Given it’s primary role of fishing we decided to play it safe. I have the parts lists if anybody wants them. Partsvu.com says it’s $3k out the door

xcomunic8d

I have given up on getting a terminator x from Holley. They have moved shipping dates to end of October for the unit I need.
I did find the lingenfelter trg-002 that allows a 58x/4x to run on a 24x/1x. Holley only had ev1 injectors and I have ev6 and I thought adding $300 to the 1k price to do something even ling was a little like “I don’t know man…it should work?” Add it about 1400 for this one engine I figured I depin and tune for much less.

I ordered a harness and ecm for $275 shipped. I’ll depin the harness and program the ecm. I plan on HPTuners ($600) unless there is better advice. I’ll just need a pair of O2’s and I’ll be in business.

I made a run stand and here pics as of now. I’m waiting on the new bell housing for the flywheel and starter.
run stand is 4x4’s, casters, and a 2x4, some pocketholes, lag bolts. I figure I will get it running and tuned out of the boat before I lift it in with gantry crane…







im trying to get the cooling system sorted out. It’s been a little bit of a pain finding the hose and fittings.

pdxmotorhead

When I needed the T-X both Summit and Jegs had it in stock.. As well as Amazon.. LOL
But that was last summer/fall

xcomunic8d

i know. eBay, Amazon, Jegs, summit, Holley directly and every search I’ve tried. No 58x/4x in stock since June. 371 already ordered ahead of me with no guaranteed shipment date. Crazy!

oh well I’ll go this route and at least I should be able to tune in future and do other swaps cheaper.,,

xcomunic8d

so the first pic shows the manifold at top and the coil as is. The plug wire is up against manifold. I’ll relocate it with ict billet stuff see below.

but it’s really looking like an engine.





I’ll have to relocate the coils using ict billet stuff. #’s 551115-01, 551532- don’t forget custom length plug wires not sure which ones yet I’ll use.




I’m working on the cooling system. I’m trying to get a drawing of what I envision but I’m artistically challenged. It’s not going to be cheap… I have a friend that runs a local plumbing shop.

The harness and ecm should be here Tuesday.
I’m working on ordering the HP tuning supplies and fuel system as we speak.

Zanie

Nice Project. You might get more help/advice if this was in the hybrids section with all the conversions. Where are you going to put your O2 sensors? Thanks!